AO-44 distortion amp

[Toxophilite]

So I'm making this little distortion amp out of an AO-44 to use with a single 12" speaker.
I want to play around with actual amp distortion rather than pedals so I'm going to do some switching between this amp and my clean amp


Because I might want to add tremelo I used this schematic (see attached drawing..from a gretsch forum guy)


But instead of using the12ax7 in paralell I just used one half as suggested by S. Luckey


Annnd because I wasn't thinking I used a fender style cathode bypass 1.5k resistor and 22uf 25V cap
Also because I'm fender centric I used a 33k resistor between the input and grid instead of the 68k shown


my basic A0-44 isn't exactly the same as S. Luckeys peewee or the one shown in this schematic(I've heard there were variations.)
It looks to be the same as the schematic I attached


Nevertheless I have it up and running
With nothing plugged in and cranked it has some white noise, not terrible but there. I suspect this comes from all those carbon comp plate resistors and old caps. that's my guess


It sounds pretty *&(*& loud!! Maybe too loud  starts to break up around...2 maybe 1.5 on the volume!


I'm curious about a few things:


1- Does using just one triode of the 12AX7 make for more or less gain than using both triodes on parallel...or no difference


2 - and perhaps related, does using one half make the fender style bypass arrangement okay or should I switch to the one in the schematic


3 - Would I be better off (noise and gain wise) with the 68K resistor on the input


4 No negative feedback in this  drawn schematic
I see you have a a 68 resistor in the negative feedback circuit of your AB763 preamp style AO-44 peewee S. Luckey
This setup has a 82K resistor going to the speaker tap
does this look okay with the setup


thanks!

I'll l see if I can Jschem something up too

[Toxophilite]

This is what I have so far


I'm wondering if the .0047 cap coming from the plate of the 12ax7/ecc83 to the volume control isn't taking A LOT of bottom end out of the sound

[sluckey]

I'm confused about your drawings... You have a stock AO-44 schematic, another schematic, and a layout. That layout does not match either of those schematics. So, do any of those three drawings actually match your amp?

[Toxophilite]

Okay
You actually have it pretty well figured out.
As you said in your Peewee build on your site, There are variations with the AO-44



-1st 'layout' was made and given to me by a  fellow as an example of a simple preamp that he likes to put in front of an AO-44 power amp. i though his power amp was stock but another variation. he might've monkeyed with it as it has NO NFB


- 2nd is a stock AO-44 schematic as you said . THis is what mine is.(you'll notice it's a little different than yours)



-3rd schematic in my second post is the one I made to represent what I've built.
 It combines the preamp from the 'layout' with the power amp from AO-44 I should've just made this and posted it



Sorry for the confusion

[Toxophilite]

Is it too straightforward now?


Is it this tweed style tone stack that's making this amp sound kind of midrange and honky with not a lot of bottom?

[DummyLoad]

Is it too straightforward now?


Is it this tweed style tone stack that's making this amp sound kind of midrange and honky with not a lot of bottom?

.0047uF on first preamp. try a .01uF - .022uF


--pete

[Toxophilite]

I tried that and swapped in a .02 Not a big difference

[sluckey]

Is it this tweed style tone stack that's making this amp sound kind of midrange and honky with not a lot of bottom?

Yes. That is the exact same tone circuit that's found in the tremolo channel of the original Marshall 1974 (18 watt) amp. It's also used in the popular 18 watt lite IIB amp. This tone circuit will sound quite different from all your AB763 amps.

Try replacing the .0047 on the bottom of the tone pot with a .01 for some more bass.

BTW, since you are considering adding tremolo, you may want to look at the Marshall 1974. You already have the preamp. Very easy to add the trem using the other half of the preamp tube for the oscillator, just like on the original Marshall.

[PRR]

> kind of midrange and honky with not a lot of bottom?

Let's find out if it is the stack or some other issue.

Snip the tone pot network. Size the coupling cap for full bass. If possible, add 100pFd across the top of the Volume pot to carry the highs past 6KHz. Now the whole amp should be _flat_ far beyond the guitar band. If it isn't, look for other wrong values or a sad speaker.

[Toxophilite]

I tried the .01 cap to ground on the tone pot in lieu of the .0047 as per S. Luckey suggestion
Then I tried the amp at volume today and found it sounds basically the same it does at low volume
mids and poky highs, no bottom.
I can't try bypassing the tone circuit here but I will at home and try it at apartment volume, now that i know it's not the volume I was playing at that was affecting the sound.

Also this thing is ^%$&^%$&^% LOUD!
I was going to use it alongside a 2x10 homebuilt Ab763 deluxe but when you crank it enough to get it completely distorted it flattens the clean sound of the deluxe! They sound great together but the difference in volume is pretty extreme
I though this thing would be pushing 10-12 watts..whew!
It's almost like I'd be better off with a cranked Champ (build!..I'm NOT going to buy one at today's prices)

I used it with tow different 12" speakers, both around 50 watts and 8 ohms, one an older Rola the other a modern fender Emminence
Both have sounded good with the deluxe heads and in other applications

[Toxophilite]

Okay so I bypassed the tone control and put a bright cap across the volume
Sunds better but still not tonnes of bass. Maybe it's the .02 blocking caps everywhere
Would bumping it up to ,1 on the power amp and .47 elsewhere like an AB763 make a  significant difference?

[sluckey]

I had plenty of bass on my pee wee. I used .02 coupling caps everywhere. I had to remove the 25µF cathode bypass caps from the preamp triodes to lower the bass.

I would think you would want to lower the bass also since this is your "distortion" amp.

[Toxophilite]

Yeah your right about wanting the distortion amp to be more poky but It's weird when the bottom drops out of your sound.
I'm going to try the AB763 preamp and see if that's more what I'm used to hearing.