I'm a noob with a broken mig muff and big dreams

[wordsandsigns]

I am new to stompbox making/modding, but I've been reading a lot recently and am about ready to start doing.

Enter my big muff.  A black russian pi that decided to crap out on me the other day.  With effect bypassed and engaged, it lets only a VERY small amount of my signal through - barely audible but definitely there if i turn up my amp.

So i opened the sucker up and everything looked fine, except that one of the pots has a terminal with nothing connected to it, and some wires hanging around like they should be connected to it...
The other two terminals have the same wire soldered to them, and that wire leads to the switch.  This wire is wrapped around three smaller wires, which are the wires that seem to want to connect to the now empty terminal.
I'm not sure which pot this is, but I think it may be the sustain.

Does anyone recognized this sort of wiring situation?  If so, will soldering these wires to the pot's terminal fix my pedal (or get me closer to fixing it)?

I am also interested in true bypassing my big muff and giving it an ac adapter port.  I think I can true bypass it from reading instructions I found in old forum posts (install 3pdt switch, rewire...), but I'm not so sure about the ac adapter.  All I've seen is that the pedal is negative grounded, which doesn't mean much to me yet.

Another random question:  I would like to be safe while working.  I've heard about capacitors that have not been discharged being dangerous.  Do I have to worry about this while working on stompboxes?  I'm pretty sure I can pick a cap off a PCB, so is the general safety rule "don't touch it?'

Any and all help is appreciated, and since this is my first time posting I apologize if I have been unhelpful in any way.  Constructive criticism is appreciated so that I can make better posts in the future!
Thanks!

[ianmgull]

It sounds like the pot you're referring to is is the volume pot because it connects to the stomp switch (if not disregard everything I'm about to say).
If you look at the big muff schematic here: (PDF)

http://www.generalguitargadgets.com/pdf/ggg_bmp_grus_sc.pdf

you will see that the only pot that should connect directly to the switch is the volume pot.

One connection (an outer lug) should connect to ground. This means it might be connected to several other places which all make their way to the negative terminal on your battery. The other outer terminal should connect to the PCB somewhere. The middle lug will connect to the stompswitch. I hope this helps, if not I've got several drinks in me right now and thats my excuse. Good luck!

Ian

[wordsandsigns]

That does make sense, but actually it looks like the pot in question is the sustain pot.  It is connected to the switch's bypass row, so that when the effect is bypassed it connects to ground on the PCB.  When the effect is engaged I guess that this wire just connects to nothing (?)

[theehman]

That does make sense, but actually it looks like the pot in question is the sustain pot.  It is connected to the switch's bypass row, so that when the effect is bypassed it connects to ground on the PCB.  When the effect is engaged I guess that this wire just connects to nothing (?)

That's correct.  When in bypass mode the Sustain wiper is grounded.  In effect mode that wire connects to nothing.

[R.G.]

Another random question:  I would like to be safe while working.  I've heard about capacitors that have not been discharged being dangerous.  Do I have to worry about this while working on stompboxes?  I'm pretty sure I can pick a cap off a PCB, so is the general safety rule "don't touch it?'

The caution about capacitors being dangerous is based on capacitors which have stored up dangerous amounts of energy. At high voltages, this can literally stop your heart, and at slightly lower voltages can cause you to jerk and fall, perhaps hurting yourself. At low voltage and with large capacitors, the energy is stored as lots of available current, so it can weld things or heat them to melting - things like screwdrivers, wires, ... rings...

That being said, in general voltages under about 40Vdc or 25AC are not dangerous to touch momentarily with dry skin, that being lower than the "flinging" voltages. They can still be dangerous if they can provide lots of current, so even low voltage caps over maybe 1000 microfarads should be discharged before handling. Capacitors over 10,000uF should definitely be let drain before handling.

It is rare for the voltage in a stompbox to be over 9Vdc, and for the capacitors to be bigger than 1000uF, so generally stompboxes are safe to handle. You have a good attitude - learn first - and it will help you a lot.

If you can , take some digital pictures of the inside of your pedal, the broken wires, etc. and post links to them, we may be able to spot specific things to do.

A question - do you have, or have access to a digital multimeter? You'll need one. You may be able to borrow one. Or, if you're in the USA, Harbor Freight has them for under $20, sometimes under $5.00.

[wordsandsigns]

A question - do you have, or have access to a digital multimeter? You'll need one. You may be able to borrow one. Or, if you're in the USA, Harbor Freight has them for under $20, sometimes under $5.00.

My multimeter just arrived.  I am not sure where I should be measuring, but after poking around a bit with a voltmeter it looks like there is voltage at every terminal and trace.  This is what the effect now sounds like:
When engaged, the effect seems to work as it should.
When bypassed, the signal is very quiet, and has a lot of distortion (not the good kind though).

When I get my camera back I will take pictures of the PCB and the solder jobs on the pots, etc.  Any ideas in the meantime as to where/what the problem could be?

Thanks again for all your help!

[newfish]

Have you read the 'what to do when it doesn't work' thread?

There's an excellent piece of kit you can make - the audio probe - which will help you trace the point at which the signal stops. 

You could always freshen up the solder joints in the meantime.

[petemoore]

  I constructed a black DMM wire with a clip on the end, Then when I want a 'poker / probe, I clip a solid core wire probe in the alligator clip.
  but a clip>wire>clip hooked on the DMM lead probe works just as good until the clip falls off the end of the probe contact...
 
  Clip the black lead to ground...you can now use your right hand again.
 

[newfish]

Wordsandsigns - how goes the Muff?

