JAT EZ amp Part 2 amplifier blows up during testing

[@whiskyguzzler982]

Thanks for showing us this failure. As a learner, seeing knowledgeable professionals deal with failures is extremely valuable and very rare. My condolences for your loss.

[@antibrevity]

I realize that this failure mode is frustrating, but it made the project even more interesting . It's so much more realistic and intriguing when things fail than when they work correctly at first power-up. I look forward to seeing how you resolve this and wonder whether some other Darlington might work instead. Still, I know that you already sought out the most appropriate Darlington IC when you began, so I am just as interested in your discrete design, if that's what you eventually do. Thanks for the great videos!

[@joohop]

Stay Cool Buddy Just Remember " The Hotter The Battle , The Sweeter The Victory "

[@killcar5nbike2]

Problem with Darlington rather than discreet EF stage. You don't have that low impedance base-emitter resistor you need to stop the cross conduction. Or even better a floating driver not referenced to the output. As soon as you load it up the charge carrier density increases needing a low resistance path to discharge the base-emitter junction. As you say, going discreet is the way around your problem.

[@tebbi67]

You have the only right answer!

[@christophschuermann6512]

Hi, if you take a look at the datasheet of the darlington transistors, you see that the gain drops very fast with high frequency. The main problem of the darlington is the slow switch-off time in conjunction with a small C/E-current.

[@tangerinq]

Maybe another Darlington IC would do a better job and would be easier to implement than going discrete? Love your channel BTW.

[@eatdrinkwineguy]

I'm no expert but I was wondering that too.

[@Ziggerzzz]

Are you making a transmitter or an audio amp ?

[@JohnAudioTech]

To have low distortion at high frequencies amplifiers require high loop gain at 20KHz. In order to meet this, the closed loop frequency response will run out to a few hundred KHz.

[@ahmedalshalchi]

John Audio Tech ... Don't go extreme... 3rd harmonic is fair enough for cut-off freq. for audio amps and must be attenuated heavily by 40 dB or more.....

[@bob4analog]

I'm wondering if something is resonating in the output at that frequency, like the wire wound resistors and the parasitic choke in the output. At that frequency, wire wound resistors and wire wound anything can become reactive.

[@EngineeringVignettes]

@@bob4analog There is an inductor freq response point where the inter winding capacitance becomes the dominant factor and the inductor turns into a capacitor. I would suspect that would happen in the low MHz though... The wire wound resistors are not trying to be inductors. Cheers,

[@bob4analog]

@@EngineeringVignettes - Spot on! However, it would be interesting to see the reactances that are occurring at a few hundred khz. Whats the point! Even the profssional amps I've tested start rolling off around 40 khz. This is good design practice. This is an audio amp, not an RF amp. If you want DC to Light response, you'll have to change the design. Otherwise, this amp is solid for audio. Chees mate!

[@Ratkill]

Troubleshooting can be an even better learning opportunity than otherwise. Very curious! Cant wait to see any new developments.

[@larspedersen1546]

Have you considered using a decoupling capacitor between the bases of the darlington output transistors? Often the pnps are slower than the npn transistors. Perhaps the pnp is still open at high frequencies when the npn turns on?

[@BriansModelTrains]

Snickers makes a cameo appearance! Back to the drawing board. Cheers and thanks for sharing.

[@tangerinq]

If the issue is exclusive to high frequencies then maybe a low-pass filter would solve the problem?

[@pliedtka]

But he wants to test for oscillations, distortions and other issues at very high freqs., so LP filter is out at this stage.

[@bob4analog]

Something in the output is becoming reactive at that frequency, like the wire wound resistors, and causing those outputs to pop. I think the amp is working fine for audio. If oscillations were to occur, they would've been seen already during normal operation.

