EEVblog

[@MrCarlsonsLab]

Hi Dave. The reason they are using that simplified 6688 tube, is due to cathode area or (size.) Larger cathode area in a small vacuum tube means they will operate at lower Voltages ( providing they don't have to produce much drive power) They would have been better off to use a "space charge" tube and arrangement. A space charge tube is designed to work with 12 Volts on the plate. Enjoy your holidays!

[@jackneff179]

+Mr Carlson's Lab Whats a "space charge" tube??

[@MrCarlsonsLab]

+Jack neff Hi Jack. Space charge tubes were used in equipment when no high voltage was present (IE: late 50's car radios.) They use the space charge grid principal to accelerate electrons at low plate potential. They differ a little in operation from a normal tube... EG: The control grid is is positively charged to act as an accelerator grid. The screen grid is where you feed your signal to be amplified. The suppressor grid (if any) in some applications is also positively charged. The tube 12K5 comes to mind.

[@cyberdragon3699]

+Mr Carlson's Lab China needs to start making space charge tubes again if they are going to make things like this instead of sticking random tubes in a random circuit.

[@MrCarlsonsLab]

I agree!

[@cyberdragon3699]

Unless...no...they wouldn't...of course they would, it's China, the home of cheap and electrocuting electrical ;-; *unboxes new amp wall wart, reads back* Class I Power Adapter Input: 100 - 240VAC 0.2A Output: 200VDC 0.1A

[@rbduffer3263]

You brought a tear to my eye, I didn't know anyone still uses vacuum tubes. Back in 1959, when bits were flat, I went to a very good Engineering school we were taught vacuum tube circuit design. . Seeing the plate characteristic graph brought it all back. Immediately after graduation I went directly into computer programming.

[@transistortester]

Not trying to start a war, but I think putting LEDs under tubes ruins the look of them. The dim glow of a tube looks great on it's own, so I see no reason to overpower it with gimmicky, incredibly cheap looking lighting. On that topic, I personally think LEDs under nixie tubes should be considered a crime.

[@neilhuband995]

+jjensen2492 and cycle through RGB heh

[@travis4798]

+transistortester Ikr? Plus being the color blue, makes it look like a dyeing tube lol!

[@scottfirman]

I agree, nothing like the soft glow of those tubes. blue...what the hell is blue doing in a tube? i grew up around that stuff. my dad was always fiddling around with that stuff. he was pretty good at it. i wish I had his collection of radio tubes and amps.

[@stevenbirch]

+Travis Piper Yeah, last time I saw tubes glowing blue it was a set of four EL34s experiencing The Who at extreme volume. The audience were happy but the tubes weren't.

[@ggklncnoifewAsdarp]

+transistortester fully agree, seeing a blue led under any kind of tube makes me very sad. It's not anger anymore, just disappointment in humanity.

[@NatureAndTech]

23:40 "so the tubes actually do something..." Yes. They add 1.6% distortion.

[@AltMarc]

+NatureAndTech But at least, it doesn't have an output transformer...

[@TheOriginalEviltech]

+AltMarc adding a transformer will significantly reduce any static noise.

[@88djdmepfdnkjf94]

+NatureAndTech I find the best bit being the tube in the "Tube Amp" is actually removing amplification.

[@IvoTrausch]

+NatureAndTech They heat up the room too.

[@Keith_Ward]

+Ivan Taranov "Where's the Beef?", That's a few years back.

[@MattExzy]

These things remind me of that one friend I had that re-ripped his entire MP3 collection into FLAC (from the MP3 files, not original source), telling me it was for 'better sound quality'. Biggest thing though, as with 'oxygen free' cables - don't engage with them in argument or present logic. *backs away slowly*

[@asdf155]

+MattExzy Well, using FLAC is not that stupid. You typically won't hear the difference, but when MP3 is used with a high compression rate, definitely will. You normaly don't run into space problems on your hard drive nowadays, so I see no point in not using loss less compression formats like FLAC. No need to say that oxygen free cables are ridiculous.

[@decompyler]

+MattExzy Sunk costs need some kind of justification. I cannot believe he actually insisted it sounded better though. Belief is a hell of a drug.

[@nickguy6820]

I had a long conversation once with some folks who SWORE that there's a difference in audio quality between FLAC, Apple Lossless, and Wave. I even encoded a source file into each, then back into raw PCM samples, and ran a binary compare on the result. The (totally unsurprising) result: 0 differences encountered. "Well, *I* heard a difference." sigh.... You can't save everyone.

[@steen8156]

+as df You missed the point... This guy converted MP3 to FLAC...

[@nickguy6820]

***** Yeah I know - that's my point.

[@hobo1452]

Keep it up Dave, you're informative and fun to listen to. I'm old enough to remember when a TV or radio went on the fritz, pulling out all the tubes and riding to the drug store on my bike to run them all through the tester, then hoping that they had a replacement in the cabinet underneath. Also, TV repairmen who made house calls and always had a red and black RCA tube caddy. The good old days!

[@BrandtRedd]

Since the tube output is nearly the same level as the input, I would love to see what happens if you pull the tube and simply short from pin-to-pin - letting the op amps do all the work. If I'm reading the schematics right that should give a fairly good quality result. Probably too late since the video is from a year ago.

[@Harlequin314159]

"They're filled with vacuums." :D 8:39

[@austria117]

Harlequin314159 They put a lot into it 😂

[@harrisaastamoinen]

Hilarious.

