GGG Russian Muff - Volume Loss

[oakst8]

Hi,

I just finished wiring my second build - a GGG muff built to the Russian specs. I can follow directions ok and I think my soldering is decent, but I'm pretty much clueless about the theory behind what I'm doing.

I have an original Russian muff and my build sounds pretty darn similar, however, I'm experiencing a major volume loss when it's engaged - like 50% loss.

I can't imagine I've provided enough info to find the problem, but can someone suggest a troubleshooting process for me? What do I start checking first?

I did search the forum, but didn't find something comparable.

Thanks!

[Jhouse]

Welcome to the forum!

HERE'S a good tutorial for giving us all of the information we need.

[oakst8]

Here goes (note that I've never used a multimeter before and may be confused):

I'm under the assumption that, when facing the flat side of the transistor, the pins are emitter, base, and collector from left to right.

DC adapter = 8.74

Q1
C 4.5  (3.9)
B 0.72 (0.6)
E 0.13 (0.03)

Q2
C 4.46  (3.
B 0.72 (0.6)
E 0.14 (0.03)

Q3
C 4.4  (3.
B 0.71 (0.6)
E 0.13 (0.03)

Q4
C 8.72  (4.0)
B 1.36 (1.
E 0.86 (2.5)

The numbers is parentheses are what is supposed to show per this:
http://www.generalguitargadgets.com/pdf/ggg_bmp_instruct.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Also of note is that, while moving everything around trying to figure out how to read the voltages, I somehow managed to get the LED to stop working. Pedal still functions the same though.

Final disclosure, I had a tough time reading the resistances on the four (but really five) band resistors. But I've rechecked the board 3 times and can't find any issues that I can see.

Parts layout: http://www.generalguitargadgets.com/pdf/ggg_bmp_grus_lo.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
Schematic: http://www.generalguitargadgets.com/pdf/ggg_bmp_grus_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Thoughts?

[Jhouse]

I would look at the resistor that is going to the C leg of Q4. That seems to be where your problem is at. All of the other voltages are fairly ballpark.

[oakst8]

Thanks

R24 seems to be reading at about 0.1 when the schematic calls for 10k. (But I swear, the colors are what they should be! )

Is this possible? Could it be the culprit?

[Jhouse]

When you take the resistor out and measure it with a DMM on ohms it registers as .1? Try replacing that bad boy with another 10k resistor or something really close to that.

[oakst8]

Found another 10k in the bag of 1,000 resistors that came with this kit. Soldered it in, fired up the pedal and ... no sound.

So I started to recheck all the voltages when I realized the battery wasn't plugged in.

Lo and behold, we are now in business. Oodles of volume and everything sounds good.

Thank you for the help! Obviously, I couldn't have gotten that solved without some assistance.


Not to get too greedy, but any tips on troubleshooting the LED?

[oakst8]

The positive lead for the LED gets 8.82v, and it worked before, so I'm guessing something went awry with a ground connection (?) although I can't find anything obvious.

[Jhouse]

Glad to hear it is working.

You might have fried it if you didn't put a resistor in between it and your V+.

[oakst8]

Guess I'll be hitting the Shack tomorrow.

Would that just sticking a resistor between the "L" and the LED lead on this diagram? If so, what amount of resistance?
http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

I'm not sure what V+ is.

[Jhouse]

Nevermind. R27 has you covered on the resistor part of it. Silly  me.

Anyway, try unsoldering it and hold it up to the light. See if there is a thin metal film running through the entire thing. If it's not connected, it's probably shorted out and is no longer good. It might just be that you wiggled the cables around and messed up the soldering joints. Check those out too.

[oakst8]

the film looks like a little flag (right?) and it appears to go 99% of the way across.

I bought a new one (but foolishly wired it in before examining it). It also didn't work. I then examined it and it looks the same as the original.

Any other tips to troubleshoot this? I desoldered and resoldered the connection from the circuit board with no change. I looked through the other connections and didn't see anything obviously wrong.

Full disclosure, after my resistor changing, the whole pedal is a chaotic mess of wires, so problems could be hiding in there somewhere. It would just be helpful if I knew where to focus my efforts.

Thanks, once again.

[Jhouse]

It's either the resistor that goes to the LED (r27 I think), the LED itself, or where the LED goes to the bypass switch. See if any part of that is touching metal and shorting. Make sure that you don't have any solder bridges. If you still can't get it, put up some pictures of the wire beast and I'll see what I can do.   

[oakst8]

No luck. The resistor tests out ok. And I unconnected and reconnected a handful of the grounds, but that didn't help and is starting make things messier. I'll take some shots tomorrow and post them. Whet should I show? The switch, the LED, and the LED's connection to the board, I presume?

[Jhouse]

Yup. Just put a bunch of pictures on here.  . We'll figure it out. Send some of the underside of the board too so we can check for any solder bridges.

[oakst8]

Here some shots. I re-did each of the grounds from the board with no changes. And, unfortunately, I feel like the chaos factor increases with each new action. Hopefully the photos show something, if not, it may be time to re-wire this sucker from the beginning.

[oakst8]

The thing has now completely stopped working. 

Voltages all read about 8 and seem to be either climbing or falling. Consistent across all transistors.

[oakst8]

well, I rewired every wire and got the pedal working again. but no change to the LED problem.

I'm guessing I blew both of them, but I'm still ready 8v on both sides of R27 and at the end of the lead to the LED, so wouldn't that suggest that hooking up another LED will just blow that one too? something is probably wrong upstream, right?

[Jhouse]

Try replacing R27 with a 2.2k-4.7k resistor and put in a new led. That will probably fix it. If it is reading exactly 8 volts on both sides (other than your power source being fairly low) then the resistor is busted.

[petemoore]

  The LED diode can be checked with the DMM. One way should show the foreward threshold the other way no response.
  LED in right hand, 2k2 or bigger in left hand, find the cathode first or second.
  Another way to find LED orientation is with the current limiting resistor/LED string, use a battery to light it. If it doesn't light, reverse +/-.
  Put the resistor where you want it [can be on either side of the LED], just remember which battery pole the resistor went to so as to keep the LED direction correct.
  So, we have PS, LED [and CLResistor] power supply and know the polarity that lights the LED...outside.
  Check inside the pedal connect the LED/R to +/- of supply and it should light.
  Put a switch in the LED circuit [separate from the audio circuit], to turn it on/off.
  Pick two lugs [pole and throw] on the 3PDT that aren't doing anything else..find the two lugs that connect when effect is on, disconnect when the effect is off...connect the LED circuit through this switch.
  The switch, the power supply and the LED/resistor can all be tested/checked.