Volume difference - Higher on right channel even after burn in [resolved]

[thewatergod]

So as I mentioned at the end of my last thread, after all my checks passed, I noticed on some songs that there was a bit of a bias towards the right channel. I noticed that if I turned the volume up slowly that the right channel would become audible noticeably before the left.

After taking Doc B's advice and giving roughly 30 hours of play time to burn in, the bias was still there. So after reading through some other threads, I saw some advice saying that someone could try disconnecting the cables at the headphones and measuring the AC voltage there. So I turned up the volume to about a quarter and measured the following AC voltages at the ends of the headphone cables while playing a 150hz tone:

Left: 0.160v

Right: 0.184v

I hope those numbers make some sort of sense. Both were steady. Can anyone offer any advice here? Do I need to let it burn in more? I love the amp but the difference in the channels is driving me crazy and I'm on the verge of giving up here.

[ideal.hat]

PB has mentioned that you can resolve the channel imballance with finding and adding the correct resistor.
If you want to go that route, PB or someone more expirienced then I am can provide that information.
PB: "If you have the low level channel imbalance, the stock pot can simply be padded down to get more usable range out of it."


The way I resolved this in my kit, was with replacing the stock volume pot with an ALPS Blue.
I regret not getting the "Audio Note 100K Potentiometer" instead since there is not much price difference.

[diynewbie]

Your values indicate the right channel is 1.2 dB louder than the left.

I would to repeat what you did (half turn on pot as well), but measure voltage from ground to center tip of rca jacks or at the pot input (outside lugs) and also pot output (middle lugs) to ground.

I believe this would show whether the imbalance is present at input or due to the pot.

[Paul Birkeland]

You'll want to do that test at 50-60Hz so that your meter is accurate. 

The first places to measure are at the input of the pot (the red and white wires that connect from your RCA jacks to the outer pot lugs on each level), then the output of the pot (the two middle lugs).

You'll want to check the middle lugs at about 25%, 50%, 75%, and 100% of the pot's rotation, then report those results. 

-PB

[thewatergod]

Thanks guys!

PB, I did as requested and got the following using a 60hz tone and measuring between the outside & ground and middle lugs & ground for each set of wires:

Outside lugs:

Red - 1.570v
White - 1.572v


Inside lugs:

1/4 volume - white: 0.051v, red: 0.060v

1/2 volume - white: 0.178v, red: 0.187v

3/4 volume - white: 0.645v, red: 0.650v

Full volume - white: 1.572v, red: 1.570v

So it looks like up until the end, the right channel is slightly higher in voltage than the left, but it gradually drops as the volume is turned up.

[Paul Birkeland]

1/4 volume - white: 0.051v, red: 0.060v

That's about 1.5dB.  If this is where you are listening to the amp and having the problem, then padding down the pot will remove this problem.  (See the Crack FAQ sticky).

1/2 volume - white: 0.178v, red: 0.187v

That's a little less than half a dB, which shouldn't be super noticeable.

3/4 volume - white: 0.645v, red: 0.650v

This is 0.06dB, no problems here.

[Doc B.]

I think these numbers need some context. 1.5 dB channel difference is audible to just about everyone. I would say that for the average audiophile a 1/2 dB difference is inaudible. That is right around my threshold and I've been doing critical listening for a lot of years. I do know engineers who can discern 1/4 dB some of the time, but they can usually only discern that small a difference on a system they have many years of experience with.

[thewatergod]

That's about 1.5dB.  If this is where you are listening to the amp and having the problem, then padding down the pot will remove this problem.

I think these numbers need some context. 1.5 dB channel difference is audible to just about everyone. I would say that for the average audiophile a 1/2 dB difference is inaudible. 

Yup, there's the issue. 1/4 is right around where I listen. Much louder for an extended period and I'm afraid I'm gonna start damaging my hearing. But if I start to verge up on that 1/2 mark the imbalance does pretty much disappear for me - though depending on the song it the volume can be overwhelming enough that I might not notice anyway.

I took a look at the FAQ and it looks like my next steps are to track down some resistors.

One point of clarification on the #3 of the FAQ though:

It says "Attach and solder one 33K resistor between each outer pair of lugs on each level of the volume pot."

Do I correctly interpret this to mean I need to attach a 33k resistor between the leftmost and rightmost lugs on the top and then another between the leftmost and rightmost on the bottom, skipping the middle lug for each? Just wanted to make sure I was reading that right before I made a dumb mistake.

[Paul Birkeland]

Do I correctly interpret this to mean I need to attach a 33k resistor between the leftmost and rightmost lugs on the top and then another between the leftmost and rightmost on the bottom, skipping the middle lug for each? Just wanted to make sure I was reading that right before I made a dumb mistake.

Yes, you have that correct.

[thewatergod]

Thanks PB!

I'll update once I've tracked down some resistors. I think there's a shop in town here that should have what I need.

[thewatergod]

Thanks PB!

I'll update once I've tracked down some resistors. I think there's a shop in town here that should have what I need.

That did the trick. I haven't tested voltages yet but I can already hear a difference at the lower volumes. This worked beautifully. Thanks guys!!