A little less PAB (Q)

Pete · Post by **Pete** » Fri Aug 10, 2007 9:57 pm

If you wanted to make it a bit more subtle, how would you go about getting less boost from your PAB?
I'm wondering if using two 15M in place of the 22M could work, but I doubt it.

Funkalicousgroove · Post by **Funkalicousgroove** » Fri Aug 10, 2007 9:59 pm

Sure it would, Just reduce the resistors. Keep in mind that your resistors are in paralell so whatever value you are using is effictively cut in half, ie 22M actually makes 11M of lift, so 15M would make 7M5.

chris_sanford · Post by **chris_sanford** » Fri Aug 10, 2007 10:41 pm

Funkalicousgroove wrote:Sure it would, Just reduce the resistors. Keep in mind that your resistors are in paralell so whatever value you are using is effictively cut in half, ie 22M actually makes 11M of lift, so 15M would make 7M5.

Funk,

Perhaps you wire your pab relay differently than I do... but with the normal D-style pab, the bass 22M PAB resistor is inserted from the wiper to the top of the bass pot, so no matter what size your treble PAB resistor is, it is limited by the value of the bass pot itself in terms of how far above ground it can be, not by the bass side PAB resistor per se.

chris

heisthl · Post by **heisthl** » Sat Aug 11, 2007 12:07 am

It's true the PAB changes the direct connection of the top of the bass pot (P1) to the bottom of the treble (P3) to a 22M between these points. It also separates the direct connection of the wiper(P2) and P1 of the basspot and leaving 22M. By going to a pair of 10M or even better 4M7s you will notice a lessoning of the PAB volume. Try it you might like it.

ampdork · Post by **ampdork** » Sat Aug 11, 2007 12:58 am

Could I barge this thread and ask which schematic shows a correctly wired PAB for a non-hrm ODS?
Thanks,
Shad

Pete · Post by **Pete** » Sat Aug 11, 2007 3:38 pm

ampdork wrote:Could I barge this thread and ask which schematic shows a correctly wired PAB for a non-hrm ODS?
Thanks,
Shad

Barge away, but sorry I can't help with the schematics, they are around here somewhere. I think most of 'em don't show the resistors in question. (so that would be incorrect/incomplete)
I just tried 10Ms and it seems to reduce the boost some

. Amp is HRM.
(just found related info, may be some help >> https://tubeamparchive.com/viewtopic.php?p=22272#22272)

FUCHSAUDIO · Post by **FUCHSAUDIO** » Sat Aug 11, 2007 4:10 pm

If you haven't noticed already, when you jiggle the Rock/Jazz switch in between positions, you get PAB. Andy Brauer claims he "discovered this back in the day", and told Dumble to use 3-position switches for the boost.

In any case, by interrupting the two center lug connections to the R/J switch you get PAB, and can adjust how much, buy reducing the values of the resistors across your switch.

22-M is a good value to stop popping, and reducing down to 10-M or lower (Dogears has gone as low as 470-k I bleieve) can reduce the gain jump substantially. BUT: Remember that the amount of jump is relative to where the tone stack is. With the amp in Rock mode, and everything turned up, the gain boost is subtle. With the amp in jazz mode,tone controls low, the boost is substantial.

ampdork · Post by **ampdork** » Sat Aug 11, 2007 8:07 pm

I see said the blind man.
Thanks!!!

Luthierwnc · Post by **Luthierwnc** » Sat Jul 12, 2008 2:17 am

I'm resurrecting this old thread to float a question on my current non-HRM build. Background; hardwired for rock mode, standard (not lite) PAB circuit, triple checked for connections, grounds and continuity, 22m resistors.

The boost on this is really overpowering. On the scope the increase over the standard tone circuit is slightly over 4X with no visible distortion in the waveform. I'm getting ready to try some resistor changes but I wondered in the intervening time if anyone has some favorites values to recommend. This is basically the "grail" schematic with a couple unrelated tweaks. Given time to turn some knobs it actually sounds good but it isn't useable at these levels.

Thanks, Skip

ic-racer · Post by **ic-racer** » Sat Jul 12, 2008 11:13 am

Luthierwnc wrote:I'm resurrecting this old thread to float a question on my current non-HRM build. Background; hardwired for rock mode, standard (not lite) PAB circuit, triple checked for connections, grounds and continuity, 22m resistors.

The boost on this is really overpowering. On the scope the increase over the standard tone circuit is slightly over 4X with no visible distortion in the waveform. I'm getting ready to try some resistor changes but I wondered in the intervening time if anyone has some favorites values to recommend. This is basically the "grail" schematic with a couple unrelated tweaks. Given time to turn some knobs it actually sounds good but it isn't useable at these levels.

Thanks, Skip

If you read between the lines on the other posts they are also saying that if your tone stack loses too much signal, your PAB jump will seem to be too large. Are you sure it is wired in Rock and not Jazz, for example? Or maybe you have a pot that is too small in value somewhere in the tone stack?

jelle · Post by **jelle** » Sat Jul 12, 2008 2:03 pm

FUCHSAUDIO wrote:If you haven't noticed already, when you jiggle the Rock/Jazz switch in between positions, you get PAB. Andy Brauer claims he "discovered this back in the day", and told Dumble to use 3-position switches for the boost.

In any case, by interrupting the two center lug connections to the R/J switch you get PAB, and can adjust how much, buy reducing the values of the resistors across your switch.

22-M is a good value to stop popping, and reducing down to 10-M or lower (Dogears has gone as low as 470-k I bleieve) can reduce the gain jump substantially. BUT: Remember that the amount of jump is relative to where the tone stack is. With the amp in Rock mode, and everything turned up, the gain boost is subtle. With the amp in jazz mode,tone controls low, the boost is substantial.

Here's another thought: the 1M vol pot limits the impedance to max 1M. If you want add. boost, lift the vol ground too. However, I'd expect grid clipping at V1b....

Luthierwnc · Post by **Luthierwnc** » Sat Jul 12, 2008 2:18 pm

Yeah, the 0.1 bass cap goes to both poles. One N/C throw goes to the 1 pin of the treble pot and the other N/C throw goes to the wiper of the bass pot. There are 22m resistors from the poles to both throws. There is no mid boost and no R/J.

This one is a little different because I am using the "strat switch" diagram I threw up here a few months ago (see below) but in the N/O position I reference ground through the bass pot. BTW, the strat switch works really well and I'll update that thread when I get this thing in the box.

sh

Luthierwnc · Post by **Luthierwnc** » Sun Jul 13, 2008 1:13 am

I pulled the big resistors and put a 1m pot across the throws set at about 480k. It is now much more useable. My sense is this amp will take a bit of fiddling to reach it's full potential. It will also take some care setting the OD pots so it doesn't get too frisky -- the boost still packs quite a wallop. With the OD and PAB, it has a lot of bite. I'm testing it right now through a Thiele with an EVM12L.

Thanks all for looking, sh

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