[wordsandsigns]

Wordsandsigns - how goes the Muff?

I have isolated the problem: I found a loose cable that needed to be connected to a lug on the switch so that the signal could go through in bypass mode.  Once I soldered this together I tested the pedal, and both the effect and bypass mode worked, with the exception that the Sustain pot was not functional.  I looked at this image that I found on another thread



and realized that I was wiring the sustain pot wrong.  I am now about to solder the connections marked S1, S2, S3 to their respective terminals on the sustain pot.  My question is: there is another cable that connects from the sustain pot to the switch.  I mentioned this cable earlier and confirmed that when the effect is engaged, the switch connects this to ground, and when the effect is bypassed, it gets connected to nothing.  Does anyone know if this cable connects to terminals 2 & 3 on the sustain pot, or does it just connect to terminal 3?

Thanks again for all the help. as well as the advice on the audio probe.  One curiosity: what does the cap do on the probing lead?  Does it stop DC signal from coming through?

[petemoore]

 One curiosity: what does the cap do on the probing lead?  Does it stop DC signal from coming through
  It blocks DC.
  Though DC leaking into the signal path does can make noise, 'signal' generally implies or refers to AC, something with current / voltage rising and falling at a frequency or frequencies.

[theehman]

Wordsandsigns - how goes the Muff?

I have isolated the problem: I found a loose cable that needed to be connected to a lug on the switch so that the signal could go through in bypass mode.  Once I soldered this together I tested the pedal, and both the effect and bypass mode worked, with the exception that the Sustain pot was not functional.  I looked at this image that I found on another thread



and realized that I was wiring the sustain pot wrong.  I am now about to solder the connections marked S1, S2, S3 to their respective terminals on the sustain pot.  My question is: there is another cable that connects from the sustain pot to the switch.  I mentioned this cable earlier and confirmed that when the effect is engaged, the switch connects this to ground, and when the effect is bypassed, it gets connected to nothing.  Does anyone know if this cable connects to terminals 2 & 3 on the sustain pot, or does it just connect to terminal 3?

It goes to terminal 2.

[wordsandsigns]

Wordsandsigns - how goes the Muff?

I have isolated the problem: I found a loose cable that needed to be connected to a lug on the switch so that the signal could go through in bypass mode.  Once I soldered this together I tested the pedal, and both the effect and bypass mode worked, with the exception that the Sustain pot was not functional.  I looked at this image that I found on another thread



and realized that I was wiring the sustain pot wrong.  I am now about to solder the connections marked S1, S2, S3 to their respective terminals on the sustain pot.  My question is: there is another cable that connects from the sustain pot to the switch.  I mentioned this cable earlier and confirmed that when the effect is engaged, the switch connects this to ground, and when the effect is bypassed, it gets connected to nothing.  Does anyone know if this cable connects to terminals 2 & 3 on the sustain pot, or does it just connect to terminal 3?

It goes to terminal 2.

Terminals 2 and 3? or just terminal 2?

[theehman]

Just terminal 2 (the wiper)

[wordsandsigns]

thanks theehman!

[bumblebee]

and realized that I was wiring the sustain pot wrong.  I am now about to solder the connections marked S1, S2, S3 to their respective terminals on the sustain pot.  My question is: there is another cable that connects from the sustain pot to the switch.  I mentioned this cable earlier and confirmed that when the effect is engaged, the switch connects this to ground, and when the effect is bypassed, it gets connected to nothing.  Does anyone know if this cable connects to terminals 2 & 3 on the sustain pot, or does it just connect to terminal 3?

That would be Non true bypass wiring, theres two extra wires in this set up, one to the sustain pot and one to ...i forget, but its weird. SO I gather you are wiring it stock non TB then? You can wire it TB and keep the DPDT just exclude the LED or use a millennium setup for it.

BTW, what sovtek do you have? old? green? new? black?

[wordsandsigns]

and realized that I was wiring the sustain pot wrong.  I am now about to solder the connections marked S1, S2, S3 to their respective terminals on the sustain pot.  My question is: there is another cable that connects from the sustain pot to the switch.  I mentioned this cable earlier and confirmed that when the effect is engaged, the switch connects this to ground, and when the effect is bypassed, it gets connected to nothing.  Does anyone know if this cable connects to terminals 2 & 3 on the sustain pot, or does it just connect to terminal 3?

That would be Non true bypass wiring, theres two extra wires in this set up, one to the sustain pot and one to ...i forget, but its weird. SO I gather you are wiring it stock non TB then? You can wire it TB and keep the DPDT just exclude the LED or use a millennium setup for it.

BTW, what sovtek do you have? old? green? new? black?

The pedal is a black russian bmp.  I think it's the new () version - I'm really unsure, since I bought it used.  And yes, currently I'm just working on getting it fixed, and not so much about true bypassing it.  I'm leaving everything stock.  I had read somewhere that I could true bypass it without an led, but if I were to do that project I would rather just buy a 3PDT and keep the led working... what's a millennium setup?  I have some other projects lined up that take precedence over tru bypassing my bmp, but it is something that I plan on doing in the future.

[bumblebee]

Millennium bypass:
http://www.guitar-pedals-effects.com/MillenniumBypass.html
http://www.generalguitargadgets.com/diagrams/switch_lo_dpdt_mil.gif

BTW, glad to see someones getting use from my diagrams. I found that PCB layout on the web ages ago, I've since edited it for NYC mods which sounds better IMO. I have another one for tru bypassing the sovtek muff too if you need it just PM me.