single passive attenuator for idiots

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Cybananna
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single passive attenuator for idiots

Post by Cybananna » Sat Nov 01, 2008 10:39 pm

I want to make a few of these. I want just a simple single passive attenuator for audio or CV attenuation. I found some stuff on the Doepfer website that appears to be what I want, that is extremely simple. Am I correct that you just wire an input jack and an output jack to a pot (like a 50k log for example)?

Is it really that easy? no other resistors needed? :hyper:

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Post by thermionicjunky » Sat Nov 01, 2008 10:47 pm

Yes, it's that easy.

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Post by Cybananna » Sat Nov 01, 2008 10:57 pm

thanks for the reply! :party:

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Post by DGTom » Sun Nov 02, 2008 2:23 am

Thanks from this DIY idiot to both of you, thats exactally what I was looking for!

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Re: single passive attenuator for idiots

Post by governor blacksnake » Sun Nov 02, 2008 5:11 am

Cybananna wrote:I want to make a few of these. I want just a simple single passive attenuator for audio or CV attenuation. I found some stuff on the Doepfer website that appears to be what I want, that is extremely simple. Am I correct that you just wire an input jack and an output jack to a pot (like a 50k log for example)?

Is it really that easy? no other resistors needed? :hyper:
input jack to one side, output to middle, ground to the other side

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Post by fluxmonkey » Sun Nov 02, 2008 1:02 pm

Image

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Post by Cybananna » Sun Nov 02, 2008 2:25 pm

Thanks again everyone for all the good info. I've done several Blacet kits and am stepping more into DIY, starting with a simple utility box. A few passive attens, mults, and some 1/8 to 1/4 conversion jacks.

gotta start somewhere right! :hihi:

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Post by fonik » Mon Nov 03, 2008 2:11 am

if you add a 10k resistor from the 100k potentiometers wiper to ground you can modifiy a linear potentiometer to act like an logarithmic one. that's quite nice for audio, i use it for control voltages, too.
http://www.elby-designs.com/documents/t ... meters.pdf
http://www.mindspring.com/~clist/PotGraph.html
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Post by felix » Mon Nov 03, 2008 2:37 am

fonik wrote:if you add a 10k resistor from the 100k potentiometers wiper to ground you can modifiy a linear potentiometer to act like an logarithmic one. that's quite nice for audio, i use it for control voltages, too.
http://www.elby-designs.com/documents/t ... meters.pdf
http://www.mindspring.com/~clist/PotGraph.html
Wow, hot tip!!! Of all the basic books and sites I've read, none of them have ever mentioned such a thing. Very cool to know.

Does the same apply to other size pots? Is it simply a 1:10 ratio? For example, a 1k resistor on a 10k pot?
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Post by fonik » Mon Nov 03, 2008 4:53 pm

felix wrote:Does the same apply to other size pots? Is it simply a 1:10 ratio? For example, a 1k resistor on a 10k pot?
certainly, it does. :grin:
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Post by A Dingleberry Monstrosity » Thu Nov 06, 2008 1:20 am

welcome to freshman electrical engineering :guinness:

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Post by slow_riot » Sat Jul 30, 2011 6:22 pm

will a passive attenuator work in both directions? or just input... attenuate... output ?

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Post by 10011001 » Sat Jul 30, 2011 6:45 pm

thank you everybody :tu:

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Post by daverj » Sat Jul 30, 2011 9:01 pm

slow_riot wrote:will a passive attenuator work in both directions? or just input... attenuate... output ?
What do you mean by "both directions"?

You can't connect an attenuator in reverse. If you connect the output of a module into the output of an attenuator then when you turn the attenuator down you will short circuit the module's output to ground.

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Post by slow_riot » Sat Jul 30, 2011 9:54 pm

yep that's how I meant, should have enagaged my brain and looked harder before asking the question! the answer is pretty obvious now you mention in.

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Post by intellijel » Sun Jul 31, 2011 12:52 pm

fonik wrote:if you add a 10k resistor from the 100k potentiometers wiper to ground you can modifiy a linear potentiometer to act like an logarithmic one. that's quite nice for audio, i use it for control voltages, too.
http://www.elby-designs.com/documents/t ... meters.pdf
http://www.mindspring.com/~clist/PotGraph.html
this is exactly what I did on the Intellijel uATT module. There is a jumper to select whether this resistor from the wiper to ground is connected.

Good article here:
http://www.geofex.com/article_folders/p ... tscret.htm

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Post by GeoffC » Tue Aug 02, 2011 5:53 pm

Thanks for those links.

However I think I will click on the link to "potsecret.htm" from home, not here at work.

:doh:

Geoff

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Post by Just me » Tue Aug 02, 2011 7:05 pm

You might want to look at these.

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Post by ersatzplanet » Wed Aug 03, 2011 1:11 pm

On our passive Slide pot modules (Synthwerks SP-1P) we also add a 1K resistor in line between the wiper of the pot and its jack. This prevents a total short from ever happening. Just as a safety measure. The SP-1P has the other legs of the pot normalized to ground though to act as a attenuator. The added resistor keeps the wiper from ever producing a direct short to any modules down stream.
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Post by nuketifromorbit » Thu Aug 04, 2011 11:01 am

I've got a broken rolls line mixer I want to salvage pots from. Anyway the pots in the mixer are 100k and I'm guessing stereo since they have six connectors rather than three. Can I still use these to build passive attenuators?

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Post by jimboburgess » Fri Feb 24, 2017 4:08 pm

nuketifromorbit wrote:I've got a broken rolls line mixer I want to salvage pots from. Anyway the pots in the mixer are 100k and I'm guessing stereo since they have six connectors rather than three. Can I still use these to build passive attenuators?
yup, just use only one side on the pots

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Post by 21hertz » Fri Apr 21, 2017 5:58 am

I'm trying to make my own attenuators for CV purposes.
I have tried three different pots, Alpha A50k, B50k and B100k.

NONE of them goes down to zero, if connect a LFO (0-10v) the pots only attenuates by maybe 25-50% when having the pot full CCW.

I have read somewhere that 50k or 100k should be fine. I don't get why 50k och 100k works for other people. I suspect that I have to get a 500k to make this work. Any insights?

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Post by PWM » Fri Apr 21, 2017 6:41 am

21hertz the problem doesn't lie in the overall resistance of the potentiometer. When connected properly there should be no resistance between CCW and W when the pot is turned all the way CCW.
Try measuring your pots.

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Post by ersatzplanet » Fri Apr 21, 2017 9:49 am

The important thing in the passive attenuation is the connection to Ground. Without that connection, the pot's resistance will probably not be enough for the level of signals in a modular. I find the Doepfer DIY page is a good resource for simple circuits like these. Here is what he suggest for an attenuator.

Image

The important bit is as you can see, the output is shorted to ground when fully attenuated. The input of the connected module will have protection resistors so don't worry (to be safe you can add a 1k resistor after the pot). With this circuit, there is no way signal will pass.
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Post by PWM » Fri Apr 21, 2017 1:06 pm

ersatzplanet wrote:The important thing in the passive attenuation is the connection to Ground. Without that connection, the pot's resistance will probably not be enough for the level of signals in a modular. I find the Doepfer DIY page is a good resource for simple circuits like these. Here is what he suggest for an attenuator.

Image

The important bit is as you can see, the output is shorted to ground when fully attenuated. The input of the connected module will have protection resistors so don't worry (to be safe you can add a 1k resistor after the pot). With this circuit, there is no way signal will pass.

What I was trying to explain done properly...

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