[@larkenfield179]

I actually own one, and even using only two tubes, this fine little amp has the delightful, noticeable *soundstage* of a tube amp. I find that quality of sound unmistakable without dismantling it technically. The tubes also make it easier to notice where the musicians are located in space. So, it's a hybrid amp with a genuine tube ambience... Regardless of whatever its distortion may be rated at - and that's probably going to vary according to the tubes being used - I have personally noticed much less listener's fatigue... I have enjoyed this amp hours on end playing music that I usually avoid because it's not a warm or full, especially at the bottom bass end of the musical spectrum. The tubes add warmth and fullness and spaciousness of sound. But my initial impression is that I was amazing at the improvement of the soundstage that even my Grado GS1000 headphones could not produce. As a musician, this is the most fun I've had improving the sound quality and my entire library. So, I'm disappointed that the technician in this video apparently didn't actually describe the amp's sound before technically analysis it. The only analysis that truly interests me are by those who have the ability to hear the different qualities in the equipment they are analyzing, and I found that lacking here... This means saying right off the bat whether this or any other amp sounds pleasing to the EARS... or why bother going to the trouble of analysis it? In the meantime, I've ordered some NOS GE 6688 tubes that should make this little amp sound even better. It's the EARS that take over after the analysis ends. So of course the tubes are having their effect.

[@BikerSupichai]

i have one also and totally agree! its noticeable to soundstage. this review just talk about electric thing but amplifier is about sound.

[@robertromero8692]

Subjectivist audiophiles just LOVE not talking about noise, distortion, etc. (IOW, objectively determining how good something is). It's all about using purely subjective terms like "soundstage", one of the favored buzzwords.

[@LazerLord10]

What I want my audio to be is what is stored on the file on my computer. No coloration, no distortions, no filtering. I want to listen to sound the way it's intended to be heard, and what's on the file is what I want to hear. Note how I said *MY* sound, and not *everyone's* sound. Some people (actually, probably a lot) enjoy the coloration of a tube amp, or a specific EQ setting, or some tasteful deviations from what the sound file actually contains. That's fine, it's what they enjoy. For me personally, I would want an amp (really, a DAC-amp combo) because the headphones I have can't be properly driven by what I already have. Although I think we can all agree that _"audiophile"_ grade SD cards and Ethernet cables do absolutely nothing. I really wish that the term audiophile didn't have such a negative connotation to it. When I (and maybe other people) see 'audiophile' on something, it immediately triggers our snake oil detectors. Just thoughts :)

[@Paul-gz5dp]

That is one thing I dislike about Windows and many of the drivers as there are so many forms of electronic distortion that can easily be added by the software drivers, if I wanted my audio to sound like it was music out of a well I would buy the cheapest speakers.

[@AmbientWanderer]

But even all solid state amps sound different from one another, so in effect they are all adding coloration to the 'original' sound.

[@YAUUN]

I have to say you are really good at explaining circuits. I was expecting to be totally lost with my high school knowledge of circuits, but I followed the gist of most of what you had to say.

[@NoFear4XJs]

What would be SUPER AWESOME is for Dave to point us in the right direction with a link or 2 of some choices of TRUE tube pre amps that are headphone sized and or a little more powerful... Thank you for the great detail Dave top quality as usual, hope the masses can help you find some proper choices for us, Cheers !

[@RandyLott]

I'm a musician and an electronics engineer. Tubes are not better for purely listening to music. I want to hear the music as close to the original as possible. Give me a low noise solid state amplifier for that. No filtering or "coloring". However, for guitars and basses, the tube sound is real! Tubes sound fantastic for their dynamic range compression and harmonics they add. Not ideal for playing recorded music at all!

[@ronb6182]

I disagree tubes are best all the way around. I remember even an AM radio with tubes the sound sounded like stereo. Not the all American 5 tube radios I mean Atwater Kent and Zenith radios. they mainly used 6V6 or 6F6 amplifier tubes, even the rectifier made the sound better. The youth of the 80's and beyond havent heard the real Hi Fi sound only tubes can produce. I had an Admiral Record Player that used 2 6aq5's and one 12ax7 and a 5y3 rectifier and the sound was outstanding especailly when I used a 10inch woofer from an old B and W TV set. Tubes rule in good HI FI audio.

[@j.w.8663]

@@ronb6182 No Ron B, it's because the music was better then. ;-)

[@ronb6182]

@@j.w.8663 the music is the same same songs we are talking about fidelity. I have and played the same records on both type of amplifiers and tubes win every time. Even the rock song seasons in the sun sounds better on a dynaco amplifier than on modern stereo equipment. My friend listens to rock music I don't as a general rule. I may have a handful of popular tunes I like but my main is classical music. Big band music was what I grew up listen to when I was young, I had a few years listening to 50's rock when I stayed at my birth mothers house but when I was really young like 3 years old my adopted parents listened to big band music. The classical music came into my life when I was 7 years old when I started piano lessons. I agree the over the air music was better then because you had a choice what type of music to listen to. The old Atwater Kent radio could pick up stations all over the country on AM. The tv antenna was also used for my radio I just used one side of the 300 ohm twin lead line. I don't remember grounding the radio. AM today has nothing to offer. You can get choices on the internet like you could over the air in the 70's. I haven't tried cds on my tube amplifiers yet because I need to recap my equipment, I just aquired a varac that my work gave me for helping unload a storage hanger at the local airport. He said he used the varac when he repaired tvs and radios.i will try it on some of my tube amps. I would never run on 125 volts the tubes need 110 volts for that was the voltage back then. I believe the best of both worlds will sound good. I will post later when I hook my cd player to the tube amps I will also try my computer sound on the tube amplifiers as well. They sell headphone tube amps on amazon and ebay, but I don't have that kind of money to spend.

[@elsaarmstrong-zp6ng]

Tubes/Valves adds presence to recordings, mainly because of even harmonics and soft clipping! Guitarists like overtones like the octave 5th’s , minor 7th’s etc - physco acoustics, Fourier analysis, Taylor series, mathematics way beyond my uni days!

[@dogastus]

I wish Dave had spent 5 seconds longer and switched the input to a square wave.

[@steen8156]

+dogastus Now that would have been very revealing and a good indication of performance with a 24v potential.

[@SONOFAZOMBIE2025]

+dogastus what would be the difference?

[@dogastus]

+Son of a Zombie It would give an indication of frequency response. Rounded slanted edges would indicate an HF roll off, sloping top and bottom would indicate LF roll off. Any ringing on the edges would indicate poor phase response and/or marginal stability.

[@FrozenHaxor]

+dogastus I wish he would have done a frequency sweep!

