Channel imbalance issues

[Paul Birkeland]

Just to be thorough, with the amp off, measure the AC voltage again at A2 and A7.  It should match what you measured previously.


If that checks out, then with the amp on, carefully measure the AC voltage at terminal 6 and terminal 10.  If you have the shorting modification at the headphone jack, let me know and I can give you some options for bypassing it.


-PB

 

[arkrazor]

A2 and A7 voltages check out. Maybe + or - .001V

I do have the shorting mod for the headphone jack installed.

 

[Paul Birkeland]

The next thing to do is to try measuring the AC voltage at terminals 1 and 5 with the amplifier on and the volume control all the way up.  Your meter may not be able to measure the AC voltage there with the DC voltage present, but it's worth a shot. 

-PB

 

[arkrazor]

If I measured correctly, terminal 5 is at 7.68 and terminal 1 is at 7.73

 

[Paul Birkeland]

Excellent, that's 0.05dB of difference between channels, which is difficult to measure, and impossibly hard to hear.

The next set of measurements should be done at terminals 6 and 10.

Since you have the shorting jack, these will both be 0V unless we take some action.  If you can find a pair of toothpicks, you can pop them in under the spring contacts for the tip and ring on the jack, just to lift the short.  Alternatively, if you have a 1/4" TRS to 1/8 TRS adapter plug, go ahead and plug that in to release the spring contacts. 

I would not use a pair of headphones to break this connection, as we want the signal level high and we want the headphones themselves out of the equation.

-PB

 

[Strikkflypilot]

Or attach headphone cables but detach at the cups if lacking an adapter?

 

[Paul Birkeland]

Yeah, if the cables can be unplugged from the drivers (HD580/600/650), that may work.  There still may be a cabling issue, but it's a place to start.

-PB

 

[arkrazor]

Hey guys, I managed to find a right angle 1/4" TRS to 1/4" TRS and it looked like it did the trick. Terminal 6 measures at 4.77 and Terminal 10 measures at 4.88

 

[Paul Birkeland]

That's 0.2dB of difference, still not much.

With the adapter still plugged in, measure that voltage at the headphone jack (red and white wire terminals on the jack).

-PB

 

[arkrazor]

I'm getting similar measurements. White terminal is measuring at 4.87; red terminal is measuring at 4.77. Nothing out of the ordinary, it seems.

 

[Paul Birkeland]

Which headphones do you have?  If you have HD580/600/650, I would recommend unplugging your headphone cable from your headphones, plugging the cable into the amp, then measuring the AC voltage at the headphone end of your cables.

The good news is that your Crack has no channel imbalance to speak of.  The bad news is that it's either your headphones, source, headphone cables, or you still have an installation issue with the padding resistors that go on the pot.  (maybe post a pic?)

-PB

 

[arkrazor]

I have the HD650's. I just measured through the headphone cables and the measurements match the terminal's 6 and 10 measurements. I believe I installed the padding resistors correctly because the resistance measurements match those you previously said (~24k at the input for both). I attached some pics of it to the post (sorry for the rubbish quality).

I did an AB test with my solid state amp and the crack and I swear I can still hear channel imbalance. Could it be caused by the tubes? I only have the stock ones and another set I bought second hand off of eBay. I won't rule out the possibility that I might've gotten unlucky twice in a row. It's either that or I need to get my hearing checked.

 

[Paul Birkeland]

I have the HD650's. I just measured through the headphone cables and the measurements match the terminal's 6 and 10 measurements.

Well, that confirms that there is a channel imbalance, but it's about 10X too small to be audible.  You may want to consider checking the channel balance of your solid state amp.

-PB

 

[fullheadofnothing]

Furthermore, are you hearing this imbalance on the 60Hz tone, or are you just listening to stereo recordings that will present different channel information?

 

[Paul Joppa]

Just checking here, without re-reading the whole thread ... but you did turn the headphone around to see if the imbalance moved to the other ear, right?