low range of S&H on CP 251?

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deadhedgehog
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low range of S&H on CP 251?

Post by deadhedgehog » Fri Mar 18, 2016 10:46 am

Hi

I get a much smaller range when using the unattenuated S&H from CP251 on a freqbox osc out than on 101 cutoff. But in both cases the range is less than one might expect. On the freqbox the pitch varies by about a minor 3rd at most.

Is this normal or have I got power issues?

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GregAE
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Re: low range of S&H on CP 251?

Post by GregAE » Sat Mar 19, 2016 7:15 am

The most likely explanation is that it has to be due to the different tracking parameters in the respective devices, i.e. X Volts/oct, not a power problem with either device.

If you want more range from the S&H, plug the output into a Mult and then route two (or three) copies into the Four-Input Mixer. This will double (or triple) the S&H signal. You can then adjust the overall range using the Mixer's Master control, and raise/lower the base frequency voltage with the Offset control.

Try it! :D

deadhedgehog
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Re: low range of S&H on CP 251?

Post by deadhedgehog » Sat Mar 19, 2016 8:52 am

Thanks so much for the reply Greg. It was strange because I found the output from the S&H was surprisingly small, especially considering the range of the other waves.

I tried routing multiple copies of the S&H to the mixer, and oddly it didn't do much. In fact, the chief result of sending more copies, or of increasing the master knob on the mixer, was to make the overall pitch go DOWN, without increasing the range of the voltage. But then, I tried sending the carrier out from the ringmod to the "in" of the S&H on the CP, and suddenly I was getting the results I had expected in the first place. The funny thing was that even after unplugging the carrier the CP S&H continued to behave more normally, but when the carrier is plugged into the "in", the range is greater.

Both my CPs were showing this small range on the output of the S&H, but after having "Doctor" carrier plugged into their ins, both reverted to what I would consider normal behaviour.

I'm happy that it seems to work now. But do you have any theory on what was the cause? To be honest I still don't 100% understand what the S&H "in" does.

Much appreciation for any help

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GregAE
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Re: low range of S&H on CP 251?

Post by GregAE » Sat Mar 19, 2016 11:28 am

deadhedgehog wrote:To be honest I still don't 100% understand what the S&H "in" does.
By default, the S&H circuit in the CP-251 normally takes it's input from the Noise source (the jack just to the left of S&H IN). If you plug something into the IN jack, it bypasses the Noise and connects to whatever signal appears at the input. Since Noise is a constantly varying signal, the output of the S&H will always be random, but if you were to input an LFO Triangle wave set to a very slow rate, the S&H output would be a series of stepped voltages that follow the rise and fall of the LFO wave.

One other thing you could try is to mult the Noise and route copies into the Mixer, then feed the Mixer OUT into the S&H IN. The boosted noise signal should give you a wider S&H range.

hellomikmik
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Re: low range of S&H on CP 251?

Post by hellomikmik » Sun Mar 20, 2016 6:21 pm

deadhedgehog wrote:I get a much smaller range when using the unattenuated S&H from CP251 on a freqbox osc out than on 101 cutoff. But in both cases the range is less than one might expect. On the freqbox the pitch varies by about a minor 3rd at most.
I think that osc out on freqbox is output (not input) so you are not supposed to plug in there S&H output.
Minitaur / DSI Mopho KB SE / 2xMF Delay / CP-251 / Roland SBX-1 / Pigtronix Dual Expression Pedal

deadhedgehog
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Re: low range of S&H on CP 251?

Post by deadhedgehog » Mon Mar 21, 2016 4:39 am

Thanks Greg.

hellomikmik: I plugged the S&H into the freq input, and the osc out, er, out. No problems there

Bryan B
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Re: low range of S&H on CP 251?

Post by Bryan B » Tue Mar 22, 2016 8:41 am

If you are using the filtered/smoothed S&H output (can't remember if that is 1 or 2), the LFO rate affects the filter frequency (they are internally connected). You may want to check out the manual for more specifics as this is just from my faulty memory.
MemoryMoog Plus (with Kenton Midi Upgrade Kit) MF-101 Lowpass Filter, MF-102 Ring Mod, MF-103 Stage Phaser, MF104M Delay, MF-105M MIDI MuRF, MF-107 Freq Box, MF-108M ClusterFlux and CP-251 Control Processor.

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Re: low range of S&H on CP 251?

Post by Bryan B » Tue Mar 22, 2016 12:10 pm

Update: I found the S&H description (of what I was referring to in the previous post) to give you better information. It is on page 13 and 14 of the CP-251 PDF manual.

"In addition, the OUT 1 signal is fed through a special lowpass filter which smooths the signal out and then delivers it to the OUT 2 jack. The cutoff frequency of the special lowpass filter is directly related to the LFO rate, so turning the LFO RATE knob affects how smooth the OUT 2 waveform is.

When no patch cord is plugged into the IN jack, the NOISE waveform is bridged to this jack. When no patch cord is plugged into the TRIG jack, the LFO square waveform is bridged to this jack."