[@johnc8910]

cbbuntz: "+dogastus That dual opamp thing looks like a stability nightmare." No. That is not an uncommon circuit configuration.

[@unclebarry78]

Dave, I loved this bit. I've always been fascinated with vintage technology. I'd love to see more pre-transistor teardowns and explanations of how they work.

[@neilhuband995]

So it's not a skookum choocher then Dave, is that what you're telling us?

[@Blacktronics]

+neil huband Nope, she is many things, but a skookum choocher she ain't.

[@Blacktronics]

digitalradiohacker right into the art bin

[@neilhuband995]

+JinzoDefiler yeah, I'm an engineer myself (CNC programmer/operator), so I find some of his videos interesting. I do wish he'd do a couple more in depth power tool teardown reviews, not seen one for a while.. +AvE if you're listening? ;-)

[@Opsecable]

+neil huband NEED MOAR BOLTR!

[@neilhuband995]

+Bindo yeah, +AvE ! we need moar of teh BOLTR! He's not done an in depth tool review for ages now. That was the main reason that I subbed to his channel. I miss them. :-/

[@parentteachernight]

I know it's not necessarily your area of interest, but I really enjoy your audio equipment teardowns. I would love to see more!

[@keyen3]

+EEVblog, Dave, a video on audio distortion theory (for beginners) and measurement might be pretty popular.

[@runardamnes6359]

Fun fact: The European ECH83 mixer/oscillator tube will work with a plate (or anode) voltage as low as 6 Volts. It was mainly used for car radios.

[@tubical71]

+Runar Damnes yea, but this EF80 alikes aren´t made to operate at low plate voltages

[@runardamnes6359]

+TubiCal  EF183 will work down to 20V or so. Not sure about the EF80.

[@SeanBZA]

Biggest improvement is remove the 2 tubes and install 2 links from grid to cathode, and remove the cathode resistors. You save 2W of power and improve reliability by at least an order of magnitude and reduce the noise....... Of course if you want the valve sound leave the resistors in and use a 1N4001 for the link so it is forward biased and able to generate the lovely distortion with less power and noise.

[@weylin6]

Aw, I wish you used a square wave on the scope, it would have revealed a lot more

[@Vhbaske]

You waked in me the electronic's fever again! I was an electronics tech in my early age and was dedicated to repairs

[@JerrySmithKociak]

I remember I saw a schematic of a all-tube automotive radio receiver in which ECC86 double-triode tubes were used. They were designed to operate at low anode voltages like 12 Volts at the cost of higher distortion. In comparison to other car radios with vibrating voltage converters these tended to sound "dirtier", mainly because of that relatively low voltage. If you get your hands on one of those radios - that would be great. Worth of mentioning: in many guitar amps with tubes on input they use tubes like ECC81, ECC83, and so on (triodes) that are interchangeable, meaning you can swap one type for the another in most cases.

[@DrRChandra]

Just to be clear, there are two types of JFETs, enhancement mode and depletion mode; tubes/valves operate like the depletion mode variety.

[@NecromancyBlack]

Best part is watching Dave's arms swing around in the reflection on top of the tubes. Hows does that man have so much energy?

[@Namejjvkkr]

How can people possibly know this much about this 26 minutes long video 5 minutes after it being uploaded?

[@jtn191]

they don't? people read the title or skipped ahead

[@stiff629]

valves do have a different sound by them selves if used in a old school full valve job running at the full 160v with the beefed up components but as a hybrid its a wanking matirial just to say u got valves. I reckon valve should stick with valves and silicon should stick with silicon.

[@TinkerbatTech]

+John Ridley Agreed. I was hoping he'd just go ahead and jump grid to cathode across the missing tube socket and fire it up with a tube channel and the 5532 channel and compare the two. Take a bit of messing to set up to test it, but might be fun to see the results. And the reactions... If someone had gifted me one of those things, that's the treatment it would get. Make a decent headphone amp, the simplified way. (And chop out those LEDs!) Stu

[@johnc8910]

"How can people possibly know this much about this 26 minutes long video 5 minutes after it being uploaded?" Because some of us are old farts who grew up using tubes.

[@tasmedic]

Thanks Daveo! Enjoy your hols..... you've earned them! I was born in the valve era, and my first ham HF transmitter was a Hallicrafter, which kept the room warm in winter... but transmit frequency drifted all over the place. It was very good for an isometric work out when cleaning out the shack, though! I'm glad we've gone solid state, I got fed up of 180v DC shocks working on this kind of tech.

[@ronettreker]

Valves are like the guilty pleasure of electronics... They're old tech and don't have the performance of a modern transistor. But they look so cool...

[@kinggreene]

@eevblog Dave, one reason for tying one of the grids to the ht was to use it as a space tube, the low voltage ht, often just 12v. This was very popular in car radios before the proper dedicated low ht voltage tubes were developed for the car industry in the 50-60's this was short lived with the advent of more reliable transistors.

[@elsaarmstrong-zp6ng]

It’s all to do with even harmonics and soft clipping that valves/tubes bring into the sound! Guitarists love it as it brings out overtones from the vibrating strings- octave, 5th’s , minor 7th’s etc . long sustain notes using feedback near the speakers! Listen to Brian May on Queen recordings, he uses many of these natural effects! A valve pre amp with a solid state power amp gives pleasing effects also and the music gives a feeling of presence especially in the bass and mid range! I used to own 2 Leak TL50 power amps with point one pre amp! Wow what a sound-like the musicians were in my living room live! I sold it off stupidly as new KT88 valves were getting too expensive! I think you are about £150 now for a matched pair! A small valve pre amp into a Fet power amp seems like a cost effective solution to get a decent response from medium sized domestic speakers!

[@SeanBZA]

Seen a few OHJ "tube" amplifiers where they just stuck in any random tube into the front window to show. Not even in circuit as one was cracked.

[@agenteblasco89]

very interesting! I love this kind of reverse engineering, op amps, tube etc...thanks for the explanations

[@alankingvideo]

By the way I didn’t buy my one as a headphone amp, I use mine as a signal tracer, it’s a cheap way to make one with a good uncoupled input.. You also get a spare tube (or Valve if you are British) to play with, solder some wires onto the pins and you can experiment with it in triode and pentode configuration. You need about 90v to make it work properly, so rubber gloves are a good idea.

