Cp251 Mixer and Noise

EricK · Post by **EricK** » Fri Jul 11, 2008 11:45 pm

Friends,
I know that this has been raised in the forum before and I haven't had any luck in my searches for it.

Using the CV Mixer as an audio mixer in the past, its been totally silent. During that time I was running it into the Audio IN of the micro for processing and then to the recorder unit.

Since then I have mounted my CP in a Rack and I had to undo the power and reinstall it in the back of the unit. My rack is set up without a power conditioner. Im powering the 107, 102, delay and the cp251 seperated equally into 2 power strips, each with a 45 foot extension cord so that I can run a cord into a different outlet. THe most that is on the power strip is 2.

THe last time that I trued to use the Mixer as an audio processing signal I got a high pitched whine that the filter of the Moog woudln't filter out. Now for this it WAS going into the Fender Rhodes amp so I imagine that it boosted the crap out of the audio signal.

My question is...was this the result of me removing the power harness and installing it in the back or is this an issue with the way that Im providing power to the unit.

I do know that its generally NOT supposed to be used in this way but I was curious if it worked 1 way in the past why it was so noisy this time with minimal units sharing a power supply and with a minimum of cords between the source and the end signal.

If anyone can please shoot me a link or answer this question Id be very appreciative.

Right now its looking like im going to have to buy a mixer module instead of using the CP's mixer.

Most Respectfully,
Eric

narrowcaster · Post by **narrowcaster** » Sat Jul 12, 2008 9:26 am

FWIW, My CP-251 has always done this, with a wide variety of power supplies and in different buildings. I've tried asking around but the only advice is always to try different power supply situations, which hasn't made a difference for my unit. Since I know that some people have this problem and some don't, my conclusion was "it happens with some units and not with others." But since you have one that didn't do it before and does now, I guess the new conclusions need to be either that the situation can develop over time in a unit that used to be OK, or, that it does have something to do with the power and I just haven't found the magical power source yet (although that still seems unlikely to me, since I've tried it in so many different situations).

So anyway, I don't know if that's directly useful to you, but that's been my experience. I still love the CP-251 for what it was primarily designed to do, but mine at least doesn't do audio signal mixing as a bonus.

EricK · Post by **EricK** » Sat Jul 12, 2008 10:37 am

I remember when you said that, some do and some don't. That was the first thing that I tried when I got my cp251 really going. I was thinking, Im blessed mine doesn't do that. But when I removed the wire to install it in the back and started using the power strips it did it.
WHen i get home Im going to try it again going into a different amp because the Fender Rhodes Amp will really boost the signal.

I have to get a mixer module anyway for my oscillators when i get those so Im not really that bothered about it.

THanks for your response, if its something major, Im sure Moog will fix it.

Eric

Alien8 · Post by **Alien8** » Sun Jul 13, 2008 3:17 pm

When you rack mounted the CP did you isolate the rack from the unit? Maybe you have a ground leaking through the rack, and showing up in the audio... just a thought...

I had a problem like this with my pedalboard, one of the chassis was touching the frame, and grounded out to the power supply...

Kevin Lightner · Post by **Kevin Lightner** » Sun Jul 13, 2008 4:32 pm

Generally speaking, you should have one source ground.
If you're plugging some interconnected gear in one outlet and other gear in another, you may get noise or a ground loop.
Ideally, you want one ground source that's fanned out, not grounds from multiple sources fanned in.
I don't recommend lifting grounds to remove hum unless you truly know where your main ground is coming from and if it's very solid.

Also, 45' of power cord means your ground is actually going through a resistor.
It depends on the gauge of the wire as to how bad things can get.

I hope something here helps.

ikazlar · Post by **ikazlar** » Sun Jul 13, 2008 6:11 pm

Also make sure that the Offset knob in the CP-251 is in the center position.

EricK · Post by **EricK** » Thu Aug 07, 2008 12:03 pm

Update:

First of all I thought the offset should be totally counterclockwise..i could be mistaken.

So Far, Ive tried to use the mixer of the Cp251 for audio a total of 4 times.
Each time I was trying to use both the 107 and the 102 as outboard oscillators. Here are my results:

1. Ran through the Micro's audio input and into the recording console. Worked perfectly

2. Second time I tried to run it into the Micro's audio input and into an amp and I heard audible distortion that I figured was due to an old cord.

3. I tried to run the Freq and Ringmod into the Micro and then into the Fender Rhodes amp and I heard the infamous high pitched whine.

4. Last night I ran both the 107 and the 102 into the mixer and into the Voyagers external audio input and ran that into the Fender Rhodes amp and it worked perfectly.

So really, I think depending on if you are using a high gain output like the Micro's hi gain output into something like the Rhodes which I am pretty sure boosts the input signal then you will hear the high pitch whine. But if you use the mixer in this fashion with a device that will let you control the gain of the audio output signal from the Cp251's mixer (unlike the Micro) then you may not hear the whine.

My power supply going to my rack is 2 power strips with long extension cords so that I can greatly seperate them from other outlets.

I hope that this can clear up some of your issues with the CP251 mixer and the noise issue some of us have faced.

Respectfully,
Eric

EricK · Post by **EricK** » Thu Aug 07, 2008 12:05 pm

Kev,
Just FYI, the gauge of the cords are heavy duty for outdoor usage. I don't know the actual gauge.

E

Kevin Lightner · Post by **Kevin Lightner** » Thu Aug 07, 2008 2:59 pm

Isn't a Rhodes a pickup device and thus the amp would be a high impedance input?
If that's so, you may be overdriving the input or having it amplify all sorts of other noise (ground, cord, etc.)

Just a thought.

EricK · Post by **EricK** » Thu Aug 07, 2008 5:18 pm

Yeah the Rhodes is a pickup device.

I say its a high impeadance amp because I would plug the theremin straight into it and it was totally too loud. (How do you like my technical assertation?) I always use the Micro's High output when running into the amp so that it can compete with the Rhodes at louder volume levels.

That is the reason why Im theorizing that sometimes I get the noise and sometimes I dont.

Eric