Dyna Comp Crackle problem!

[KrazyKarl]

So my Dyna Comp has a major crackling issue. I recently did the Monte Allums mod, which sounds great, but it crackled before the mod and it still crackles after it. It gets worse the higher you turn the volume and/or sensitivity, as you might expect. It's ridiculously annoying.

I tried swapping out the pots for other pots and then I just hardwired some resistors in to where the pots were, as if they were turned all the way up, to make sure that it was definitely not the pots. Still crackles. Sounds kind of like burning leaves. 

Has anyone had this issue? Does anyone have any idea as to what this might be?

[KrazyKarl]

bump

[Thomeeque]

Does it crackle itself or only as a reaction to some input signal?

Are you able to set Senstivity to the point, where it does not crackle?

T.

[Thomeeque]

wrong button.. again and again..

[KrazyKarl]

Does it crackle itself or only as a reaction to some input signal?

Are you able to set Senstivity to the point, where it does not crackle?

T.

Nope, it crackles all the time. It's not the pots, though I really wish it was...

[Thomeeque]

Does it crackle itself or only as a reaction to some input signal?

Are you able to set Senstivity to the point, where it does not crackle?

T.

Nope, it crackles all the time. It's not the pots, though I really wish it was...

Have an audio probe and check at what point crackling starts (Q1/E, CA3080/6, ..).

What PSU do you use btw.? And/or does it crackle with battery?

Btw. try to tap by something to the 2K trimmer (or mark it's position and try to turn it) and listen, if there's crackle reaction..

[KrazyKarl]

Have an audio probe and check at what point crackling starts (Q1/E, CA3080/6, ..).

What PSU do you use btw.? And/or does it crackle with battery?

Btw. try to tap by something to the 2K trimmer (or mark it's position and try to turn it) and listen, if there's crackle reaction..

Thanks for the tips, I'll definitely try those. I think I did try it with a battery once, but it's worth another shot.
I did try fiddling with the trimmer a bit. Doing so, I managed to fix another problem where it would cut out when I held a note for too long. But it crackles regardless...

[KrazyKarl]

Ok I finally got a chance to test this with a signal probe. It's dead quiet at pin 6 of the opamp, but at the emitter of Q2, as well as at the base, it's full on crackle.

[cobra94]

According to the MXR performance test sheet (which they check this with a scope).

"If ther is popcorn noise, replace CA3080, located at point C.  If noise is still present replace the input transistor Q2 (MPS5172), located at point D."

So it looks like one of these two or both may be the cause so swapping either or both should do it.  Good luck.

Cheers,
Peter

[KrazyKarl]

According to the MXR performance test sheet (which they check this with a scope).

"If ther is popcorn noise, replace CA3080, located at point C.  If noise is still present replace the input transistor Q2 (MPS5172), located at point D."

So it looks like one of these two or both may be the cause so swapping either or both should do it.  Good luck.

Cheers,
Peter

Where did you find this test sheet. I'd like to have a gander at it
Thanks for the advice, I'll keep that in mind. I kinda doubt that that's what it is, because I did a monte allums mod on it and both of those parts were replaced, which didn't fix the problem. But at some point, I may have to try that anyways. Nothing seems to be working...

[R.G.]

The nature of the popping or crackling is important.

If it's only when you move a control, it's either a bum control or DC across the control. If it's all the time, it's either a noisy part, a bad/intermittent solder joint, or an almost broken wire or connection.

Since it happened before and after the Monte Allums mod (whatever that is) , the mods are immaterial.

[KrazyKarl]

RRRGH! Replaced Q2 and the IC and there's still crackle. This is getting on my nerves.

As for the nature of the crackle, it's not the pots because I hardwired in some resistors for testing just to take them out of the equation.

I really appreciate all your info. Any more suggestions people?

[MmmPedals]

The nature of the popping or crackling is important.

If it's only when you move a control, it's either a bum control or DC across the control. If it's all the time, it's either a noisy part, a bad/intermittent solder joint, or an almost broken wire or connection.

Since it happened before and after the Monte Allums mod (whatever that is) , the mods are immaterial.