[@nycsaba]

I did not expected a cathode follower design for the "true tube sound"/"distortion". Also as @Dave and datasheet said, you will need at last 160V B+ for that :)

[@Itapirkanmaa2]

The equivalent tube to the E180F, which is special quality industrial tube is the 5A/170K, the 6688, or the CV3998. The 6J9P is originally a Russian standard-grade tube, 6J9P-E is the strengthened version, but it could be 10,000 hours type, instead of the 100,000 hours special quality tubes.

[@terracethornhill]

What would be a better tube and circuit design for that application? What would be the "genuine article" so to speak? If you wanted to run your audio signal through a valve, what would be the audiophile approach?

[@RadRider33]

Thanks Dave! Learned some stuff about tubes, which I'm too young to have formally learned anything about! 👍

[@kwastek]

funny times we have you explain what tubes are using jfet analogy. i'm quite young, but still 25 years ago in early ground school I remember reading my father's electrical engineering school books and I was learning about lamps. i always knew more or less how BJTs work. but only last week I learned about JFETs :D

[@williambickham2042]

Without getting into plate voltages and all, I have to say that tubes sound different than transistors. In my college electronics class years ago, our instructor said something to the effect that a good quality transistor amp will treat the odd and even harmonics evenly. However the human ear doesn't find odd and even harmonics to be equally pleasant. He said that a tube amp tends to "cheat in your favor" as far as doubling up on the harmonics that the ear tends to like and attenuating harmonics that are less naturally pleasing. I am so old school that I actually like the sound of a phonograph coming down on a vinyl record!

[@youtuuba]

William Beckham, I wonder if your old teacher was correct......as I understand the human ear, it is just a series of tiny hair cells that respond to excitation by different sound frequencies. If that is true, would they be able to distinguish between the different harmonics? One note's 5th harmonic can be the same as another note's 8th harmonic, and how is the ear supposed to react differently (and one is an odd harmonic while the other is an even harmonic). Seems to me that a lot of audio snubbery is really just folks misunderstanding, or improperly applying, physical truths.

[@TheRealSasquatch]

"Filled with a vacuum" - Best Dave quote so far ;)

[@danmcbmusic]

A headphone amp doesn't need much voltage gain, and you *can* do it with just a 5532. But better is to have some extra current output for low Z cans. Running a triode/pentode at low voltage is fairly common in products where they just want the "valve sound" - the low volts if helps the typical distortion sound. You could have just pulled the tubes to see if it still passes signal, and saved a bit of time. ;-)

[@cemx86]

Second question - What is the point of the tube/valve if the gain is one? Isolation? Impedance matching to the source? Looks "cool"?

[@ethanpoole3443]

To impart the harmonic distortions that are characteristic of tube amplifiers...in other words, to inject added "desirable" distortion into your output signal. Many prefer the warmth of the distortions added by traditional tube amplifiers to their music sources, and there is absolutely nothing wrong with that so long as they also realize that the warmth is, in fact, a distortion and not true to the original recording. We all have our personal preferences and many of us will fine tune the bass and treble response curves of our audio systems to our own personal tastes and choice of music.

[@MichaelBeeny]

If you are feeding in line level 100/500mV all you need to drive a low impedance headphone will be a current amplifier. Very little gain is required. If a valve only is used it will need a transformer to converts it's high impedance to the low impedance headphones. Which will lead to phase shift, more distortion and poor bandwidth ie a valve amplifier.

[@mrjohhhnnnyyy5797]

+Michael Beeny I fully agree on that. I built a simple transistor amp with small voltage gain, but decent current gain. Even at same volumes on the output, sound with the amp in the circuit becomes a lil' bit better (better bass)

[@AstralS7orm]

+Michael Beeny Good transformers won't cut much subbass or introduce any appreciable amount of phase distortion in audio band either. Some people actually even build transformer coupled amplifiers specifically because they're easyto make. The downside is mostly weight and output impedance - in audio applications.

[@cyberdragon3699]

+Michael Beeny LOL totally not true unless you use a garbage transformer. There should be very little distortion in a good transformer.

[@DirtyRobot]

What pisses me off about this subject is that it is really subjective. I used to be a recording engineer, not a sound engineer or a mix engineer. My job was to capture the performance or sound source as close to original as possible. For this job you needed an objective ear, one that can pick out small imperceptible things that many other people would miss. A simple thing like positioning a microphone 20 cm to the left would change what was being captured and recorded. We would use expensive everything to monitor the recording. Everything from the mics and their cabling, the mixing desk, the headphone pre-amps and the headphones, no expense spared. The most expensive part of this chain were our ears. Myself and the guys I worked with could hear an aircraft or local traffic in a noisy concert hall, or on location we could hear insects that were going to tape but the rest of the crew could not hear until we pointed it out. Anyway, to my point... With modern equipment, and we can even include smartphones here. You are able to EQ or tune your sound to how you want it. 90% or greater of users don't know how to do this in any way close to correct. I have even worked with professional engineers that disputed the clear evidence from the expensive digital readouts and ended up screwing up the recording. When it comes to sound, every person seems to be a professional. And fuck valves. Whatever they did for audio can be simulated and tweaked beyond your imagination in software. Even down to adjusting the element temperature and the surface area of the grid and so on. Rant over. Nice vid Dave.

[@AmpApps]

Might frequency response, harmonic generation and dynamics be changed in a different way through tube topography rather than solid state even though it is a cathode follower?

[@6F6G]

The quick way to test if the valve did anything would have been to yank the valve out and see (hear) if anything came through. In this case nothing but linking pins 2 and 3 (grid and cathode) would have restored the audio with probably very little difference in audio quality. When you first showed the video of the inside I wondered where the HT rail was because only 16V surface mount electrolytics were visible then I noticed the radial electrolytic and thought that must be across the HT rail. It turns out that the HT is only effectively 24V (± 12V) so the 16V capacitors are adequate.

