Minor buzz in right channel [resolved]

[MikeSattler]

This isn't a major issue but one I'd like some guidance on solving

There is a slight buzz in the right channel that increases with volume (it becomes audible around 12 o'clock on the pot) and increases until the pot is at max and then it disappears completely.

I've pretty much ruled out the RCA inputs and the pot itself as the culprit by using shorting jacks and re-soldering the wires leading to the pot (the noise didn't move over to the left channel).

Where would be the next place to start looking for the culprit?

Thanks!

[Paul Birkeland]

I've seen some folks pop in mentioning a right channel buzz similar to what you're mentioning, and it has either turned out to be loose transformer hardware or an improperly soldered wire between the tab on the chassis and the lug of the 6 lug T-strip that it grounds.

Other possibilities can include a tube that needs 50 or so hours of run-in time, or potentially a different solder joint in the amplifier that isn't all the way cooked.

[MikeSattler]

Thanks for the suggestions! By loose transformer hardware do you mean the 4 screws that are mounting the transformer to the chassis?

[fullheadofnothing]

Yes.

[MikeSattler]

Thanks for the help so far guys. I just finished re-soldering every joint (including the speedball boards) and this buzz is still there

I've also tried multiple sets of tubes and that didn't solve anything either.

What would the next step be here?

[Paul Birkeland]

Did you tighten up all the screws?

[MikeSattler]

Yup, forgot to include that in the last post.

[Doc B.]

(the noise didn't move over to the left channel).

I'm not following this. Why would you assume that the noise would change channels after reflowing the solder joints. Did you swap wires?

[Natural Sound]

Thanks for the help so far guys. I just finished re-soldering every joint (including the speedball boards) and this buzz is still there

I've also tried multiple sets of tubes and that didn't solve anything either.

What would the next step be here?

Have you checked your interconnects? Maybe swap left to right?

[Paul Birkeland]

Get a wood chopstick and plug in an inexpensive pair of headphones.  Poke around in the circuit until the noise changes in order to find where the issue may be.

[MikeSattler]

I'm not following this. Why would you assume that the noise would change channels after reflowing the solder joints. Did you swap wires?

Hey Doc! Yup, the first thing I did was to flip the RCA inputs on the pot to see if the noise was coming from the RCA jacks. Then, I flipped the outputs on the left/right channels on the pot to see if it was coming from the pot itself.

I just went through and did the chopstick test and the right buzz didn't seem to change. However I did notice that while i was poking around on the 9 pin socket I'm getting ground hum when I touch the left/right input and output joints on the socket. I'm also getting the same hum when I touch the 12au7 tube with my hand, or when I touch the volume knob so something weird is going on there.

I'm using an alps blue velvet pot with a metal washer on the top/bottom of the chassis to screw it down. Is my chassis forming some sort of grounding issue with the pot?

[Doc B.]

Yeah, it sounds like it could be the pot. Does the hum change character when you turn the pot up and down with no signal present?

[MikeSattler]

The ground hum doesn't change character, but I did just realize something: when I touch nothing but the 12au7 tube I hear the ground hum, and when I keep my hand on the 12au7 and touch the chassis or pot with my other hand it goes away.

[Doc B.]

That also tends to indicate an issue at the grid of the 12AU7, which is of course connected to the output of the pot. If the hum didn't move when you changed the output connections from the pot to the 12AU7, you might want to reflow the joints at the 12AU7 socket and the pot. Maybe also clean the tube pins.

[Paul Birkeland]

This still potentially points to loose hardware on the transformer or #8 screw by the power entry module.  A missed solder joint on that small wire that ties the three together would also be a possibility.