2015 Sunking Gain pot not working properly / not making any gain

[Lurktastic]

Good day/good morning everyone!

Yesterday I finally got the last parts in for my Sunking build. I still had an old board laying around and decided to populate it. Made a nice looking enclosure for it and all. Fired it up yesterday and... well it works, but the gain pot doesn't do much. I get a slight change of volume when the pot travels around it's midpoint, but other than that the gain level stays more or less the same - pretty low. The Level and Tone knobs work properly though, as does the bypass. I wired the circuit to be buffered bypass.
I implemented a couple of mods. One being the obvious clipping switch as described in the build documents, the other being a capacitor switch which switches between ~4nF, ~7nF and ~14nF. The cap switch works properly, I can easily hear the difference between different settings. The clipping switch however, just like the gain pot, doesn't do much of anything... which is logical of course because there's hardly any gain produced.

I've tried debugging it a tonne yesterday, spent a good 4 hours measuring/checking values, continuinity, voltages etc. So far everything seems to check out. I also reflowed a couple of suspect solder joints around the gain part of the circuit, namely around IC1B. I even tried connecting the dual gang pot in reverse and tried swapping the gangs around but to no avail.

Could one of you be so kind as to take a look at this? I'm at a complete loss, I don't know what the issue could possibly be...
Here's the build document. The board I'm using is the 2015 version.
Below are the voltages on all the IC's, which seem to check out when comparing them to the build document. I've also included pictures of the component side and solder side of the board, below the table displaying the voltages.
As you can see, I paralleled some capacitors on the solder side of the board, and put some resistors in series on the component side of the board. I did this because I didn't have the correct values on hand. I did this for:
-R7, making a ~423k out of a 33k and a 390k.
-R15, making a ~392k out of a 390k and a 2k.
-C3, making a ~390nF out of 68nF and 330nF.
-C7, making a ~82nF out of a 47nF and a 33nF.
-C9, making a ~390pF out of a 39pF and a 330pF.

Code Select Expand


IC1 - TL072CP
1 -  4.55v
2 -  4.55v
3 -  3.48v
4 -  0v
5 -  4.54v
6 -  4.56v
7 -  4.56v
8 -  9.02v

IC2 - TL072CP
1 -  4.59v
2 -  4.55v
3 -  4.54v
4 - -8.78v
5 -  4.54v
6 -  4.55v
7 -  4.51v
8 -  17.33v

IC3 - 7660S
1 -  9.06v
2 -  4.43v
3 -  0v
4 - -4.44v
5 - -8.78v
6 -  4.58v
7 -  6.97v
8 -  9.06v







Thank you in advance!

EDIT:

Messed up the image links... fixed it...

EDIT #2:

I've also checked the bypass switch wiring, to see if it checks out with the schematic. In bypass, the buffer is switched and the output of IC1B (through C10 and R10) is connected to ground. When the effect is ON, the LED is switched to ground and no short exists between IC1B and ground. Figured I'd include this because the build documents state the following on page 6: "09/12 - Buffered wiring diagram corrected (pads 4 and 6 were originally shown reveresed)."

EDIT #3:

I'm aware the sleeve of the output jack isn't wired. I only have the sleeve of the input jack wired, using the enclosure to ground the output jack in order to avoid ground loops.

[Lurktastic]

Somebody? Please?

[Lurktastic]

Bump...

[Zerro]

At the central "runner" pin of pot Gain A has to be VR potential: 4,5V. Is it there? And, if you maximalize Gain, this VR must be at R9, which is connected with this pot Gain A. At the second part of this tandem pot, at Gain B must be in this moment VR too, at the runner - central pin. Is it there?

[gordo]

Hmmm, any chance the pot itself is bad?  Voltages look good, and VB looks correct.  If you're getting VB at pin 2 of both halves of the gain pot you could try jumpering pins 1&2 on both and then pins 2&3 on both to compare extremes.

