Intermittent distortion

[pofofo]

Hi,

The last days my SEX have had some intermittent distortion.

It comes and goes in both channels, not necessarily at the same time, it kind of wanders. Ive heard it to nights in a row now and it starts maybe after an hour or so. It sounds kinda like electronic tapping and a vinyl like sound. When the distortion accured, I plugged out my DAC and it continued. I also powered off my monitor, phone charger and active studio monitors to no avail. It can last from a few seconds up to 20-30s

Ive used it daily for hours since early august without any problems. I did do the mod described here: https://forum.bottlehead.com/index.php?topic=11676.0 to avoid USB noise with lower impedance headphones. And it has been working fine since I did it a couple of weeks ago.

Any idea what this could be?

[Paul Birkeland]

I'm a little confused, you say you have intermittent distortion, but then you describe hearing noises through your SEX amp.

Is there noticeable distortion when playing back music?

If you just have some random noises, the most likely cause would be an intermittent connection that got jostled when you added the diode modification, and you would need to go back through your build and reheat all the solder joints as a precautionary measure.

[pofofo]

My english isnt very good, Im from Norway, so it a bit difficult to explain.

I described the distortion as intermittent since it comes and goes.

The distortion comes from the amp, I reckon. Most of the time theres no distortion at all, either playing back music or pausing it. But once in a while theres distortion as I described, and the distortion is at the same volume no matter how the volume knob is set.

[Paul Birkeland]

Is it a noise that you hear or does the amp just make noises on its own?  Either way I would reheat all of the solder joints in the amp, that often fixes problems like this.

[pofofo]

I hear the noise through my headphones and its in both channels and kind of wanders.

Ill reheat the joints and hope for it to go away, thanks Paul.

[pofofo]

Im finally back to to working this problem after awhile.

I did a resistance check and got the following:

1   0
2   *
3   888
4   250k
5   0
6   *
7   *
8   0
9   0
10   *
11   677
12   0
13   *
14   0
15   0
16   *
17   887
18   249k
19   0
20   *
21   *
22   0
23   0
24   *
25   674
26   0
27   *
30   *
31   *
32   *
33   *
34   *
35   *
36   0
H1   0
H2   108.8
H3   308
H4   108.7
H5   108.8
H6   *
H7   108.7
H8   0
GROUND TAB   0

I do not trust my cheap multimeter, but the measurements at H2, H3, H4 and H5 are worrying.

[Paul Birkeland]

Your resistance readings at H2, H3, H4, and H5 are not concerning. With the big 10,000uF cap being involved, sometimes those resistances can't be resolved by some meters.

[pofofo]

Aha, thanks for the reply. I guess voltage checks are next.

[pofofo]

I did the voltage checks:

2   73v
3   17v
4   0v
5   0v
6   370v
7   390v
10   367v
16   77v
17   18v
18   0v
19   0v
20   369v
21   389v
24   364v
H2   3.1v
H5   3.1v
H4   2.9v
H7   2.9v

They look good too and I`ve reheated/resoldered every joint twice.

I know the lead free solder I got is probably not the best. But the amp worked fine for months before it more or less suddenly started with this.

I had the C4S mod, which I later removed and I had the ground diode mod, which I later removed. None of these mod had anything to do with the distortion I´m hearing.


The distortion is through the headphones and floats between left & right. It comes and goes and lasts about 5-30 sec. It sounds like popping and electronic noise, a bit like dust on a vinyl maybe and its pretty low volume.
The sound is there even when there is no source connected.

Got any more ideas?

Grateful for the help.

[Paul Birkeland]

Oh lead free solder sucks!

Try the amp in a different location (building) to see if you're picking up interference from something.  You could just be picking up noise from a wireless device that's close by.

[pofofo]

Darn straight!

Since the problem started, I have moved and it followed, so I don´t think it´s interference.
But I do and did have a wireless modem just a couple of feet nearby. And I´ve been using my phone as a source, streaming through wifi.

[Paul Birkeland]

So one thing that comes to mind here is that distortion and noise are two completely separate problems, and it would help to separate them.

When you say you have periodic distortion, what that would mean is that when you are playing music through your amp, it doesn't sound like it should. The amp would otherwise be perfectly quiet though.

Noise is something that doesn't belong that's there with or without the music.

[pofofo]

I guess you are right about that. Since it has nothing to do with the source or music, then its noise.

I know the tubes are rarely the problem, but could that be it?

[Paul Birkeland]

If it's in both channels, it is very, very, very likely a source of noise external to the amp.

[pofofo]

The noise, when its there, is kind of panning between the channels and it is still there with the volume down and with source disconnected. So I really think it´s from the amp itself.

Sometimes it´s just on the left channel and sometimes it is panning between L & R.

I had the same problem before I moved to a new apartment and before and after I changed all the electrical wiring while renovating the new place.