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December 06, 2022, 09:25:28 AM

Author Topic: Channel imbalance issues  (Read 5347 times)

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Offline arkrazor

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Re: Channel imbalance issues
« Reply #15 on: June 18, 2015, 06:54:40 PM »
Unfortunately, yes.

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #16 on: June 19, 2015, 07:14:04 AM »
OK, start by playing a 60Hz tone into the RCA jacks.  Measure the AC voltage from ground to the center pin of each RCA jack and post those here.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline arkrazor

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Re: Channel imbalance issues
« Reply #17 on: June 20, 2015, 06:34:59 AM »
AC Voltages from Ground to the Center pin of each RCA jack measure at around 1.538V.

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #18 on: June 20, 2015, 01:35:37 PM »
Next, turn the volume control all the way up and perform the same measurement at each of the center lugs of the volume pot.  (Amp still off)
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline arkrazor

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Re: Channel imbalance issues
« Reply #19 on: June 21, 2015, 02:10:06 PM »
I'm getting .375 for the top lug and .370 for the bottom lug

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #20 on: June 22, 2015, 06:50:55 AM »
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
Paul "PB" Birkeland

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Offline arkrazor

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Re: Channel imbalance issues
« Reply #21 on: June 22, 2015, 07:31:02 AM »
A2 and A7 voltages check out. Maybe + or - .001V

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

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #22 on: June 23, 2015, 11:07:48 AM »
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
Paul "PB" Birkeland

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Offline arkrazor

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Re: Channel imbalance issues
« Reply #23 on: June 23, 2015, 07:36:42 PM »
If I measured correctly, terminal 5 is at 7.68 and terminal 1 is at 7.73

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #24 on: June 24, 2015, 09:13:38 AM »
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
« Last Edit: June 24, 2015, 09:15:31 AM by Caucasian Blackplate »
Paul "PB" Birkeland

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Offline Strikkflypilot

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Re: Channel imbalance issues
« Reply #25 on: June 24, 2015, 10:01:42 AM »
Or attach headphone cables but detach at the cups if lacking an adapter?
Home system:
Sources: Ibasso DX90, Google Chromecast Audio optical out
DAC: Schiit Gumby
Amp: Bottlehead Mainline
http://bottlehead.com/smf/index.php?topic=7463.0
Phones: HD800S

Office:
Sources: Iphone/ Ipod
DAC: Dragonfly Red+Jtrbug
Amp: Crack/Speedball heavily modded
Phones: HD580,HD600 grilles

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #26 on: June 24, 2015, 10:23:16 AM »
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
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline arkrazor

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Re: Channel imbalance issues
« Reply #27 on: June 24, 2015, 02:17:48 PM »
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

Offline Paul Birkeland

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Re: Channel imbalance issues
« Reply #28 on: June 25, 2015, 08:21:06 AM »
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
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline arkrazor

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Re: Channel imbalance issues
« Reply #29 on: June 25, 2015, 11:12:30 AM »
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.