Did I get a bum CP-251? Mp3 examples of odd noise behavior

DinosaurSR · Post by **DinosaurSR** » Fri Jul 28, 2006 12:45 am

I just picked up a Moogerfooger CP-251 to go with my synthesizers.com setup; I figured I could use the extra processing and CV stuff without having to start another DotCom cabinet just yet.

However, when I started using the CP's sample and hold section, I was confused by the fact that the S+H's output range seemed to be very narrow, producing just a minor warble in the pitch of my DotCom oscillator rather than the wild "calculating" that I've gotten from sample and hold circuits before. Here's a sound demo:

Http://www.hardtoexplain.net/hortonmusi ... 0noise.mp3

I had noticed that the CP-251's noise output, when used as an audio, was pretty weak and quiet, so I started to wonder if this was to blame for the "weak" sample and hold output, as the CP's noise generator is normalled to the sample and hold input. So I patched my DotCom's noise output into the CP-251 to override its normalled noise, and then the sample and hold's output was much more like what I expect from a straight sample and hold--->oscillator patch. Sound demo:

Http://www.hardtoexplain.net/hortonmusi ... Source.mp3

That's more like it!

So, here's what I'm wondering - did I get a bum noise source in my CP-251, or are all of them like that? It seems weird that the onboard noise would be so weak on purpose, since when sampled by the S+H circuit, it produces a very unremarkable output effect. Whether I patched it to my oscillator or to filter cutoff, the result was ho-hum at best. But when I overrode the CP's internal noise with my DotCom's noise source, the result was perfect! If all CP's are like that, I guess I'm willing to just always plug my DotCom's noise output into it to override it, but it seems abnormal and I wonder if I need to just exchange my CP or get it fixed.

What are your experiences?

Impossible Sound · Post by **Impossible Sound** » Fri Jul 28, 2006 5:10 pm

Maybe it's the normalling. Have you tried patching the noise directly into the S&H instead of relying on the normalling? Does it make any change in level?

chris allert · Post by **chris allert** » Sat Jul 29, 2006 8:54 pm

the synthesizers.com noise source is definitely a stronger signal than the moogerfooger. according to the cp251 manual (see the tech specs at the end) the noise source puts out a signal between +- .6 volts, which would be about an octave and a quarter range. the output of the sample/hold, when internally patched to the noise source, is supposed to be +- 2 volts, which would give you a four octave range. so the mp3 file sounds about right. the synthesizers.com noise source will output a signal from 0 to 10 volts, which is about a 10 octave range. probably the easiest way to deal with the signal is to run it through a signal processor or instrument interface module on the modular system.