[@threeMetreJim]

@@pliedtka You are meant to see if oscillations occur under all possible operating conditions. So only audio frequencies (unless you are constructing an RF amplifier) and variation in supply voltages. The boucherot cells purpose is to damp any tendency to oscillation; shorts HF to ground as was demonstrated with it's resistor getting hot - which is another way to detect oscillation problems if they are severe enough, even without an oscilloscope.

[@tangerinq]

I don't have a lot of experience with amplifiers but I don't think the issue is oscillation. Transistors don't die so easily just because if oscillations. They die when shoot-through conditions occur. I would attribute that to maybe some sort of asymmetry in input impedances between the two Darlington pairs. So maybe there is an issue with the design but I wouldn't think that it's the oscillations.

[@bob4analog]

@@threeMetreJim - True, but 100+ khz is not a possible operating condition. This is why the FB resistor is usually bypassed with a small value capacitor to limit the amps frequency response to something reasonable for audio. Therefore, if the amp is to oscillate, it would occur under normal operating conditions, but this is what these circuits are for; to prevent such occurrences under 'normal' conditions. 100+ kHz is not normal for audio amps.

[@kokodin5895]

what if you build eqivalent darlington network with bd912/911 outputs and something like bc547 as a first stage just to test what broke , was it thespecyfic behavior or capacity of the driver transistor or was it simply current spike on the output stage of that darlingto, or was the transistor used just not good enough?

[@ford1546]

Hello. in 2018 you test the TPA3116 D2 MONO. I have TPA3116 stereo with 1 ic. and the edition with 2 pic TPA3116 ic. which is bridged to 2 channels. I use the oscilloscope and fixed resistor. In 4 OHM stereo I only get 37watt in 50HZ 4 OHM. With the other amplifier bridge I only get 34 watts. power supply 24.8V 2A. full load I measure 24v. How do you manage to get so many watts out of TPA3116 D2 MONO? 51.8w

[@threeMetreJim]

Shoot through would be more likely supply voltage divided by any resistance. The small pulse destroys the transistor, discharges the capacitors that have insufficient energy to explode them [the transistors], then the supply limits, preventing smoke. Collapsing output is usually a sign of heat stress internal to the transistor or in things I've done with RF, a phenomenon known as secondary breakdown (which usually results in a collector to emitter short). I can't see how it's a fail, if it reproduces audio frequencies up the required frequency at the target distortion and power. Just make sure no High frequencies get into the input (like from, maybe, a cheap class D headphone amplifier) and it should be fine. You may be able to use your distortion meter and _two_ separate audio tones for checking for high frequency distortion, by checking for intermodulation products that fall in the audio band, which will be visible on your distortion meter too, without the need for trying to amplify a high frequency directly.

[@cassvirgillo3395]

Hi John, No matter, you will figure it out, your JAT after all. You have Snickers for moral support. All the best, C.

[@lezbriddon]

i replaced 30n50 's with more 30n50 's , blowing... why? both 30a, both 500v, but my replacement manufacturer rates them at 420w and the original manuf at 690w... that's quite a difference in available useable power...

[@pliedtka]

No diodes from out to rails, but that's for inductive load back EMF. Maybe they were one of the masterious tranies that like to change an amp into oscillator, especially Darlington triple. The big Motorola 250V, 15A, 30MHz based on Toshibas are good. Also the big 15-17A Sankens (2292 something like that). I remember reading somewhere that slower outputs are less prone to problems with capacitive loads something like electrostatic loudspeakers. Maybe you should try something like MJE 1503x for drivers and MJ15023-24 for outputs but they are 5MHz devices, and then something faster if everything passes the test. Sanken also makes audio Darlington complementaries up to 15A, 10-20 yr old AV receivers such as Sony are full of them but they are usually 10-12A rated. Also the phase margin might be some issue, but you don't have oscillations at least visible ones on the 'scope. Do you have base stoppers on the Darlington bases?

