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 (https://imgur.com/woPK6v5) 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. (https://www.madbeanpedals.com/projects/archives/DistBoostOD/Sunking.zip)
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.
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
(https://i.imgur.com/WO9z70V.jpg)
(https://i.imgur.com/dW1RFmZ.jpg)
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.
Somebody? Please? :(
Bump...
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?
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.
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.
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.
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...)
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...
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.
Quote from: Zerro on June 30, 2021, 03:24:49 PM
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...
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.
Quote from: matmosphere on June 30, 2021, 05:14:15 PM
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.
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.
Quote from: Zerro on June 30, 2021, 07:58:01 PM
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.
Alright let me re-assess something here: I am getting 4.55v (VR) on ALL lugs of the Gain pot regardless of it's orientation... is this normal? It appears to connect to all the points it should connect to, without any shorts - I measured continuity to be sure.
I'm getting signal on pin 7 of IC1_B, but it's very weak and not very gainy at all (regardless of orientation of the Gain pot).
When turning the Gain pot the tone goes from bright to dark, around the midpoint there's a slight volume drop. I'm guessing something is awfully messed up with the pot (yet when desoldered it measures properly to it's intended value). Also on Gain B I measure 1.5ish K between the wiper and either 1 or 3, when pot is turned to either extreme. I guess this is normal because there's a 1.5k (R4) in parallel over lugs 1 and 3 of the pot.
I just did another hour of checking and testing and I'm stumped. Maybe I'll just order a pedalpcb kliché and rebuild it, I'm getting tired of chasing a ghost :(
Moving Gain pot at the min. position will almost wipe away signal at the input of IC 1B. It is normal.
4.5V potentials at IC1B is not a problem. Maybe I would wait slightly less voltage at pin 6 of IC 1B. But finally it will be some mechanical issue, I guess. Crackle of pcb track around IC1, bad socket....
If straight connect of resistors with VB doesn't make gain jump, something is wrong here. Maybe shortage at output? Here is capacitor C10. Measure it, if it is not kicked thru. After it, controll, if switch bypass BYP_B is not bad, to ground output signal.
Quote from: Zerro on July 01, 2021, 05:07:36 PM
Moving Gain pot at the min. position will almost wipe away signal at the input of IC 1B. It is normal.
4.5V potentials at IC1B is not a problem. Maybe I would wait slightly less voltage at pin 6 of IC 1B. But finally it will be some mechanical issue, I guess. Crackle of pcb track around IC1, bad socket....
If straight connect of resistors with VB doesn't make gain jump, something is wrong here. Maybe shortage at output? Here is capacitor C10. Measure it, if it is not kicked thru. After it, controll, if switch bypass BYP_B is not bad, to ground output signal.
I have checked the socket, socket is good because I measure directly from the IC pins to the corresponding resistor pins (skipping the traces, to test continuity). Also checked on high ohm setting to check if the resistors are the correct values and making good contact, for example measuring between IC1_B pin 7 and R7/R8/C7 node. I have checked everything around IC1_B this way for shorts, continuity, values, etc.
C10 is not broken, it measures a good 1.1uF. I also checked BYP_B to check if it's not switching to ground when the effect is engaged. I measure no connection between R10/C11 node and ground when the pedal is "ON".
EDIT:
I even checked if the signal is reaching IC1_B, which is the case. Checked with audioprobe and the signal arrives at IC1_B pin 5. Continuity between IC1_A pin 1 and all components until IC1_B pin 5 is good, too. No shorts, correct values etc... I don't know where to look anymore :(
Last thing I can offer is to measure if pins put in socket have the same values as nodes, where they are connected around. Continuity in circuit with socket. Now I am really wonder, what shit will be there engaged.
Quote from: Zerro on July 04, 2021, 10:10:18 AM
Last thing I can offer is to measure if pins put in socket have the same values as nodes, where they are connected around. Continuity in circuit with socket. Now I am really wonder, what shit will be there engaged.
What do you mean exactly? Should I measure from the pins of the
socket without the IC in it directly to the nodes to check if the values are correct and if there are no shorts? Or should I check with the IC in the socket? I measured from the pins of the IC, while the IC was in the socket... so I would think that if I measure it that way the socket is tested for faults too...
This way sometimes helped to me - to measure what is at pins in socket, and what is at nodes around, connected with those pins. Even if pin is hanging in air, something can induce at it from circuit in opamp. So, you think you have contact, but it is not.
This opamp connection is nothing tricky, so, I wonder, why this issue? That's standard connection of opamp with negative feedback. The more ratio of both resistors in feedback, the more gain. Nothing more. It is really strange.
You have a good point! It is indeed really strange.
I measured the pins while the opamp was out of the socket, and I see slightly lower voltages on pin 6 and 7 than when it is in the socket! This is strange as well to me :o
These are the measurements I made:
Gain pot fully CCW
IC1_B pin 6: 4,50 volts
IC1_B pin 7: 4,31 volts
Gain pot fully CW
IC1_B pin 6: 4,54 volts
IC1_B pin 7: 4,36 volts
Still no shorts or links to ground where they shouldn't be though...
Personally, I hate sockets in pcb. I always solder detail straight to pcb. Here is only problem with sockets, espacially when time goes on, because or transitional resistances between pins and socket. In time, they are rising - for it is just mechanical contact. Try to solder it in, slightly, and then try it again. It is only way how to make it clear.
First off, I'm sorry for taking so long to reply. Life got in the way haha.
Alas, that solution did not help either. I don't know what's up with it, maybe there's an issue with the PCB somewhere which I can't find... very strange. I think I'll just order a different PCB and try again. Thanks a lot for trying to help me :)
It's pitty, that it doesn't work. I guess, that bad pcb is now most suspectable. Try to measure cunductivity of it. Use multimeter at this function (diode glyph), and measure all tracks from point to point.
Quote from: Zerro on August 01, 2021, 03:51:12 PM
It's pitty, that it doesn't work. I guess, that bad pcb is now most suspectable. Try to measure cunductivity of it. Use multimeter at this function (diode glyph), and measure all tracks from point to point.
First and foremost, I'm sorry for taking three months to reply to you...
I tried measuring the traces/tracks way back when I (we) tried to find the problem with the circuit, but alas, no luck. I decided to replace the PCB with a PCB Guitar Mania Kloned Centaur PCB. Even though it only has a voltage swing of 18v (+9v and -9v) I really like the sound of it :) I'll salvage the old Sunking PCB for parts probably someday...
Thank you for all the help and patience!