When patching to CV inputs on Ciat-Lonbarde instruments (Cocoquantus, Plumbutter, Sidrax) it can be useful to add some attenuating ability. For example, if I want to control the frequency of a Sidrax oscillator from a Castle output of Cocoquantus, I want to vary the depth of modulation. There’s no attenuator on the CV input. Hence: Inline Attenuator in a small box with two banana jacks.
The little box comes from Small Bear Electronics, part number 1090NS.
This is not a potentiometer, i.e. there is no ground connection. It is simply an inline variable resistor. It also works well for patching a CV coming out of the modular into a Ciat-Lonbarde instrument. The CV inputs on Ciat-Lonbarde are very high impedance (often 1M ohms). And they expect a relatively high output impedance (10K ohms) to drive them. If you patch a very low impedance CV (like the 1K standard for modulars) or a pot with a grounded end, the current is pulled down so much that control can be ineffective. So here I have used a 1M audio taper pot as a series resistor. It can go down to zero resistance. It’s wired so that as the knob is turned clockwise, the resistance decreases. Full anti-clockwise does not shut off the CV, but only maximizes the inline resistance to 1M.
Thanks for the detailed information (as always!)
I’ve finally got a couple of 1M pots (B curve) and tried to do the same thing. It did attenuate but even with a full rotation of the pod it leaked a lot and no where to shut the cv off… Could this be the cheap pots I got are poor quality? Sorry I’m so infant to this. I have only analog ohm meter and tried to measure the max resistance and it showed about 1.5M (not even sure if it’s correct)
Hi hajimmie. These are not pots, but inline variable resistors. That is, they are NOT supposed to shut off. The resistance varies from zero (maximum signal) to whatever the pot value is. The amount of attenuation you’ll see depends on the resistance of the circuit nodes they’re connected between. They are intended for use with Ciat-Lonbarde gear.
Hi Richard,
Thank you for your response! I think I understand that this is an inline variable resistor. And for CL gears. I wanted to attenuate cvs from AvDog, Gongs, Quantussy, and etc especially for Sidrax main pitch/chaos inputs. Also for AM inputs of coco and all.
So, is 1M not enough for those signals to attenuate to near flat? I thought I could attenuate say a triangle wave from Sidrax osc to near constant voltage.. is this not how this inline resister works?
Nope, 1M will not attenuate to zero, because it goes in series with a 100K resistor on most of the CL CV inputs. This would reduce the effect to about 1/10 compared to no attenuation. Some CV inputs have a 470K resistor internally, when means that adding 1M would reduce the effect only to 1/3.
As mentioned above, CL CV inputs want a higher impedance driving them, because they respond to the CV as current sources AND sinks. This means that putting a low impedance zero volt connection (like a ground) will still have an effect, not zero effect. Try patching from the ground jack into a CV input to see what I mean. This is why we don’t want a pot that has one end grounded. Likewise, patching from a normal low-impedance modular output will not behave as it does when connected to another module.
Thanks a lot for the detailed explanation, really appreciated, educated!
So it is indeed much more involved than what I imagined like doing simply shutting of a faucet.. input resistance has to be take into account.
So it seems making an attenuater which can reduce to near zero (for various inputs of CL) would be much more complicated..
The simplest way to reduce a CV to zero on Ciat-Lonbarde is to unpatch it. 🙂
If you look at the Plumbutter schematics (Labrolzpaperz.pdf) you find that there are two kinds of CV input jacks, purple and blue. The purple ones have an attenuverter with them, which can reduce the effect to almost zero when centered. The blue ones, VER and INV, have no attenuation. The design of the PB is such that attenuation is not needed for most patches.
ah yes, I’m happy working within PB mostly. However I have always wanted an attenuate signal for master pitch of Sidrax from the day one 😉 for subtle vivrato effect. I wonder why those two grey inputs didn’t have attenuaters! Coco’s blue AM inputs would also benefit from much attenuated CV from quantussy.