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Favorite three or four gain stage circuit...

benadrian

Member
Messages
425
Hey all!

I have a heavily modded Traynor head. Right now it had a topology somewhere between a JCM800 and a Bogner shiva; both amps with three gain stages and then a cathode follower feeding a tone stack. I'm growing a little bored with the amp at the moment, which usually means that I go in and play with the circuit. I can't help but feel that I've exhausted all my usual resources looking for unique takes on the three or four gain stage preamp circuit.

So, i ask you amp nerds this question: what is your favorite three or four gain stage, medium gain preamp circuit. Essentially, what can be made with two dual-triode tubes.

Thanks!
 

oldhousescott

Gold Supporting Member
Messages
2,879
Well, there's always the Trainwreck circuit, I suppose.

I actually like the Emplexador version of the JCM800 with different tone stack values -- 56k slope, 330p, 22n, 22n. Nothing unique about the topology, though.
 

benadrian

Member
Messages
425
I'd reckon Marshall got it right with the 2203 and 2204.
It's pretty great. I used it for years with a few tweaks to get it to work better for me with single coils. then I started digging for "inspired by" circuits. I'm pretty well-read when it comes to amp variations, but I just have this feeling tugging at my like I'm missing something.
 

TimmyP

Member
Messages
2,488
I cannot find P7a on the Prosonic schematic (the low side of the pot between gain stages 2 and 3.
 

Steppin' Wolfe

Silver Supporting Member
Messages
5,788
Okay...I pulled my chassis. P7A is the 'back' pot on the Master volume control. P7B is the MV control. The contact on the PCB is right in the middle of the board.
P = potentiometer. The first 3 pots are not numbered in the schematic, but from P4(treble) through P8(reverb) the pots are numbered in the schematic, as you can see. All pots are dual-ganged pots in this amp. P1, P2 and P8 each have one unused 'pot'. I cannot explain the functions any further than that. I can manipulate the controls, but I don't totally understand the wiring.
 

71strat

Member
Messages
9,536
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dazco

Member
Messages
15,294
from 1 -10 there is a huge increase in mids.
wow, thats interesting. I may have to try that and make it switchable. of course whether i like it or not will depend on where the center frequency lies and the way it sounds at that point in the amp. I already have plenty of the highest mid frequencies.
 

mvanstee

Member
Messages
23
wow, thats interesting. I may have to try that and make it switchable. of course whether i like it or not will depend on where the center frequency lies and the way it sounds at that point in the amp. I already have plenty of the highest mid frequencies.
For those interested the tone stack on the prosonic is active. Start with TMB at zero and work up from there.
 

diagrammatiks

Member
Messages
3,024
3 gain stages and a cathode follower would require 3 dual triodes not 2...

4 stages is pushing into high gain territory as well...

for exactly 2 dual triodes into a pi

the ods circuits
splawn qr
 

benadrian

Member
Messages
425
3 gain stages and a cathode follower would require 3 dual triodes not 2...

for exactly 2 dual triodes into a pi
I think maybe we have a misunderstanding. I consider an amp like a jcm800 2203/2204 to have three gain stages and a cathode follower, and that preamp is made with two dual triodes.

Cheers!
Ben
 

gldtp99

Member
Messages
4,062
I think maybe we have a misunderstanding. I consider an amp like a jcm800 2203/2204 to have three gain stages and a cathode follower, and that preamp is made with two dual triodes.

Cheers!
Ben

I agree----- JCM 800 2204/2203 preamp is two 12ax7's (four available stages)----- three gain stages and a cathode follower stage.
If you haven't already built the "Plate Driven Tonestack" type of modded circuit (giving four gain stages without adding another 12ax7), this one works quite well and has some interesting tweaks: Pre Tonestack MV, several switching options, and some unique voicing in the preamp and PI:

http://bmamps.com/Schematics/Splawn/Splawn_QR.pdf

Here's a 50 watt version based on the gain channel that I built several years ago---- the current owner (named Erving) is playing it on the night he picked it up from my old shop:

 

diagrammatiks

Member
Messages
3,024
I think maybe we have a misunderstanding. I consider an amp like a jcm800 2203/2204 to have three gain stages and a cathode follower, and that preamp is made with two dual triodes.

Cheers!
Ben
That's quite an important semantic distinction...The cathode follower is an important part of the tone. It will distort jcm800 inspired circuits...and it's necessary to drive the tone stack in those circuits...

a jcm800 preamp made with 2 dual triodes and no cf tone stack doesn't sound like a jcm800 at all.
 

benadrian

Member
Messages
425
here's how my brain parses the 2204 preamp.
V1a is the first gain stage.
Then the drive knob.
V1b is the second gain stage.
Then the 470k/470k voltage divider.
V2a is the third gain stage
Directly coupled to
V2b cathode follower (it clips, yes, but it adds no gain)
Then the cathode follower drives the tonestack that feeds the master volume.

And that's three gain stages and a cathode follower with two dual triodes.

The PI is part of the power amp to me due to the NFB. It makes it one interactive, dynamic system.
 
Last edited:

JTH20

Member
Messages
36
Maybe try an Engl Powerball type circuit? It eliminates the cathode follower and uses the last triode stage as another gain stage. A quick google search turned up this preamp schematic online but I'm not sure if values are 100% correct.


Only two dual triodes and it's a gain monster!
 






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