[SOLVED] Buzz sound when inserting RCA cables after speedball upgrade

[winston]

I just finished installing the speedball upgrade and am getting a steady buzz that increases with volume as soon as I plug in my RCA cables. This happens with two different pairs of brand new RCA cables from different manufacturers. The amp was working perfectly fine before the speedball upgrade. Last night I found if I wiggle the red RCA cable at the right angle, the buzz completely disappears. However, I had trouble recreating that workaround this morning. Additionally, this was totally unnecessary before adding the speedball upgrade.

Upon disassembling my amp, I discovered that the plastic tab on the bottom of the 6080 tube that covers a glass bit had broken off. Is this creating the problem, and should I hold off on further testing until I get that replaced?

Here were my resistance checks before noticing the plastic bit on the 6080 had snapped off:

Small Board

• OA: 0.009
• IA: 0.022
• B-A/B: 0
• IB: 0.024
• OB: 0.008

Large Board

• OA: 0.015
• OB: 0.015
• G: 0
• B+: 0.029

All of the LEDs turn on. I can post pics if needed.

 

[Paul Birkeland]

Can you post your voltages?

The small plastic piece at the bottom of the 6080 ensures that you plug the tube in properly, otherwise you have a 1 in 8 chance of inserting the tube properly and a 7 in 8 chance of not.

There should still be enough of the keyway to tell where the ridge is so you can properly insert the tube. 

 

[winston]

Ok well I'm definitely inserting the tube properly in that case. Here are the voltages:

Small board

• OA: 80.4V
• IA: 184.8V
• B-A/B: 0V
• IB: 184.7V
• OB:76.9V

Large board

• OA: 102V
• OB: 106.2V
• G: 0V
• B+: 184.5V

 

[Paul Birkeland]

Since your voltages look good, what you're likely running into is a loose connection in the amp, and most likely this is a connection that isn't part of the Speedball.  One really common solder joint that I find that is frequently not well done is the junction of the black wires on the headphone jack. Wiggling RCA cables and getting the buzz to disappear does tend to suggest something is loose inside the amp.  A loose 220uF/250V filter capacitor could also cause an issue like this.

 

[winston]

Hmm I just tried resoldering the rca cables (and noted it’s only the red cable that when wiggled forward stops the buzz sound completely) as well as the capacitors, and am still experiencing the same problem. Everything was operating perfectly fine until I added the speedball upgrade, so my thought is that it has something to do with the shared solder areas around there, but I’m not seeing anything obviously wrong or bad looking.

EDIT: Quick update. When actually playing music, the buzz is still there, but more noticeably, the sound is in mono. But adjusting the cable ever so slightly totally fixes the problem. I’ve tested this with many different RCA cables too. So hopefully that helps clarify what the issue may be.

 

[Paul Birkeland]

But adjusting the cable ever so slightly totally fixes the problem. I’ve tested this with many different RCA cables too. So hopefully that helps clarify what the issue may be.

This issue is still most likely a soldering issue. When you move the cable, you move the loose solder joint and resolve the problem. 

Can you post some build photos of the area in question?

 

[Doc B]

Try tightening the nuts on the RCA jacks. That might solve the buzz issue. The "goes to mono" issue is at the headphone jack. It can go mono if the headphone plug is not fully inserted and both tip and ring touch the same contact in the jack. This might also happen if the jack was overheated in soldering and the contacts in the jack got loose. Also you didn't mention if you reflowed the black wire connection at the jack that PB suggested. That could cause the buzz.

 

[winston]

You’re right, that area is probably my sloppiest, but I tried my best. I tried reflowing where the black wire is as well as tightening the nuts. Now it’s less of a buzz and sounds more like static feedback that’s annoying enough to be unlistenable. The mono is gone though.

Here are some photos: https://imgur.com/a/LGt8vbR

 

[Deke609]

It looks like you've got the rca jack parts installed in the wrong order. The solder lug washer goes between the colored plastic isolation washer and the fastening nuts.

cheers, Derek

 

[Paul Birkeland]

Derek is correct, you'll need to pop those apart and correct that.  You can use more heat to clean up those joints.

The work that you've done on the 6 lug strips that I can see looks excellent.

 

[Thermioniclife]

Nice call Derek!

 

[Deke609]

Nice call Derek!

Just trying to get my batting average back up. This one gets me back to about 200.  ;D

 

[winston]

Solved! Something so simple, yet I never would have seen it on my own. Thankfully that didn’t cause any major shorting problems with that setup.

Thank you so much Derek and everyone else for all of the help. It sounds amazing now with the speedball upgrade and everything functioning s it should  ;D

Cheers!

 

[Thermioniclife]

Derek, This brings you over the Mendoza line. Congrats!.