how to get bypass cap tone w/o gain?

[daz]

I have a .68uf bypass cap on V1A and also on V1B. However, the V1B cap is on a switch as a gain boost. I have found however that the tone is better with both caps in, but the gain is too much for my normal setting. I have a 2.2k in series with the switchable cap, and i realize i could use a bigger value there to reduce the gain even further. But then the tone of the cap will be lessened. So what i want is the tone of that second bypass cap but w/o the extra gain. problem is, i've exhausted ways of getting less gain. I have a split load on V1B but not on V1a because that just seemed to hurt the tone. The cathode resistors are already pretty high, 2.2k/4.7k, plus changing those always seems to hurt tone because i settled on those values after months of experimenting and those just work best.

So is there a way to get the tone of that.68uf cap w/o adding more gain?

[tubeswell]

voltage divider between the two stages?

local NFB on 2nd stage?

[daz]

How would i do NFB on a preamp stage? been wondering about this anyways, so maybe now is the time to try it.

[hasserl]

This may not vbe the help your looking for, but I noticed on the schem you posted in another thread that your running 220k or so on the 1st stage plate load, then the split plate load on the 2nd. Why? Have you tried 100k on the 1st stage? Seems to me that your building too much gain there to begin with. I've found 220k plate loads tend to result in a fizzy or hairy distortion, if that's what you're trying to reduce or eliminate, I'd try there first.

Back to your question, if you eliminate the bypass cap but want the tone that the cap gave, you'll have to shape it using the coupling caps between stages.

But again, I think you need to review your gain scheduling, and I'd revisit the plate loads your using.

[hasserl]

How would i do NFB on a preamp stage? been wondering about this anyways, so maybe now is the time to try it.

Basically you connect the plate back to the grid thru an RC network to drop the voltage and block the DC. Do an internet search for the Fender silver face Bassman #AA371 schematic to see how they did this on the 3rd gain stage in that amp.

[daz]

Thanks, i'll check that out. As for the 220k, it's just one of those things where you try anything else and you keep going back because it just sounds right. I had 100k there when i built it and when i tried 220k things just sounded so right. every time i try and go back to 100k, and i have tried many times, it just doesn't sound as good. however i have made a lot of PSU changes in the last few days so i may try again, tho i just know it won't sound as good. Anyways, it doesn't matter because 100k never makes enough difference in gain to matter.

[tubeswell]

What Hasserl said about local NFB.

Put the resistor between the 'far-end' of the coupling cap following the stage, and the grid of the stage.

Valve Wizard has an article about designing it right:

http://www.freewebs.com/valvewizard/localfeedback.html

[daz]

Ahhh....i remember trying this now. Just tried again and as i recall from the last time it compresses the signal. Anyways, i'm ok as far as gain now, as i figured out a way that works well. I'm chasing way too many things at once right now ! Gotta focus on one at a time, so hopefully i won't be pestering y'all so much. I think it's pretty darn good as is tho. i just want to find a cure for one of the things i've been chasing since i built this thing....that really wide hollow fat midrange. it's something that i think needs to come from the guitar or the very input of the amp before the majority of distortion is created. I find the biggest challenge in trying to nail tone is the midrange, and with tube amps all you can do it manipulate the high and low end and hope the results affect the mids the way you want. But there doesn't seem to be a way to control the type of mids you get, at least not w/o inductors i guess.

[kleptocracy]

I find the biggest challenge in trying to nail tone is the midrange, and with tube amps all you can do it manipulate the high and low end and hope the results affect the mids the way you want. But there doesn't seem to be a way to control the type of mids you get, at least not w/o inductors i guess.

I know I'm still a noob, but what's your tone stack like? I've been digging through piles and piles of tone stack schems and response curves and I've noticed most of them steal a ton of mid from the signal. I know a bit of a mid-cut is necessary for "normal" guitar sound, but maybe after your stack there's just nothing left to play with. Maybe your tone stack is throwing out the mid-baby with the mid-bathwater, so to speak. Just a thought.

[daz]

I've tried all that. I've spent more hours playing with the tone stack than most people do with thier kids over a lifetime. I've come to the conclusion that it's the preamp that has the mids the way it is. But it's tricky because to get the high gain preamp to sound good you tend to find there is only one design that tends to work best depending on a lot of things including the voltages and filtering. And once you find that you're sorta stuck with whatever type of midrange you then have, and messing with component values the tone stack or anywhere else doesn't work to change the mids. If it does, it doesn't do it in a good way. the mids i want can be pretty much duplicated by putting the guitar into a graphic EQ and doing a reverse "V", tho a bit heavier towards the bass/lo mid area. Thats PRE DISTORTION, and therefore a whole different thang and sounds nite and day different than if you put that EQ after. there it would sound horrible. thats why i believe it's something i need to do in the fisrt stage before most of the OD is created.

[kleptocracy]

Gotcha. Fair enough. What does that reverse-V EQ sound like through the pre-amp?

[daz]

Like what i said i was after...a wide fat, transparent midrange and it cleans up any hi end harshness or flab in the low end. same EQ after distortion as i said would be horrible sounding like a wa wa in the middle position.
I can already roll of highs easily enough at the input, so i think if i could figure out how to roll of low end too i could accomplish this because that would leave the mids unaffected and in effect do what that EQ is doing. A cap of the right value possibly in series with a resistor to ground will adjust the highs, but i'm not sure how to roll of lows.

[chipaudette]

You mentioned a Wah-Wah pedal after the distortion...how do you like the sound of wah pedal *before* the distortion? The Wah pedal is a device that cuts both the highs and the lows to leave just the mids. Does it give the sound you want?

If it is anywhere close, you could mod the wah circuit to put a pot in to control the width of the wah's frequency response. That way, you have the normal wah control that shifts the center frequency and you'd have the new wah control that would widen or narrow its pass band. Is this the type of mid-range control that you're looking for?

Chip

[daz]

No, i used a wah as a extreme example. Plus rather than stuff solid state devices in my amp i'd just use an EQ pedal in front. But it's all about making the amo sound the way i want, not by doing that via SS devices.