Channel separation or imbalance?

[kill_surf_city]

The Crack (running without Speedball) sounds incredible. Before my build I was using the Little Dot MKII with my HD650's. One thing I've noticed that sort of bugs me is what at first I thought was a slight channel imbalance favoring the right channel, but as I kept listening to more/different music, it would sometimes shift to the opposite channel. So maybe it's not channel imbalance but it's just an amount of channel separation that I'm not used to with. I just wanted to know if anyone else noticed this too. I think I wanna do some tests to check imbalance. If not I think I need to find a music player that can introduce a little bit of cross talk - any suggestions for Mac?

 

[Paul Birkeland]

What are the AC voltage ranges on your meter?  It's possible to measure channel balance, but it helps to have a mater with a low AC voltage setting.

You may also find FAQ #3 to be helpful.  If you can turn your source down and turn the Crack up a bit, that will allow you to check for channel imbalance in the pot at low level settings. 

I don't see how channel separation applies here.

 

[kill_surf_city]

What are the AC voltage ranges on your meter?  It's possible to measure channel balance, but it helps to have a mater with a low AC voltage setting.

You may also find FAQ #3 to be helpful.  If you can turn your source down and turn the Crack up a bit, that will allow you to check for channel imbalance in the pot at low level settings. 

I don't see how channel separation applies here.

Just checked the AC voltages. I think I did it correctly. With the amp off, I turned the volume to halfway, black plug to the ground and then checked the RCA inputs and center lugs on the potentiometer and played a 60hz tone. All 4 came to 0.3. I tested terminals 6U and 10U and both were at 00.0. Then repeated it with the volume turned all the way up and got the same readings. The only 2 AC settings on my multimeter are 500 or 200.

What I meant by channel separation is that stereo mixes can sometimes sound unnatural on headphones as opposed to speakers because of crosstalk. So I was thinking one channel might appear to be louder due to frequencies varying in the L/R channels but really isn't louder. My Little Dot amp had a much more narrow soundstage, so it's possible that it might be something I'll just get used to.

 

[Paul Birkeland]

Just checked the AC voltages. I think I did it correctly. With the amp off, I turned the volume to halfway, black plug to the ground and then checked the RCA inputs and center lugs on the potentiometer and played a 60hz tone. All 4 came to 0.3.

Well, your meter doesn't have the low voltage range but it's doing a good job of adequately resolving millivolts. 

I tested terminals 6U and 10U and both were at 00.0. Then repeated it with the volume turned all the way up and got the same readings.

Well, with the amp off there won't be any signal at the outputs.

You can turn the amp on and measure the AC output voltage at the white and red wires on the headphone jack.  They will show 0V unless something is plugged into the 1/4" jack to defeat the shorting function.  A like to use a 1/8" to 1/4" headphone adapter, but you can plug a cheap pair of headphones in if you want to test the levels loudly, or a chopstick of appropriate diameter may hold the contacts open so you can grab that measurement.

 

[kill_surf_city]

Well, your meter doesn't have the low voltage range but it's doing a good job of adequately resolving millivolts. 
Well, with the amp off there won't be any signal at the outputs.

You can turn the amp on and measure the AC output voltage at the white and red wires on the headphone jack.  They will show 0V unless something is plugged into the 1/4" jack to defeat the shorting function.  A like to use a 1/8" to 1/4" headphone adapter, but you can plug a cheap pair of headphones in if you want to test the levels loudly, or a chopstick of appropriate diameter may hold the contacts open so you can grab that measurement.

Ok I was able to test the red and white wires on the headphone jack. turned at halfway they're equal at 0.2 but turned up all the way, the white is at 2.8 whilst the red is at 3.2. Is that large enough to make an audible difference, or is this all in my head?

 

[Paul Birkeland]

That's 1dB.  It's not huge, but is audible. 

 

[kill_surf_city]

That's 1dB.  It's not huge, but is audible.

What can I do to fix it?

 

[Paul Birkeland]

If you don't see it at the output of the volume pot, then it's likely a bit of imbalance from one of the tubes.  Unfortunately, your meter doesn't resolve AC voltage well enough to really tell if this is happening before or after the tubes.  I would suggest grabbing a meter with a 2V AC scale on it (let me know where you're located and I can suggest some retailers), then you can resolve your signal levels a bit better and know exactly where things are going awry. 

