Turntable-like static in left channel only (not volume dependent)

[big_n8_dawg]

Howdy all!

I have built both a SEX and a Crack, and the SEX works flawlessly, but I am having some difficulty tracking down an issue with the Crack. I built it last year, but for various reasons, I am only now able to get back to work on fixing it. (It has not been used in the interim.)

I have a not quite constant, scratchy, static-y noise in the left channel only, with intermittent minor quiet pops, very reminiscent of record/stylus noise. It begins within 30 seconds after turning on the power, as the circuit energizes, and continues from that point. It was not present during my initial post-build testing, but manifested shortly later (not sure exactly when, but it was within the first few days of intermittent use).  It is present with or without inputs connected, and it is not affected by the volume pot. Other than this noise, the amp sounds good.

I had hoped to resolve this myself with research and testing, and I have scoured the forum for threads regarding like-issues and the recommended troubleshooting and fixes, but unfortunately, many relevant threads end abruptly, and the recommendations in the others do not seem to be getting me anywhere closer to resolving this, so I am asking the gurus here for any assistance you may be able to provide.


I have done the following (with no change in the noise):

1. Tried multiple different input and power tubes
2. Moved the amp to a different room with no electronics to rule-out interference
3. Retested all resistance and power checks (all within allowable ranges)
4. Inspected and reflowed all solder connections for the left-side of the circuit
5. Inspected and reflowed headphone jack connections (tip connections and all ground connections, I didn't touch the ring connections since the right channel is fine)
6. Fliped the chassis over, powered on with tubes and headphones, and carefully poked and prodded every component, wire, and solder joint on the left-side circuit with a wooden chopstick (no change in the noise was observed).


I initially thought it to be a bad solder joint that took a few power-on heat cycles to manifest (due to using a worn-out 25 year-old 35w soldering iron when I built it), but after reflowing all the left channel joints with a new 80w adjustable soldering iron (at 780F), the issue persists. I am now beginning to wonder if I may have overheated a component during the initial construction due to the old soldering iron.

I have attached pics of the main solder joints. (They aren't the prettiest, but my work never is.)

I humbly defer to your knowledge and experience to further diagnose and resolving this issue.

Thanks,
Nate G.

[Paul Birkeland]

The upper green wires at B7 and B8 don't look to be well soldered.
5L doesn't look well soldered.
6L doesn't look well soldered.
B1 needs more heat/more solder.

Poking around with the chopstick is the correct method to isolate this issue, but you need to poke at everything in the circuit, not just the components for the offending channel.

780F is not too hot for soldering, and it could be too cold depending on how long you're holding the iron against the joints.  (For reference, I solder at 900 degrees F)

[big_n8_dawg]

Thanks for the prompt reply Paul!

I'll bump the temp up between 850-900 or so and re-solder.

If the issue persists I'll chopstick everything.

Either way I will report back here.

[big_n8_dawg]

The upper green wires at B7 and B8 don't look to be well soldered.
5L doesn't look well soldered.
6L doesn't look well soldered.
B1 needs more heat/more solder.

Poking around with the chopstick is the correct method to isolate this issue, but you need to poke at everything in the circuit, not just the components for the offending channel.

780F is not too hot for soldering, and it could be too cold depending on how long you're holding the iron against the joints.  (For reference, I solder at 900 degrees F)

Paul,

I re-soldered the connections you pointed out (at 875F), and initially it appeared to have resolved, but it did come back after about a minute, though it did "seem" quieter than it was.

Since I thought I perceived an improvement, I re-soldered them one more time, and then went ahead and re-soldered most of the other connections on the amp to be a little more sure. (I have attached updated pics - please let me know if you would like to see any other angles or pieces of the circuit.) Again, it seemed much better at first, and was quite quiet for a few minutes, but it did eventually return, so I rechecked everything with the chopstick, on both sides of the circuit, but there was no discernable change to the noise at any component, wire, or solder point.

(Also, for clarification regarding my prior concern about potentially overheating components - during the initial build, I used a flakey old 35w soldering iron that I really shouldn't have (actual temperature unknown), and it took quite some time to get enough heat into some of the component legs for soldering. This is why I was wondering if I might have overheated something.)

Thanks Again,
Nate G.

[Paul Birkeland]

You can also try cleaning the pins of the tubes, as oxidation on the pins can sound like crackling.

[big_n8_dawg]

You can also try cleaning the pins of the tubes, as oxidation on the pins can sound like crackling.

Thanks Paul,

Please pardon my ignorance, but if it was oxidation on the tube pins, would it be not be restricted to that particular tube? I'm happy to clean them, just curious.

I'll go ahead and clean the pins on a couple different sets of tubes. Would contact-cleaner and a brush be sufficient?

While I'm at it, should I also clean the sockets? If so, any suggestions on how to best do it? Maybe some sort of small cosmetic brush?

Thanks,
Nate G.

[Paul Birkeland]

Ah, I see that you've tried different tubes, never mind on the pin cleaning then.  Please do not attempt to clean or mess with the tube sockets, as that tends to make new problems that aren't otherwise there. 

Just to rule things out, I would also add this mod:
https://forum.bottlehead.com/index.php?topic=11676.0
It's not all that likely to resolve your issues, but it could help.  Also be sure that all your hardware is nice and tight.

[Doc B.]

Have you measured voltages when the amp is making noise? One possible source of that kind of noise is a resistor that is either not well.soldered or internally damaged. If that is the case it could make voltages shift around when it is misbehaving as it heats up.

[big_n8_dawg]

Ah, I see that you've tried different tubes, never mind on the pin cleaning then.  Please do not attempt to clean or mess with the tube sockets, as that tends to make new problems that aren't otherwise there. 

Just to rule things out, I would also add this mod:
https://forum.bottlehead.com/index.php?topic=11676.0
It's not all that likely to resolve your issues, but it could help.  Also be sure that all your hardware is nice and tight.

Thanks Paul, I have ordered a 10-pack of your recommended diodes from that thread and I will give that a shot.
I will also recheck all the hardware connections and put a little more torque on all of them.

Have you measured voltages when the amp is making noise? One possible source of that kind of noise is a resistor that is either not well.soldered or internally damaged. If that is the case it could make voltages shift around when it is misbehaving as it heats up.

Thanks Doc, I have not measured voltages while actively listening to the noise. (I have only measured with no headphones connected.)
I will recheck the voltages while listening, and look for any fluctuations in conjunction with the noise.
Heating up does seem to be a factor, as it is usually quiet initially, only to manifest after 30 seconds to a minute, so I will make sure it is warm for the checks.


Thank you both for your replies.

Unfortunately, the soonest I might be able to work on the amp again would be this weekend, but I will report back when I have an update.

Also, I can't believe that I didn't think about this before, but would it be of any benefit if I were able to capture an audio recording of the noise?

Thanks Again,
Nate G