New crack build, two different hums/whines [resolved]

[carlman14]

Hello, I just got done building the crack (no speedball yet), and I have two separate noises that I would like opinions on.

First, there is a low hum in the left channel. It seems like it randomly gets quieter and louder, and I haven't been able to correlate it with any other part of my set-up.

Second, there is a higher pitched hum/whine/something in the right channel. This noise alternates between a couple higher frequencies. I have found that with this noise, I can tap the side of the larger tube and the noise goes away for maybe up to one second, then comes back.

Both noises stay the same volume when turning the volume knob. Both noises also seem to be more present once the tubes have warmed up a little. I have also verified that neither noise is related to upstream equipment. I can hear both even with the RCA's unplugged.

Based on what I've read in the forum, step one is to touch-up the solder on basically everything. But I was wondering with the information above, is there anywhere in the circuit in particular that I should look at?

Here are my resistances and voltages.

Power transformer secondary test (AC):
Black on 7, red on 9. Expected: 6.5, actual: 6.2
Black on 11, red on 12. Expected: 175, actual: 178.8

Resistances:
1. Expected: *, Actual: *
2. Expected: *, Actual: *
3. Expected: 0, Actual: 0
4. Expected: *, Actual: *
5. Expected: *, Actual: *

6. Expected: 0, Actual: 0
7. Expected: 2.9k, Actual: 2.99k
8. Expected: 0, Actual: 0
9. Expected: 2.9k, Actual: 2.98k
10. Expected: 0, Actual: 0

12. Expected: 0, Actual: 0
13. Expected: *, Actual: *
14. Expected: 0, Actual: 0

20. Expected: 0, Actual: 0
22. Expected: 0, Actual: 0

B3. Expected: 2.9k, Actual: 2.99k
B6. Expected: 2.9k, Actual: 2.97k

RCA left center. Expected: 90k - 115k, Actual:  100k
RCA left ground. Expected: 0, Actual: 0
RCA right center. Expected: 90k - 115k, Actual: 90.8k
RCA right ground. Expected: 0, Actual: 0

Voltages (DC)
1. Expected: 50 - 100, Actual: 78.5
2. Expected: 170, Actual: 177.4
3. Expected: 0, Actual: 0.4
4. Expected: 170, Actual: 177.4
5. Expected: 50 - 100, Actual: 79.3

6. Expected: 0, Actual: 0.4
7. Expected: 90 - 115, Actual: 109.4
8. Expected: 0, Actual: 0.6
9. Expected: 90 - 115, Actual: 106.8
10. Expected: 0, Actual: 0.3

LED's lit? yes

Thanks,
Carl

[Doc B.]

Clean the tube pins and let the tubes cook in for a while, like 20-30 hours.

[Paul Birkeland]

Second, there is a higher pitched hum/whine/something in the right channel. This noise alternates between a couple higher frequencies. I have found that with this noise, I can tap the side of the larger tube and the noise goes away for maybe up to one second, then comes back.

This is usually indicative of a flaky solder joint.

[carlman14]

Thanks for the suggestions. I will re-solder anything that looks flaky, clean the tube pins, then let them cook for a day or two. If I still have problems, I'll post back with some pictures.

Is there a recommended way to clean tube pins? Isopropyl alcohol maybe?

[Doc B.]

https://bottlehead.com/smf/index.php?topic=8888.0

[Karl5150]

 The pin cleaning method Doc prescribes / relates will no doubt yield steller results. I have to admit that I'm lazy and haven't employed it...yet.
 For reasonably good results I plunge the tubes into a new "Magic Erasure" several times, hitting fresh melamine each time. I then apply a tiny amount of a silver-bearing contact lube.   

[Neil]

i know nothing about electrical engineering but can offer my experiences with hums/buzzes coming from the Crack. before installing the speedball, there was always a very very low hum. i am pretty sure it was due to not re-soldering as i should have. but, here's what happened after my speedball upgrade:
here's a recent post about issues that were resolved with my own kit: https://bottlehead.com/smf/index.php?topic=11291.msg102656#msg102656
I'm enjoying the Crack more than ever now - wishing i did the speedball upgrade years ago! tube rolling is next...

