Rebuilding my kit - shielded twisted pair options, and a film cap [resolved]

[Paul Birkeland]

Oddly enough, that is a noise I would expect from conductive flux arcing over periodically.  I'd leave the amp on for a very extended period (10 days or so) to see if anything more concrete develops.

[twofires]

Interesting. Pretty much the only place left that flux could be is inside the transformer itself, impregnated into the material around the guts of it. That could've happened when I tried to clean the initial build with isopropyl back before the rebuild. That mixture (ChipQuik and isopropyl) may have dripped in there and dried. I'm not sure that's the case, though, as I can't see any of the chalky residue that was everywhere else. That said, everything else is either new, or very, very thoroughly scrubbed, so if it's flux, the power transformer is likely where it is.

When you say something "more concrete", what kind of behaviour are we talking? I doubt I can leave it on that long as I can't keep an eye on it consistently. I should probably be close by if something dramatic could happen.
I'll see what can be done, though.

Strangely, when I bypassed my DAC (a Topping D90) and plugged the amp directly into the headphone out on my computer (so using the soundcard), I listened to music for another 2.5hrs without any pops. Hardly definitive, but, is there anything about a DAC with an internal switching supply that might cause issues like that popping? Doubtful I know, but I'm keen to rule it out.

Also hoping to rule out the thing with the sanding the sides of the power transformer - could sanding the coating off the sides and then blasting it with paint have caused some issues?

One other thing - it seems to be more common with more sensitive headphones than with speakers or high impedance headphones. That may be some other factor at play, but if it provides any clues...

Thanks for all your help.

[2wo]

I seriously doubt that this will end up being the transformer.

[twofires]

I seriously doubt that this will end up being the transformer.

That's certainly my hope, but I have to admit I'm stumped.

I realised the other component I kept was the Alps Pot I used, although I don't remember using any ChipQuik on that, and I was under the impression those are sealed anyway. I also cleaned and reflowed that breakout board pretty thoroughly.

At this point I'm holding out hope for either bad tube(s) or weird input issue, unlikely as those are.

[twofires]

Quick question while I'm running this amp for extended periods:

Is it normal for the amp to have a bit of a fit when you unplug headphones to switch to the attached speakers?

I was listening with headphones, and needed to step away, but wanted to keep listening for issues, so I paused the music and pulled the headphones from the socket. This resulted in 'POPOPOP POP CRACKLE POP... POP... ... ... POP... ... ... ... POPOP' for at least 10 seconds from the speakers (mainly the left). When it seemed like it wasn't going to calm down easily, I turned the amp off (another single POP), waited a couple minutes and then turned in back on. No issues after that.

Is that an expected response to me doing something silly (like changing load from 55ohms to 8 ohms by pulling a jack out of a TRS socket), or is it unusual and indicative of some other issue?

This is the socket I used: https://www.digikey.com.au/en/products/detail/cliff-electronic-components-ltd/CL1323A/13663625

Note that powering it up again with headphones connected and then tapping on the headphone jack and twisting it in the socket didn't produce any pops, and all the joints look solid.

[Doc B.]

Sure sounds like a bad or missing solder joint.

[Paul Birkeland]

That sounds a lot more like a soldering issue than a flux issue.

[twofires]

Okay. If that's the case I'm honestly sorry to be taking up your time with the most obvious problem. I really did try to double check everything.  Any hints on where I could look based on the symptoms, or how I might diagnose? Everything really does look intact to me on the surface (I will visually inspect again though). Should I be powering it on upside down and tapping things with a chopstick or similar?

[Doc B.]

I would start by reflowing all of the headphone jack and speaker binding post connections as well as the output transformer secondary connections.

[twofires]

Thank you. Will do.

[twofires]

So I reflowed the headphone jack (all), the OT secondaries (all), speaker terminals (all), H1 & H8, and both sides of both output caps. The headphone plug/unplug pops are now completely gone, and it feels like maybe the noise floor is a touch lower.

All those joints looked pretty shiny already (definitely nothing like the 'bad' examples in the manual) so I'm at a loss as to which it was that resolved it, but I'm also very happy to eat humble pie and nail that one down.

I'm unsure if this issue is the same as the once-hourly pop, so I'll continue to monitor for that and post back if I either hear it again, or feel it's gone completely. It would be wonderful (if embarrassing) if they were the same issue, and unrelated to the problem with the original build. Faulty reasoning on my part I suppose, trying to connect unrelated dots.

Thank you both for your help.

[twofires]

Nope. The random popping persists.  This time I turned the amp on and just sat here with the headphones on and no music playing while typing an email. Maybe 10 minutes in, with no movement or change of any kind, the left channel went 'pop'.

I just received a few extra sets of tubes today, so I'll see if I have any more luck with them.

[Paul Birkeland]

You might want to poke around in the circuit with a wooden chopstick to see if you can actuate the popping by moving anything.

I'd also use very, very hot water to clean off the tube pins on the tubes that were originally used in the amp, as there may be some flux remaining there.

[Paul Joppa]

Is it possible that this popping comes from outside the amp itself? Easy to check - remove all inputs and turn the volume all the way down and see if it stops.

[twofires]

So the GE tubes I swapped in didn't give me any grief for the hour I was able to listen last night, although that's not enough time to be certain, and I'm also mindful that reseating tubes is a confounding variable every time I do it. I'll listen more today.

You might want to poke around in the circuit with a wooden chopstick to see if you can actuate the popping by moving anything.

I'd also use very, very hot water to clean off the tube pins on the tubes that were originally used in the amp, as there may be some flux remaining there.

Flux on the pins of the old Sylvania tubes is certainly possible. I remember that back during the first build there was definitely flux on them - jostling the tubes before I realised that elicited a thunderous sound like a box of heavy books being kicked down a flight of carpeted stairs. This time around I gave them a bit of a clean with iso but it may not have been sufficient. I'll try the water thing. Would standing them in 80C water for a bit and then taking to them with a (clean) toothbrush do the job? I'm hoping they haven't contaminated the new sockets - if I have to pull the thing apart to replace those I might need to go swear loudly for a while. I don't think it's likely, though. Jostling the new GE tubes did nothing at all on the B side, and only elicited the slightest of susurrus noises I would expect is normal on the A side. Definitely no pops.

Is it possible that this popping comes from outside the amp itself? Easy to check - remove all inputs and turn the volume all the way down and see if it stops.

I did have that thought (earlier in this thread) about my DAC. It has an internal switching supply and I understand that sometimes those can do unexpected things re: ground. I wasn't sure if having nothing on the inputs was good for the amp but if it's fine I'll certainly give it a try.

I think my plan of attack will be:

• Keep listening with the GE tubes. If there are still pops...
• Remove the input and keep listening. If there are still pops after that...
• Poke with a chopstick until pops happen.

Thanks again everyone. We're gonna figure it out eventually!