[@winstonsmith478]

One more thing I'd like to see - a THD measurement, 20 - 20kHz.

[@Aleksanti]

You should have compared the input from the output on a spectrum analyser. Tubes add harmonic distortion in a different way then transistor do. So there is a difference.

[@harryconover289]

Cathode follower refers to the out put it gives low impedance drive to the next stage , and gives a Av of less than one Harry .

[@hankus253]

Remembering the power supply requirements needed by tube circuitry, I was hoping to see what value B+ voltage was being supplied to those tubes and how it was being generated from that small circuit board.

[@1101nz]

double blind testing done by the BBC showed that INCREASING distortion improved perceived sound quality . ....purity of audio reproduction. There is no such thing. Purists look down on things like tone controls in amps, yet overlook the many multiband eq's used in the recording process. And the many meters of non audiofile cables used in the studio :-) Will an audiofile 2m cable make any difference after the 20M of ordinary cable its gone through when recorded.. Perhaps Dave could test "audio' 240v amp fuses that cost $100's . People swear they make a big difference in sound. Just kidding, please dont.

[@deusexaethera]

When you're *producing* sound, you can use any method you want to achieve the sound you want, so using vacuum tube amps for recording purpose is fine. When you're *reproducing* sound, you should use whatever method produces the mathematically most-accurate amplification of the source signal, so you can be sure you're hearing exactly what the artist intended. That's why my home stereo uses a set of self-correcting JBL studio monitors with built-in digital amplifiers, rather than some ridiculous glow-in-the-dark vacuum tube setup, so I can hear my vacuum-tube-amplified rock albums with perfect clarity.

[@francisgeorge7639]

Supposedly 2nd order distortion 'harmonises' whilst 3rd order would be inharmonious, but I tried adding 2nd order using a plugin and it sounded dreadful.

[@rabautios]

the same with Tripath and some other amps, they ad distortion, but "good" distortion not the kind of distortion crappy Class B silicon amps ... there are of course good transistor amps, Class A, Class AB, even some good Class B amps ...

[@dcan911]

@@deusexaethera how do you know that the sound on the record is what the artist intended?

[@deusexaethera]

@@dcan911: Because they get to hear the master after the recording engineer is done with it, and request changes to the final mix. Or at least, _good_ musicians do that. I suppose Justin Bieber probably doesn't care.

[@laernulienlaernulienlaernu8953]

How exactly do valves work on audio amps? Or should I say, why do audio anoraks say that you get a better quality sound with valves?

[@bricomage]

what about replacing opa by betters one instead of replacing tubes ? Wich mono OPA do you recommand ?). Thanks

[@MM-jt6ly]

Hi Dave, you could use your Analog Discovery to look at the Bode plot, gain etc.

[@d3115uxor]

i have a question for the electron wranglers... would this """amplifier""" benefit if i moved the output from the cathode and moved to the plate?

[@demef758]

19:52 I'm no expert in tubes, but I can see right away that if this tube were biased as the datasheet says to do it, the tube power would be 160V * 16.5mA = 2.6 watts. Times two because this is stereo, and you're talking about a lot of power. Now try to generate that power from a little tiny boost converter powered off of 6V. You need a hefty >200V filter cap for the boost (read: $$$), too. It's much harder to fully bias this tube for this thing than it might appear, which is why they adopted a very simple ±12V rail system. Otherwise, the power supply would have been more expensive than all the other circuitry combined. So it's okay to bias a tube filament with a DC voltage?

[@dannybeckett01]

Why was one ne5532 inside the feedback loop of the other, as opposed to them both independantly amplifying the output of the tube and then have their outputs connected in parallel?

[@PileOfEmptyTapes]

+Daniel Beckett Puting two opamp inputs in parallel halves input impedance, including doubled input capacitance. I don't think it would have mattered much here though. BTW, in a parallel circuit it is generally recommended to have them share the same feedback network, depending on how large current sharing resistors are. Otherwise resistor tolerances may mean unwanted cross-currents.

[@0MoTheG]

I did not understand the R_12 resistor. Why? Transients? Stability?

[@conoba]

You can actually can check the frequency response and distortion with just a laptop and audacity. It has FFT and a sweep generator function. Takes only a few minutes.

[@mauriceorris8374]

Thanks for making this video Dave. Saw the title, and thought "this'll be interesting" and it is.

[@mikeissweet]

A true audiophile understand the importance of a good signal chain; which is even more important than which tubes you use (as for as those- I only accept a few specific models that were produced by Phillips in the late 60s (which I was fortunate enough to procure a stockpile of at auction after much searching), but I won't get into that). Everything that exists within the signal chain will modify the sound. I use exclusively analog hardware due to its superior accuracy, though I do make one exception: my record player happens to be a few meters from the rest of my equipment (which is in a specially designed cabinet to shield it from the earth's magnetic field), and to get the signal over there, the signal from my preamp enters an ADC then sends s/pdif using a custom white laser (merged and color-balanced RGB) through a rigid glass fiber and then received by a dedicated DAC and then tube preamp. This signal then either feeds into my tube power amplifiers that feed the main speakers (through solid brass, oxygen-free, shielded speaker wiring, terminated with gold-plated connectors (I find that the brass with gold plating doesn't give that "dulled vocal depth" in the mid-high range that you get with stranded copper), it is also fed into a second ADC, similar to the first one, which is used to carry the signal to a similar set of equipment for the rear of the listening room.

[@Spirit532]

+mikeissweet Good troll, but it has to be slightly more subtle.

[@mikeissweet]

+Spirit Lmao ding ding! Damn those audiophools.

[@Roflcopter4b]

+mikeissweet You almost had me until the magnetic field stuff. That is just a wee bit too far for even the nuttiest audiophiles I've happened across.

[@andygozzo72]

ugh, theres so much 'audiofool' bullshit 😉

[@christophertstone]

Awesome... until the Earth's magnetic field, then it goes off the tracks. White laser? All fiber is "rigid", glass is glass. You redeemed yourself with the gold-plated brass however.

