Attenuverters on every CV input

[neandrewthal]

I am considering going the Serge route on my in progress modular and adding attenuverters to every CV input. This would be a fairly large undertaking so I have a few questions before I go ahead.

A search through the archives(gotta love this place) brought up a couple schematics, the most simple being this one:

http://www.buzzclick-music.com/inverter.jpg



Now on to the questions:

Does this circuit require any hidden power, that someone who isn`t a noob like me just assumes and knows?

What should the value of the resistor before the output be?

Is there any way I could use a 100k pot instead of 50k? I order these in large quantities since they are more commonly used in synths.

Does anyone have a PCB layout for something like this? I know Fonik has layouts for his attenuverting mixer and Buchlaesque voltage processor but that`s overkill for what I need.

If I decide not to go through with this, a dedicated attenuverter panel would be unnecessary since I would already have regular attenuators on every CV input, but I would have use for a few straight inverters. So what should I omit from that circuit to make it just two jacks, Input and Reverse Out?

In previous threads some stated that they don`t like this type of circuit because it cuts the control sweep in half and makes fine tuning too hard. I don`t know what kind of knobs and pots they were using, but do you think this would be a problem with 24mm pots and large MOTM style knobs?

[fonik]

for what you want aaron crams attenuverter circuit might be the right one.
just very few parts.
i implemented it on my forthcoming wasp vcf clone and it works fine. you may want to multiply the resistor values by 10 to have more common values. the 4.7k resistor should be replaced by a trimmer to be able to calibrate the center position of the potentiometer. the 10k should be matched if you are working with 1V/oct voltages.
i tried to open his apache project site but was not able to open it for now (maybe the site is down?). since he already published this circuit on the net it will be okay if i post it here, i guess.

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[Funky40]

i use to modify Filter Cv Inputs on my DIY Filters just with an Inverter,
and then wire it both ( non inverted input and the inverted signal )to a on-off-on switch.
in my Opinion this is much more useful than a attenuverter.
But that might be a thing of own taste.
But for groove generating it's no more a Thing of taste, IMHO

[frijitz]

Good grief, why are these all so complicated? The one given here:
http://electro-music.com/forum/topic-21851.html
(the modulation input circuit at the bottom) works fine.

Oh well, I just lost an argument with a guy who said he wanted a simple circuit and ended up using something three times as complicated as my design.

Go figure.



Ian

[Scott Stites]

Don't think I didn't spot that one, Ian .

I've been using that general design for years, though with different values. Rene Schmitz showed it to me; that one used a 1M pot and (IIRC 10K resistors(?). I used that for the longest time, then found that it didn't fully attenuate hard edged signals (at least that's what my scope told me). I then went to a 10K pot and I forget which resistor value, which got rid of the spikes, but I lost decent input impedance, so I killed the simplicity by buffering it with a 100K resistor/voltage follower. Thanks for sharing this - those values will get me back to the simplicity!

Cheers,
Scott

[neandrewthal]

Thanks a bunch guys, I'll definitely have to try those out when I get my order of op-amps in. About the power, which pin gets the + and which gets the -? Also, can I daisy chain the power from whatever module I'm using this with or do I need to run a new line from the distro board?

[fonik]

[frijitz]

[v-un-v]

[frijitz]

[fonik]

[v-un-v]

Sorry Ian It's not the first time I've fucked up either

But hey, its all part of life's little learning process!

[frijitz]

v-

Not a big deal, especially since the drawing makes it look like they go together.



Ian

[etaoin]

[fonik]

[etaoin]

I got a few from either someone on this forum or on the sdiy list a while ago. He ordered a huge amount directly from Alpha. I paid $0.80 per pot I think. I'll need to check whom I got them from.

[edit] mailed you

[etaoin]

On closer inspection the Alpha tapped ones I have don't seem to have the carbon-less mid-pot section I've seen on other pots.

[Tim Servo]

[fonik]

[etaoin]

[etaoin]

[loopcycle]

thanks for this conversation, bump for super useful info

[mickey76]

What am I missing here guys?
Why not just use a pot to ground to attenuate a cv in?
Why would one prefer the type of circuit proposed here?

[Dave Kendall]

Mickey76 - with an attenuverter, you can have negative values of the CV as well as positive, depending on which way you turn the knob. In the centre you get zero.

cheers,
Dave

[mickey76]

thanks!