Brassmaster Popping Sound problem

[audioguru]

Hi folks.

I'm having a problem with a Brassmaster kit when I switch the 3PDT....the pedal work fine except for that.

I've read all kind of thread and I've troubleshoot a bit so here is my problem:

At the output when the circuit is ON,  I have 0.4v DC.

The Brasmaster does have a Output Cap (1uF) I tought it might be reversed or gone bad so I've unsoldered it but even without it I still get 0.4v DC, there is pulldown resistors at both input and output so I've took them out as well and now the output is at 0.19v DC.

I understand that everytime the popping sound comes from that DC offset, how can I remove that?

Any help would be really appreciated.

Pascal

[R.G.]

I'm having a problem with a Brassmaster kit when I switch the 3PDT....the pedal work fine except for that.
...
At the output when the circuit is ON,  I have 0.4v DC.

The Brasmaster does have a Output Cap (1uF) I tought it might be reversed or gone bad so I've unsoldered it but even without it I still get 0.4v DC, there is pulldown resistors at both input and output so I've took them out as well and now the output is at 0.19v DC.

I understand that everytime the popping sound comes from that DC offset, how can I remove that?

You remove that by finding what is causing it. You have something that is bleeding DC into the output signal line. There is no way we can tell you with any certaintly from this distance what is bleeding DC into the signal lines without more data.

The fact that removing the pulldown resistors is significant, as these should have reduced it. If you use input-jack DC switching, a problem in wiring might cause this, but the only way to tell is to start measuring DC voltages and comparing them against how this should work until a mismatch shows you what is wrong.

If it were mine, I might take the input and output caps out entirely. That forces them to be "high quality" as regards DC leakage anyway. If the voltage is still there, then it's leaking in through the circuits themselves or through the power/ground wiring.

[audioguru]

First thanks R.G. for the quick answer  

The fact that removing the pulldown resistors is significant, as these should have reduced it. If you use input-jack DC switching, a problem in wiring might cause this, but the only way to tell is to start measuring DC voltages and comparing them against how this should work until a mismatch shows you what is wrong.

You are right I'm using input-jack DC switching, I can't compare any voltage because I don't have any other functioning unit and neither voltage on my schematic, I've check so far for capacitor leakage but I haven't found any significant trouble.

If it were mine, I might take the input and output caps out entirely. That forces them to be "high quality" as regards DC leakage anyway. If the voltage is still there, then it's leaking in through the circuits themselves or through the power/ground wiring.

I will do that but I would need your opinion, is there a way to begin troubleshooting...meaning that I have 0.4v DC at the output, would it be better going from the output to the input?
Do you think just by removing Capacitor I might find the problem or do I have to remove transistor as well?

I plan first to remove the jack, switch and pots from the case to see if there is something wrong with that.

I'll do that and I'll be back to you.

Thanks again.

Pascal

[meltunes]

I just finished troubleshooting a booster pedal I built that was popping when pressing the 3PDT. After taking voltage readings at my caps, I found that the output cap was leaking DC, similar to what you describe.

After replacing the output cap the pop was gone. I'd look at replacing the output cap first before tearing more into the pedal, it sounds like its bad to me based on my limited experience.

HTH, Mel

[R.G.]

Do you think just by removing Capacitor I might find the problem or do I have to remove transistor as well?

Only remove the capacitors, nothing else. A capacitor is supposed to be an open circuit to DC. Since there is a DC problem, we can test the hypothesis that it's a capacitor problem by removing only capacitors. This should change nothing about the DC conditions, in theory. If anything changes, then there was a problem with one or more of the capcitors we removed.

I plan first to remove the jack, switch and pots from the case to see if there is something wrong with that.

You could do that, but try just the capacitors first.

[audioguru]

Thanks guys for the inputs.

Yesterday I already did change the output Cap and it didn't do nothing.

Today I've removed the input Cap but I have the same problem, I've unscrew the jacks from the case...but I still have the same problem.

Next move I'll do is go backward ( from the output ) and remove any Electrolitics that I found.

Thanks again.

[R.G.]

