Adventures in a one transistor audio amplifier

[@snaprollinpitts]

great video, thanks John, I'm really like that you show us the distortion, it gives us an idea just how good it is in that application.

[@Ogma3bandcamp]

Excellent video John.

[@acmefixer1]

The original Delco radios with the big heatsink on the back didn't use a transformer for the speaker. They used an autotransformer with a 1:1 ratio. 😁 In other words, they used a choke, with the speaker connected across the choke winding.

[@cassvirgillo3395]

Hi JAT, oh, and Snickers, Excellent video, I learned a lot. Very timely, I have just been experimenting with one transistor audio amps of late. I really enjoy your videos, Thankyou for the time and effort you spend to make them, a goto channel. Take care, C.

[@thermionictube7832]

This curcuit sounds way more musical than your other dual transistor one.I think Id rather build this for my turn table and forgo with my plans of a tube preamp stage. Thank you so much for this informative video. And yes a simple coupling cap would block DC and keep the transformer and speaker safe.

[@MichaelBeeny]

Uses almost as much power AS a single ended valve amplifier! To get the best results you really need a transformer with a primary and a secondary which will load both sections correctly. Probably about a 20/1 ratio. An old Ford car radio I once owned did have this kind of single ended class A amplifier, and did use almost 1 amp under quiescent conditions. Because valves were used prior to this, 1amp was a very low power consumption compared to a valve radio drawing 5-10 amps.

[@HillOrStream]

+Michael Beeny 20 to one? Seems high to me, explain?

[@MichaelBeeny]

+HillOrStream The relatively high collector impedance vs the low 4 ohm loudspeaker. Maybe 20 is a little high, probably nearer 10:1

[@HillOrStream]

I was thinking they'd make the primary side quite low being that they only had 12V to deal with and would have wanted to push a lot of current through the transformer to maximize power output. I'm thinking of the early car radios for this circuit. I remember those old Delco radios with one huge (stud mounted ?) round Germanium transistor in the middle of a large heatsink.

[@petesclark]

Maybe you could try hooking the speaker up to the 8 Ohm tap to act as an auto-transformer for impedance matching and get a cleaner sound.

[@JohnAudioTech]

+Peter Helgeson I tried that and various other combinations and the sound was tinny. This was as good as I could get it with that transformer

[@judges69]

Great channel my friend, keep it up and going.😀

[@auroredelfosse2202]

Each time I fall on your videos, I'm always amazed of your calculator... :-D

[@tiagoqueiroz6002]

Awesome explanation

[@chrisramosbushcraft866]

Wow. I'm impressed. What transistor are you using.? I wasnt paying attention. Where are you located. I wish I can meet you. I'd really like you to teach me this stuff.

[@ferrumignis]

It would have been interesting to see the effect of moving the top of the bias resistor from the supply rail to the collector to add negative feedback.

[@Raz82000]

What resistor modifications I have to make if I use 2n3055?

[@KarlAdamsAudio]

Good fun. Interesting how little the bias current changed when removing the emitter resistor - I suspect there might be more voltage dropped across the current shunt of the multimeter than that resistor, though.

[@KarlAdamsAudio]

...not to mention the transformer winding - actually that might be contributing to the unexpected thermal stability, since the DCR of the winding will increase by just under half a percent for each degree C of temperature rise..

[@smartclassupdater8741]

why not you put Vbe resistor and ground capacitor from base of transistor

[@listerine-pr5lt]

What if you add a large electrolyte capacitor say 2200UF series to your speaker lead ? Will it oscillate?

[@gerardovalle4794]

What kind of capacitor did you use?... What is the value?

[@fernandogarcia7250]

Hey I have the TDA7057AQ and I was wondering if you could help me with a circuit to connect it to a speaker. Thank you

[@jemussi7842]

tried a circuit like this without the emitter degenerator resistor for a qrp rf amp using a power npn transistor rated for rf frequencies. I had a 1Hz 'motor boating' issue using a small guitar amp 12V supply and no useful output. Using a heavier duty PSU from a yamaha keyboard the 'motor boating' went away and I have slught amplification. So yes it's power hungry!

[@maeve3149]

So what could i do to get more power with a build like this? I mean something around 5 watts.

[@sawajiri100]

how many turn of coil in transformer for secondary and primary?

[@Detailverliebt]

hey John this was a nice test. Have you ever tried to build a SE transistor amp with decent power output like 10-20 watt? coz thats what everybody wants but does not exists ;-) (ok the nelson pass stuff but I mean with an output transformer)

[@researchandbuild1751]

Youll definitely never hear that distortion at 100hz

[@wilbertmorales1461]

can i use tip29 transistor here instead?

[@noelj62]

are you using a signal generator or a portable player as the source. I wonder what is the distortion of the source in this case since this amplifier does not have a feedback loop.

