CP3 Mixer Question..

System 55 • System 35 • Model 15
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Rarecomponentadsr
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CP3 Mixer Question..

Post by Rarecomponentadsr » Sat Oct 24, 2015 10:22 am

I saw someone's patch chart for a modular recently and saw that an audio signal was being sent from the minus output of the CP3 into a 904a....when ever I tried this all I get is a click...no audio. I had always assumed the minus output was for control voltage etc and not audio signals.
No matter how I adjust I do not get any audio signals from the minus output...can anyone enlighten ?

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noddyspuncture
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Re: CP3 Mixer Question..

Post by noddyspuncture » Sat Oct 24, 2015 1:10 pm

You must have a faulty mixer... it should *sound* exactly the same, but be visually (on a 'scope) 180 degrees out of phase with the positive output.

Cheers
Tom

Rarecomponentadsr
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Joined: Mon Aug 24, 2015 5:08 pm
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Re: CP3 Mixer Question..

Post by Rarecomponentadsr » Sat Oct 24, 2015 3:10 pm

Thanks .......Oh no ! I made four clones a while back and was sure they were spot on...I have to take another look...so I get DC from the minus outputs but no audio ?? I wonder if it's anything to do with the trimmer setting ? As there is no direction for the trimmer setting I've left them all at half way...I will tinker about and see what happens ...

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noddyspuncture
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Re: CP3 Mixer Question..

Post by noddyspuncture » Sat Oct 24, 2015 9:58 pm

Which ones did you build *clones* of.... the transistor CP3 mixer or the op-amp CP3A mixer...?

Cheers,
Tom

Rarecomponentadsr
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Re: CP3 Mixer Question..

Post by Rarecomponentadsr » Mon Oct 26, 2015 7:44 am

Tom...it's the transistor version ..funny, I've done some tests and found I do get audio signals from the minus output ...but only when the master volume pot is set to roughly half way ...any further either way and the signal disappears ...also it's only about 50% of the positive output.
I probably have a wiring or component problem somewhere so the only thing to do is take a CP3 module out and fully test it.
The trimmer is there ( I think) to balance the volumes of plus and minus.

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noddyspuncture
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Re: CP3 Mixer Question..

Post by noddyspuncture » Mon Oct 26, 2015 8:47 am

Rarecomponentadsr wrote:Tom...it's the transistor version ..funny, I've done some tests and found I do get audio signals from the minus output ...but only when the master volume pot is set to roughly half way ...any further either way and the signal disappears ...also it's only about 50% of the positive output.
I probably have a wiring or component problem somewhere so the only thing to do is take a CP3 module out and fully test it.
The trimmer is there ( I think) to balance the volumes of plus and minus.
Sounds like you got some phase cancellation going on there..!?
When I built my two IC versions I found that the two 'output offset' trimmers didn't actually do all that much... the transistor circuit is a lit simpler. Do you have a 'scope to check what's going on in there, and are all four of your builds the same...?

Cheers,
Tom

Rarecomponentadsr
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Re: CP3 Mixer Question

Post by Rarecomponentadsr » Mon Oct 26, 2015 11:53 am

Yes, I built them last year and so far there's been no problems until I saw someone taking audio from the minus output, then when I tried it I got nothing , only DC signals went thru.

I will take one out tonight and examine it , as I say it's probably a component that's wrong or maybe wrong connections...

I'll post up when I find the problem.

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