How to bypass the tone stack on a Marshall?

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xcpointx
Junior tube assistant
Posts: 2
(2/5/04 6:19 am)
  How to bypass the tone stack on a Marshall?
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 My amp is a Marshal JMP MKII Super Bass (dated around 76 I think). Its the kind that has 4 inputs (2 are high gain normal, and 2 are lower gain 'bright'), and 2 volume controls (no pre-gain volume!)

I'd like to know if its possible to 'bypass' the tone control stack on this amp and have the signal go through uaffected?

reason being... Im getting a Carvin Quad X-amp rack unit (9 12AX7 preamp powered) and this is designed to go into a power amp. To avoid having to buy a new amp not an instrument amp, but I'd like to run this into my Marshall head !!

Essentially 'convert' it into a pseudo tube power amp kind of like the Carvin TS100
Carvin TS100

Do you think this is possible?

 
gammelnalle
Junior tube assistant
Posts: 1
(2/5/04 7:44 am)
  tonestack
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 Yes, just open up (lift) the leg that goes to ground from the tonestack.

greeting from sweden
 
xcpointx
Junior tube assistant
Posts: 3
(2/6/04 4:50 am)
  Re: tonestack
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 i just unground the tonestack!?
 
GroundhogKen
Forum Moderator
Posts: 2240
(2/6/04 8:39 am)
  Re: tonestack
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 That's right.

With the tone stack floating, no current flows through the components, so there is no voltage drops. What ever signal comes out of the cathode follower at its 100K load resistor is passed right into the phase inverter.

There may be some increase in volume when you lift the stack.

Ken
 
xcpointx
Junior tube assistant
Posts: 5
(2/9/04 3:04 am)
  Re: tonestack
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 sounds good, will the volume controls still work?

Another suggestion made to me is to wire in an effects loop thus:


but apparently then id have no volume control, relying on the preamps volume only... it outputs 22dBv (whatever that means)

Ideally, id like to have the power amp running on Full (as power amps should be), and then control the volume using the preamp.

But the MArshall does tend to have noise (hiss, and slight hum) when cranked up full, so it might be better to have a master volume to set it to a reasonable playing volume. (unless that noise comes from the onboard preamp section, in which case it might be better using my outboard preamp)

-
Maybe I should rephrase my original question:
What is the best way to run a rack preamp into my Marshall head? (bare in mind that the preamp IS tube powered and sounds pretty darn good)
--
id like my amp head to work something like this
carvin ts100
--

my understanding of your suggestion:

--
all your help is really appreciated!


Edited by: xcpointx at: 2/9/04 3:50 am
 
xcpointx
Junior tube assistant
Posts: 6
(2/10/04 1:53 am)
  Re: How to bypass the tone stack on a Marshall?
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 bump
 
xcpointx
Junior tube assistant
Posts: 7
(2/11/04 3:13 am)
  Re: tonestack
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 bump bump
 
ganzonimx
Hey get your own solder
Posts: 366
(2/11/04 11:18 am)
  Re: tonestack
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 yes, if you unsolder the marked wire the tone stack will pass all signal straight trough to the PI.

The effect loop looks right to me, you could try to plug the preamp directly into the return of the effect loop and listen... you might get some hum problems because I think you will create a ground loop over the power cords - I'm not sure about that...

Cris
 
xcpointx
Junior tube assistant
Posts: 8
(2/12/04 1:49 am)
  Re: tonestack
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 okay, my rack unit has a ground lift so maybe that will help with that...i'll check it out on the weekend.
 
 
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