Bypassing the Preamp on a Sovtek Mig 50

[Lowfreq]

Hey all,

A long time ago I had an effects loop added to my Sovtek Mig50, so I could use my Marshall JMP-1 preamp with the Sovtek power section.

But also, long before I knew anything bout DIY, another tech took the loop out and put it back to it's origional format.

I've been itching to use the Marshall again, so I've been looking at this schematic http://blueguitar.org/new/schem/sovtek/mig-50.pdf , and trying to figure out where i would put the loop. I remember seeing one of the caps lifted off the board going to the 1/4" socket.

I'm more interested in the return of the effects loop so I can acess the power tubes, but I'd set up both if I can.

Should I be looking around the 47pf cap? or the .022uf caps?

Any guidance for this bonehead would be great. :wink: :thumb:

 

[okgb]

The master volume seems to be done a little differently than usual ,
i would say after the 250k pot and before the .022 , but then it's level will affect your send . it doesn't look like there is a great place for it without adding a tube for buffer drive & recovery .

You could take it off the cathode before the tone stack and that would be
better drive but but then it would need decent return level to drive the
tone stack .

So if you were using a different preamp then input into the .022 , but
someone smarter than me will speak up NY Dave ?

anyway have fun & rock on !

 

[mikka]

Sounds fine to me..... I'd lift the .022 after the tone stack and take it to the jack ......

Here's the schematic for the JMP-1

http://www.drtube.com/schematics/marshall/jmp1-61-04.pdf

 

[walter]

I think you can put the effects loop between the treble wiper, and the .022 cap. If you use it for effects, the guitar signal will be shaped by the tone circuit before effects are added. If you use it as a power amp input, the entire pre-amp is bypassed.

 

[okgb]

In this case where he is using a separate & different preamp , there
won't be the problem of wanting a different treble setting and needing a different drive setting to the effects loop . Rackmount things with level
controls would be o.k. but the average stomp box which doesn't usually go there anyway , may be a compromise .

go forth & rock !

 

[Lowfreq]

Ok, so am I heading in the right direction here?

 

[okgb]

looks good , most fx loops have a switching jack on the return so that
inserting break the normal when you plug into the return , but allows the preamp signal to continue through if you are not feeding a different preamp into it [ as a bonus there is a preamp out always available ]

Check for a boogie schematic for the proper wiring of it , one of the
older ones before they added the paralell blend knob .

regard Greg