[@adarshraksh]

Hey John, I needed some advice from you ; i had a single TDA7498 AMp that worked well on it's own (3+years) Then i decided to add one more with a common power supply and added 2 pre amps one for each. But issue is both amps burnt off when my rca cables moved and made some noise. I never had this problem when running a single amp. I suppose it's some grounding issue? All connections done were the same as the single amp setup except now both amps sit on the same PSU TIA

[@jeffm2787]

Hey I have one of those Tek meters in my collection. Not a bad meter IMO, but yes certainly large.

[@bijouxbijouxbijoux]

Sorry to hear that John.. My guess a 1meghertz or so oscillation that went straight up to the rails, asking so much that it blew the output stage.. "bon courage" as we say in France 🇫🇷

[@poptartmcjelly7054]

I'd personally etch a PCB because prototype boards get quite messy and remaking them is a hassle.

[@cocosloan3748]

Stay away from darlington outputs! They just trouble!

[@HimanshuSharma-dm8ol]

Sir in ur video which was one month before there were driver transistors . Why not use that circuit ?

[@Nono-hk3is]

Time away from a project can work wonders.

[@larryshaver3568]

hi i tried to find your community page even though i subscribed your page doesn't show in my list

[@harryconover289]

Very high frequency for a audio amp what are you trying for ?

[@davekazoroski6548]

A lot of "packaged Darlingtons" do not perform well at ultrasonic frequencies - trust me, I've blown them professionally. Not enough space to fully explain, but they are just plain too slow to operate reliably above 30 or 40 kHz. Your idea of building Darlington pairs from discrete transistors is the only sensible way to go. I don't think I have ever seen a commercial Hi-Fi amp that uses packaged power Darlingtons as the output stage.

[@hendryparman3782]

Wow, stk chip, nowadays the Chinese copy blows in a instant

[@PileOfEmptyTapes]

It is not entirely uncommon actually. A fair amount of AV receivers come to mind (e.g. Kenwood, Denon), or some '80s Grundig amps.

[@davekazoroski6548]

Yes, as long as you keep it below 20 kHz, packaged Darlingtons are usually OK. As far as A/V receivers go - the Darlintons are probably driving the subwoofer channel - 100 Hz and below - no issues whatsoever at these low frequencies.

[@PileOfEmptyTapes]

@@davekazoroski6548 The kind of AV receivers I was referring to are meant for *active* subwoofers as is standard in home theater (bargain basement systems excepted), so their power amps are for the main speakers.

[@AstrosElectronicsLab]

Sony used Sanken Darlington transistors for a while in the 5.1/7.1 receivers for a while

[@kirknelson156]

ok maybe you can explain why you are testing an audio amplifier to such hi frequencies, since most people cant hear over 20k and I don't hear anything over 13k.

[@AstrosElectronicsLab]

I think it's a test of stability assuming the amp was run at full power with a high THD with third, fourth and fifth order harmonics (not that it go above 100kHz). That, and probably to test how stable it is if for some reason the amp goes into parasitic or ultrasonic oscillation when driving difficult loads into the MHz range.

[@kirknelson156]

@@AstrosElectronicsLab shouldn't there be some band pass filtering, you don't want an amp using power to amplify frequencies that A. no one can hear, and B, no speaker can reproduce. the frequencies he was testing to run the range of ELF to LF in the RF spectrum. Attach it to a 1000 foot antenna and he can talk to subs. ok maybe it doen't have quite the power for that :)

[@aljenkins9748]

John , are the tantalum capacitors resonating at that rf frequency ? .. .... ...shalom,a.j.

[@jeffmassey4860]

Maybe the BACK-EMF diode in the Darlington went nucular?

[@jaredgray7872]

Do you have some positive feedback somewhere leasing to increasing current?

[@Theineluctable_SOME_CANT]

The totem pole had both transistors conducting..... BANG!