[Zerro]

It is better to controll things I suggested and by the way, take some needle and clear ALL spaces between welded points from tin dust and another polution coming from welding - very important!!! See picture.

[Lurktastic]

Hi guys, first of all thanks for your replies! I'm sorry I took so long to get back, some stuff came up and I had to deal with it.

I get VR (which is 4.55 volts) at all pins of the pot, regardless of orientation. I did also desolder the pot before and checked if it didn't have any shorts and if the value is correct when I rotate the pot to it's extremes. I scratched the parts you mentioned to clear off some flux and dirt, but this didn't produce any results unfortunately.

There's something else that's a bit strange, which I forgot to mention in the first post: when I rotate the gain fully CCW, the pedal gets really bright, when it's at center the pedal sounds almost clean, when the gain is fully CW it sounds a bit darker with a tiny bit more gain than unity.

[Zerro]

Now you must connect VR point with that resistor R8, as I showed in picture I attached. There you should hear high gain changes at output of IC_1B. If not, than this R8, or R7-C7 line is wrong. Or IC_1B is wrong. Cotroll pins, if they are inserted properly. (bent or broken pin...)

[Lurktastic]

Alas, no change when I apply VR to the point you specified at the R9/R8 junction. I've also reflowed everything between IC1_B pin 7, R7, C7, R8, R9 and also measured continuity, but everything looks good. I also measured continuity between the wires of my gain pot to check if one of them isn't broken, but it's all fine. I also reflowed all the pins of the IC socket of IC1_B.
I still receive the same sounds as I described before, this is really strange...

[Zerro]

Gain for IC1_B is defined now by ratio of R7/R8. This must be now cca 28. This is high gain. So, or R7 is wrong, showing low resistance, or R8 is corrupted, showing high resistance. OR, C9 has shortaghe, so signal is not going thru R7. Those 3 details are now suspicious. If measurements will show they are ok, then replace IC1.

[Lurktastic]

Gain for IC1_B is defined now by ratio of R7/R8. This must be now cca 28. This is high gain. So, or R7 is wrong, showing low resistance, or R8 is corrupted, showing high resistance. OR, C9 has shortaghe, so signal is not going thru R7. Those 3 details are now suspicious. If measurements will show they are ok, then replace IC1.

I checked R7, it's aroundabout 428k. R8 is a solid 15k. C9 is not shorted, I measured across it's legs and it's got no continuity - I measure 428k but that's because R7 is in parallel with C9. I tried swapping IC1 over with IC2, no change. I tried swapping IC1 with a MC1458P I had laying around (which is essentially a dual opamp), no change...

[matmosphere]

Check your diode orientation and make sure the switch wires are connected to the correct lugs. The pads for the switch also look like they could stand to have some more solder.

[Lurktastic]

Check your diode orientation and make sure the switch wires are connected to the correct lugs. The pads for the switch also look like they could stand to have some more solder.

Diode orientation is good, I did check that before. They are opposite eachother in direction. Also, when the clipping switch is in the middle (in the OFF position) the pedal should oscillate/whine at the highest gain setting, yet it doesn't. Continuity is good between pads and switch.

EDIT:

It seems to me continuity should be bad (or there's a short) somewhere between pin 7 of IC1_B and pin 5 and 6 of IC1_B, just like Zerro said. I just can't seem to figure out where the problem lies.
Everything else in the circuit works properly, because the tonal shift I hear when turning the gain pot is logical - the filters at R12-R14 are responsible for that I preasume. Volume and tone pot work fine too.

[Zerro]

It will be some stupidity, mark my words :@)Power for IC, bad socket or so... Maybe crack in PCB track. Measure those tracks around that place.

[Lurktastic]

It will be some stupidity, mark my words :@)Power for IC, bad socket or so... Maybe crack in PCB track. Measure those tracks around that place.

Yeah, it probably is something stupid that I'm missing :') I'll give it another whirl today. Power for IC's is good tho', measured that before I measured anything else. Voltages are good, see OP.