Fender Frontman FM212 mods and questions

[aab0mb]

Fender frontman FM212 schematic:
http://music-electronics-forum.com/attachments/8509d1268780730-frontman-212r-schematic.pdf

I got this broken Fender frontman FM212 for $20 and fixed it. It was the common switching resistors with bad solder joints. Now I'm modding it to my taste. Hoping this is valuable to someone as this amp (and most of the FM or frontman series) is pretty usable for a cheap 2x12 solid state when it's tamed a bit. I've yet to try it with my pedal board but I'll update the thread when I can try it with some pedals in the front and the loop.

Mods so far:

Lifted one leg of c12, c13, and c14 to get rid of the mid scoop that happens before going into the clipping stages. Anyone have ideas for this section? 

Replaced r30 with a 500k trim pot for trimming gain to taste. It has way to much for me so I set it to about 250k to start and the drive is much more usable.

c17 coupling cap changed to .1 or .22 for a bit more bass roll off

c15 to .1 or .22 for more bass roll off in the first op amp drive stage

r24, r25, r28, r29, r32 and r33 if you look closely and remember that those transistors are switches, can be used to adjust regular drive and more drive gain characteristics.

Removed c8 on the clean channel to tame the brightness

Place a panel mount 250k pot in parallel with r51 to act as a "master volume" for both channels. The volume knobs are super touchy and it was near impossible to dial in level for playing at home. Now I can do whisper to face melt volume with no issues.

My question:

Can someone illuminate for me the EQ section on the drive channel? Am i missing something or does this not resemble any of the common tone stacks shown in the Duncan's tone stack calculator?

Is using the r51 feedback resistor to lower overall volume a bad idea? Is there a better spot for such a control to be patched in?

Thanks for reading and any insights offered.

[PRR]

You can dink R51 to taste. I don't see why you would want the PreOut level much lower. And R51 does not scale down reverb return.

> the EQ section on the drive channel? ...not resemble any of the common tone stacks shown in the Duncan's tone stack calculator?

There's globs of fixed EQ in Drive. Yes, the EQ with knobs does not resemble any of the common tone stacks. This is unnecessarily "modern" re-thinking. Me, I'd torch it out with prejudice.

The non-Drive channel has THE tonestack everybody copies, dunno why Fender had to re-invent Leo's best invention. (The "right" stack here has been scaled-down in impedance to better fit opamps.)

[teemuk]

It's overall more versatile circuit, that's why. For instance, bass and treble controls can both cut and boost. T-notch midrange control still has similar 'interaction' as midrange control of generic Fender tonestack.
Btw, there's an obvious error in the circuit diagram. ;-)

[aab0mb]

You can dink R51 to taste. I don't see why you would want the PreOut level much lower. And R51 does not scale down reverb return.

I was clipping a pot in different spots topside on the board looking for any easy "master volume" to control both channels. The reg volume controls are basically useless unless I'm trying to get evicted. 

Obviously I can use the right taper but i was looking for quick and dirty tack solder solution. I do like the idea of having an overall master volume for both channels.

It's overall more versatile circuit, that's why. For instance, bass and treble controls can both cut and boost. T-notch midrange control still has similar 'interaction' as midrange control of generic Fender tonestack.
Btw, there's an obvious error in the circuit diagram. ;-)

Could you point out the obvious error for those of us who are learning? Thanks for the help.

[teemuk]

Signal path through the t-notch filter (midrange control) leads nowhere. There's one connection missing. Refer to FM65 circuit diagram for correct version.

[aab0mb]

Signal path through the t-notch filter (midrange control) leads nowhere. There's one connection missing. Refer to FM65 circuit diagram for correct version.

Just had a look at the two schematics. Thanks for that. Not a familiar circuit block to me so that would have gone completely unnoticed.

Any suggestion on a better location for an overall master volume than my pot tacked across r51?

[aab0mb]

You can dink R51 to taste. I don't see why you would want the PreOut level much lower. And R51 does not scale down reverb return.

Been thinking about this and I'm looking around the effects loop for a good spot to patch in a regular master volume to ground so i can dump level for home playing. Is there a place you can see that wouldn't complicate the function of other components?

[PRR]

R61

[aab0mb]

Thanks for taking a minute.

Gotta say, you and some of the other vets here are incredibly generous with your time and knowledge. I've read countless threads on various forums where you've laid out super helpful info for those trying to learn more about the hobby and their gear.

Really. Thanks for what you're doing.