[@proffessasvids]

dave thanks for the excellent vid, please forgive my ignorance.. i'm trying to up my level of understanding in electronics. my understanding is that a valve produces a pulsed dc output when the grid is fed with an ac input signal (replicates the ac waveform but above the 0v line). i understand that having a transformer after the plate effectively resets the outputted pulsed dc wave form to straddle the 0v line again, recreating ac. as you've shown in your breakdown, the coupling cap is fed from the cathode. i'm stuck with visualizing how the coupling capacitor or a transformer (which is biased negatively at rest in this case) can transfer the wave form, totally accurately.. surely if the first signal pulse swing is in the negative direction for instance, the cap will ignore it as it's already fully biased in that direction? i always try to imagine a capacitor as a double ended hydraulic ram. so would i be correct in thinking the piston of said ram always be bouncing off the negative bias end of the cylinder as when the signal stops the cap will charge fully negatively from the cathode feed? if this is correct then is there a form of distortion added when a higher amplitude wave form is transferred through with regard to a smaller amplitude wave? like a 0 point drift? my thinking hydraulically.. a large oscillating swing on a ram, biased to one end, will have a different cycle centre point within the cylinder than a short oscillation. correct me if i'm wrong please dave... or anyother of you wonderful system heads. cheers, peace xx

[@jgrimsley2000]

I was surprised to output at the cathode was that clean and linear (minus the switch mode noise.) The tubes were operating in starvation mode. I was expecting some soft clipping on the negative swing of the sine wave.

[@peterschmidt9942]

Thanks for the vid Dave. I was shopping on Ebay and bought a 6J1 preamp kit which I thought I'd play around with. Still waiting on it, but I reckon it's probably a similar design except they run it direct off 12VAC from what I can see (no dc boost) and 6J1 toobs. At least it was only $10. I don't know how much this puppy would set you back

[@jacekschneider4686]

Pls supply "moding" scheme for skipping this valve ;)

[@jrose92081]

Awesome video..Would love to see a reverse engineering of the peavey 6505mh (mini head). A lot of talk on whether the tubes are functioning as most tube amps do..

[@sixstringedthing]

From the Peavey product page: *2x EL84 power tubes and 3x12AX7/ECC83 preamp tubes* Those are pretty standard types/quantities of tubes for a guitar head. Sounds like a normal tube amp design to me. EDIT: Electronics repair tech here... I've got a Marshall solid state head sitting down at the shop right now, really should get around to looking at that... :)

[@zorroloco_ok]

fets are tubes without a pilot lamp ;) are those NE5532 capable to provide enough current to drive let's say a 32 ohm headphones?

[@tubical71]

Hi Dave,wow cool to see you´re doin TubeStuff :) :) I love you´re sayin´ JFets with pilot lights....Great clarification for unexpirienced people! :) But in this case, the tubes running on "starved plate" configuaration in where the plate voltage is to low for a typical bias point, you´re finding in datasheets.... Therefore to let the tube at least do something you need to wire it up like how it´s done here... But as a cathode follower the tube will not add a "tube-sound". A cathode follower can´t do this, there´s no saturation. Instead it´ll go straight into clipping, just like any Jfet or BJT will do....

[@witeshade]

+mipmipmipmipmip Tubes, even crappy tubes, are more than capable of producing excellent quality audio. Even this one with a 1.6% specced distortion can most likely be coaxed into being plenty clean with a high enough voltage (which provides headroom) and relatively careful choice of biasing and impedance. The thing is though, transistors do all that stuff way better and easier and smaller and cheaper and less dangerously .. one of the only real uses I see for tubes these days is in guitar amplifiers, where the whole point is to slam the shit out of the tubes with insane gains and voltages, and really ride them past the edge of their standard characteristics. With all their analog goodness, the real fun comes when you mistreat them. The boring, linear region is not exciting and is better represented by transistors.

[@cyberdragon3699]

+TubiCal As MrCarlson said they would have been better off using space charge tubes. China needs to stop making random tubes and sticking them in stuff but building tubes designed to work on low voltage. Or they could simply use a tiny boost converter to generate the high voltage instead.

[@EJP286CRSKW]

TubiCal The 1.6% figure is for a common-cathode topology with no NFB. Not a practical circuit.

[@Paul-gz5dp]

If the signal level is low, there is no clipping due to bias.

[@1fertube]

Interesting video. The tube should stay to add some kind of "nice distortion" but what for in a hf amp?

[@asdf155]

+Fer Cava Tubes don't necessarily add "nice distortion", it depends on the circuit you use.

[@1fertube]

+as df I agree but what's the reason adding the tube apart of having a fancy blue light?

[@steen8156]

+Fer Cava There is no such thing as 'nice distortion'.

[@inactivated0]

+St een Yeah, Jimi Hendrix sounds like shit *rolls eyes*

[@steen8156]

I wouldn't say that as I am a big fan. But you're entitled to your opinion.

[@davidg4288]

Drive the thing into distortion and see which distorts first the valve or the op amp. If it's the valve then it's working as advertised. If you *want* distortion in a headphone amp is matter of personal preference.

[@1234garrett1993]

i would love to see you do the same thing for something like a Fiio E10K now, great video Dave you answered the questions i had about tube headphone amps

[@1234garrett1993]

***** since i started seeing those headphone amps with tubes lately ive wondered if they really use the tube or if its just bs and now i know its basically just bs lol

[@clynesnowtail1257]

If you had one of these, would it be possible to modify the tube out so it only uses the OpAmps as mentioned at the end?

[@tubical71]

+Clyne Griffon of course,simply connect the input straight to the first ne5532 stage, that´s it....may you change the value of the resistors to match your needs....47k may be a bit to low in some cases...but usually it´ll work

[@IvoTrausch]

Hey Dave, if you don't use the amp, which I guess you won't, could you smack one of the valves and take it apart under the Mantis? Would be inderesting to see, as probably no-one born after 1970 will have seen a valve from the inside.

[@nemanjatodorovic2803]

Great video! I don't know what is penthode or triod till now.

