Debugging a tonepad green big muff

[GiulioGratz]

Hi!
I'm building a Russian Green Big Muff from the Tonepad's pcb layout, i'm using a dpdt switch and a millennium bypass 2 to control the LED. Q1, Q2, Q3 and Q4 are bc550c and i used bat41 instead of 1n914 diodes.
Here my problems:
when the pedal is bypassed, the signal passes correctly;
when the pedal is switched on, i can hear a very very slim sound from my amp only if i completely turn up the volume control of the amp;
the LED is always lit up, even if the effect is bypassed.
I controlled all the pot, switch and jack connections, but the result doesnt' change.
What could i try to do?
Here my values:

Voltage: +8,83 V

Q1
E: 0,13
B: 0,73
C: 4,53

Q2
E: 0,13
B: 0,73
C: 4,52

Q3
E: 0,12
B: 0,72
C: 4,42

Q4
E: 0,87
B: 1,42
C: 4,88

Any idea? Thanks!

[PRR]

Did you use a 3-pole switch? 3x3 pin array?

Could you have wired the switch 90 degrees wrong? (It looks almost the same either way.)

[GiulioGratz]

No, i'm using a 2-pole switch and millennium 2 bypass... thank you for your reply!

[GiulioGratz]

Any idea? I can't understand why it doesn't work... a small particular: the thin sound produced with the amp's volume pot at max is heavily distorted! But why so low volume?

[bluebunny]

What happens if you unhook the Millenium2 from the switch?  I.e. just leave behind the *audio* connections.

[GiulioGratz]

Just tried to unhook the "control" wire from millennium 2 to the switch... same story, the led is always on and the volume is absurdly low BUT less low than before!

[bluebunny]

Sounds like the M2 isn't working correctly (quite apart from the BM).  What happens if you short that control lead to ground?

[GiulioGratz]

Yeah, i noticed that the volume pot (of the big muff) wasn't working. So i tried to remove it and - TA-DAAAA - the big muff came to life.
I will change it the next week.
There is always the problem with the led: it's always on! There must be something bad in the bypass. But hey! The pedal works! Thanks!

[bluebunny]

If your volume pot was broken, then there may not have been a path to ground at the output.  This would have upset the M2 (the control line needs a DC path to ground in order to switch off the LED).

[GiulioGratz]

  so what can i try to do? Should i control the ground wirings?

[bluebunny]

Sorry if I wasn't clear.  It sounds like the muff circuit is working now (or at least it will do when you've replaced the broken volume pot).  I was suggesting something to see whether the M2 circuit was working.  It's a separate circuit.  Just power it up and then connect the "control" line to ground.  The LED should go out.

[GiulioGratz]

Ok, that's clear now! Thank you! I'll try later thank you!

[bluebunny]

Good luck with that.  If it helps, I've posted before how to make little M2 boards from scraps of Vero (click on the thumbnail below).  Q1 is BS170 and Q2 is 2N3904.  If you want to use 2N7000 for Q1, then face it in the same direction as the 2N3904.

[GiulioGratz]

Hey, very kind! Thank you for that! 
I see in your boards you use 2 transistors, in the schematic i'm using there's only the bs170 (the schematic i used is this: http://www.geofex.com/article_folders/millenium/milckt.gif). Could be a problem? Maybe i could try also your schem, but i'll have to make another order so i think i'll try to connect M2 control to ground, first. If it works, i'll keep my schematic.

[Roger Martin]

sometimes soldering tip and sleeve by mistakenly the opposite to one another can cause a dead unit too.
check out those resistors too.

[bluebunny]

Hey, very kind! Thank you for that! 
I see in your boards you use 2 transistors, in the schematic i'm using there's only the bs170 (the schematic i used is this: http://www.geofex.com/article_folders/millenium/milckt.gif). Could be a problem? Maybe i could try also your schem, but i'll have to make another order so i think i'll try to connect M2 control to ground, first. If it works, i'll keep my schematic.

The 2N3904 (with the unconnected emitter) serves as the "low leakage diode".

[GiulioGratz]

Roger Martin
I checked them. Seems to be all okay...

bluebunny
Powered up the M2 and connected "control" line to ground. The LED doesn't go out! 
Could a photo be an help?

[bluebunny]

Powered up the M2 and connected "control" line to ground. The LED doesn't go out! 
Could a photo be an help?

It wouldn't hurt to see your circuit - top and bottom views.  In the meantime, check and double-check orientations of diode and transistors, short-circuits, etc.

[GiulioGratz]

Unfortunately i have no time now to take photos however i've checked, double-checked, triple-checked orientation of diodes and transistors, short circuits, ground connection etc. I've also checked the voltage between cathode and anode of the LED: 1.78 V. Operating voltage of my yellow 5 mm LED is 2.2 v. Could it be a problem? 

[bluebunny]

Could it be a problem? 

Nope.  Your LED is lighting up, so there's no problem there.  (The only problems you could have with the LED would be wrong orientation or CLR too small.  Either way there would be no light.  And in the second case, fire/smoke/heat, then dark.)  The problem has to be with the parts that switch the LED off.  I guess you could have zapped the MOSFET?  Not sure if that would result in an always-on LED...

You could try a rebuild?  Or build one of my vero scrap M2s?