Need some quick help with my Big Muff

[seadi123]

I need this pedal done today, the circuit is not completely dead when connected, but the volume is low with almost no gain, like clean sound. Voltages:
Q1 q2 q3 : 4.4v 0.14v 0.8v
Q4 : 4.8v 1v 1.4v
Diodes: 0.8v 0.6v

NYC Big Muff pi ec3003, 2n5088 trans, 1n4148 diodes

Layout : http://2.bp.blogspot.com/-dhrzj6JgnAQ/VDkrfpxRgZI/AAAAAAAAIpk/H-6aMtpt0CQ/s1600/EHX%2BNYC%2BBig%2BMuff.png

Schematic : http://4.bp.blogspot.com/-uYM0v6H2q-s/VDlz5ZgvKVI/AAAAAAAAIp0/N33_ifLfqf0/s1600/Big_Muff_PI_Ec-3003_ver_C_.png

I already ran a knife through the rails. Where should i look at?

[Slowpoke101]

Your Base voltages on Q1, 2 & 3 are very low. The expected base voltage would be somewhere near 3.6 V. Check the values of the 470K resistors going from the Collectors to the Bases on those transistors.
Make sure that you have the transistors orientated correctly.
Some pictures would be very helpful too.


Edit: I am an idiot. The base voltages should be near 0.6V not 3.6V Your emitter voltages seem to be a bit higher than expected, 0.05V is to be expected. Sorry for the error.

[Elijah-Baley]

I write quickly. Check all the orientations. Check the value of the resistors. Check the position of the component, wires, cut track and jumpers.

[slashandburn]

Did you flip your transistors? The pinout is different on the 5088s compared to the BC550 on the vero layout.

Failing that, photos would help.

[seadi123]

I checked everything and didn't find the solution, but putting a ts9 in front of this sounded soo good and unique. So i'm just keeping this board and i'll build another one from scratch. Thanks everybody!

[Plexi]

Post some photos of your board!
(Closer solder side )

[seadi123]

Ok now i really need some help. I built the second board and got the exact same results: there's almost no gain, only with the sustain at maximum i do hear some fuzz, it's like a warm overdrive. I replaced the 2n5088 with 2n5089 assuming it was just that the transistors had low gain; same thing. I have double checked the orientantion and soldering and its all right. What should i look for?

[EBK]

Failing that, photos would help.

Post some photos of your board!
(Closer solder side )

See above.   

[seadi123]

Here's the copper side, looks terrible because i replaced the transistors, but i ran a knife through the rail so they're not touching: https://s13.postimg.org/q0f2op913/image.jpg

Here's my normal soldering job from the previous board: https://s13.postimg.org/3pr7oaoh3/image.jpg

Component side: https://s13.postimg.org/mgt4yyqwn/image.jpg

Component side from previous board: https://s13.postimg.org/qr7suftdz/image.jpg

I've also double checked resistors and pots values

[Elijah-Baley]

Component side: https://s13.postimg.org/mgt4yyqwn/image.jpg

I'm seeing the diodes in the centre of the board. I guess them should be in anti-parallel.

[duck_arse]

^ me too.

just for the educational value - can you measure the resistance of all your 120R resistors, and all your 10k resistors? and, funny colours/light, can you also measure the resistance of the 27k in the middle of the board?

[seadi123]

Component side: https://s13.postimg.org/mgt4yyqwn/image.jpg

I'm seeing the diodes in the centre of the board. I guess them should be in anti-parallel.

Nice catch! Will flip one now

[seadi123]

Flipped the diode, now i hear fuzz only with all knobs turned up full. The volume is low, with volume in half i almost cant hear anything. Tone pot is ok, fuzz also works but there is no aggressive distortion whatsoever.

[seadi123]

^ me too.

just for the educational value - can you measure the resistance of all your 120R resistors, and all your 10k resistors? and, funny colours/light, can you also measure the resistance of the 27k in the middle of the board?

Also measured 120ohm and 27k resistors, everything is fine. It's also intriguing that i have the same problem on both the boards i've built, it's like i've done the same mistake twice

[seadi123]

Additional info: I've used the upper ground rail of the muff as a ground point for everything. This is a 2 in 1 pedal, the other effect works fine and true bypass also works fine

[seadi123]

Solved. Besides the diode which was in the wrong direction, one of the cuts was made in the wrong place

[Cenzoru]

Hello, I have almost the same problem. Sustain pot kills the volume. It sounds only with sustain pot from middle range to full open. I used the same schematic and vero board as seadi123.

What could it be ?

[antonis]

<Sustain pot kills the volume. It sounds only with sustain pot from middle range to full open.>

Is sound volume constant or does it rise in accordance with pot wiper setting..??

[Cenzoru]

Volume rises whilst the sustain pot is anywhere between middle and full range; but if i close the sustain pot, then everything is muted.

I checked the continuity, the holes and the rails. Actually there is some difference between the schematics and the vero board design if you look on the seadi123 attachment. In the schematics C5 is placed before the R15, but if you track on the vero board design you will notice that from sustain 2 goes first to R15 and after that to C5. Would that make a difference ? I mean is a verified built on that tagboardeffects web page.

[antonis]

You pobably mean R19 (R15 in schematic is the feedbck resistor of Q3..)

The order of C5 & R19 doesn't mind as far as they are set in series..

That Sustain pot behaviour seems to me like a Log pot (not Linear) without R1..
(mute at full CCW with very "low" responce a about 1/3 of initial wiper travel..)