Shaping the distortion

[chunkitup]

One word first of all on the Heyboer iron being discussed in the other thread. I bought the beefier Heyboer Tweed Deluxe OT from Allen Amplification and it is just fantastic and only 45$.
Anyway, my problem right now is that my 4 gain stager (SLO based)20 watt build is a bit too much like a distortion stomp box. I am seeking sustain and compression not buzz. I have a mp3 sample but I dont know if I can post it here. Where do I start in trying to combat this? Also, which TUT vol would help me in this area as well as non clone builds (shaping the sound) and that sort.
I dont like asking more than one question but if someone can get me in the right direction.

[Chuck H]

usually the buzz heard in multi preamp stage distortion is caused by too much bottom end in the early gain stages. There are exceptions though. But for marshallesque type stacked channel preamps with a master volume, I usually sneak up on the bottom end using smaller coupling and bypass caps on the front end and going larger as I approach the PI. Because the signal is overdriving each successive grid you can still get plenty of bottom end by doing this. But too much bottom end in the early stages just squares the wave too much too soon. You can end up with an atonal buzzy mess.

If you get to the tone your after (ie: the right amount of definition, harmonic balance, note separation, etc.) and you still have a little buzz, you can try using top end bleeder circuits in the later gain stages like local NFB and/or signal caps to ground, both in small pf values. These often do almost as much harm to the tone as good. But I've never seen (or built) a really high gain preamp that didn't use them as a final resort for tone and stability.

Oh, also, at 20 watts (2x6V6s or EL84s) if your only getting buzz cranking this amp you may be hearing some crossover distortion in the power amp. This is especially so with EL84s. You can try reducing PI output and if that doesn't work check out the "Paul Ruby zener mod" on the AX84 site.

HTH

Chuck

[chunkitup]

Chuck,
I just replaced the first .022 Orange Drop coupling cap with a .0022 Mallory 150 and WOW! I am testing thru a 1x12 Governor by Em and alot of the buzz is gone. I really cant tell about the low end since a 1x12 isnt going to shake the ground but it has a nice low end thunk. I almost perceive it as having lost some gain but you explained about the low end. I replaced all the OrDrop .022 coupling caps to .022 Mallory's and the high end sharpness is now well rounded, more pleasing sound. I love hi hi gain amps but I hate the peavey type sharpness, almost piercing. Thanks again

[Circuit1]

If you want to have some fun, try paralleling a small value ceramic cap or silver mica cap with your poly coupling caps. Really, small value caps allow you to fine tune/tweak out the values to the nth degree. I do this in all my amps and it does matter when getting notes to "pop" along the fretboard. You may only notice a 1-5% improvement in tone--not a lot, but just enough to push an amp into supremely good territory. Besides, that last few percent of perfection is what all the hifi guys pay big dollars for--that's where it all comes into play.

FWIW, I like silver mica paralleled with a polypropylene/foil coupling caps and ceramic discs in the tone stacks...

[chunkitup]

Hey Jason, What values of ceramics or silver micas do you suggest starting with?