[@6F6G]

The quick way to test if the valve did anything would have been to yank the valve out and see (hear) if anything came through. In this case nothing but linking pins 2 and 3 (grid and cathode) would have restored the audio with probably very little difference in audio quality.

[@SirMo]

The whole point of a tube amp is to get distortion. Of course conventional solid state or discrete amps will perform better. Honestly, this product doesn't appear to be a rip off at all. I am not into tube amps, but for those looking for the tube amp distortion on their signal path this is probably a cheap way to get there.

[@Phantasmotronogun]

In some jurisdictions this could be seen as a Trading Standards issue, since it isn't actually a valve AMPLIFIER at all. Even if they made the argument that a cathode follower is a current amplifier that doesn't hold here since the input resistor on the first op-amp is a much higher value than the volume pot resistance. The op-amps provide a gain of about 6 by my reckoning, and probably a bit of tone shaping which leads to the subjective, "Wow, that sounds better" user response. Though,a 5532 isn't designed to drive a low impedance load like headphones, and the use of a purpose-designed headphone driver would almost certainly give lower distortion results and more drive power. In fact, the design min load impedance of the 5532 is 600R according to the Ti datasheet, and the current limiters will operate at about 40mA typically (0.6v across 15R) so they really are stretching things here. Even with two in parallel that's going to hit a current overload situation at about 3v peak output with low impedance headphones and two 47R's. That would actually be more than adequate volume with most headphones, but it's a very bad way to design an amplifier, basically running the ICs way outside of design envelope. Exactly why they didn't use the valve as an amplifier, not sure, possibly because a higher supply voltage than 24v would be needed to achieve a linear response.

[@johnc8910]

"Exactly why they didn't use the valve as an amplifier, not sure, . . . " Because that would take work and circuit complexity. There's no way they could meet their price point.

[@PIXscotland]

I wonder why they didn't use a 12v power supply and run the heaters in series? That would save them the trouble of the DC-DC units and half of the board components/space. Any thoughts?

[@MichelPASTOR]

+PIXscotland Because they need + and - 12V ?

[@PIXscotland]

+Michel PASTOR Yeah, I get that. But starting at 12v would save the whole +6 to +12 components. Let's go whole hog and take a single 12v input and drive a Boost converter and have 35v (say) out and offset the DC input to half rail. The valve would probably be happier/quieter and we'd have endless rail-rail swing on the op-amps (Not that we need it.) In the end the valves were pointless to this circuit other than adding colouration (which may be desirable to some.) The circuit is interesting as it is, but the product is endlessly complicated for the purpose of driving high impedance headphones. You can do that (I do) with a couple of LM386's and a PP3 battery (but maybe a little noisier.)

[@timramich]

The difference between +12v and -12v is 24v...

[@PIXscotland]

+Tim Ramich Umm.

[@NivagSwerdna]

I'm quite surprised... I saw this in the previous mailbag and thought the valves were just fake and made to glow and not part of the circuit.... but they do actually do something. In the CF configuration do they introduce a distortion that can be perceived? Does it sound like something that could be construed as "Tube Sound"? It would be interesting to follow this up with some time domain analysis, what sort of distortion etc?

[@PrinceWesterburg]

Triodes sound sweeter than pentodes - its a complex subject, best just listen!

[@synaesthesia2010]

cant find the previous video looking at the valve amp, van you give me the link for it please?

[@zazio5535]

LOL the Xuanzu Headphone amp! It used to be an ebay bestseller for sometime, though the design was really crappy. And the tubes are made by SGEL, not by syvania, which is more expensive.

[@6p1p]

12：11 i think they are cathode follower , just the G3 usually connect to cathode and they are cathode output to the Op-amp..

[@PaulHigginbothamSr]

Hey, no, not a simplified transistor to me, but the other way around. see, I just wish they used the tubes for gain, as in a pentode, but then the voltages would need things like tuned coils and such.

[@cmj20002]

I have to ask, It makes sense to me to have two tubes and two NE5532P's to cover the left and right channel for stereo sound. So what is up with all the tube amps that use one tube and one NE5532P? I just built a headphone amp using two of the NE5532P's but not sure why you would use one. They must be losing output power with one as opposed to two of them.

[@jammin023]

The larger single-valve one that TechMoan tested is clearly two valves in a single package - you can see two separate heater elements in it. Same applies to the smaller one if you look up the datasheet, it's a dual triode. As for the NE5532P, well it's a dual op-amp so I guess they are just using one per channel. Maplin sells a stereo headphone amp kit which does the same (code N47FL) for the princely sum of six quid (so it probably costs about 6p from China).

[@cmj20002]

My headphone AMP was cheap. About $9.00 US. It uses two NE5532P's and to my surprise it sounds good with little audible noise. Kinda nice because there are so many of these on the market and the price can go really high for one, but the sound may be terrible. You can never tell unless you try it out. If mine had sounded bad I was only out $9. I had fun building it though.

[@LOMlabel]

Thanks a lot! Really appreciate audio teardowns/explanations!

[@noco-pf3vj]

Tube... Valve... Tube... Valve... Tube... The heat from tube cause flamewar everywhere, I love it...

[@ettiennegroenewald2901]

+Faisal Kadal except with guitarists. we have to feel and listen, audiophiles are just retards.

[@noco-pf3vj]

Logan Le Roux I don't know about guitarists, but I used to modifying and upgrading components in stompbox and guitar amplifiers, on request from my friends, I have many friends are bassist and guitarist, but I never know how to feel and listen to. But, yeah, audiophiles are ridiculous about how can they "feel", like they can "feel" the sound of cable touches the floor, because cable should not touching the floor, wow, just wow...

[@theoriginaldylangreene]

Come now, there is as much BS in the guitar community as there is the audiophile world. From "tone wood" to nitrocellulose lacquer. There are idiots who believe that the amount of beer spilled on their guitar adds all that "tone".

[@danxepha4535]

I'd really like to see you look inside a "high-end" valve headphone amp, just to see if there's much of a difference. Surely just writing off all valve headphone amps based on this one is a bit presumptuous? Its like buying a cheap Chinese micro hifi amp from Amazon and then just saying all hifi amps are rubbish.

