Scratchy sound, channel imbalance + weird voltage readings.

[Carolus]

Hello folks! 

I finished my Bottlehead Crack yesterday and did a resistance check that looked OK. I therefore made the decision to try the amp with a pair of old headphones and skip the voltage check (stupid idea, I know). I guess all the warnings about life threatening voltage and current made me a bit unsure about fiddling around with live circuits. I double checked all circuits before powering on the amp, and thought that was enough. 

Anyhow, all seemed fine at first. The sound was nice and crisp, the channel balance was perfect and there were no strange sounds.
So today I decided to try the amp with my HD650, but after a couple of minutes I noticed a scratchy sound, kind of like white noise, that came and went multiple times. It disappeared for maybe a minute when I restarted the amp but then came back. I think it was mostly or only in the left channel. After some time I also lost almost all sound in the right channel.

That's when I did the voltage check. Here are the results:

1. 79
2. 184
3. 0
4. 184
5. 81-82
6. 0
7. 16
8. 0
9. 108 second time: 25
10. 0
11. 0
12. 0
13. 188
14. 0
15. 200
20. 0
21. 213-214
A1. 82
A2. 0
A3. 1-2
A4. 0
A5. 0
A6. 80
A7. 0
A8. 1-2
A9. 0
B1. 80
B2. 184
B3. 11
B4. 81
B5. 184
B6. 107
B7. 0
B8. 0

From what I can tell, 7 and 9 are way off.

When I checked the TSR-connections, the voltage rose to 46V. At least I think so. I don't know if I measured it correctly. I had to use the 20V option on my multimeter to get any readings and it showed 0.46. It then dropped to zero, but started rising to 0.05 multiple times. It did not seem to go allt the way down to zero and stay there.

What do you guys think is wrong with my amp, and how can I fix it? Do you think that my headphones took any damage from the amp during the short time  (a few minutes) that I had them plugged in?

Thanks in advance!

//Carolus

[Paul Birkeland]

Are the 2.49K resistors on your headphone jack looking unusually burnt?

I think you have the wires going to the headphone jack feeding from the wrong terminals.  With voltages like that, I would absolutely not listen to the amplifier until you've repaired the wiring error.

[Carolus]

Are the 2.49K resistors on your headphone jack looking unusually burnt?

I think you have the wires going to the headphone jack feeding from the wrong terminals.  With voltages like that, I would absolutely not listen to the amplifier until you've repaired the wiring error.

They look completely normal. I did have to work a little to get them in the right position. Maybe that damaged them?

Are there any particular wires I should check?

[Paul Birkeland]

The next thing to check would be the solder joints on all the black wires.

-PB

[Carolus]

The next thing to check would be the solder joints on all the black wires.

-PB

Thanks for the tip! I have looked on all the joints several times, and all of them look fine. I can't see any joint that I would immediately suspect to not be ok. Almost all of them look nice and shiny.
Should I reheat them just to be sure?

[Paul Birkeland]

Yes, you can also tug a little on each black wire, one may just pop right out (which would indicate a bad joint).

-PB

[Carolus]

Yes, you can also tug a little on each black wire, one may just pop right out (which would indicate a bad joint).

-PB

All cables seem to be correctly fastened. I haven't reheated anything yet, but I just tested my multimeter on a 9V battery that shows up as 9.37V on the 20V setting, so I have apparently interpreted the readings the wrong way. The 0.46 is 0.46V, not 46 Volt. And 0.05 should be 0.05V.

So there doesn't seem to be any high voltage on the TSR. That's quite a relief. But that means that the voltage doesn't go up to 9V as it should.

[Carolus]

I tried the amp with my old headphones again, since there doesn't seem to be any high voltage to the TSR. Now another symptom showed up: low volume. I have to set the volume to max to actually hear anything properly. With all these different issues, my feeling is that some component is broken. The voltage reading on terminal 7 and 9 are really low, could that have something to do with it?

Should I reheat every joint anyway?

[Paul Birkeland]

I tried the amp with my old headphones again

Just for future reference, when your voltage are way off, you should not listen to the amp.  There is no reason to (it will either not pass sound, or pass it with a lot of issues), and you could end up damaging whatever you plug into your amp.  There won't be any additional information available from listening to the amp that isn't available from the voltage symptoms.

Now another symptom showed up: low volume.

As stated above, this is not an additional symptom.

Should I reheat every joint anyway?

Yes.

[Carolus]

Just for future reference, when your voltage are way off, you should not listen to the amp.  There is no reason to (it will either not pass sound, or pass it with a lot of issues), and you could end up damaging whatever you plug into your amp.  There won't be any additional information available from listening to the amp that isn't available from the voltage symptoms.As stated above, this is not an additional symptom.Yes.

Thanks for the information. I won't be plugging in any more headphones. The reheating did not correct the voltages, so I guess I'm going to have to send it in for the commercial repair service.

[Paul Birkeland]

Before doing that, I would post some photos of your build.  We may be able to suss out what's going wrong.

-PB

[Carolus]

Before doing that, I would post some photos of your build.  We may be able to suss out what's going wrong.

-PB

Here are some pics that I took:
https://imgur.com/a/XkniP/

Some of them are not great, so please tell me if I should take some more.

Edit: Attachments is in my next post.

[fullheadofnothing]

You need either post your pictures on the forum or make your pictures on imgur publicly viewable.

[Carolus]

You need either post your pictures on the forum or make your pictures on imgur publicly viewable.

The whole album should be public, but i'll have a look at it.

Fixed it:
https://imgur.com/a/XkniP/

Some of the wires on the transformer look badly soldered, but I have pulled on them and they are not coming loose.

Edit: I attached all pictures as well. I didn't think of that option.

[Paul Birkeland]

Thanks for posting up all the pics.  Here's what I would do if I had the amp on our repair bench:

1.  There's some bit of bare lead poking out around the headphone jack, I would look to make sure that wasn't loose, clip it off, and reflow that solder joint if necessary.

2.  The wire from B3 to 7 looks suspicious.  It looks like on the tube socket end, the bare wire just barely pokes through the tube socket terminal, and on terminal 7, it looks like the insulation may be in the terminal strip hole a little bit.  If you wiggle that wire, does it move on either end of its connection?  I would probably just remove that piece of wire and replace it with one slightly longer, then take half a wrap on each end to secure it.  The B3 end may OK, it's just tough to tell if the bare wire is bent up against the socket terminal (which is a good thing if it is)

I'd start with those two and see if things change.  By the way, you have some of the nicest looking twisted wire that I have seen in a long time!