[@JohnAudioTech]

+noelj62 I used my portable player with uncompressed WAV files. I once recorded the player into my computer and found the distortion to be .002% but I can't tell if that is the computer's audio or the player (or both). It is so low it doesn't really matter. Any distortion the scope shows is from the circuit itself. The emitter degeneration resistor cuts down the gain and some distortion.

[@NotCaily]

can i hock up a speaker the same way as the transformer or nah?

[@NotCaily]

no i cant

[@peterjenkins886]

so much technical jargon....

[@larryshaver3568]

what colors would the bands on a 1 ohm resistor be? would it be black brown black?

[@JohnAudioTech]

That sounds correct.

[@kpanic23]

Should be brown black gold (10x.1)

[@larryshaver3568]

thanks for letting me know of that discrepancy

[@sergioasoliveira]

What music is this?

[@MrTigger015]

Can I make this circuit without transformer?

[@JohnAudioTech]

Yes, replace the transformer with a current source. Use coupling cap with speaker.

[@MrTigger015]

imgur.com/gallery/U1wm2 me and my friend figured out some schematics which one is the best?

[@raykdreisatzgehtanders7239]

I don't get it. Normal amplifiers use two transistors, one NPN nad one PNP. How can, when using only one transistor, the output be AC? A transistor only works in one direction, so where does the opposite polarity part of the wave come from.

[@JohnAudioTech]

The output is a varying signal. Think of it as AC with a DC offset that prevents it from crossing zero where the transistor won't work. Using a capacitor you can remove the DC offset and get an AC signal.

[@raykdreisatzgehtanders7239]

@@JohnAudioTech Oh interesting, I already assumed that you are biasing that input with the resistor to make it DC. Pretty amazing that I works so well converting it to AC again.

[@Tbonyandsteak]

@@raykdreisatzgehtanders7239 I think since you put it through a transformer it will be as if it is push pull. Since Transformer only transmit the change of current. No matter if the primer side goes negative or not. The secondary output will be + - sinus.

[@azzamastronaut]

Hi JohnAudioTech, What is the music used here please?

[@JohnAudioTech]

KZbinr Cooldudeclem gave me this music.

[@azzamastronaut]

Nice Music though...

[@ebiscaia]

Hi, Is it possible to use a SE tube circuit as a pre? Thanks

[@ebiscaia]

BTW, are subminiature triodes any good for audio?

[@JohnAudioTech]

Single ended typically describes a power output stage for driving a speaker. In a manner of speaking I guess you could call a preamp single ended as this is the way the circuits are often designed.

[@ebiscaia]

What is your opinion of hybrid (tube/ss) amps? Have you ever tried to build one? Thanks

[@JohnAudioTech]

To me it is all about low noise, distortion and flat frequency response, if you can get that in a hybrid, no problem. Tubes are impractical to me because they need significant power to heat the cathode (among other things). Tubes look cool and are vintage technology, but I'll take the opamp IC any day. As far as "technical perfection" of the amplified signal, they are as close as it gets.

[@ebiscaia]

+JohnAudioTech Thank you for your insights!

[@EYEONEVENTS]

you are amazing

[@darshanaprasad852]

Good vidio

[@SciPunk215]

Noob question here, but how about just an inductor instead of that transformer, if that's really what you're using it for.

[@JohnAudioTech]

+SciPunk215 An audio quality inductor would work much better (this one rolled off the bass). I simply don't have one available. In a new video I will post soon, I did away with the inductor/transformer and used a current source.

[@watup110875]

nice 😎

[@RandomSTUFFzors]

At the risk of sounding like a complete doofus, I have to ask. If the transformer/coil in this circuit was designed to isolate the DC current from the speaker, wouldn't a decoupling capacitor do the trick instead?

[@JohnAudioTech]

Replacing the transformer or coil with a current source and using a capacitor is another way of making this circuit.

[@RandomSTUFFzors]

Oh, I see. Thanks, man!

[@NotMarkKnopfler]

What is the function of the capacitor on the input? Thanks.

[@JohnAudioTech]

There is a DC bias voltage on the base (input) of the transistor and you don't want this to be affected by whatever you connect as a signal source or affect the signal source itself, so it is best to block the DC with a capacitor.

[@EYEONEVENTS]

works as a diode

[@markanderson8066]

The Future Sound Of Egypt no, diodes work as diodes... diode allows current flow in 1 direction. cap blocks all DC but allows ac in both directions.

[@joohop]

i sent you a gmail boy let me know what you think

[@Markoul11]

that's not a class A amp more like a class AB. For pure class A you need a 100 ohm resistor in the CB. Quiescent current will be at 5.35 A and at full scale operation peak power on the transistor will be 200W and on the 8 ohm load 13W, less than 7% efficiency. Voltage amplification is 8 and maximum unclipped Vout(rms)=3.45V or Vp-p=9.75V with Vin=0.458 mVrms or Vinp-p= 1.3V .

[@thalestiago1]

classe a

[@Nolanyoyo]

can you be my friend on Skype or something

[@val.juazeirodonorteceara6471]

show John