a tiny amp w/power amp distortion

[Joe Davisson]

You won't be sorry, unless you expect volume:
http://www.analogalchemy.com/pedals/kathode.html

Power tube saturation without the tubes :mrgreen:

-Joe

[Lonestarjohnny]

Hey Joe, Where ya goin with that Mini-Amp in your hand ? That's somthin interesting, can it be slaved to a bigger amp ? maybe a way to Give my poor Ol Peavey classic a lil tube Saturated tone ?
JD

[Mark Hammer]

How should the speaker be rated for wattage?  I'm not expecting massive volume, but given that there ARE speakers rated for only 250mw, etc., I just want to gauge appropriately.

[Joe Davisson]

I'm guessing not more than one watt. You can also ditch the preamp and use something else instead, if you want. I previously tried a Class-A version but the output was too low. Bummer...

You could use a small cab and mic it. Or take the signal off the transformer output through a cap, into a high-impedance buffer or amplifier input. I think some sort of speaker should be attached, though.

-Joe

[aaronkessman]

do you have any sound clips?

[Doug H]

Cool. I have one of those transformers, it's the same one used for "Bob's Octavia". I will give it a try.

Looks nice, Joe.

Doug

[Marcos - Munky]

Cool, Joe. Thanks for share it with us.

[Tim Escobedo]

Very cool, Joe. I've never tried a push/pull setup. The single transistor transformer coupled amp I made is killer tone, though truly "bedroom" volume. I tried working it out once with my faulty math and found the power level somewhere in the tens of milliVolts. Loud enough to drive a speaker cab  at bedroom levels, but that's it.

As far as slaving it to a bigger amp, I found that the transformer secondary needs a low value load at all times. I used a 10 Ohm resistor. Without it, the circuit gets thrown way out of whack.

I've also done a couple single ended direct coupled (oops, meant capacitor coupled) amps using small signal TO-92 transistors. BJT, Darlington, MOSFET... These can get significantly louder, though without heat sinking, they run the risk of frying. But, man, I was getting some incredible tone just before that 2N7000 melted...

[Brian Marshall]

ive never actually looked at a push pull amp schematic before.  i had to look at this for about 10 minutes to figure out what was going on.....

At first i didnt see the +9v  center tapped on the transformer.  

do you run in to any problems with the didoes, and cross over distortion?

[Joe Davisson]

do you run in to any problems with the didoes, and cross over distortion?

It's anyone's guess. I think the circuit should be enclosed in a metal box, because of the diodes. I compared the top and bottom halves of the push-pull section by ear, and it seemed fairly equal. I'll worry about that more when I get around to a larger version.

Very cool, Joe. I've never tried a push/pull setup. The single transistor transformer coupled amp I made is killer tone, though truly "bedroom" volume. I tried working it out once with my faulty math and found the power level somewhere in the tens of milliVolts. Loud enough to drive a speaker cab at bedroom levels, but that's it.

I might attempt a Class-A in a headphone amp, or a larger amp. The 9-volter just can't swing it. I'm pretty amazed at the output difference between the two, though.

-Joe

[aron]

>The single transistor transformer coupled amp I made is killer tone, though truly "bedroom" volume. I tried working it out once with my faulty math and found the power level somewhere in the tens of milliVolts. Loud enough to drive a speaker cab at bedroom levels, but that's it.

I tried that one Tim and it was cool although really low volume.

I need to try Joe's one too.

[Ansil]

mental note on this..  mousers verrsion of this output transformer can handle more current..  just thought i woudl drop my .02 here..  also it makes a nifty little micro tube amp if you get the ma right.. i am still working on not frying them.. but they take like up to 300v...

[Alpha579]

Im suprised the 2n3904 could handle passing that much current. Do u think mpf102's could do that?

[Jered]

Hi Joe, I built this last night and it sounds good. With headphones it sounds GREAT !
  Thanks, Jered

[Mark Hammer]

Is 9v the power supply "destination" here, or is the circuit tolerant and well-behaved (maybe even better behaved) at higher supply voltages?  For instance, would or should one expect more oomph with an 8-pack of AA's?  I know it makes a helluva difference with 386-based amps.

[Jered]

Hi Joe, I built this last night and it sounds good. With headphones it sounds GREAT !
  Thanks, Jered

[Joe Davisson]

Jered, thanks for checking it out, with the headphones even...

Mark, I haven't raised the voltage yet. It would need rebiasing. I think it's around .75 watts @ 9v, the transistors should handle about double that. Changing the 1k resistor won't help much either, it doesn't really work like that. I'll post more on increasing output when I can test it out more.

Been playing on it for a few days, and it seems good. It's growing on me a lot, actually, so I can't wait to make a bigger one. The power amp has overkill gain, but that lets a single stage preamp do the job, keeping it simpler.

-Joe

[Jered]

With the proper, matched, speaker I think this would be one incredible sounding bedroom level amp but I'm not to sure about matching a speaker to a circuit. Ohms, watts, sure, no problem, but freq. response, etc, I'm clueless.
  I'd prefer to buy one new, the smaller the better, needs to be 8 or more ohms. Any ideas?
Thanks for any help, Jered

[RDV]

With the proper, matched, speaker I think this would be one incredible sounding bedroom level amp but I'm not to sure about matching a speaker to a circuit. Ohms, watts, sure, no problem, but freq. response, etc, I'm clueless.
  I'd prefer to buy one new, the smaller the better, needs to be 8 or more ohms. Any ideas?
Thanks for any help, Jered

Well, you know the smaller you go, the less bass response you'll get. I'm thinking of buying the cheapest, lowest rated wattage 12" I can find for my bench amp purposes. I've already got a small(barely bigger than the speaker) cab for it. It has a 12" Black Widow guitar speaker in it now which was not my best purchase I ever made. It's loud and all, but a 50 watt amp will barely budge it, so it's about a brittle sounding mother. It seems a really low wattage rated 12" would give it up for these little 1/2 watt to 1 watt amps.

Regards

RDV

[Ansil]

i got a good working beat up tube radio speakr that is 12" for like three bucks if sounds stellar  but it looks awful

i had two of them but i used one in an amplifier i did some timeago