[@abdadkhbqefkehfkf]

Hey John. I've a bit of confusion. The mono version tpa3116 you tested delivered about 50w into 4ohms mono. However, the same chip is used in another Amp you reviewed from breeze Audio. And it's 50w into TWO channels. Can you tell me why is that? Love from Pakistan!

[@AstrosElectronicsLab]

Maybe comment on the video that's relevant to your question?

[@abdadkhbqefkehfkf]

Yes sir! But urgent measures result in desperation.

[@luisbulek65]

Base resistors on darlingtons to limit current ?

[@anindyamitra5091]

Must put Low Pass in the pre-stages, I think this design isn't somehow meant for higher frequencies, unlike JAT501!

[@adamp9553]

Looked like spikes/clipping on the oscilloscope when switching frequencies. Don't want to push high amperage with unpredictable voltage even if just for a fraction of a second.

[@pabloibaceta5932]

Those effect it's produced by the feel tech frecuency generators. I have the same one.. every change you make the processor starts the sinewave again.

[@HimanshuSharma-dm8ol]

Very curious to know what is the real problem

[@AstrosElectronicsLab]

Most likely crap transistors

[@ayylasco]

Hello. Can you please help me select the right amplifier? I have a clone bose soundlink mini driver which is 10W max i believe. And has 4ohm impedance. Im planning on building a portable bluetooth speaker. Many thanks!

[@pliedtka]

Get clone of Sym Asym for real amp. It's very basic, other than asymmetric VAS (voltage amplification stage). Many yrs ago Mike from Germany design it and a lot of people build it. There are Chinese clones available on the net. The original design was published in DIYAudio.com There are mamy other amps, some are really stinking good and complicated. If you want something w Bluetooth then Dayton based amp from Parts Express might do the trick, but with limited power. Please remember you need almost ten fold power increase to get perception of doubling the acoustic power (including power compression in loudspeakers due to voice coil heating up).

[@ayylasco]

@@pliedtka Thanks for your response. Unfortunately, I've already completed the build using yamaha yda-138E board which sounds just fine for my application. I'll take a note of that when building another speaker. Thanks!

[@pliedtka]

@@ayylasco Good for you 👍. The class D technology gets better every day. I heard the top of the line Hypex N Core module based amp and other than being brighter sounding than class AB it's a very good one. ICE modules are also very good. But if ever you will have desire to build something from scratch on discrete components Mike's SymAsym (class AB) is a good amp to start with. Sounds nice and warm, w/o the glare and harshness of cheap class D amp. Toid, guy on YT with diy spkrs channel did review of some little amp that was actually quite good, I think it was one of the Dayton amps. My friend also uses their biggest class AB 2ch amp, not bad for the money.

[@DAVIDGREGORYKERR]

High strength Acetone will strip the casing off.

[@uK8cvPAq]

Have the heatsink transistors got insulators? Sometimes they can puncture during prototyping and intermittently short the tabs to the heatsink.

[@linorocchi9339]

Thats why i dont like Darlingtons. Go with drivers and output transistors. Good luck.

[@TAXCOLLECTOR-mx3mg]

I worked with Dual Darlingtons and wasn't impressed. Yes, stick with regular output transistors.

[@pliedtka]

Maybe the ones he uses suck. But there are plenty of designs that use Sanken Darlingtons, even my Denon AV receiver. It's not the fastest or cleanest but can do 100W at 8ohm from one pair of 15A devices and drives my SB Acoustics 2ways that use 4ohm midwoofers without too complaining. But yes for a serious amp, driver and separate out transistor would be my choice.

[@イエンスヨハンセン]

Sorry to see this. Some potential solutions in the comments below - worth looking into?

[@Mritsraining]

driver bc639...... output stage driver bd139/140 main output transistors tip35c/ tip36c....

