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Attenuating Buchla CV's, resistor values needed.

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Attenuating Buchla CV's, resistor values needed.

Postby Arpangel » Sat Oct 26, 2019 8:15 am

I want to reduce the level of Buchla LFO CV's, the outputs are too high for my Easel, just a very small amount of input makes a dramatic change. I want to make up some banana leads with in-line resistors, but don't know what values to start with, the voltage range for Buchla CV's is 0v > 10v.
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Re: Attenuating Buchla CV's, resistor values needed.

Postby ef37a » Sat Oct 26, 2019 8:55 am

Arpangel wrote:I want to reduce the level of Buchla LFO CV's, the outputs are too high for my Easel, just a very small amount of input makes a dramatic change. I want to make up some banana leads with in-line resistors, but don't know what values to start with, the voltage range for Buchla CV's is 0v > 10v.

To make up any attenuator you need to know the input load resistance and often the resistance of the source, which I suspect in this case are open collector drivers?

Folderol is probably your man.

Dave.
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Re: Attenuating Buchla CV's, resistor values needed.

Postby Arpangel » Sat Oct 26, 2019 9:08 am

ef37a wrote:
Arpangel wrote:I want to reduce the level of Buchla LFO CV's, the outputs are too high for my Easel, just a very small amount of input makes a dramatic change. I want to make up some banana leads with in-line resistors, but don't know what values to start with, the voltage range for Buchla CV's is 0v > 10v.

To make up any attenuator you need to know the input load resistance and often the resistance of the source, which I suspect in this case are open collector drivers?

Folderol is probably your man.

Dave.

Thanks, I'll try and find out the load and source resistances.
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Re: Attenuating Buchla CV's, resistor values needed.

Postby James Perrett » Sat Oct 26, 2019 2:17 pm

You could always use something like a 10k potentiometer to find the best setting, then measure the resistance from the wiper to each end and choose suitable fixed resistors to make a fixed attenuator.

The input signal and ground go to the outer pins on the potentiometer while the output is taken from the wiper and ground. I'll bet Hugh has a diagram somewhere.
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Re: Attenuating Buchla CV's, resistor values needed.

Postby resistorman » Sat Oct 26, 2019 4:48 pm

James Perrett wrote:You could always use something like a 10k potentiometer to find the best setting, then measure the resistance from the wiper to each end and choose suitable fixed resistors to make a fixed attenuator

Yes, you need two resistors to make a voltage divider, not just an inline resistor.
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Re: Attenuating Buchla CV's, resistor values needed.

Postby Hugh Robjohns » Sat Oct 26, 2019 5:28 pm

Image
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Re: Attenuating Buchla CV's, resistor values needed.

Postby Arpangel » Sun Oct 27, 2019 12:13 pm

Hugh Robjohns wrote:Image

I'll try and work out a good starting point using a pot as suggested, thanks Hugh for the diagram, I think I'll need to build this into a plug, but if there are two resistors involved do I split the ideal value between the two resistors? If the pot suggests 4k for instance do I use two 2k resistors?
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Re: Attenuating Buchla CV's, resistor values needed.

Postby Sam Spoons » Sun Oct 27, 2019 12:35 pm

Select the resistors by measuring the wiper to V in (signal) for R1 and wiper to ground for R2.

Looked at another way, if it's a 10k pot and it says 4k between the signal and wiper then R2 will be 6k
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Re: Attenuating Buchla CV's, resistor values needed.

Postby Martin Walker » Sun Oct 27, 2019 5:24 pm

Would some of these help Tony?

https://www.musicradar.com/reviews/tech ... ble-616225

Image

Basically a modular synth patch cable with an integral pot.


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Re: Attenuating Buchla CV's, resistor values needed.

Postby resistorman » Sun Oct 27, 2019 6:02 pm

Martin Walker wrote:Would some of these help Tony?

https://www.musicradar.com/reviews/tech ... ble-616225

Image

Basically a modular synth patch cable with an integral pot.


Martin

That’s pretty cool! The only thing is that the pot is likely to move over time, so if he wants something solid and repeatable, fixed resistors might be better. Of course there’s always super glue...
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Re: Attenuating Buchla CV's, resistor values needed.

Postby Arpangel » Mon Oct 28, 2019 8:28 am

Martin Walker wrote:Would some of these help Tony?

https://www.musicradar.com/reviews/tech ... ble-616225

Image

Basically a modular synth patch cable with an integral pot.


Martin

Thanks a lot Martin! This would save a lot of bother, but I'll still have to make up banana to mini jack leads, but that's not a big deal.
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