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 Forum index » DIY Hardware and Software
Attenuverters on every CV input
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neandrewthal



Joined: May 11, 2007
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PostPosted: Tue Nov 20, 2007 3:18 pm    Post subject: Attenuverters on every CV input Reply with quote  Mark this post and the followings unread

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

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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?
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fonik



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PostPosted: Tue Nov 20, 2007 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.


AaronCram_Attnv.jpg
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AaronCram_Attnv.jpg



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Funky40



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PostPosted: Tue Nov 20, 2007 5:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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

It needs power if you mean that .... Wink ( the OP Amps allways need power : 1x per IC ))
V+ and V- and 1-2 Caps ( afaik: 100NF) from V+ to ground and V- to ground ( or just one between V+ and V- )


I got this schematic once from serenadi.
You see he use 100-470 R for the output.
most People seems to use 1k for the output resistor


pic3.jpg
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Inverter. R1 must be = R2 for no amplifying. As shown it has an amplyfing factor of 10x
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frijitz



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PostPosted: Tue Nov 20, 2007 6:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

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. Rolling Eyes

Very Happy

Ian
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Scott Stites
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PostPosted: Tue Nov 20, 2007 6:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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

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neandrewthal



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PostPosted: Tue Nov 20, 2007 6:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

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?
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fonik



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PostPosted: Tue Nov 20, 2007 11:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
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.

you are right, ian. and that's actually the method i used for the attenuverting mixer Shocked . i just added a trimmer for calibration...

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frijitz



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PostPosted: Wed Nov 21, 2007 5:52 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
you are right, ian. and that's actually the method i used for the attenuverting mixer Shocked . i just added a trimmer for calibration...

Right, I noticed that. And sure, if you use a center detent pot you may want a trimmer. But most of the time if you want zero you can just unplug the input. Very Happy

Ian
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v-un-v
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PostPosted: Wed Nov 21, 2007 6:22 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
Good grief, why are these all so complicated? The one given here:


I really dislike embedded links- too many windows! Shocked

here;


attenuverter.png
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ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
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frijitz



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PostPosted: Wed Nov 21, 2007 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

v-un-v wrote:
I really dislike embedded links- too many windows! Shocked

OK, but you did it wrong. The 220k at the far right is part of the circuit being controlled and will be different for different applications.

Very Happy

Ian
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fonik



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PostPosted: Wed Nov 21, 2007 7:08 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
...most of the time if you want zero you can just unplug the input. Very Happy

speaking words of wisdom.

i tried center detent pots and i don't like them. the center detent is not sharp enough IMO and it is not precise (at least the alps and the alphas ia had on hand). as soon as you touch it the resistance would change slightly. to prevent this diodes from/to the wiper would create an "voltage hole" which i found undesirable too.

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v-un-v
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PostPosted: Wed Nov 21, 2007 7:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Embarassed

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

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

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DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
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frijitz



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PostPosted: Wed Nov 21, 2007 7:44 am    Post subject: Reply with quote  Mark this post and the followings unread

v-

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

Very Happy

Ian
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Etaoin



Joined: Jun 30, 2005
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PostPosted: Wed Nov 21, 2007 7:45 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
i tried center detent pots and i don't like them. the center detent is not sharp enough IMO and it is not precise (at least the alps and the alphas ia had on hand). as soon as you touch it the resistance would change slightly. to prevent this diodes from/to the wiper would create an "voltage hole" which i found undesirable too.


Have you tried centre tapped pots? Even if you don't use the tap, the tap itself is a small area with no resistance, so once it's on the tap it won't change with small amounts of movement.

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fonik



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PostPosted: Wed Nov 21, 2007 8:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Etaoin wrote:
fonik wrote:
i tried center detent pots and i don't like them. the center detent is not sharp enough IMO and it is not precise (at least the alps and the alphas ia had on hand). as soon as you touch it the resistance would change slightly. to prevent this diodes from/to the wiper would create an "voltage hole" which i found undesirable too.


Have you tried centre tapped pots? Even if you don't use the tap, the tap itself is a small area with no resistance, so once it's on the tap it won't change with small amounts of movement.

do you know a good source for center tapped alphas? i would give them a try.

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Etaoin



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PostPosted: Wed Nov 21, 2007 8:03 am    Post subject: Reply with quote  Mark this post and the followings unread

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

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Etaoin



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PostPosted: Wed Nov 21, 2007 1:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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Tim Servo



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PostPosted: Wed Nov 21, 2007 6:02 pm    Post subject:
Subject description: Center tapped pots
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Etaoin wrote:
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


I'm pretty sure that was Tom Arnold on the SDIY list

xyzzy | at | sysabend | dot | org

He had a bunch of 50k center-tapped alphas that he special ordered. Dunno if he still has some, but he ordered a whole buncha buncha of them so it might be worth giving him a shout. I bought 20 or so myself, but I've yet to use them Embarassed

Tim (they're #437 on the 'DIY to-do list') Servo

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fonik



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PostPosted: Wed Nov 21, 2007 11:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Etaoin wrote:
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.

thank, etaoin. i will give them a try nevertheless.

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PostPosted: Thu Nov 22, 2007 12:09 am    Post subject:
Subject description: Center tapped pots
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Quote:
I bought 20 or so myself, but I've yet to use them Embarassed


Which sounds awfully familiar...


Tim (they're #437 on the 'DIY to-do list') Servo

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Etaoin



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PostPosted: Thu Nov 22, 2007 12:47 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
thank, etaoin. i will give them a try nevertheless.


If he still has them but you want to try one before you order a whole bunch of them, I will send you one.

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loopcycle



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PostPosted: Sat Jul 02, 2011 9:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for this conversation, bump for super useful info Very Happy
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mickey76



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PostPosted: Fri Aug 26, 2011 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

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?
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Dave Kendall



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PostPosted: Fri Aug 26, 2011 4:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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mickey76



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PostPosted: Fri Aug 26, 2011 5:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks!
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