I bet if you ran a VCO square wave to the trig in, you could get a bitcrusher effect on the output and then use the LFO rate as a cutoff frequency for the filtered 2nd output. Fun! I need to try this soon.
MemoryMoog Plus (with Kenton Midi Upgrade Kit) MF-101 Lowpass Filter, MF-102 Ring Mod, MF-103 Stage Phaser, MF104M Delay, MF-105M MIDI MuRF, MF-107 Freq Box, MF-108M ClusterFlux and CP-251 Control Processor.

Bryan B
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Re: low range of S&H on CP 251?

Post by Bryan B » Tue Mar 22, 2016 12:18 pm

Under Technical Information (page 25) there is a little more information too:

"Nominal input resistance at the IN jack is 10KW. Nominal voltage range which this input will sample is ±3 volts.

Nominal input resistance at the TRIG jack is 10KW. Triggering occurs when the voltage at the TRIG jack descends through the +1 volt nominal trigger threshold.

Nominal input-to-output gain is unity. If the noise source is sampled, then the output waveform appearing at OUT 1 is about ±2 volts peak-to-peak. In between samples, the maximum output voltage drift rate is no more than 0.1 millivolt per second.

The nominal input-to-output gain from the IN jack to the OUT 2 jack is X2.

A two-pole direct-coupled lowpass filter is placed between OUT 1 and OUT 2. The cutoff frequency of this filter is proportional to the LFO frequency. Thus it is possible to voltage-control this filter, and to set its cutoff frequency to as low as a small fraction of 1 Hz."
MemoryMoog Plus (with Kenton Midi Upgrade Kit) MF-101 Lowpass Filter, MF-102 Ring Mod, MF-103 Stage Phaser, MF104M Delay, MF-105M MIDI MuRF, MF-107 Freq Box, MF-108M ClusterFlux and CP-251 Control Processor.

deadhedgehog
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Re: low range of S&H on CP 251?

Post by deadhedgehog » Wed Mar 23, 2016 11:05 am

Thanks for your replies Bryan.

This is an interesting thread and I did some investigation of the behaviour of the CP's sample and hold module.

Set-up: CP S&H modulates cut-off of self-resonating filter on 101. I have 2 cps and I include the results with each.

Direct modulation of 101 cut-off, S&H output 1: Pitch varies within about an octave
S&H output 2: smooth swoops, as expected, similar pitch changes

When 102 carrier out to S&H in, outputs 1 and 2: pitch variation of filter increases considerably, circling around the pitch of the input carrier from the 102

BUT on the second module:

Direct modulation of cut-off, CP(2), S&H output 1: Pitch drops by almost an octave, pitch varies within max 2 semitones
Same setup, output 2: pitch drops by more than 2 octaves, little variation in pitch

However when plugging the carrier from the 102 into the S&H input, the results are similar to those with the first unit, with a wide range of pitches from the output 1, but an EXTREMELY wide range of frequencies from output 2, covering the entire audible range.


It looks like unit 2 is behaving strangely. Any thoughts? Could there be a problem with the circuit sending the noise circuit to the module?

hellomikmik
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Re: low range of S&H on CP 251?

Post by hellomikmik » Thu Mar 24, 2016 8:12 am

deadhedgehog wrote:It looks like unit 2 is behaving strangely. Any thoughts? Could there be a problem with the circuit sending the noise circuit to the module?
Hi again, as I understand it:
1/ S&H is sampling, in terms of voltage, what you feed into it (output is 1X for OUT1 and 2X for OUT2). Moog usually mentions what is the voltage of outputs on their units in respective manuals but I think there is no info about 102's VCO OUT.

2/ CP's Noise output is +-0.6V, however when it's fed internally to S&H (so nothing plugged into IN) the S&H OUT1 is giving +-2V. I suppose there is something inserted into Noise and S&H internal connection amplifying the signal. Try to compare OUT1 without anything plugged into IN vs OUT1 with cable going from NOISE directly to IN to see what I mean.

Your problem might be related to that amplifying part or the noise source itself. I suppose you had the frequency (LFO rate) same on both units when you were testing them.

As you have 2 units you can are kind of lucky as you can compare them and use noise from A to feed into B, etc... to see what happens.
Minitaur / DSI Mopho KB SE / 2xMF Delay / CP-251 / Roland SBX-1 / Pigtronix Dual Expression Pedal

Bryan B
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Re: low range of S&H on CP 251?

Post by Bryan B » Thu Mar 24, 2016 11:30 am

When you say unit 1 and unit 2, I am assuming you have 2 different CP-251s and they both have different results from each other. Is that correct? If that is correct, I would say the problem is internal (callibration or even just different components). I have read on here that Freqboxes are not callibrated very tight to the v/oct, so each one is slightly different in frequency response. I imagine the same might be true with CP-251s. There are probably a couple trimmers on the PCB to adjust the hi and low range. Even different opamps could throw the results off a little. These are all just guesses, I am not a Moog tech by any means.
MemoryMoog Plus (with Kenton Midi Upgrade Kit) MF-101 Lowpass Filter, MF-102 Ring Mod, MF-103 Stage Phaser, MF104M Delay, MF-105M MIDI MuRF, MF-107 Freq Box, MF-108M ClusterFlux and CP-251 Control Processor.

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