Peavey PAG 120 - Can I lower the touchy Ultra gain?

[marvintm]

Hi All,

My first thread was about this amp, and did a few mods and like it a lot now. One last thing should be simple but is kicking my head... How can I lower the gain of the ultra channel to clean it up for no distortion? Its active EQ is great. I like to use this channel underdriven and clean with the Pre down low, and the Post and Master past 6 but its still a tiny bit dirty even in that configuration, not to mention how jumpy the pre-pot is.

I have tried putting 500meg or less across the 1M pre pot, but that just limits the upper end of the pot. Need to soften the entire pot range (thinking of chaning R8), or reduce the gain of these stages somewhere at the tubes.

Will changing the cathode bypass resistor value mess up tube bias?

I have colored the schematic as Blue=Tube Inputs and Yellow=Tube Output

[Jazz P Bass]

Did you attempt to jumper the clipping diodes Cr1 & CR2?

[marvintm]

Clipping diodes are jumped, however I did this way before I realized that there is a relay contact that keeps a short across these unless the Crunch channel is on, making the jumper pointless.

This amp has three channels, Clean, Ultra, and Crunch.
Clean uses the first two stages.
Ultra uses the remaining stages with its own pre/post pots.
Crunch uses the remaining stages with its own pre/post pots AND throws the clipping circuit in.

[tedmich]

the diodes are not a clipping circuit, they are a "coring" network which serve as a poor mans noise gate, and as such jumpering them does very little to the sound IME

you want to calm down the Ultra channel? To sound like... the Crunch? Putting a ~52k accross the 1M ultra pot makes it equivalent to the 50k Crunch pot, and this is a mod people have done on JSX etc, but without the seperate EQs it isn't very useful IMO.

If you want to remove the "angry bees in a blender" 5150 type tone in the Ultra channel, replacing the cathode bypass caps (C15, C17 0.47uF -> 1.0uF) does this really well, as well as upping the 0.001uF C14 to a less screechy 0.0022uF. I love my Ultra 212 with these mods, with the best sound coming with everything dimed EXCEPT the active EQs which are at full cut and then delicately upped until the volume/tone is right.

[Gtr_tech]

I notice quite a difference when the coring diodes are removed, but thats me. If yer onna these guys whos old school enough to use the guitar vol to clean up, the diodes really make a mess of that. Eliminating them smooths out the transition from clipping to cleaning up. Even running balls out I noticed strange artifacts in the tone that went away when the diodes were removed. I'm just picky I guess....

[marvintm]

tedmich,
I can just envision my 12 year old self (many many years ago) and a couple friends gathered wide-eyed around a blender full of bees ready to hit the button. Very funny mental visual.

Anyway, I already did the cap mod sometime ago and it did wonders. Since this thread, I pushed the 22k input resistors up to 47k to help tame my EMG's. I also pushed R8 from 220k up to 1meg and that took a bit of the touchyness out of the bottom of the pre gain. I tried lowering the 3rd stage gain by taking R20 from 150k to 100, and it was smoother but without the clarity (as expected). I didn't like it as much, so back to the original gain.

With the input resistors and R8 now at higher values, it's manageable. It is after all a 120watt amp; a bit much for basement playing. Pulling a pair of output tubes works as well I guess.

I never thought of running the tonestack down low. Have to try that.

P.S.
I got a MXR 10 band EQ now. I hate having EQ's because you tend to keep messing with them, but it's certainly the most flexible amp "mod" yet.

Thanks

[tedmich]

The key to my "bedroom volume godzilla" sound is a small (2x5") Focal ported cab and a nanoverb in the FX loop, it allows the vol level to be cut down to very low with a nice flanged tone and a good low end rumble at low vol. Many people love a MXR 10/6 band EQ in the FX loop, where it both adds a level of tone shaping and can attenuate the output level. Pegging everything on the amp EXCEPT the tone stack creates a lot of PA dist, so if the tubes sound good, this does too. The EMGs tend to skew most mods IME, the amp was not designed for their output and words like clarity and articulation are seldom associated with active pickups (or ULTRAs).

in another post (JSX mods on an ultra) i described putting a 75k resistor across the Ultra's 220k R7 which gives it the 56k value found at JSX R6, I don't like the loss of overthetop gain but I'm not running actives; you may like it