As far as the attenuators are concerned (on new one with white circles around inputs), I use a powered cv pedal, does this just add 5v to whatever voltage I have selected on the pedal if attenuator turned full clockwise? I am trying to increase the range of the pedal, any ideas?
No, it won’t go over 5V, it is an attenuator not an amplifier.
If you need more juice, patch through the mixer and add an offset voltage.
I feel stupid, but if it attenuates, why is there a + voltage on the knob? What is the difference between active and passive attenuation? The manual is lacking in the explanation of this. Also, how can you raise the amplitude of a CV? Is this analogous to the mod wheel on a mini? Can anyone direct me to some literature that explains this stuff?
I’m guessing, but it’s probably called an “active attenuator” because the CV goes through an op amp, and not just a pot as would be the case for a passive attenuator. This is how the negative/inverted signal would be generated. In this respect, you could mod it to produce gain. This is done by varying the resistance in the feedback loop
Again, I don’t know for sure, but the mod wheels probably are attenuating a voltage not amplifying it.
Here’s some wikipedia circuit diagrams under Op Amp. First one is non-inverting, second is inverting.
The + and - are reference to ground. You can invert a signal and drive your target source higher or lower. But since it is an attenuator it can’t ADD to the signal. If you have a 3V CV signal you can use the attenuator to set the signal anywhere between -3 to +3 volts. Passive attenuation can not invert the signal, only atteniate it.
The mixer is a summing mixer and you can use it to add (offset) to the CV signal. Eg: You have a -5 to+5V sine LFO signal you want to open and close a filter from your base setting. If you use it as is it will push the filter open the +5 volts and then close it below the baseline the same amount. You can use the mixer to offset the CV signal up 5 volts and now it will open and close the filter from the baseline up 10V and back. You can then attenuate the signal to 5V so it opens the filter from baseline to +5 and back.
Clear as mud?
okay, thanks, this gives me an idea of what is going on. from what people were saying sometime before, the newer cp’s with the white circles had active attenuators, and the manual was not changed. So I want to increase the range of the pedal controlling the cutoff, I would just add an offset voltage, right? Since my pedal is only 0 to +5, it would go from 0 to 5+ the offset voltage, right, or is it possible to go lower than 0?
Adding an offset will only adjust the centre-point of the waveform. If you have a 5V peak-to-peak LFO centred at 0V, the range is -2.5 to 2.5V. Adding a 5V offset will push the range to 2.5 to 7.5 volts. Because no gain has been applied to the waveform itself, the “LFO amount” remains the same.
The CP-251’s mixer has powered sockets, meaning you can plug a passive (non-powered) expression pedal in to generate your 0-5V. Adding an offset will again change the range only, to 5-10V.
Can I ask what you are trying to control with your 10V signal?
I’ve read that again, MF-101 cutoff? Or another manufacturer?
I can’t quite understand your question, but with a -5V offset, your CV pedal would go from -5 to 0 Volts.
no, the expression pedal controlling the cutoff of the mini. I like where the baseline is, I just would like to increase the “highline” as it were, or increase the whole range and and just turn up the cutoff knob on the mini. I guess I understand the CP mostly for an LFO wave, but I can’t wrap my head around how it applies to a manual pedal CV.
If you need to boost a signal run it into the mult and run 2 or more patch cables to the cv mixer
That’s what I was thinking! There’s even a file on KnobTweak:
http://launch.groups.yahoo.com/group/KnobTweak/
files >> Moogerfoogers >> CP-251 Control Processor >> Voltage Booster
The CP-251 is worth it for many, many reasons. If you’re on the fence about getting one, you won’t regret the decision after it arrives and you play with it.