Need help with a Muff

[stoiker]

Hey guys, I'm new here and need some help. I build a Green Russian Muff based on the tagboardeffects vero layout (http://tagboardeffects.blogspot.de/2012/06/ehx-green-russian-big-muff.html), trannies are 2n5088, it seems to work fine, but when I play my bass through it and sustain is cranked I get a weird distortion drop. It's not easy to describe, it's like it's stopping to distort, especially on low notes. Any Ideas?

Voltages: (C / B / E)
Q1 3.95 / 0.63 / 0.04
Q2 3.95 / 0.63 / 0.04
Q3 3.93 / 0.63 / 0.04
Q4 3,79 / 1.70 / 1.22

[GibsonGM]

What's your battery voltage?  Collector voltages look a little low, to my eye.

[Elijah-Baley]

Here the voltages according GGG.
http://www.generalguitargadgets.com/pdf/ggg_bmp_instruct.pdf

Q1
Collector 3.9
Base 0.6
Emitter 0.03

Q2
Collector 3.8
Base 0.6
Emitter 0.03

Q3
Collector 3.8
Base 0.6
Emitter 0.03

Q4
Collector 4.0
Base 2.5
Emitter 1.8

Your Q4 has the voltages a bit lower.

[stoiker]

What's your battery voltage?  Collector voltages look a little low, to my eye.

9.4 V

Here the voltages according GGG.
...
Your Q4 has the voltages a bit lower.

Yeah, I've seen that. I also read the Muff analysis on electrosmash and it says Q4 is the output booster, so I thought a lower voltage on Q4 drops the overall output, but not the distortion.

[Elijah-Baley]

Maybe you're right, but look anyway around the output stage, the low voltage could be a hint of something wrong.

As usually in these case, check resistors value (measure it, or compare them the colour stripes with other resistor you have in stock), check cap values, unwilling contact between the trace or some missing cut trace, if all the grounds are connected, the wiring of the pots. Oh, and the orientation of the transistors!

[GibsonGM]

^ Yep, what he said.  Look it over VERY VERY good, being sure all parts are the right VALUE as called for.

Only other thing I could think of, would be to make sure your diodes are really pointing (electrically of course) in opposite directions.  Long shot, but they DO create most of the distortion. 

Could something be so 'off' as to turn off those diodes?  something shorting or bypassing the diodes in Q2 or Q3??

[duck_arse]

don't forget to welcome a first-poster, fella's.

does the lacking distortion sound like it squats, and then blooms again in the decay? is there a chance you've changed a cap value, and are getting blocking distortion? or an electro backwards, maybe?

oh, and welcome to the forum. can we see photos of what you've built?

[stoiker]

Thanks guys. I checked everything on the output section, checked for unwanted bridges, measured the resistors, swapped the caps (just to be sure), but compared to the GGG voltages Q4 is still to low.

don't forget to welcome a first-poster, fella's.

does the lacking distortion sound like it squats, and then blooms again in the decay? is there a chance you've changed a cap value, and are getting blocking distortion? or an electro backwards, maybe?

oh, and welcome to the forum. can we see photos of what you've built?

Thanks. Yeah, it does get back in the decay. Cap values and directions on electros are all right, the only thing I changed from the original layout is to leave the polarity protection diode out.

Pictures, sorry for the quality:

https://dl.dropboxusercontent.com/u/23698350/BMP1.jpg
https://dl.dropboxusercontent.com/u/23698350/BMP2.jpg

[bloxstompboxes]

Looks like a solder bridge between the the 5th and 6th rows up from the bottom on the left.

[antonis]

Looks like a solder bridge between the the 5th and 6th rows up from the bottom on the left.

It doesn't look like..

It IS a solder bridge..!! 

[Elijah-Baley]

Pass a cutter between the row if you think there is a bridge, and check always with the multimeter. Sometime it happens to me, too.

[stoiker]

It might sound stupid, but there is no bridge. It was just a tiny bit old solder from my desk. I guess I should clean up a little bit better  I'm sure it got there, when I took the first picture. Removing it didn't solve anything.

[antonis]

Then you'll have to ensure about firm trasistors socketing..

[Elijah-Baley]

It might sound stupid, but there is no bridge. It was just a tiny bit old solder from my desk. I guess I should clean up a little bit better  I'm sure it got there, when I took the first picture. Removing it didn't solve anything.

Did you check with the multimeter and now we can exclude this issue? Sorry the picture it was really suspect .

About the transistor, what are you using?

Did you wired jacks and footswitch? What is your "off board wiring" layout?

[stoiker]

Did you check with the multimeter and now we can exclude this issue? Sorry the picture it was really suspect .

About the transistor, what are you using?

Did you wired jacks and footswitch? What is your "off board wiring" layout?

I use 2n5088. The circuit and jacks are connected on my breadboard, footswitch isn't wired in yet. How should I use my multimeter to check for bridges?

[Elijah-Baley]

Transistors are ok. I guess the jacks on your breadbord are well wired, I assume you tested them with other projects, else, try to take a look at some wiring.

I think almost all multimeters can check the continuity, and confirm it with a beep.
That is the setting I mean: https://d3nevzfk7ii3be.cloudfront.net/igi/oRtw5jQFedJRfnWP.medium.
Easy. Point a tip on one of the two spots you think are in contact, and the second tip on the second spot. If you hear a beep there is a contact, else there's no.

If this helps you, you can check all the wires of the pots, and something else, too.

[duck_arse]

as E-B says, do the continuity tests with the power off/disconnected/battery-less.

[straws_grabbing] have you tried swapping the transistors about? [/straws_grabbing]

if you could also pull Q4 outta its socket, and measure the resistance from each of its pins to ground, and then to the supply line, and give us the results, that would be nice. the voltages on that transistor look very close to right, but maybe not quite.

[stoiker]

I didn't know about the continuity test. Now that's handy! But no beeps at all.

Stupid me, I just realised that I DID change a cap value. The layout asks for a 4n cap in the tone-section, but I used 4.7n. I've read in the comments on tagboardeffects that it should be fine. Can this be the reason why Q4 voltages are slighty off?

[Elijah-Baley]

I don't know what change for Q4 with a different value of that cap, but it enhance a bit of midrange. If you have problem with the sound should be another mistake.

I have to say I never tried the big muff with a bass. Someone did, but there is a version right for bass. I guess it is pretty similar with one or two bigger caps in the bass version.
Can you try the circuit with a guitar?

[stoiker]

It just occurs on lower notes so I guess it's fine with guitar, but I heard the Green Russian is the best Muff for bass, so at least I thought it should perform well on every note.

And yes, I did swap the transistors, but it didn't change anything. I looked at the schematic and the layout again and realised that lug 2 from the sustain pot should go to a 1u electro and then into a 8.2K resistor, but in the vero layout they're switched. I guess this doesn't matter, because the layout is verified?!