Eternity volume pot strangeness

[lukeferg]

Hi all,

I finished a Lovepedal Eternity build today. Using this layout, http://tagboardeffects.blogspot.com/2012/02/lovepedal-eternity.html

So I fired it up and was sounding great. I was using it for about 5 minutes or so and then the volume suddenly reduced while I was playing. I'd had the volume up quite high, probably about 3 o'clock, so it was quite noticeable.
Now, when I turn the volume knob the first 1/3 of the turn works as normal, volume increases as it should, then it suddenly drops out and is very quiet for the rest of the turn with only a small increase in volume. It doesn't get anywhere near the volume it has at 1/3 of a turn.

I have tired to find the problem to no end. I've looked for solder bridges and ran my soldering iron between the vero strips countless times.
I've also replaced the volume pot (tested before replacing) and the IC and this hasn't changed anything either.

My voltages are slightly low but they were also like this when it fired up the first time, so while there may be a problem somewhere here, I don't think that's the cause of my volume issue. My meter also loads things so some readings aren't trustworthy.
1. 4.00v
2. 4.00v
3. 2.01v
4. 0v
5. 4.00v
6. 4.01v
7. 4.01v
8. 7.75v (This one is very odd, my supply reads 9.35v. Like I said, the pedal had this reading before the volume issue. I've triple checked all my resistors and caps around the power supply too)

Is there anything that anyone knows of that can cause this kind of effect? It seems really strange for it to be working one second and not the next. Nothing else in the pedal seems to be a problem. The gain and tone pots work as they should for the whole pot travel. It makes sense that it's some kind of bridge somewhere but I can't figure out where it might be. Does anyone have any suggestions on where to look?

Thanks for your help,
Luke

[duck_arse]

I suggest we look at some photos. of your build. please. and a circuit diagram to suit.

[lukeferg]

The layout is using this schematic:
https://photobucket.com/gallery/user/IvIark_2006/media/bWVkaWFJZDo3NDA5OTA2MQ==/?ref=

Here are some photos of the build. Sorry if the soldering looks a bit messy, I've run my iron between the gaps that many times that it certainly looks worse than it started with.

I also should note that I replaced the volume pot wires when I replaced the volume pot as well.

Finally, there were two changes to the layout I made. First is putting a switch for asymmetrical and symmetrical clipping, this works fine. The other was replacing the 470R resistor with two resistors in series that got me to 490R. I don't think this arrangement is overly visible in the photos due to wires.

I'll post photos in a separate post because it's easier

[lukeferg]

[Mark Hammer]

I made one a while back, using the Madbean "Neutrino" PCB layout, and added a Timmy-style variable bass control to the circuit.  I will confirm that there is nothing instrinsic to the circuit itself that would do what you describe.

However....

The usual suspects should be considered:
- lousy power-jack contact
- heat-damaged stompswitch
- bad cables
- fractured wires to pots

All of these can momentarily turn what ought to be a zero-resistance straight-wire connection into a high-resistance contact.

[lukeferg]

Thanks Mark. I'll look into all those areas when I get home.
I already replaced the volume wires when I replaced the pot but I'll play around with the power and switch contacts.
It shouldn't be anything heat damaged but I'll check that too, I'm pretty gentle with switches usually. Learnt the hard way on that one.

My only other thought is that the enclosure is cursed.
This was one of my first enclosures from years ago and I've tried about 3 or 4 circuits in it, none of them have ever worked. It's not the prettiest box but it looks ok for my purposes.

[willienillie]

Now, when I turn the volume knob the first 1/3 of the turn works as normal, volume increases as it should, then it suddenly drops out and is very quiet for the rest of the turn with only a small increase in volume. It doesn't get anywhere near the volume it has at 1/3 of a turn.

I had a VERY similar experience recently with an OCD type build.  I had been trying different opamps in it.  When the problem happened, I found the opamp wasn't fully seated in the socket.  Looked like good contact all around, but the chip was sitting a little high.  Same type of socket as yours, too.

[lukeferg]

Thanks for the heads up. I'll give it a strong shove and see how it goes.

[duck_arse]

looking again at this pic shows a number of hairline cracks across the top of the board, where is has not been carefully enough cut. you should probably run a linking wire across/along any of the traces that are showing the substrate cracks, as the copper might look good, but is actually open, or goes open.

a hacksaw and some sandpaper always does a good jobbe.

[lukeferg]

Ahh yeah. I had a small piece of vero left over and was a bit rushed when cutting to size. I'll try solder the entire line.

FYI, reseating the op amp didn't work.

[willienillie]

FYI, reseating the op amp didn't work.

Right on.  It's probably a similarly dodgy connection, but somewhere else.

[lukeferg]

Well I'm about ready to say this one has beaten me.
I've replaced a heap of wires, reflowed solder to everything that looked remotely suspect, rewired every grounding wire and soldered along the edge of the board with cracks in it.

The pot is slightly more responsive now though. It has normal volume increase for about 3/5 of the pot travel now and then takes a dip at the end.

Interestingly, I've audio probed the thing to death and can't find a fault. The volume issue is only present when I plug the pedal into the amp. I've tried different leads and different amps, just in case. I'm going to replace the output jack as one last attempt. If that doesn't work then I'm done with it.

[lukeferg]

I finally bloody found it!
The 22uF coupling cap before the volume pot was rotten. Not sure what was wrong exactly but I replaced it and the thing is perfect now.

Is there any electrical reason an electro cap would do something like this (leakage is something I don't really understand well)? Or was it just a case of bad solder joints around it and replacing it was just an easy way to fix them?

[pinkjimiphoton]

maybe it got too hot n gave up the ghost...it happens