Russian Big Muff: Little to No Sound

[neutronarmy]

Friends,

I will try my damnedest to describe what exactly is occurring here. I have built a Civil War Big Muff Pi from Sabrotone's layout.
Here is a layout link: http://www.sabrotone.com/wp-content/uploads/2010/04/Big-Muff-Pi-Civil-War-Russian.gif
And the schematic is based on: http://www.generalguitargadgets.com/pdf/ggg_bmp_grus_sc.pdf

Here are the transistor voltages (Q1-4 as listed on layout; battery at 8.7V):
Q1: E .228 B .85 C 1.4
Q2: E .247 B .87 C 1.04
Q3: E .246 B .87 C 1.04
Q4: E 2.0 B 2.7 C 2.0

I realize that Q4 is an issue. Perhaps it is not the only issue, but it is definitely an issue. I've tried as hard as I could to find any kind of solder bridge, running an x-acto blade through the tracks, looking at it under a magnifying lens. I have yet to find any different in the readings.

Here are some mods that I did to the circuit:
1). I changed C11 to 12nF, R18 to 3.3K, and R21 to 2K. These changes were to match a Green Russian schematic I found.
2). I installed a tone-stack lift switch which removes the ground half of C11 and R18 from ground (engaging/disengaging seems to make no difference; those component numbers are from the layout).
3). The circuit is proceeded by a Buff-N-Blend for clean blend, but have jumpered that circuit out of the equation and noticed no difference.
4). I added diode clipping lift switches on both diode pairs, but have noticed no difference with the switch (all readings are with diodes in circuit).

I get battery voltage at the supply side of all of the collector resistors and a drop to ~1V at the collector side. I know the collector voltages are way low and I assume that Q4 drawing excess current has something - though perhaps not everything - to do with that issue. I have tried swapping Q4 with another 2N5088 to no avail. All pinouts have been triple checked.

If you need any more information I will be glad to provide it. I am honestly baffled at this point. Thanks in advance for any help.

-Chris

[LucifersTrip]

the fact that all 4 collectors are so off (should be ~4 to 5v) suggests possibly a more general problem like the transistors aren't oriented properly.

i would first see if you can just get the 1st stage to bias correctly. just look at everything up to c3 on the schematic. it should be separate anyway if you disconnect the sustain pot, so you can easily see if stage 1 is working without any affect from the others

[neutronarmy]

I totally assumed that the were oriented improperly as well - but double checking the pinout of 2N5088s shows a proper orientation (I have them oriented as they are in the layout, which according to the datasheet is proper). Perhaps I can try to isolate the first stage, I just assumed the voltages were wacky because of the mess of an output stage. Thanks again for the help!

[LucifersTrip]

I just assumed the voltages were wacky because of the mess of an output stage. Thanks again for the help!

sounds cool...though, I doubt a mess at the output could affect all the previous stages' voltages

[neutronarmy]

I just assumed the voltages were wacky because of the mess of an output stage. Thanks again for the help!

sounds cool...though, I doubt a mess at the output could affect all the previous stages' voltages

You make a good point, sir.  I am getting full supply voltage prior to the 12K resistors attached at the collectors and measure the ~1V after said resistors. The values seem proper according to the schematic. That was why I was assigning blame at the output - however theory improper that may be. Befuddled I am.

I know troubleshooting individual pedals can be a hassle, so I don't mind getting my theory brushed up on. If anyone can direct me to a relevant website/article that would also be really great. My lack of proper transistor theory can be pretty embarrassing.

The help is so very appreciated.

[Mike Burgundy]

Q4 looks shorted - probably shot (as long as there isn't an extaernal short). R21 2k? EH used many different components and values over the years (basically what they could get their hands on at the time) but combined with a 390k R22 that will seriously throw Q4's bias - R22 and 21 form a devider which sets the bias voltage for Q4's base..
Have you actually tested the transistors? If your DMM has a transistor test, use it. You can use the diode test to verify the transistor's pinout and that it is actually (probably) working. It should look like two diodes, conducting from Base to Emitter and Base to Collector, BE having a slightly larger threshold. Nothing else should conduct.
Check the transistors, then take it stage by stage. Maybe include pictures of your build, to see if there's a layout error. For now, my money is on the transistors though.
It also helps to get it working with a proven schematic (such as the GGG one) first, then change things.

Oh hang on - did you mean R21 on the schematic or the layout - they don't match? I'm looking at the schematic! 2k7 to 2k isn't much of a problem (layout) - 100k to 2k (schematic) is.
*edit*: the transistors need to be tested out of circuit, otherwise the measurement will be thrown by the surrounding resistors.

[neutronarmy]

Q4 looks shorted - probably shot (as long as there isn't an extaernal short). R21 2k? EH used many different components and values over the years (basically what they could get their hands on at the time) but combined with a 390k R22 that will seriously throw Q4's bias - R22 and 21 form a devider which sets the bias voltage for Q4's base..
Have you actually tested the transistors? If your DMM has a transistor test, use it. You can use the diode test to verify the transistor's pinout and that it is actually (probably) working. It should look like two diodes, conducting from Base to Emitter and Base to Collector, BE having a slightly larger threshold. Nothing else should conduct.
Check the transistors, then take it stage by stage. Maybe include pictures of your build, to see if there's a layout error. For now, my money is on the transistors though.
It also helps to get it working with a proven schematic (such as the GGG one) first, then change things.

Oh hang on - did you mean R21 on the schematic or the layout - they don't match? I'm looking at the schematic! 2k7 to 2k isn't much of a problem (layout) - 100k to 2k (schematic) is.
*edit*: the transistors need to be tested out of circuit, otherwise the measurement will be thrown by the surrounding resistors.

I meant R21 on the layout. I wish they matched as well - would make this conversation much easier. 2k7 to 2k, not 100k to 2k.

Today's agenda is to work solely on the first stage and then move further. There is certainly a chance that the transistors are shot - I'll double check them - but they are fresh out the bag and swapping Q4 didn't change readings at all. My guess is I screwed something up over component failure.