Sound problem

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WouterK
 
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Joined: Tue Aug 19, 2014 5:14 pm

Sound problem

Post by WouterK »

Hi. I've got a problem with my x0xb0x. When I play a note the sound is very bad. It start with a click. Then a drops in tune for a second and then plays the the normal tune. https://soundcloud.com/avocet/bad-x0xb0x
All the test during the building proces are correct. I don't know where to start the troubleshooting and in which direction I have to look.
I hope someone can point me in the right direction. Thanks

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antto
 
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Joined: Thu Apr 15, 2010 3:21 pm

Re: Sound problem

Post by antto »

so that's the sawtooth
in the begining of the note, it gets saturated, i'm not 100% sure if it's saturated inside the filter or the VCA
and during most of the note, the waveform's gain is crazy high, so it's heavily saturated, which isn't normal, and maybe some resistor value is wrong somewhere

use a scope or the headphones method which is described in the build manual, and probe at the waveform switch, see if you get saw/square there and nothing crazy happens in the beginning of notes

then, probe the same way at the point where C14 (in the filter section) connects to the resonance pot (that point is the filter output) ... test that part with both waveforms and try the different filter parameters - cutoff/reso/envmod ... see if it sounds properly at that point

and then, probe before the VCA - at the point where R121 and C21 connect together

and finally, after the VCA - at C38/volume pot

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WouterK
 
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Joined: Tue Aug 19, 2014 5:14 pm

Re: Sound problem

Post by WouterK »

Yes, that's the saw. Thanks for your reply. I did the tests with a scope and headphones.

The vco fine. The signals looks good on the scoop and sound good thru the headphone.

The vcf seems not so good. At C14 I can hear the drop in tune at the beginning. With the scope I can see a little voltage drop in the beginning.
In the tb-303 schematic I can see the waveform above the 5.2 volt and with the waveform on top 5.8 volt. The 5.2 volt isn't there at C14 and the waveform is about 2 - 2.5 volt.
The components in the filter section are all on the right place. Can it be a broken component?

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