[@unregistereduser2]

I've sketched up this circuit, and am going to play with it myself; see my drawings here: github.com/prosper00/Circuits/blob/master/JAT%20EZ%20amp/JAT%20EZ%20amp.pdf Ive implemented a few of the suggestions from the comments here, and I'll buuld it up and test it myself over the next little while. Personally, I'm not too fussed about really high bandwidth performance or HF distortion, so I'm sticking with darlington outputs. We'll see what distortion looks like. Project repo and drawings here: github.com/prosper00/Circuits/tree/master/JAT%20EZ%20amp

[@hamid185100]

So how it goes Is it working fine or not ? Hopefully it won't blowing your output transistors

[@hamid185100]

He mate I want to design a single supply transistor amplifier need some help from you if can if you have any contact I can send you schematic that I am trying to build

[@unregistereduser2]

@@hamid185100 I haven't done too much with this yet. I decided I needed a function generator to test it, so, that's what I'm working on lately: github.com/prosper00/STM8-AD9833-Function-Generator

[@EngineeringVignettes]

What's the frequency response characteristics of your darlingtons? It's clearly a high freq issue... Or its some other component in the system reacting to a hundreds of kHz signal. Don't get discouraged by this. If you can determine the root cause of failure then you learn something new about amp design. Cheers,

[@poptartmcjelly7054]

Your darlingtons might just be too slow. Darlingtons aren't really good for high frequenscy applications as far as i know.

[@quantumleap359]

If you look through quality audio amplifier schematics, you will never find single pack darlingtons in the output stage. Discrete EF design is much more reliable.

[@iblesbosuok]

May be it is time to switch to mosfet power transistor. IRF530, IRF9530, IRF620, IRF9610 are good alternatives. Cheers from Indonesia

[@ferrumignis]

MOSFETs have terrible SOA compared to bipolar transistors They are great for switching operations (e.g. class D) but not for linear amps.

[@larryshaver3568]

i finally found the sad news i was heartbroken when i had to euthanize Duchess

[@JohnAudioTech]

No fun having to put a pet down.

[@1pcfred]

Why are you testing an audio amplifier at 100 KHz?

[@shutdahellup69420]

To check if it wont distort too much around 20k

[@1pcfred]

@@shutdahellup69420 why? No one can hear that.

[@ahmedalshalchi]

3rd harmonic is fair enough as cut-off freq. for audio amps and should be attenuated heavily by 40dB or more...

[@ferrumignis]

@@1pcfred The point is not to amplify signals up to such a high frequency, but to ensure you have plenty of open loop gain remaining at 20kHz. John did explain this in the video.

[@threeMetreJim]

@@ferrumignis John has a distortion measurement system. Why does he just not sweep the input up to the highest frequency of operation and monitor distortion? Wouldn't that make more sense for an audio amplifier. Then work out why the distortion isn't meeting required spec. I'd be more inclined to input a low frequency square wave and measure the slew rate of the amplifier, to see if it could work quickly enough at the highest required frequency. www.audioholics.com/audio-amplifier/amplifier-slew-rate

[@alexpmK3]

Better off building a harry lythall 4w amp son..

[@ahmedalshalchi]

John Audio Tech ... Don't go extreme... 3rd harmonic is fair enough for cut-off freq. for audio amps and must be attenuated heavily by 40 dB or more.....

[@Mr_Meowingtons]

well that Sucks

[@scottmiller3025]

Hope you didn't get them from Cheng chzen or something like that..lol I lost my -ss on about 100bucks of trans from there.

[@MagruderSpoots]

I'm not gonna say first.

[@Theineluctable_SOME_CANT]

Very interesting!

[@Theineluctable_SOME_CANT]

Darlingtons....

[@adarshraksh]

Hey John, I needed some advice from you ; i had a single TDA7498 AMp that worked well on it's own (3+years) Then i decided to add one more with a common power supply and added 2 pre amps one for each. But issue is both amps burnt off when my rca cables moved and made some noise. I never had this problem when running a single amp. I suppose it's some grounding issue? All connections done were the same as the single amp setup except now both amps sit on the same PSU TIA