The more you describe this, the more my intuition tells me that it's a wiring problem.

It may be time for you to read and follow "what to do when it doesn't work".

[audioguru]

The more you describe this, the more my intuition tells me that it's a wiring problem.

It may be time for you to read and follow "what to do when it doesn't work".

Not quite sure if I have the right document, do you have a link to this text?

[audioguru]

Hi guys, here is some data that I took from my circuit any help would be nice.

There is 7 transistors, 1 to 6 are 2N3391 and Q7 is 2N5308, I've check and Q7 is really a 2N5308, so ther is no mismatch, here is the data on each transistors
Q1
E 0.29v
B 0.91v
C 2.32v

Q2
E 0.39v
B 1v
C 3v

Q3
E 2.39v
B 3v
C 11.36v ( I think my meter doesn't read RMS as I'm using 9v adaptor on that circuit? )

Q4
E 0.09v
B 0.7v
C 5.76v

Q5
E 5v
B 5.75v
C 8v

Q6
E 4.52v
B 5.13v
C 13.10v RMS???

Q7
E 0.27v
B 1.4v
C 0.87v

I have 4 iN914 diode and they share the same data, that is: Anode 4.5v and Cathode 4.7v

I have 7 electrolytics, they are
C2
+post 0.29v
-post 0v

C4
+post 1.02v
-post 0v

C6 ( output capacitor )
+post 2.48v
-post 2.6v

C8
+post 5.15v
-post 4.75v

C9
+post 8.2v
-post 4.6v

C16
+post 13.3v
-post 0v

C17
+post 11.55v
-post 0v

I will send a schematic from what I'm working on.

Thanks for your help

Pascal

[audioguru]

I'm trying to put the schematic online but without sucess

[R.G.]

Not quite sure if I have the right document, do you have a link to this text?

It's the seventh of the sticky messages at the top of this forum that you have to ignore to get to the normal messages. It's entitled "Debugging thread: what to do when it doesn't work".

C6 ( output capacitor )
+post 2.48v
-post 2.6v

This is why you have pops. The output capacitor must have 0V on one side, that being the output jack side. It is likely that this capcitor is in backwards. If it's not, then you may have something else feeding voltage into the output.

I will send a schematic from what I'm working on.

]
Better to send a link. Or even better, read "what to do when it doesn't work" and follow all of the suggestions.

[audioguru]

IT FINALLY WORKS!!!!!

But I wanna share my problem.

After checking my transistors voltage and Caps, I've re-done all my solder....without any luck at all, I was kind of desperate and could not understand that without the output Cap I was still seeing DC at the output.

I tought it might be the footswitch so I un-soldered the wire going trough it and at the footswitch it was good but at the end of my wire I could see around 0.5vDC...Now I'm suspecting a problem with the PCB, it's a PCB bought in a kit from General Guitar Gadget, I'm quite sure that the layout is good but there is something bleeding trough the output, with the help of my X-acto I've cut any solder joint that was near the output trace....without again any result...I could not find where it was bleeding trough, I finally put back my Output Cap but I've cut the trace going out to it and I've solder a wire straight to the output of the cap going to the footswitch, at the footswitch I've put a 1Mohm pull down resistor going to ground and VOILÀ!!!! it works.

Thanks again RG, couldn't make it work without your help....I have a gig this weekend I guess I'll have a ney toy to play with.

Pascal Sauvageau

[R.G.]

I really would like to get a picture of what you did if possible.

That PCB is my layout, licensed by GGG. It's been built many times successfully. It is possible that there is a problem with etching that one board. In any case, I'd like to find what the problem was so I can help J.D. at GGG fix it if there is a problem other than a random problem with one board.

Good work fixing it, by the way!

[audioguru]

OK R.G. here is the pict...I finally understand how it work.... man...

So here it is under the PCB I've cut the trace from the output Cap going to the pull down resistor and "N" hole on the PCB, a wire is going straight to the swicth, I did put a pulldown ( 1M ) resistor straight on the footswitch.



A look inside the box.


And outside


It must be a solder joint that is touching my output but anyway now it work so I don't care

Thanks again R.G.