Peavey Delta Blues to Hi Gainer

[chunkitup]

I am modding a PV delta blues to hi gain status. Everything is going great except I need to curb the bass. Here is where I am at:
c4 and c2 is .0022
c14 is 250pf and the boost cap is 250pf (trying for more marshall)
r19(slope R) is 100k
For more gain I reversed C5 and R7 and added the coring over the 1M.

The gain is there and is great but I need to rearrange the eq. The combo is using the blue marvel 15in and is bass heavy. I am looking for the sweet spot on the mids and bass. The high end is good.

[Enzo]

OK, the existing C4 and C2 are 470pf and 0.001uf, and you have increased them to 0.0022uf each? If you want to reduce the bottom end, making those caps larger is going the wrong way.

I don't know that changing C14 from 270pf to 250pf will be much of a change, that is less than 10% difference. And keep in mind the part was already a 10% tolerance anyway. At 10% tolerance, a 270pf could measure 243pf, and a 250pf could measure 275pf, all of which would be good parts within tolerance.

Your midrange boost cap C11 is now reduced to 250pf? SO instead of a mid boost it is more of a brightness boost. Yes?

If you want to change the overall tone of the amp, remember the tone stack is only one part of it, there are plenty other places to shape tone. Due to the way the dirt channel is done - they add a tube into the middle of the clean, more or less - I often caution folks to watch wwhat they do, because many tweaks for the dirt channel wilolo wind up also affecting the clean, but if all you care about is the gain/dirt channel, then go nuts.

Some places to look, starting at the front. C12 affects full range, drop its value to keep the gain increase more towards the highs. C7 is a highs rolloff, reduce it or lose it. (But be aware sometimes they roll off a high gain signal path to reduce fizziness) See how much smaller C13 is than C12? C1 is adding brightness. C15 is yet another opportunity. I can't imagine what swapping places between C5 and R7 might change. But R13 and C16 are another tone shape, see how they resemble the tone control in a guitar? C6 is a full range step, could be pared. But note that it does not just go to the tone stack, there is also C52 there rolling top end off.

You can play with the tone stack, I hope you have gone to Duncanamps and downwloaded their Tone Stack Calculator.

Then down below V3a and C36 is the presence and resonace circuit. Tis one is not adjustable, but you could make it so, or alter the parts at adjust it that way.


Plug your guitar into the FX return, that bypasses thye preamp, and will let you hear what the speaker sounds like.

[chunkitup]

Enzo,
Yea changing the coupling caps to .0022 is my culprit. I modded a PV ultra plus with great success and I was going with alot of those mods on this amp since they are sort of similar. I reversed c5 and r7 because I put diode clippers(coring section as some say) over r7 and I didnt know how the dc voltage would affect it. With the majority of my extra clipping coming from after the 3rd stage and before the 4th stage I kept the clean.......clean.
Thanks again for your input. I should have known that upping the coupling caps would let more low end thru(slapping hand to my head). You also answered my next question about the purpose of r13 and c16 as well as c52.
One question though is how could I get the post control to gradually raise the volume? As soon as I turn it the volume is loud.

[Enzo]

Change the taper.



Or don;t hit it with all the extra gain...