The Amp Garage

Latest update - put a 1m across each resistor, lowering them both to 500k. It's different - might sound a bit... "crunchier" in a good way. But I still hear the buzz. Anyways, for fun I just hooked the scope up again, and made a single trigger on the guitar - this is the output i got. Yellow is the ...

please, by all means, keep giving me suggestions!

I actually havent tried that yet - will see if I can do that one.

change the PI stopper back to 10k put a 100p fizz cap across the PI I use 5k6 grid stops on my big tubes similar gain amps ok, changed the pi grid back to 10k. I put the 100k's on the power tubes just to be extra completely sure :-) Put the fizz cap in (120pf) still same buzzy distortion. Hmm... wo...

ok, tried it out: paralleled the 330k with a 180k for about 116k. Left the 220k as is. It's the same as described before - the PI distorts the same, just at a different setting on the gain knob. The buzzy distortion is still there. (btw, I've taken the ppimv out for now - also the cut control. Also ...

Thanks. But that resistor isn't in the Komet circuit. There is the 220K/330K divider there though. However, I previously messed with it - and put a 500k pot in there instead - unfortunately it only made a difference in where the gain knob had to be, before the pi distorts. Hmm.. wonder if it would m...

Well, it doesn't sound "bad" per se - it's a bit fizzy, but I think it's possible to dial that out with the cut and presence controls. I've had the schematic and docs lying around for a while, and finally chose to build it after hearing those demos on youtube. However - aiming for those sounds he us...

Yeah. I' tried a balanced JJ 12ax7, a balanced tung sol 12ax7, also a few "normal" jj's plus also an EH 12AY7.
With the 12AY7 it's like the sound is the same, biggest difference is where the gain knob has to be before breakup.

Still messing around, and getting increasingly frustrated. I did try playing around with the 220K/330K divider, replacing it with a 500k pot. I could change when the PI would start distorting, but it still started distorting the same way - a buzzy distortion, like it's overdriven a lot, and then "fa...

Hey again. Yeah, I've tried another guitar, and another cable. Same thing: plucking the D A or E string produces a buzzy distortion that fades out rather suddenly, in a sort of raspy way. I think I'm quite certain that it originates in the PI. I've been using a headphone amp to listen to various poi...

I'm not using the official layout, I made a PTP layout myself.
You can see it here: Tried lowering the cap on the second grid to 47nF.
Didn't remove the buzz. :-/

Managed to put together a headphone amp thing, for testing out the signal at various places. The distortion does seem to appear simultaneously at the pi plates and the ot, so I presume the problem originates around the pi. Reading up on Merlin, among other things he suggests putting a smaller cap on...

ok, tried disconnecting the cut-cap. No difference in the buzzyness.
Tried upping the grid stoppers on the power tubes to 5k6. Still no difference.

The buzzy distortion is most evident when plucking the lower strings, E, A, D.
The gritty raspy decay mostly on chords.

There must be coupling caps on the PI plates? It would be extremely unusual for the PI to be dc coupled to the power tubes. This is one of the problems with trying to get help with one of these amps where there is no schematic. It is hard to tell what is going on. I'm going to assume that the PI pl...

@reeltart: Ok, I think I understand. No, my cable doesnt “gwuable” :-) @Mike: The onlly cap between pi and powertubes is the cut control I really hope my treble pot isn´t bad - its a pec pot. Theyre kinda expensive :-) Anyway the tonestack seems to work as intended, so Im hoping thats ok. The Larmar...

I would always advise people to build the amp and make it work before installing PPIMV. That has to be the fail here.. has to be.. Whats that guitar? Why am I hearing what sounds like an antenna picking up Sun spots? at those settings even flipped over and unshielded I think that is too much cosmic...