Third channel mod for Studio Pre!

[JT_Marshmallow]

I just found this little snippet in a guy's review on Harmony Central:

"I modded the reverb for an extra lead channel, unsolder the reverb leads and solder a 470k resistor between the hot leads instead.
this makes an extra switchable channel with the reverb pot for gain."

Anyone ever heard of this?

I might try this sometime. It doesn't sound like this would hurt anything.

 

[Razor]

Hmm never heard of this, though it sounds interesting. Any idea of what type of sound would you get from making that mod?

 

[JT_Marshmallow]

Perhaps it would be another instance of the lead circuit where the Reverb pot acts as another "Lead Drive" control...?

 

[helen_bach]

It *should* allow use of the tube as another stage of gain. Would need to check the schematic.. does the Reverb do a send and return, out thru V5b and back thru V5a? If so, that adds the full tube- 2 triodes. Done well, it could be.. interesting...

 

[JT_Marshmallow]

Yes:

V5b - reverb send
V5a - reverb receive

I guess this also means that if one were to do this mod, they should put a regular 12ax7 in V5, as opposed to the 12at7 typically used in this slot.

So in this case would V5 be functioning just like V3 but for this third channel? (On the schematic V3 is labeled as "Lead overdrive tube".)

 

[sixtonoize]

It seems to me that it wouldn't truly add two more stages of gain - the gain that it would add would be in parallel to the regular signal, as opposed to series (which is what most people consider "adding a gain stage").

It looks like it would be more like jumpering a 4-input Marshall head than anything else.

Anyhow, I've got a Studio in the mail, so I just might try this mod out. I'll let you know how it goes.

 

[axisman5150]

This sounds like a great idea, if it really works.

So it should be able to add gain to both channels and using a footswitch or switching system to turn the cuircut on/off.

I might call mesa this week and see if this will work.

 

[sixtonoize]

I'm not so sure that it's as simple as originally posted. Here's a schematic that I found of the reverb circuit:

It looks like removing the reverb tank from V5B will interrupt the B+ supply, so you won't pass any signal. It looks like for this mod to work, you'll have to pull the reverb tank, short the reverb leads from V5B (to provide B+), and run a cap (probably .02mF) from the point where you installed the short to where you disconnected the reverb from V5A to block DC from the grid. You may also be able to re-route the cap between the plate and cathode of V5B to the grid of V5A in stead.

Of course, it might work just fine by installing just the one resistor.

I'd like to hear what Mesa has to say about it.

 

[axisman5150]

If this mod can work, I woudn't mind pulling the reverb out since I don't use it. I just wonder how this will add to the tone of the unit.

 

[axisman5150]

I called Mesa today and asked if this mod was possible to do, and they said that they've never heard of this mod being done before.

Mesa told me that they wouldn't do the mod themselves but if you know how to read schematics, the mod would be plausible.

So there you go. I have a tech close by, so I might ask him to see if this is doable.

I'll keep you posted if I follow through.

 

[joe web]

any updates on this mod?
did somebody do it allready?

 

[axisman5150]

I put off the mod idea for now, just don't have the funds do it right now.

 

[mrcomputer]

This may be relevant...

I have a Fender Princeton Reverb II Rivera-era combo (1983). The amp uses the reverb stage to create the "lead" sound. When in the lead mode, the bulk of the reverb input stage is redirected around the transformer and used as an additional gain stage.

Schematics are available through most of the regular on-line sources.

Just my .02

jbw

 

[Mongo1]

Has anyone tried this?

 

[elvis]

I did something very much like this with a deluxe reverb in the 1980s. Sounded terrible. The reverb driver components are chosen to tune the sound of the reverb. You would need to redo a few components to get this to sound OK. You would also want to mimic the lead drive circuit and put it in series, rather than parallel.

Having said all that, there's no harm in trying, as long as you know how to put it back. Tube circuits are pretty straightforward. if you're changing one component, what's another half-dozen? It could probably be wired up in 15-30 minutes if you know what you want.

 

[Mongo1]

I'm definitely not familiar enough with amp mods to play with circuit mods unless they are well defined and proven. Plus I like using my SP's reverb to add a touch of depth.

Mostly curious if this mod has been beneficial to anyone.