BMP Tone Bypass mod - Am I understanding correctly?

[rratajski]

So if I am reading/understanding Jack Orman's tone bypass instructions in regards to JD's GGG-Tuned BMP layout, am I right in that to do a tone bypass mod to a GGG-Tuned BMP I would...

1. desolder the bottom of R18 (39K) and C11 (.01 uF)
2. connect both bottom leads of R18 and C11 to one lug of an SPDT
3. connect the middle lug of the SPDT to ground
4. leave the remaining lug of the SPDT open

If this is correct, I can use the BMP in stock mode and tone bypass mode via the SPDT, right?
If this is not correct, please advise.

Jack Orman's diagram: http://www.muzique.com/lab/tbypass.htm

JD's GGG circuit: http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf

[bumblebee]

Yeah, the resistor that goes to ground in the high pass filter  (the top half of the tonestack) and that cap in the low pass filter (lower half), desolder,connect them together on one lug of a SPST (or SPDT,makes no difference) switch then solder a ground connection to the other lug on the switch.

When the two components are not grounded the tonestack is basically bypassed, when they are grounded it works.

[rratajski]

Thank you. I just got some time to do this mod and it worked.

A little bit more 'open' of a sound than with filters grounded, akin to the comp cut setting of the Fulltone Bass Drive w/ MOSFET.

Thanks for the assistance!

[eurekaiv]

Why not just jumper the in to the out?  That way you don't have to lift any parts off the board, you just tack a couple wires to a pad.  I've done this countless times and it works well, you do get an ever so slight effect from turning the tone control but we're talking minuscule, and the volume boost is HUGE.

[bumblebee]

The best way is to just drill four holes in the PCB and make four new solder pads by scratching of the mask and put a DPDT in there, but this isn't n00b friendly.

[johnadon]

I had one of the BMP's back in the early 80's that had the tone bypass switch, but I was never fond of the pedal switched either way, the beginning of a life-long love/hate relationship with the BMP. That's probably why I've built so many of them at this point. :-) Anyway, on my last BMP build I tried a half-bypass (everyone should be thankful I'm not a cardiac surgeon) by making the .01 capacitor to ground switchable in and out of the tone stack. Lifted, it opens up the sound quite a bit while still giving you some control over the tone. I think it's mostly a bass rolloff control in this configuration, but it works really well for taking some of the squish out of the BMP while retaining the distinctive BMPy sound.

[Skreddy]

I've tried old BMP's with the tone bypass and hated that loud, raw, effect--ugly to my ears.  IMO the best sound is with the tone stack engaged, by far.  But if you just don't like the mid scoop, you can easily tune the stack to whatever you like better.  Keep in mind that a flat-mids tone stack simply means you use the same exact resistors and capacitors on both the high-pass and the low-pass side.  I've used .0056uf and 33k on both sides with pleasing results.  If you want a mid HUMP, then make the two sides so that they don't overlap.  That gap in the middle is your hump.  For example, my latest Top Fuel tone stack uses 22n/56k on the high-pass side and 33k/3.3n on the low-pass side.  Check out the newest BuildYourOwnClone Big Muff PCB!  It features not only a transistor-array chip for making Swollen Pickle clones and discreet pads for traditional builds, but it has a 4-way rotary switch for different tone stacks, too.

Play with the tone stack calculator at Duncan Amps: http://www.duncanamps.com/tsc/