Moving the tone stack in a Plexi clone

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sher2x4
Junior tube assistant
Posts: 24
(3/22/04 8:56 am)
 Moving the tone stack in a Plexi clone
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 Has anyone ever tried moving the tone stack up behind the first gain stage in a plexi ? Leaving the basic circuit as is.
How would it alter the sound?
 
GroundhogKen
Forum Moderator
Posts: 2333
(3/22/04 9:24 am)
 Re: Moving the tone stack in a Plexi clone
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 The real beauty of the tweed bassman / plexi circuit is that the gain sucking tone stack is driven by a low output impedance cathode follower. With this arrangement more signal passes through the tone stack to the phase inverter.

If you put the tone stack after an inverting gain stage ( like an AB763 blackface Fender ), you will lose a lot of signal in the stack.

Also, there wouldn't be much point in having the cathode follower if it wasn't driving the tone stack.

I'm sure others will have comments about this issue.


Ken
 
sher2x4
Junior tube assistant
Posts: 25
(3/22/04 10:18 am)
 Re: Moving the tone stack in a Plexi clone
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 What I want to try is changing the preamp to a trainwreck design. The circuit in the amp has been returned to the basic plexi, but I've tried the hotswitch, Pre MV, Post MV, single channel with added gain with volume pot on each stage, various cathode configurations, and at times the sound is almost there, but never just quite right(for my taste).
Can I just remove the whole preamp section and replace it with a twreck A1a section? What problems might I run into?
 
Funkalicousgroove
Junior tube assistant
Posts: 27
(3/22/04 4:17 pm)
 Re: Moving the tone stack in a Plexi clone
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 You should be fine If you Ditch the cathode follower and go straight into the PI after the 2nd gain stage after the tone recovery stage, Doing this will require serious changes to your amp, from what I know of trainwreck amps you have to have All of it for it to sound right. The main thing is the OT, the ones Ken used (So I hear) have a 6K6 primary, which I understand, affects the midrange greatly. I think He used Hammond tf's but I may be wrong.
 
sher2x4
Junior tube assistant
Posts: 26
(3/25/04 7:24 am)
 Re: Moving the tone stack in a Plexi clone
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 Thanks for the info.
I wont be changing the plexi anytime soon.
Like to build a wreek tho, next project.
What's got me baffled is the amp sounds just the way you'de expect it to with a strat. Personally I think it sounds great. But plug in a LP and it sounds mushed, lacking any clarity, no balance hi to low, just noise. With the strat I can back off the guitars volume and fake a little Joe Pass, but that LP just wont clean up at all. If you turn it down it just gets thin.
Do any of you use different amps for different guitars? Am I going to have to build an amp just for the LP?
 
 
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