[head_spaz]

How old is it?
I'll just about bet that thing was built using Composite Carbon resistors.
I'd begin by replacing them with metal film types.

[KrazyKarl]

How old is it?
I'll just about bet that thing was built using Composite Carbon resistors.
I'd begin by replacing them with metal film types.

Haha, well, it's not quite that old. It's still revision D. Though having carbon comps would obviously add some extra mojo

The nature of the popping or crackling is important.

If it's only when you move a control, it's either a bum control or DC across the control. If it's all the time, it's either a noisy part, a bad/intermittent solder joint, or an almost broken wire or connection.

Since it happened before and after the Monte Allums mod (whatever that is) , the mods are immaterial.

Yeah I'd been checking around for that, but haven't found anything yet. I guess I'll keep going on that.

Does anyone know how I could check the voltages on the transistors? Which ones should I check and what kinds of voltages should I be looking for? Ideas?

[Perfboard Patcher]

Ok I finally got a chance to test this with a signal probe. It's dead quiet at pin 6 of the opamp, but at the emitter of Q2, as well as at the base, it's full on crackle.

That seems to be your problem, a broken connection between pin 6 and the base of Q2.

PP

[KrazyKarl]

Ok I finally got a chance to test this with a signal probe. It's dead quiet at pin 6 of the opamp, but at the emitter of Q2, as well as at the base, it's full on crackle.

That seems to be your problem, a broken connection between pin 6 and the base of Q2.

PP

Sweet!!! I really hope it is, I'll check that out when I get home tonight and let you know how it goes.

[KrazyKarl]

Ok, so I just jumpered the Base of Q2 directly to pin 6 of the IC and it still crackles. I'm going to power it up and post some voltage readings as soon as I can. Maybe that'll help give an indication as to what's going wrong.

[KrazyKarl]

Ok so here are my voltages. All readings are in Volts
These transistors are 2SC1849, and according to the datasheet (http://www.alldatasheet.com/datasheet-pdf/pdf/108514/ETC/2SC1849.html) I saw, if the pins are pointing down and the flat side is toward you, the pins are C B E from left to right. So the readings below assume that.
I plugged in the power as well as the input jack which was connected both to the guitar (whose volume was all the way down) as well as the pedal.

Main voltage from adapter: 9.6
Q1
C - 1.26
B - 1.24
E - 9.49

Q2
C - Varies constantly, hovers around 3 most of the time, but never stops changing, sometimes going down to 2 or up to 4
B - Varies constantly, hovers around 3 most of the time, but never stops changing, sometimes going down to 2 or up to 4
E - Varies constantly, hovers around 6 most of the time, but never stops changing

Q3
C - 8.23
B - 7.82
E - 9.47

Q4
C - 0
B - 0.4
E - 7.78

Q5
C - 0
B - 0.08
E - 7.86

IC (CA3080E)
This pinout may be wrong but I'm assuming that if the side with the half circle in it is facing up and the pins are pointing away from you, pin 1 is in the top left hand corner and the numbers go around CCW from there as shown in my little drawing below
    ___   ___
1 -|    U     |- 8
2 -|           |- 7
3 -|           |- 6
4 -|______|- 5

Here are the readings for the IC:
1 - 0.3
2 - 2.75
3 - 2.62
4 - 0
5 - 0.69
6 - Constantly changing, usually hovers between 3.2 and 4.6, but never stops changing
7 - 9.45
8 - 2.35

Any help or thoughts appreciated. Thanks guys!

[R.G.]

Remelt all the solder joints, carefully, with a bit of fresh rosin core solder and a hot, well-tinned iron.

If it still crackles, poke at the pins of Q2 and the parts around it with a nonconductive probe. If you can make it crackle with the probe, you've found the problem.

If it still crackles and mechanical prodding does not reveal the cause, remanufacture the Q2 section. Put in a new transistor and all the resistors and caps around it. This will be cheaper in time and possibly money than digging deeper.

And while you're doing this, be aware of the possibility of a cracked resistor, cap lead, or board trace.