Music only playing through one ear

[cayoung05]

Hey everyone,

Just built my crack and all the resistance and voltage checks were fine. I fired the amp up, plugged in my RCA cables into my DAC and the crack, but I can only hear music through one ear. Does anyone know of any solutions to this problem? Thanks in advance

 

[Doc B]

First make sure the headphone cable is plugged in all the way. Next swap the RCA cables to see if the dead channel follows the cable. Next, power off, power cord disconnected, measure resistance across from the center pin of each RCA jack to the ground tab with no cables plugged in and the volume knob all the way up. You want to be sure neither jack reads zero ohms. Also visually inspect to be sure that solder hasn't accidentally bridged from the center pin to the outer ring of the rca jack. do the same type of measurement at the headphone jack with the headphone cable unplugged. Measure resistance from the tip to sleeve and from ring to sleeve. Sleeve lugs are closest to the chassis, tip farthest from chassis. Each should be around 2.5k ohms.

 

[cayoung05]

I've resoldered all the joints, and all the voltages and resistance checks seem fine, but i still cant hear anything in the right headphone. I noticed, like one of the others posters on this forum, that when I plug the headphone jack halfway, I can hear from both headphones. Could this have something to do with the tube(s)?

 

[Doc B]

Hearing one channel on both headphones when partly inserted is simply the way stereo headphone jacks work. Did you do the checks I suggested along with the ones in the manual?

 

[cayoung05]

Doc, thanks for the reply. My answers to your questions are below


First make sure the headphone cable is plugged in all the way.
check

Next swap the RCA cables to see if the dead channel follows the cable.
I swapped the cables but now it seems that both channels don't work

Next, power off, power cord disconnected, measure resistance across from the center pin of each RCA jack to the ground tab with no cables plugged in and the volume knob all the way up. You want to be sure neither jack reads zero ohms.

neither jack reads 0 ohms, both have resistance

Also visually inspect to be sure that solder hasn't accidentally bridged from the center pin to the outer ring of the rca jack.

this might be a problem. The solder has overflowed from that center pin with the cable in it, down the outside sides of the pin, and into the inputs below. Could this be the problem?

do the same type of measurement at the headphone jack with the headphone cable unplugged. Measure resistance from the tip to sleeve and from ring to sleeve. Sleeve lugs are closest to the chassis, tip farthest from chassis. Each should be around 2.5k ohms.

both read around 2.4k - 2.5k ohms, so all good there

 

[Doc B]

Also visually inspect to be sure that solder hasn't accidentally bridged from the center pin to the outer ring of the rca jack.

this might be a problem. The solder has overflowed from that center pin with the cable in it, down the outside sides of the pin, and into the inputs below. Could this be the problem?

Yes, this is the problem. The "hot" of the signal from your cable is carried on the center conductor. The outer shell is at ground potential. If the center pin of the RCA jack is bridged to the outer shell you have shorted the signal to ground before it gets to the amp. Carefully reheat those RCA jacks just enough to get the solder bridge to open so the center pin and outer shell are not connected. Go easy, the insulator in between can melt if you hold the iron to the jack for a long period of time. Do this with the cables removed. Turn the volume knob up all the way and measure the resistance from the center pin to the ground tab on each of the RCA jack. It should not read 0 ohms, but rather more like 100K ohms.

 

[cayoung05]

That did the trick! Now listening to some Beethoven in pure heaven. Thank you Doc and Eileen for your help, was a blast to make and even more to listen

 

[earwaxxer]

I guess you got it solved.. I was thinking that you should check your connections in the corpus callosum. I had a short there the other day. Nothing that a good blow to the head and fifth of Gin couldnt fix. Not in that order though...

 

[cayoung05]

Haha, I stopped checking my corpus callosum, that was damaged a long time ago and they told me it was beyond repair  .

So... Having the same problem again. Everything was working fine, then the right channel decides to cut out while I'm listening. I resoldered the right pin and it worked again for 10 minutes, then cut out again. I did all the checks above, and all the voltage/resistance checks seem fine. The solder from the center pin is not bridging to the outer ring either. Any other suggestions I should try?

 

[Paul Birkeland]

Post voltages (once the right channel has cut out).

 

[cayoung05]

Here's the resistances.
1. *
2. *
3. 0
4. *
5. *
6. 2.4K
7. 2.9K
8. 0
9. 2.9K
10. 2.4K
12. 0
13. *
14. 0
20. 0
22. 0
B3. 2.9K
B6. 2.9K
RCA jack:
Center pin: both start with a number but quickly Go down to 0
Headphone jack:
Top 2= 2.4K
Bottom = 0

Voltages
1. 88
2. 177
3. 0
4. 177
5. 88
6. 0
7. 111
8. 0
9. 110
10. 0
11. 0
12. 0
13. 177
14. 0
15. 199
20. 0
21. 222
A1. 88
A2. 0
A3. 1.5
A4. 0
A5. 0
A6. 88
A7. 0
A8. 1.5
A9. 0
B1. 88
B2. 178
B3. 111
B4. 88
B5. 178
B6. 110
B7. 0
B8. 0

Thanks for the help

 

[Paul Birkeland]

Turn the volume knob all the way up, then remeasure the resistance between the center pins of the RCA jacks and ground.

Were those voltages taken when the right channel was out?

 

[cayoung05]

Ground to left channel center pin = 6.8K
Ground to right channel center pin = 0

The voltages were taken with the right channel cut out

 

[Paul Birkeland]

Ground to left channel center pin = 6.8K
Ground to right channel center pin = 0

The voltages were taken with the right channel cut out

Those are resistances with the knob all the way up (it seems unlikely)?

 

[cayoung05]

Ahh sorry, you're right. This is with knob all the way up:

Ground to left channel center pin = 100.4K
Ground to right channel center pin = 0

 

[Paul Birkeland]

Ok, you still have a short at the input, most likely at the jack.

 

[cayoung05]

Could there be anything else shorting the input besides a solder bridge between center pin and outer ring? I'm pretty sure I did a thorough check to make sure this isn't happening, but I can check again when I get home

 

[Paul Birkeland]

If there is metal debris inside the potentiometer, it could create this short, but this would be very rare.  You can lift the wires from the center cups of each of the RCA jacks, then measure from the center lug to ground of each pot as you rotate the volume control, looking for a range of 0 to 90-100K.

-PB

 

[cayoung05]

So i think I found the short (on the potentiometer the solder had bridged underneath and was touching the metal. I could hear in the right channel finally, but there was a loud buzzing. I figured out it was coming from the small tube (I think; when i touched the tube in created variations in the buzzing), so I reseated the tube and now I can hear the right channel, but very faintly. I've tried resoldering all the joints around the small tube but the right channel is still very faint. Could it be a problem with the small tube or is there a bad solder somewhere?

 

[Paul Birkeland]

If the resistance issue is gone, go back to the voltages.  A 9 pin tube that is poorly seated will most likely throw weird voltages at T1 and T5.

Otherwise, you might try a different 12AU7 and/or try cleaning off the pins.

-PB