Bobby preamp less gain mods?

[DadTheTinkerFairy]

I have built the Cobbler preamp and use it as a clean pedal platform along with the Unicab to run direct to FOH and it works great. I recently bought the Bobby preamp board planning to build a Marshall flavor to use as well. After reading some reviews of the Sheriff that it is derived from, I now realize that it is a mid-high gain circuit so it probably won’t work to turn the gain down and get a low gain JTM45 sound like I hoped it would. Any suggestions to reduce the gain of the circuit to make it low-mid gain? My first thought was to reduce the feedback resistance of the opamps, but comparing the schematics, the Cobbler actually has larger feedback resistors than the Bobby, but the r/c filters to ground are quite different as well. Maybe replace the feedback resistors with 100K trimmer pots and play around with it? Any input is appreciated.

 

[HamishR]

You could probably use a smaller value gain pot. And maybe experiment with leaving out some of the diodes in the feedback stages, as well as reducing the value of the resistors. Those with more experience than me will probably have better ideas but that's where I would start.

 

[jesuscrisp]

Why not build something that is closer to what you want? Tons of Marshall flavored pedals out there really, why get something that isn't designed for your purpose and try to bend it that way?

 

[DadTheTinkerFairy]

Why not build something that is closer to what you want? Tons of Marshall flavored pedals out there really, why get something that isn't designed for your purpose and try to bend it that way?

Yes there are lots of Marshall flavored pedals designed to make your amp sound similar to a Marshall, but few preamps to use in conjunction with a cab sim to take the place of an amp.

 

[jesuscrisp]

Yes there are lots of Marshall flavored pedals designed to make your amp sound similar to a Marshall, but few preamps to use in conjunction with a cab sim to take the place of an amp.

You realize those Victory pedals are advertised and intended to be used in front of a clean amp?

 

[Locrian99]

Completely not an answer but thought I’d share my experience with the cobbler, Bobby and Doxie.

I’ve been playing around with a tpa3118 power amp module, using an eqd tone job strip board build as a pre amp. I set it up so I could run into the power amp bypassing the tone job or with it.

The 3 victory pedals I’ve built, the cobbler, Bobby and duchess all sound way better going into the tone job than straight into the power amp. They sound thin and even ice picky straight in. Makes me think Jesuscrisp is on to something.

 

[jesuscrisp]

Not saying they WON'T work straight into a poweramp under any circumstance, but if you read the manual, they say plug them into a clean amp.
I'm pretty sure they were never really advertised as preamp pedals to run into a poweramp.

The actual Victory preamps are a different beast.

 

[TucsonSean]

I've built the Bobby and the Doxie. I reduced the gain in the Doxie to make it sound more like a blackface (cleaner tone as opposed to more breakup) and it sounds very good. The gain of the Bobby would be reduced in a similar was as to the Doxie, by increasing the value of R3 and/or R5 from the build documents. My suggestion would be to socket those two resistors and then play around with some different values. For reducing the gain I would start with a doubling of the R3 value. If you want to achieve a JTM45 type sound, this should help with that.

If your still not happy with the sound, I would check out this thread I created. I have been able to get a very convincing Plexi sound from this pedal and I believe that I could get a very convincing JTM45 sound as well with only the mods listed and tweaking the BMT controls.

 

[cdwillis]

You can try lowering R4 from 220k to 47k-100k.