Mods for the Pignose amp? [schematic inside]

[Harry]

I bought one of those pignoses and the thing is very neat. I was wondering on some mods that maybe someone could tell me if they wouldn't be too hard to implement:

• Modding so the volume works as a volume control rather than gain!
• Adjusting so that it is a little cleaner, without just using the back off the guitar's volume trick. Also without sacrificing too much volume if possible.
• Changing the 'Preamp Out' to a speaker out.
• This one may be a bit of a stretch, but replacing the speaker with something that may improve the sound/bass/headroom/volume. 5" 8ohm
• Well I've been playing the hell out if for quite a bit now without using the external adapter (hums pretty badly), but I was thinking of removing the wire wrap inside and installing a 6 C or D battery holder! I'll have to first how long the AA's work to see if it even needs this.
• Any other ideas?

[brett]

Hi.
Interesting schematic.
I wonder how much extra "oomph" you'd get if you used extra transistors in parallel with T3 and T4?  ie made a quad instead of a pair.
I suspect that the 3 ohm resistor is 2.7, not 2k7.

RE: Adjusting so that it is a little cleaner
Try upping the voltage from 9V to 12V.  That should increase your clean power output a little.
The amp will probably handle 4 ohms output impedance ok, so add another 8 ohm speaker in parallel.
You could add a "drive" pot.  Wire a 1k variable resistor in series with the 100uF cap on the emitter of Q2.  That will give control over how overloaded the output transistors are.

RE:  batteries
Go for NiMH.  Even cheap AAs are good for 2000mAH.  Six of them will give you almost 24 hours of of full volume (assuming about 600mA power consumption).

cheers

[Harry]

Hey thanks for all the great ideas, will give me something to think about for the next few days.
What about those three resistors near the preamp out, could I remove those to relocate the jack for speaker out?

[brett]

Hi
I don't properly understand the question.
The wires for the speaker out jack are usually connected to the speaker terminals.
If you want to use the preamp out jack, I guess you could just cut its leads.
cheers

[Harry]

So all 3 of those resistors aren't important to the rest of the ciruit?

[brett]

Hi
The 68k resistor is feeding a tiny amount of output signal back to the emitter of Q2. (V = output signal at junction of the 33k and 68k resistors x 47 / (68000+47)).
At a guess, I'd say that it is supposed to reduce distortion.
So it's probably best to keep those three resistors in place.

Wow.  This amp is rated at 5W, according to the advertising. 

I just can't wait for next weekend and a chance to build one of these.

Do the transformers have any markings for impedance?  Or can someone guess their impedance? 
I don't know much about how these things work, but I'd guess that the output transformer has a winding ratio around 1:1 (eg 16:16 ohm, since an 8 ohm speaker is connected across half the output winding, and the emitter resistor on Q3 and Q4 is 2.7 ohms).
What about the driver?  1:1 maybe?  The input impedance for Q3 and Q4 looks low (about 100 ohms) because their hFE is only 30 to 40 and the emitter resistor is only 2.7 ohms.  So a 1:1 transformer would make for low collector resistance on Q2, which probably explains the large bypass resistor on the emitter of Q2.

Comments?  Experienced amp people?

cheers

[Harry]

That's a marketing scam I'm pretty sure the speaker is rated at 5 Watts the amp is rated at 3 Watts. For me it's absolutely perfect volume for apartment living.

I've got the thing open and there doesn't appear to be any markings on the transformers. Let me know if there's some way I can measure it for you with my dmm.

I think I'm going to add a 1k trimmer as you suggested and try upping the voltage to see if it makes much difference. Adding another 5" speaker inside the pignose would not be possible. A smaller one maybe, but I don't think worth the extensive modding. I'd rather keep it inside it's cabinet too, because this thing is built EXTREMELY well, it's a tank. That's sorta why I wan't to change the preamp output to a speaker out. Quite a while ago a friend plugged a little smokey amp into a 4x12 cab and I always wondered how it could get that loud. Imagine what the pig could do!

Also, for all you fuzz freaks this thing has a very decent fuzz-tone when cranked. I'm not sure how much the speaker plays a part in it though. I wouldn't mind seeing some Pignose boxes around. I think the pignose is under-rated.

[Arn C.]

If I can find mine, I will see if I can get the impedances of the transformers for you.  I remember, mine do not say anything either.
But, we have several impedance testers where I work.

Peace!
Arn C.

[Torchy]

Similar schematic but this one has an LDR in place of the diode ?

http://i7.photobucket.com/albums/y278/veroboard/pignose2.jpg

[Harry]

Interesting, thanks for posting that. You sure that's an LDR, that definately doesn't sound right.

[brett]

Hi
the bases of T3 and T4 (leftmost connections in top schematic) definately want to be biased to 0.7 volts, so a diode is the most likely device. in the bias network.  The resistor and diode might be replaced by a trimpot, but a diode is much simpler for the manufacturer.

I think that some of the magic of the pignose comes from the output transformer.  When they start to saturate, they often add some great fuzzy harmonics.  It's one of those reasons why a cranked tube amp sounds so good.
cheers