[@ABaumstumpf]

+Dan Xepha No matter what you do, Tube amps are simply not any better than decent transistor based amps. Tubes are a thing form the past, obsolete, cause semiconductors are simply better in every aspect aside form looks.

[@KennethScharf]

+ABaumstumpf Depends on the application. Tubes do have their obvious disadvantages in power requirements, size, and failure rate, BUT they do have unique characteristics that are desirable in certain audio applications.

[@ABaumstumpf]

Kenneth Scharf IN places where you want distortions only - and even there for years we simply used digital equipment to get exactly the distortions and effects we want. But for a cheap clipping e guitar it is good.

[@KennethScharf]

+ABaumstumpf True, Guitarist's LOVE tube amps!

[@marko_z_bogdanca]

+ABaumstumpf no matter what amp you use, ALL speakers reproduce the sound with extremely high distortions when you compare them with distortions made by amplifiers. So ooo. .. yeah. It is all very subjective.

[@stephenhunter70]

I wonder if they actually connected the valve as a pre amp, would actually need the IC stages? I know a 6BL8 will do it. And yes I know a 6BL8 has two sections/stages in the same capsule (A Triode and a Tetrode)

[@JohnShalamskas]

Yes, the headphones are way lower impedance (8-600 ohms) than the plate of the tubes (thousands of ohms) so you'd need to have an impedance transformer for each channel. The operational amplifiers have a high input impedance and a low output impedance, which removes the need for expensive transformers. This also means the tubes aren't really needed to buffer the input, since the op amp inputs would not load down the line level signal.

[@marvinmatthewty8547]

hi. i have the exact same amp. a few days ago, something around the power switch popped and it smoked around that area. smells kinda burned but the amp didnt turn off. lights didn't dim. is it stil safe?

[@Mobin92]

What is a cathode follower, and what does buffering mean in that context?

[@cbbuntz]

+Mobin92 It can be used to raise input impedance and decrease output impedance. Another way to say that is that it provides current gain but no voltage gain. The tube almost certainly would perform that job worse than an opamp, but the opamp wouldn't add much distortion.

[@MitzaMaxwell]

Is it possible to make a stereo amplifier using only one tube? You can buy them with only one tube (valves/lamps).

[@johnc8910]

Sure. Use a twin triode such as a 12AT7.

[@1L6E6VHF]

John Casteel In the UK, there is (or was?) the British Valve Association, which forbids (forbade?) the sale of valves with multiple units in the same valve. I wonder if that would have been affected by Brentrance in 1973.

[@MrTripcore]

TDK CD's sound better than Phillips CD's.. I'm guessing that is because of the materials used, or the manufacturing process, or a combination of both?

[@claudbase]

Great analysis, but I'm not sure the average Joe will get the main fact that: in the "emitter follower" configuration (gain~1) and the low level signals, this circuit will never have the close to saturation smooth clipping, responsible for these so loved harmonics that audiophiles came to love so much. A simple harmonic distortion comparison might have been easier to understand...

[@brycemw]

Now I know I "should" know this but how do you get the -12v or is it just -12v if the 12v is the reference?

[@PeterWalkerHP16c]

+Bryce Wilson DC/DC converter

[@brycemw]

But how do you get negative voltage unless the voltage is some how running from ground to there.

[@PeterWalkerHP16c]

+Bryce Wilson have a look at the application notes for a MC34063A DC-DC converting chip. There is an examplr circuit for -12V from a 6V source. www.jaycar.com.au/Active-Components/Integrated-Circuits/Linear/MC34063-DC-to-DC-Converter-IC/p/ZK8837

[@ebiscaia]

It would be interesting comparing this amp with ifi itube that is marketed as a buffer and with higher quality.

[@proluxelectronics7419]

It needs rare earth metal coating on the valve sockets to be any good, How did they miss that? Top Vid, never knew valves would work at such low voltages.

[@runardamnes6359]

+Mike James 24 Volts, or even lower, is not unusual. It's basically a myth that ALL tubes/valves needs hundreds of volts to work. Many will and a few won't. How well is another discussion.

[@steen8156]

+Mike James Don't forget the cryogenic treatment to make it "Audio Grade". Oh, and a really expensive power cord. ;-)

[@ethanpoole3443]

+digitalradiohacker You beat me to it, I was going to mention the importance of oxygen free power cords because that 60Hz hum is so much more enjoyable with an oxygen free power cord inserted between the receptacle and transformer! And I love the whole notion of "audio grade" digital interconnect cables (HDMI, Ethernet, etc.) and flash memory devices. Some of the claims made by audiophools are so outlandish they really should be criminal. That said, those that want the "warmth" of tube amplified sound are welcome to it as far as I am concerned (there is absolutely nothing wrong with preferring a certain sound -- we all have our likes) so long as they do not simultaneously tout the tube amplifier as being distortion free as the very warmth they desire is the product of distortion.

[@johnc8910]

You know the funny thing about an "oxygen free" power cord? The owners never worry about the wiring in the walls of their house. Or the the power cabling to the house. Or the the nonlinearity of the power transformer on the pole. Or the . . .

[@deusexaethera]

Yeah, there are no rare-earth metals with better electrical conductivity than gold-plated silver. (the gold plating is only to prevent corrosion; gold actually has lower electrical conductivity than silver.)

[@pratherat]

It would be an interesting video to visualize the valve output vs. standard amplifiers, to see that the "warm" is.

[@florianhofmann7553]

1% 2nd order harmonic distortion

[@MrBolossj]

I have ZHILAI D1 with probably the same amplifier and build-in DAC. It is great for creative aurvana live (32om), but I have a problem with noise when I'm using superlux hmd660 (150om). It's should work with earphone impedance: 18-600Ohm. Any ideas why? This LED under tube looks terible.

[@thomasschwarzinger7757]

are there any amplifiers that use tubes to amplifie the sound and do they actually sound different than modern ones???

[@ABaumstumpf]

+Thomas Schwarzinger They exist, and they sound.. "tube like" - more distortions and noise.