PLEXI STYLE CLEANER PREAMP

[covil]

Hi everyone!! This is my first post, and i need some help from you guys.

I´m am building a preamp plexi style, but i´m having trouble doing a clean channel that fits my needs

The preamp has one stage + dc coupled pair, just like a plexi does.
my problem is that i´m using humbuckers on my guitar and i can´t use a lower sensitivity input like a plexi, and don´t wan´t to rely on my guitar volume to clean.
Is there any known preamp style that does this well ??
Or any mods to clean a litle a plexi circuit?

I´ve already tried lowering gain pot value and trying jtm45 style design but it´s not it yet!

Opinions please? Jorge

[stef]

Welcome to the forum. ECC81 tube in V1 or V3
Even with ecc83 it should stay clean up to 3 on the dial, w/o the big "bright" cap that is. Try a small volume bypass cap (47pf, 100pf) or no cap

[covil]

Welcome to the forum. ECC81 tube in V1 or V3
Even with ecc83 it should stay clean up to 3 on the dial, w/o the big "bright" cap that is. Try a small volume bypass cap (47pf, 100pf) or no cap

I don´t have here an ecc81, but i think you took me in the direction i need to go.
Still haven´t decided wich bright cap to use. It helps alot but i´m still having trouble with it. If i lower the gain pot too much it becomes thin sounding if i incresase the gain to get full, warmer sounding it is already breaking up too much.
So i tought of something , that might work! Is there any away of limiting the action of the bright cap?? So that when the gain pot is on lower settings it does´nt sound too bright?

[neikeel]

The ECC81 will help.

Next use a 1k5/25uF cathode combination on V1 and a 1k5 cathode resistor on V2a.

Stay with 1M volume pots and just use a 100pF silver mica bright cap (ceramic can be a bit grittier).

You can twiddle with the tone stack too.

Also make sure the NFB is pretty high (like 27k on 16ohm tap).

[herbvis]

Lower the 100k plate resistor

[neikeel]

Lower the 100k plate resistor

Which ones (both on V1 or on V2)?

I have gone the other way and raised V2 R to 300k once (by mistake - the orange first band looked yellow in the gloom) and it helped bring in the gain on a 45/100 to almost 12 series levels so I guess a 68k or 82k there might be worth trying?

[covil]

just remembered i can´t use a ecc81 on v1. It´s a 3 channel preamp and v1 is shared by two different channels. the 2nd channel is a plexy copy and the 3rd is 3 stages + Cf ( close to AFD). By the way i tried doing a 2203 clean style, well it´s cleaner but it´s missing something! The plexi is much closer to what i need.
so i returned to plexi style.
by now it´s:
Clean channel :

V1
100k plate
2K7/0.68 cathode
into 2.2n
1meg pot (and 1meg resistor parallel with pot input to ground, at least for now, might change)
100 pf or 220 pf ( still haven´t decided yet) really like that 4n7 frequency response, only if it didn´t distort so early
470K/470pf, 470K to ground

into V2 dc coupled pair
100k plate
820 ohm/ 0.68 Cathode( tried removing to lower gain but i really need it to shape the frequency response)

I´m gonna try next mess around with v1 plate and cathode resistors.

[covil]

lowered v1 plate to 82k
removed 1M resistor across gain pot
220 pf bright cap.
Sounds good enough at least for now.
Also, tried other guitars. The guitar i´m using to test these mods has too much gain and low end on the neck pickup.
Tested with another, with sd59 on the neck and it sounds pretty good (At least for me)

[revolver1]

I know this is an old thread but I wanted to understand it right. Earlier in the thread neikeel said about the cathode combination. So is the1k5/25uf combination to replace the 820/330uf combination or the 2.7k/.68uf combination?