TM3030 noisy output - due to CA3080?

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ark1971
Learning to Wiggle
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Joined: Sat Feb 04, 2012 12:28 pm

TM3030 noisy output - due to CA3080?

Post by ark1971 » Wed Jan 09, 2013 6:07 am

Hi all,
I'd just like to get an opinion
I've finished my TM3030. I've noticed though that there is some noise on the output if a note is played particularly if the filter is completely closed. I was wondering if this noise could be attributed to the CA3080 as it only appears when the note is pressed,
thanks,
joe

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Synthbuilder
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Re: TM3030 noisy output - due to CA3080?

Post by Synthbuilder » Fri Jan 11, 2013 10:38 am

ark1971 wrote:I was wondering if this noise could be attributed to the CA3080 as it only appears when the note is pressed.
The CA3080 is the final VCA. When the note is on the VCA will pass not only its own noise but also the noise from anything upstream of it. The VCF will be a significant part of that. Even when the VCF is at its lowest frequency the output stages of the filter make a significant noise contribution. So if it's hiss you hear it's both the filter's differential amplifiers and the VCA.

It is unlikely that even a fully closed filter will actually remove all traces of the VCO. So you'll also get noises from there too.

If it's buzzing you are hearing then it is quite possibly a problem with the grounding of your unit. Or if you have wired the pots to the board the wires may be unshielded, too close to a mains power source, or just too long.

The CA3080 is not a particularly quiet VCA though. There are several better ones these days although none that are pin compatible. But the venerable 3080 is no worse than the BA662.

Tony

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