Bass Big Muff volume mod

dannybuoy · #1 11-21-2010, 04:49 AM

There's an issue with the BBM that drives me nuts, and it's the fact the when in dry mode you have 100% dry signal plus however much fuzz you dial in via the volume knob... end result is you have a massive volume boost when you turn it on.

I've shyed away from modding it since it's all surface mounted and really fiddly to work with. However, I had an idea the other day that should work! If I unsolder the output wire from the end of the circuit to the 3PDT footswitch, and instead hook that wire up to a potentiometer, wire the 3rd leg to ground, and the wiper leg back to the footswitch, in theory this would then give me an additional master volume control. Then I would set the main volume knob to 1 o'clock to get my clean/dirty ratio right then dial it back a bit with my new volume control?

At the moment I am using an external blender to work around the problem, but this would mean I could sell the blender and get extra board space back!

I'm gonna order the parts to try this out, but please if anyone thinks I've got this wrong and it won't work, let me know! 100K should do the trick?

Thunderscreech · #2 11-21-2010, 07:04 AM

You could just make a super-small blender. FET and IC blender circuits can be made very tiny, and fit in into a really small enclosure. I mean, I'm not saying what you want to do wont work, i'm just saying.

McSpunckle · #3 11-21-2010, 07:10 AM

Your idea sounds fine to me.

100K would be perfect.

dannybuoy · #4 11-21-2010, 07:21 AM

Nice, I'm gonna see if I can get at the transistors to wire up a feedback loop too!

Thunderscreech · #5 11-21-2010, 07:59 AM

Quote:

Originally Posted by dannybuoy

Nice, I'm gonna see if I can get at the transistors to wire up a feedback loop too!

Do post pics/schems when you are done! This intrigues me!

Swimming Bird · #6 11-21-2010, 10:40 AM

Cool. Though it seems a little silly that you had to put your BBM in a blend loop. Hope this works for you!

dannybuoy · #7 11-21-2010, 12:49 PM

I need to open it and check but I have a nasty feeling the switch may be mounted to the PCB, which would make this much more difficult...

sutarappa · #8 11-21-2010, 05:13 PM

interested. i've thought about this exact idea. 100K audio, right?

dannybuoy · #9 11-22-2010, 05:05 PM

Yup, 100K audio/log is what I'm thinking off. Just had a look inside the pedal. The footswitch is soldered to a mini board that's connected to the main board via a ribbon cable. After studying this page, I have determined that the fuzz output is on the wire closest to the right hand edge of the ribbon, which means that I should be able to cut this in the middle and wire it to a pot. There is room near the output jacks for a small pot, plus the transistors are marked and easy to get at to add a Supercollider Beast style oscillation switch (hook up the emitter of Q3 with the emitter of Q2 through a momentary footswitch)!

As a simpler solution to the problem, it should also be possible to add a fixed volume reduction by wiring a resistor between the central and top-right pins of the switch. I'll take some pics and experiment more tomorrow.

Now, I have a gig on Thursday, so I would be taking a big gamble by attempting this tomorrow night... but I might just do it anyway! Could be a late night...

Thunderscreech · #10 11-22-2010, 08:32 PM

Quote:

Originally Posted by dannybuoy

Yup, 100K audio/log is what I'm thinking off. Just had a look inside the pedal. The footswitch is soldered to a mini board that's connected to the main board via a ribbon cable. After studying this page, I have determined that the fuzz output is on the wire closest to the right hand edge of the ribbon, which means that I should be able to cut this in the middle and wire it to a pot. There is room near the output jacks for a small pot, plus the transistors are marked and easy to get at to add a Supercollider Beast style oscillation switch (hook up the emitter of Q3 with the emitter of Q2 through a momentary footswitch)!

As a simpler solution to the problem, it should also be possible to add a fixed volume reduction by wiring a resistor between the central and top-right pins of the switch. I'll take some pics and experiment more tomorrow.

Now, I have a gig on Thursday, so I would be taking a big gamble by attempting this tomorrow night... but I might just do it anyway! Could be a late night...

Well, I know what I'm doing tomorrow...

dannybuoy · #11 11-23-2010, 10:42 AM

Just bought the parts from Maplin on the way home. Ripoff prices, but needs must. Hope I don't fudge this up, I've got my Supercollider in reserve just in case!

bassguitar808 · #12 11-23-2010, 02:39 PM

Yep sold my EHX BBM for this exact reason, the volume jump

Please post some specs and photos of the mod

dannybuoy · #13 11-23-2010, 04:28 PM

Well, I've done it, and it's made me a very happy boy!

The volume control is mounted on the bottom left and it works as intended. No need to use my [sfx] S&M blender anymore.

I've done the feedback mod too, although I wasn't entirely sure which points to bridge so I had to experiment. On my Supercollider Beast, the left switch Osc1 bridges the emitters of Q2 and Q3, which is on the left hand side of the flat edge on the transistor. However to get the same effect on the BBM I have to bridge the right hand side of the flat edge, so maybe these transistors have their Base/Collector/Emitter the opposite way around. Anyway, the oscillation is even more intense than the Beast, it sounds awesome. Shame it's too late to crank it up! I've never modded a pedal before but this was really easy to do and I managed to not botch it up - score!

For some reason my digital camera is not taking macro shots very well so these are the best I can do until I get some sunlight around here:

Caca de Kick · #14 11-23-2010, 06:50 PM

I never noticed an issue using my BBM, so let me get this straight....
The additional volume knob is to turn down the clean/dry volume signal, while you can turn the fuzz up with the original volume knob?

I don't have to wire in that additional foot switch do I?

fitz420 · #15 11-23-2010, 07:14 PM

way to take one for the team. looks great.

sutarappa · #16 11-23-2010, 09:48 PM

totally ace!!

the bbm is now a contender. this mod cut the line and is next on my list.

thanks for lighting the way, dannybuoy!

Quote:

Originally Posted by Caca de Kick

I never noticed an issue using my BBM, so let me get this straight....
The additional volume knob is to turn down the clean/dry volume signal, while you can turn the fuzz up with the original volume knob?

I don't have to wire in that additional foot switch do I?

that is pretty much the idea. in dry mode, the clean volume is fixed, so as fuzz is added in with the stock volume knob, the overall level of the signal increases quite a bit. the new volume knob works as a master. the user can dial in the desired clean/fuzz combination with the stock knob and then reduce signal level at the end of the circuit with the new volume knob. this allows the effect to be set for unity gain without compromising the function of the blend.

right, the foot switch is a separate mod and is not needed to add the master volume.

dannybuoy · #17 11-24-2010, 02:23 AM

Correct, that explains it well. The feedback mod turns this pedal into a monster! Might have to put I a latching switch instead so I can keep it on most of the time!

Thunderscreech · #18 11-24-2010, 07:03 AM

Quote:

Originally Posted by dannybuoy

Correct, that explains it well. The feedback mod turns this pedal into a monster! Might have to put I a latching switch instead so I can keep it on most of the time!

Well, you just made my life 100% easier!!

I have a SPDT switch lying around from an old project that never got done, and I think I just found a use for it!

ZombieSpacebat · #19 11-24-2010, 09:00 AM

On a scale of 1 to 10, how easy would this be for a first mod for me to do?

FunkyBassline · #20 11-24-2010, 10:47 AM

Same question as ZombieSpacebat... I've never done a mod but im super intrigued