One headphone doesn't work [resolved]

[cayoung05]

Hi all,

I built my Crack awhile ago and recently my left headphone ear stopped working and I could hear a slight popping/humming sound in both. Today I reflowed all the joints and the humming sound is gone and the right ear sounds great, but the left ear still doesn't work when the headphone jack is pushed all the way in. If I push the headphone jack 1/4 to about 3/4 of the way down, I can hear through both ears. It's only when the headphone jack is pushed all the way down that the left ear stops working. I did a little research and from this thread (https://forum.bottlehead.com/index.php?topic=4851.0) it looks like I may need a replacement jack? Thanks in advance for your help,

Chris

[Paul Birkeland]

See Crack FAQ item #12:
https://forum.bottlehead.com/index.php?topic=4295.0

How are your DC voltages?

[cayoung05]

Hi Paul, thanks for the help. Here's my DC voltages based on the Bottlehead Crack checklist in the manual:

Terminal - Voltage

1 - 147.8
2 - 164.4
3 - 0
4 - 164
5 - 148.6
6 - 0
7 - 147.3
8 - 0
9 - 147.1
10 - 0
11 - 0
12 - 0
13 - 163.6
14 - 0
15 - 190
20 - 0
21 - 215

A1 - 148.2
A2 - 0
A4 - 0
A5 - 0
A6 - 147.4
A7 - 0
A9 - 0

B1 - 147.4
B2 - 163.6
B3 - 147.2
B4 - 148.5
B5 - 164
B6 - 147.5
B7 - 0
B8 -  0

It looks like all the voltages that are supposed to be 90 (based on the manual voltages) are around 148. Is this something to be concerned about?

[cayoung05]

I also tested the tip of the headphone jack, and the voltage climbed to around 10 volts then dropped to 0

[Paul Birkeland]

Does your 12AU7 glow?

[cayoung05]

Yep, I can see light in both tubes. Here's a pic for reference

[Paul Birkeland]

Can you post some build shots of the inside?

Neither half of your 12AU7 is conducting, so you definitely don't want to listen to this amp just yet.

[cayoung05]

Hi Paul,

Here's some pics of the inside. I apologize for how messy the solders and the inside might look, it was the first solder job I did back in high school (which tells you how great and clear the manual was for learning/building an amp!). Let me know if you need additional pictures to clarify anything. Thanks again for your help,

[Paul Birkeland]

It looks like pins 4 and 5 on the 9 pin socket have been forced together, then soldered into one lump.

From what I can see, I would remove the 9 pin socket, cut out all the wiring that goes to/from that socket, and rewire it. 

[Deluk]

The short wire from the resistor should go to A6 and not A5? Wire going to A5 then bridges across to A4.

[cayoung05]

Hey all,

I rewired everything going to and from the 9 pin socket, replaced wires that looked suspect, and resoldered most of the joints, but the left ear still won't work. Here's a few pictures of the interior build. Any other suggestions? Voltages are pretty much the same as before:

1. 145
2. 162
3. 0
4. 162
5. 147
6. 0
7. 145
8. 0
9. 146
10. 0
11. 0
12. 0
13. 162
14. 0
15. 188
20. 0
21. 215

A1. 146
A2. 0
A3. 0
A4. 0
A5. 0
A6. 146
A7. 0
A9. 0

B1. 146
B2. 162
B3. 145
B4. 146
B5. 162
B6. 145
B7. 0
B8. 0

[Paul Birkeland]

You have a backwards LED on the 9 pin socket.  Please do not try to use any of our products that don't pass a voltage test.  The voltage checks tell you whether the amp is working or not, and trying to listen to an amp that isn't working could damage your headphones.

Does the 12AU7 glow?  Do either of the socket LED's glow?  Can you measure the DC voltages at A2 and A7?

[cayoung05]

The left ear works now! I switched the LED around, resoldered a few more joints, and put my original 12AU7 tube back in. I took another voltage measurement and the voltages looked much better than before (I posted them below). Both LEDs glow on the 9 pin and the tubes are glowing as well. I'm not sure which of the things I mentioned before fixed the problem, but thank you Paul for helping me out, much appreciated!

1 - 97
2 - 173
3 - 0
4 - 173
5 - 97
6 - 0
7 - 114
8 - 0
9 - 115
10 - 0
11 - 0
12 - 0
13 - 173
14 - 0
15 - 195
20 - 0
21 - 218

A1 - 97
A2 - 0
A4 - 0
A5 - 0
A6 - 96
A7 - 0
A9 - 0

B1 - 96
B2 - 173
B3 - 114
B4 - 97
B5 - 172
B6 - 114
B7 - 0
B8 -  0