Author Topic: Dirtbag v3205 signal loss  (Read 661 times)


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Dirtbag v3205 signal loss
« on: December 11, 2012, 05:05:22 AM »

It's been a while (received my board a year ago) since I've started with my Dirtbag.. and i got it working, but with the distorted repeats.
I think i had done just about all the mods (except the final revision) to get those repeats cleaner, so my board is not looking very pretty anymore... difficult to find errors...
Anyway, i decided to give the latest changes a chance, because it seems people are building v3205 versions without distorted repeats.
Now all parts are as the latest revision says they should be.
After these latest changes however i am not getting repeats at the output.
Now the part where i'm confused...

I used my audioprobe to follow the signal path.
I have output at both BBD's and i can follow the output of the last BBD up to R31. before R31 i have a signal, after none.
i checked R31. It's 680k, so fine.
i checked for shorts in this area, nothing...
also resoldered those joints.
so now i have no idea how to continue... i should have a signal there no?

hope someone can help.


« Last Edit: December 11, 2012, 05:16:06 AM by asji »


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Re: Dirtbag v3205 signal loss
« Reply #1 on: December 11, 2012, 06:53:40 AM »
After R31 you are going into an inverted input so if you are audio probing you would not expect to get any signal at that point. The important thing is getting output from that stage at pin7. If you have no output then the things to look at are:

Does IC3 get power and ground?
Are R32 and GAIN2 soldered properly?
Is the Gain trimmer turned up enough?
No matter where you go, there I am. Watching you.


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Re: Dirtbag v3205 signal loss
« Reply #2 on: December 12, 2012, 09:17:47 AM »
Thanks for the quick reply.
Learned something again :)

The Gain trimmer was not turned up, i guess that's why i had no output at IC3... now i do.
But after the NE570, it's a very soft repeat i'm getting.. it's too weak i guess as an input for the next repeats.
I'm still working on it. But it's becoming a mess to be honest.
Pots have broken off, lost a few pads and i am not confident anymore about the stability of my board.
I am thinking of starting over however... a new board for the V3205 version, but in the meantime i have found 4 MN3008's, and i would also like to try that route.
I'll keep an eye out for when the boards are available again.


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Re: Dirtbag v3205 signal loss
« Reply #3 on: December 14, 2012, 11:06:37 AM »
as it turns out, it pays to be stubborn :)

i checked everything, and found 1 trace gone 'missing', so fixed that. re-soldered and checked everything that looked suspicious, cleaned my board .. and i had repeats again!
At first i was scared a bit, because i still had distorted repeats.
But after tweaking the gain trimmers, there it was :) sounds brilliant now.
i found that gain1 in particular was responsible for the distortion i was still getting...
When setting the trimmers the first time, i gradually increased both gains simultaneously and by the time i got runaway feedback, the repeats were distorted. but by lowering gain1 a bit and increasing gain2, i got it to run away, with nice repeats.

thanks for the help