[sdiy] Multiplexed Expo Converter?

[JH.]

If you demultiplex an additional channel and use this with a known voltage you can build a servo loop that removes the drift. Again: 
Polysix.

JH.

----- Original Message ----- 
From: "cheater cheater" <cheater00 at gmail.com>
To: "synth-diy" <synth-diy at dropmix.xs4all.nl>
Sent: Monday, August 03, 2009 11:16 PM
Subject: Re: [sdiy] Multiplexed Expo Converter?


The transistor count doesn't really matter THAT much. For me the most
important thing is the coupled drifting - the voices might drift a
lot, but they won't drift *apart*.

D.

On Mon, Aug 3, 2009 at 9:24 PM, Tom Wiltshire<tom at electricdruid.net> wrote:
>
> On 3 Aug 2009, at 20:33, Ingo Debus wrote:
>
>>
>> Am 03.08.2009 um 05:06 schrieb David G. Dixon:
>>
>>> Oh, I get it! The multiplexing is on the input side of the EC (the CVs),
>>> not the output side. My bad!
>>
>> Hm, as I understand it, a muxed expo converter is used in a polyphonic
>> synth; with one expo converter driving several VCOs. So the signal flow is:
>> Voice assigner (DAC) -> expo converter -> mux -> S&H (several) -> linear
>> VCO (several).
>>
>> So the multiplexing is done on the output side of the expo converter, no?
>
> No, it's *de*multiplexing that's done on the output side of the expo
> convertor. The DAC signal is multiplexed, and passes through the expo
> convertor like that. It's then demultiplexed to give you back the multiple
> signals it represents. That way you only need one expo convertor with
> expensive matched transistors, not lots. It's a very neat idea.
>
> T.
>
>
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