[carlman14]

@Neil I have a speedball ready to go. I wanted to get the noise under control before adding it in though.


Oh boy... I re-soldered a few things and now 6 and 10 are at 2.5k ohms. Ugh, I should have just started with cleaning the pins and cooking the tubes...

[carlman14]

Now I'm a little confused. I was searching through the forums to see if anyone else had readings of 2.5k ohms at 6 and 10, and I came across these two posts:

https://bottlehead.com/smf/index.php?topic=5573.0
https://bottlehead.com/smf/index.php?topic=3661.0

Both say that they passed their resistance checks with 6 and 10 at 2.4k ohms. My manual says they should both be at 0 ohms...

If my manual is correct... what would cause 6 and 10 jump to 2.5k on my crack? I did not physically remove any joints, just added a bit more solder here and there where it looked sparse.

[diynewbie]

There are changes in the wiring of the headphone jack between versions 1 and 1.1.  Perhaps if you have headphones plugged into the jack the values will change from 0 to 2.5k?  The jack is a switch type and path to ground from 6 and 10 will by-pass the resistors on the jack when there is nothing plugged in.  I hope I have that right.

[carlman14]

There are changes in the wiring of the headphone jack between versions 1 and 1.1.  Perhaps if you have headphones plugged into the jack the values will change from 0 to 2.5k?  The jack is a switch type and path to ground from 6 and 10 will by-pass the resistors on the jack when there is nothing plugged in.  I hope I have that right.

You're absolutely right. I had accidentally left a 1/4" to 3.5mm adapter plugged in to the headphone jack. I removed it and they're both back to 0 ohms. Thank you! Man I feel stupid. At least I can continue working on my original hum problem now 

[carlman14]

Ok, here's a quick update on the build.

First, I cooked the tubes between 20-30 hours as suggested. No change in the hums.

Second, I cleaned the pins with metal polish and contact cleaner. They were a lot dirtier than they looked! I used up a lot of q-tips. They can be inserted into the sockets much easier now... But still, no change in the hums.

Now I'm poking around with a chopstick to see if I can pinpoint any joints in particular that could be causing this. So far I haven't found anything, but I'll keep poking around a little more.

Side note: One thing I noticed is that if I put my ear close to the larger tube (after it's warmed up a little), I can hear it making a similar hum to what I'm hearing through my headphones. Is that normal? Should I be able to hear the tube making that kind of noise? I wonder if that's related to the hum I'm hearing in my headphones...

[carlman14]

Ok, I'm a bit frustrated now. I have reflowed all the joints, replaced a wire or two that looked suspicious, and poked and prodded every wire and joint. I even plugged the amp in to different outlets around the apartment just to rule out interference from appliances and other electronic noise. Nothing seems to affect the hum.

Also, for better or worse right now, I installed the small board of the speedball. I was like a kid opening his favorite Christmas toy and I couldn't resist. Installing this has had no affect on the previously mentioned problems. All information I have previously provided is still accurate.

I'm running out of ideas here, so here's some pictures of my build. Please let me know if you have any suggestions!

https://imgur.com/a/MlyDOpU

[Paul Birkeland]

I would add a little solder to all the joints on the 6 lug strips where black wires connect.  It's possible that the noise you're hearing is from a loose 220uF/250V capacitor, as a loose leg on one of those caps will bring up the power supply noise significantly. 

[Deluk]

Not to be too unkind but I'd rate most of your joints as improperly flowed and rather dirty. They should be smooth and with a nice clean appearance. Your iron tip is likely dirty and needs retinning properly. Wind the heat up a bit if it's adjustable or leave the tip on the joint longer. Add additional solder only after the existing solder has steaded to liquify. You may find a flux pen useful. They are very cheap.