The reason I would suggest this is that 0.28V and 0.32V on the 200V AC scale will both probably show up as 0.3V, but they are 1dB apart.

 

[kill_surf_city]

If you don't see it at the output of the volume pot, then it's likely a bit of imbalance from one of the tubes.  Unfortunately, your meter doesn't resolve AC voltage well enough to really tell if this is happening before or after the tubes.  I would suggest grabbing a meter with a 2V AC scale on it (let me know where you're located and I can suggest some retailers), then you can resolve your signal levels a bit better and know exactly where things are going awry. 

The reason I would suggest this is that 0.28V and 0.32V on the 200V AC scale will both probably show up as 0.3V, but they are 1dB apart.

Okay, thanks. I'm in central Illinois. Also, new problem, I realized that all of a sudden the LED that used to be on is now off and all of my DC voltages, aside from the ones that are supposed to be 0, are all between 140-160.

1. 178
2. 165

4. 165
5. 149

7. 147
9. 148

I have no idea what I did.

 

[Paul Birkeland]

That sounds like a solder joint that isn't quite solid.  It's a lot easier to reheat all of them rather than go looking for the one that might be the issue.

 

[kill_surf_city]

That sounds like a solder joint that isn't quite solid.  It's a lot easier to reheat all of them rather than go looking for the one that might be the issue.

I think the culprit was 7L. I got the LED to come back on, so I re-measured my voltages. All were well within 10% of range. A little higher than before, but still good. So I decided to try it out. I turned on some music and after a minute or so I hear some sort of crackling, then it goes away. Then I hear some crackling again and then a pop and I lose all sound except a little bit out of my right channel. Fuse is good still, so it wasn't that. Headphones are fine. I've had the amp unplugged now and the 3K resistors are still very hot. Kinda not sure what to do next. I reheated all of the terminals and the 9 pin socket.

 

[Paul Birkeland]

You likely still have a flaky solder joint. 

 

[kill_surf_city]

You likely still have a flaky solder joint.

I've reheated everything now. The other LED had become disconnected; it was only connected to the center of the 9 pin socket. Luckily I'm getting a brand new set of LEDs in the mail tomorrow, so hopefully once I re-wire with both LEDs in correctly I'll get the voltage correct. Does that particular connection play a large role in getting the correct voltage? I'm thinking that when I was testing the AC voltage I may have inadvertently knocked that other LED loose which caused it to throw the voltage out of control. Without the LED or jumper cable in there the DC voltages are still the same as I posted earlier.

 

[Paul Birkeland]

If the LEDs are damaged, none of the DC voltages will be correct.

 

[kill_surf_city]

If the LEDs are damaged, none of the DC voltages will be correct.

That's kind of a relief. Narrows down where the problem is. Thanks for your help Paul.

 

[kill_surf_city]

If the LEDs are damaged, none of the DC voltages will be correct.

I remembered my Speedball I have yet to put together came with LEDs. I put two of those in the Crack and both are lit up with voltages well within their range. Seems to have fixed my balance issue as well!

 

[kill_surf_city]

If the LEDs are damaged, none of the DC voltages will be correct.

Re-did the test. I still want to get a more sensitive meter, but I got pretty much the same results. At half-volume, both red and white read 1.2. At full volume its 3.8 - white and 4.2-4.3 - red. So, still about 1 dB difference. It does however seem less noticeable.

 

[Deke609]

At full volume its 3.8 - white and 4.2-4.3 - red.

Just out of curiosity - what do you measure if you back off just a tad from full volume? I've noticed that some pots behave a little oddly at the extremes.

cheers, Derek

 

[kill_surf_city]

Just out of curiosity - what do you measure if you back off just a tad from full volume? I've noticed that some pots behave a little oddly at the extremes.

cheers, Derek

I’ll have to run it again, but I actually did measure it at like 75-80% volume and it was barely imbalanced. Ever since I replaced the LEDs it’s either barely noticeable or not at all. I usually have the volume knob somewhere between 30-50% when listening. I ordered a more sensitive meter that should be here tomorrow. I’ll run the test again and let you know what I get. But I’m beginning to think that it’s just the potentiometer that’s off sometimes.