Right Channel Seems Louder [NOT QUITE RESOLVED]

[oguinn]

I have a weird situation that I'm not sure is an issue.

With the pot all the way down, I get sound out of the right channel but not the left. Once I turn the music up it seems like the two channels balance out but I'm not sure.

Two questions, then:

• Is it typical for there to be sound on either or both channels when the pot is all the way down?
• How can I measure the output of each channel to see if there is an imbalance at higher levels? I don't think I can hear it, so maybe it really doesn't make a difference.

Here's my setup currently:
iPhone > Quickie > Schiit SYS > JDS Labs Subjective EQ (all set to the neutral, middle setting) > SEX > Overnight Sensations

[Paul Birkeland]

It's common for there to be some channel imbalance at very low levels on a volume pot. 

Have you tried just plugging your iPhone into the SEX amp?

[oguinn]

When I turn the amp on with the iPhone plugged in directly I don't hear anything with the pot at zero. I assume the Quickie's gain is providing that additional gain.

As long as a) the imbalance is to be expected at low volumes, and b) it's normal to hear noise with the pot at zero, I'm all good. If b is unexpected behavior I wanted to troubleshoot.

[oguinn]

Actually, spoke too soon. It does still happen when I just plug in the iPhone. I hadn't let the tubes warm up previously. Either way, if it's not a problem I'm not worried about it.

[Paul Birkeland]

There will be some imbalance if you have a lot of gain in the signal chain, which is why I suggested just the iPhone into the SEX amp.

If just the iPhone into the SEX amp still results in channel imbalance, you can swap the tubes to see if the imbalance follows a tube (I suspect it will not).

Beyond that, we can see where the imbalance is entering the amp by playing a 60Hz tone into the amp with the volume pot half way up and measuring AC voltages at a few places.  When you're all setup for that, let me know and I can write down some steps.

-PB

[oguinn]

I'm not super concerned about the imbalance. It does seem to be present only at low levels, and if it's present at higher levels it's a small enough difference that I can't tell.

I'm new to tube amps so I'm learning the ins and outs of this setup bit by bit. More than anything I was actually surprised that anything at all played with the volume all the way down, but this doesn't seem to be a concern to you so it won't be one to me either. I'll mark it resolved (if I'm doing this right, anyway).

I really appreciate your input (no pun intended), Paul. Thanks!

[Paul Birkeland]

The amp playing with the volume control all the way down on one channel isn't super normal, but it's not all that concerning. 

For some more detailed reading about why you might get a little signal through the pot when it's all the way down, I've found this page to be informative with lots of good photos:
http://www.geofex.com/article_folders/potsecrets/potscret.htm

[oguinn]

Hm, actually, listening today I definitely noticed an imbalance at regular listening levels. I have an iPhone and I can get a 60hz tone; could you provide the steps to troubleshoot?

I swapped the tubes. Your assumption that the imbalance would not follow was correct.

[Paul Birkeland]

The first steps you can do with the amp off.  Play that 60Hz tone into your SEX amp and measure the AC voltage at each RCA jack (black probe to RCA jack shell and red probe to center pin).

Note those AC voltages, they should be 0.25-0.5V AC if you're using a phone.

Next turn the volume pot half way up and measure the AC voltage at the middle pin of each level of the volume pot (you can use the RCA jack shells as a ground reference if you like).

Let us know what numbers you get for those values.

[oguinn]

I think this is a symptom of a bigger problem. I checked out the voltages and found A side terminal 3 had 5V. I re-soldered terminal 3, re-checked the resistances and voltages, then hooked it up and now the right channel isn't working at all.

[oguinn]

Redoing the resistance checks again. One thing stood out - on terminal 2, the reading should be in the tens or hundreds of K ohms. What I'm seeing is around 275 ohms. Is that because it's a filter capacitor, or is there a problem? Terminal 16 reads a ranging value.

EDIT: I removed the tubes and started again and everything is in the right ranges. Moving on to the voltage checks.

[oguinn]

I believe this was a cascading series of blunders. I'll enumerate:

• The right channel had a cold solder joint at terminal 3.
• I ran the resistance and voltage checks, and everything was fine but the right channel was missing.
• When I removed the tube, I think I bent or damaged a pin. I believe this to be the case since a new set of voltage problems followed the tube when I swapped positions.
• I re-ran the voltage checks with a new tube, and I hooked everything up to the speakers/headphones, and now I'm not hearing any of the issues I mentioned previously.

I'll run the balance tests soon.

[Paul Birkeland]

Yeah, measuring the AC signal voltage can generally help locate those cold solders, but it sounds like you're onto something. 

[oguinn]

Paul, when you say to measure at the rca jacks (shell and center), do you mean the upper side of the input jacks or binding posts? Or is it the bottom side of the chassis on one of those?

[Paul Birkeland]

The RCA jacks themselves.