Speedball: Building static rush in one channel - pop - repeat.

[NightFlight]

Just finished off the speedball and testing tonight.

I have an issue where after warm up the left channel starts a rushing static noise which builds until it I hear pop and then no sound in left. After a second or so, the sound comes back perfectly. This repeats.  I can't trigger the issue unless there is music playing (odd), but once the static starts it is independent of the volume control.

Sounds like a charge is building and releasing. Re-flow the grounds? Of note I'm using one standard 1.6V LED instead of two HLMP-6000 on the left channel.

 

[Paul Birkeland]

I think your instinct to reheat your solder joints is a good one!

Also, you can carefully apply signal to your Crack, then do the voltage checks.  In particular, you could look at the voltages at terminals 1 and 5 to see if they wander all over the place when this noise appears. 

 

[NightFlight]

Catching it has been difficult, nigh impossible. Seems to mostly only appear when a) the crack is mounted right side up, b) has higher impedance headphones (hd800) attached. I'm not willing to put my hd800s through another snap in the left channel. Its downright devious.

Also I think it could be static charge/discharge since I swear I got it in the left ear just a few minutes ago through the earphone. Also, when the static noise builds on the left my measurement attempts anywhere on the left side will discharge it with a snap. Also discharging with the meter, it would seem the issue doesn't reoccur again until the amp is power cycled.

I'm home today with a sick kid and sick crack.  So trying to bring both back to health.
With the crack, trying a couple things... continuously monitoring taps 1 and 5 with two meters using clips. What a novel idea.


Note: I should have this thing taken away from me. I could have done myself in a couple times. Tapping the transistors, on circuit boards A and B to determine channel - while holding the chassis in left hand. Only to discover there's voltage in the little housing!  Good thing my fingers weren't sweaty. Then looked at my left hand only to find my thumb precariously close to line in hot. Yeah that would have been nice.

 

[NightFlight]

Oh, and some tubes for rolling came, so I've ruled out that.

 

[NightFlight]

Voltages:

Terminal

1  66.9
2  178.5
3  0
4  178.8
5  63.0
6  0
7  104.3
8  0
9  104.9
10  0
11  0
12  0
13  177
14  0
15  196
20  0
21  216

A1  63.4
A2  0
A3  1.5
A4  0
A5  0
A6  (T1) 67
A7  0
A8  1.5
A9  0

B1  66.6
B2  178.7
B3  104.6
B4  63.1
B5  178.6
B6  105.5
B8  0
B9  0

 

[Paul Birkeland]

I'd really concentrate on resoldering the connections on the headphone jack. 

 

[NightFlight]

I think I've just about resoldered (re-wet) everything this morning that looks even remotely connected to ground. Testing the re-soldered TRS jack now.

 

[NightFlight]

And no, it just happened again. Can I switch the A/B Circuit boards around? Their identical so it should be a fair test.

 

[Paul Birkeland]

Yes.

 

[NightFlight]

Okay, it followed the channel change the static/rustling buildup now shows up on the right. Carefully turning the amp over to check measurements and it fades away while slowly turning it over.  Now my gut says its possibly heat related.

Montoring T1 now while the amp is in proper position.

Caught it. T1 creeps up from 66.6V to 76V while the static/rustling fades in... When it shorts and I loose sound in the affected channel it spikes up to ~163V for a couple seconds, then resets down to nominal and audio returns.

 

[Doc B]

Sounds like a transistor may have been overheated or otherwise damaged. We can send you a replacement 2N2907 and MJE 350. You can request it at replacementparts at bottlehead dot com or call us at 206-451-4275.

 

[Grainger49]

I think I've just about resoldered (re-wet) everything this morning that looks even remotely connected to ground. Testing the re-soldered TRS jack now.

You will find a sticky in the Crack folder that calls out the whole ground path.

 

[NightFlight]

Sounds like a transistor may have been overheated or otherwise damaged. We can send you a replacement 2N2907 and MJE 350. You can request it at replacementparts at bottlehead dot com or call us at 206-451-4275.

Doh! I already have 1-2 LEDs heading this way. Would have been better to bundle it all. *sigh*

 

[Paul Birkeland]

I'd reheat every joint on that offending PC board.  (Good job on narrowing it down BTW)

 

[NightFlight]

I think Doc might be right, I have intermittent conductivity between the Base and Emitter where it should be providing infinite resistance on the MJE 350 - comparing it to the other channel to confirm.

I have a pair of similar packaged transistors from my old kit here... from my old electronics 101 course I took a million years go. I think their Motorola C106D's. My money is on incompatible.

 

[NightFlight]

Dang, its a rectifier.

 

[Paul Birkeland]

Yeah, a C106 is essentially a diode. 

We can send you an extra little green board, two LED's, two resistors, and two transistors.  That will get you up and running.

 

[NightFlight]

Well, that's very kind, but I was thinking I would try and order the parts locally so I have a few on hand.  The board is obviously custom.  I may do both.

BTW I really do appreciate the help isolating the issue.

 

[NightFlight]

I never got my 'B' PCB replacement - I'll contact the Eileen to get that sorted out.

However, I did get my original missing LED in the mail. The day before it showed up I moved the standard LED from board B to A that I had swapped in for the missing one. The issue followed the LED. When the HLMP-6000 came in, I dropped it in place to find this issue completely resolved.

So, CB - you can't arbitrarily drop in standard red domed LEDs.  At least not the one I used. 

 

[Paul Birkeland]

So, CB - you can't arbitrarily drop in standard red domed LEDs.  At least not the one I used. 

No, generally the forward voltage drop is not correct.