VCF no oscilliscope/no sound

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dj_metronome
 
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VCF no oscilliscope/no sound

Post by dj_metronome »

Hello,

I'm currently building some self sourced x0x's. I've built the VCF and as I stated in the subject line I don't have a scope and when I try to listen with 32 ohm headphones I get nothing from any of the pins on vr4. I've twisted the knob like a pro too. :wink: (The VCO tested ok but the DC bias was low for both the square and saw waves. 7.8 and 6.1 respectively)

My variable power supply is hooked up correctly (3v) and the x0x is powered up. (I've checked and double checked)

Is this something I can skip over or is there a greater issue that I should be looking for?

Thanks
David

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pulsar256
 
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Re: VCF no oscilliscope/no sound

Post by pulsar256 »

Hi David,

no Signal in the VCF is not a good thing, perhaps this could help to narrow it down: http://forums.adafruit.com/viewtopic.php?f=12&t=38575 .

Cheers!
Paul

dj_metronome
 
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Re: VCF no oscilliscope/no sound

Post by dj_metronome »

Thanks Paul! Looks like I have some researching to do.... :!:

dj_metronome
 
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Re: VCF no oscilliscope/no sound

Post by dj_metronome »

Ok...
I don't think I have fake 2291's. I'm building 2 x0x's concurrently and I've replaced the 2291 in one of them but upon testing with the headphones all I'm getting is some static on the 2nd pin on vr4 from c13. Again, I twisted the knob like a pro and double checked my variable power supply and the x0x was powered.
Where do I go from here?

Thanks
David

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pulsar256
 
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Re: VCF no oscilliscope/no sound

Post by pulsar256 »

Hi David,

If nobody has an better idea - I would recommend getting your hands on a scope (lending one or getting an old 10MHz one from eBay) and tracing the signal from the VCO through the ladder and try to locate where its getting lost. You can get full schematics in the download section (http://www.ladyada.net/make/x0xb0x/download.html). Install the free version of Eagle and use the Show function to highlight connection / paths between components.

I take it you did already the obvious checks in the VCF section, such as verifying all component values and their polarities and looking for solder bridges?

Good hunting!

dj_metronome
 
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Re: VCF no oscilliscope/no sound

Post by dj_metronome »

I've downloaded Eagle and have been monkeying with it so I'm not flying totally blind. :? I'm working on getting/borrowing a scope. Yes, I've checked all my components (more than once) and near as I can tell everything looks to be correct. I've fixed a few questionable solder joints too. ...so onward and upward...

dj_metronome
 
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Re: VCF no oscilliscope/no sound

Post by dj_metronome »

OK, I got a hold of a scope and backtracked to the VCO. I tested the sawtooth wave and I'm getting 50 millivolts peak to peak. The saw wave is audible when I check the headphones too. As I stated before my DC bias is 8.17 volts.

Any suggestions of what to look for next would be greatly appreciated.

Thanks
David

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altitude
 
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Re: VCF no oscilliscope/no sound

Post by altitude »

try the head phone probe, just as useful as a scope.

dj_metronome
 
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Re: VCF no oscilliscope/no sound

Post by dj_metronome »

The headphone probe works but it's very faint. I've checked and rechecked all of my components and everything is correct.

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mmm
 
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Re: VCF no oscilliscope/no sound

Post by mmm »

Where exactly are you probing?

The voltages vary wildly depending on the exact probe point.

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