[sdiy] Something better than CD4066 to switch CVs?

Ullrich Peter Peter.Ullrich at kapsch.net
Tue Feb 19 21:30:49 CET 2019


If the ON resistance is a problem you could spend some money and use better analog switches that have a resistance downto 0.35 ohms!
I used Maxim types in the 1 ohm range in one of my projects. Some of them even have a +/- 25V signal range...

See www.maximintegrated.com for analog switches and multiplexers if you are interested.

Von: Synth-diy <synth-diy-bounces at synth-diy.org> im Auftrag von Tim Ressel <timr at circuitabbey.com>
Gesendet: Dienstag, 19. Februar 2019 20:16
An: synth-diy at synth-diy.org
Betreff: Re: [sdiy] Something better than CD4066 to switch CVs?

This is a good point. In general any resistance in series with a v/oct
vco input will introduce a tracking error. This is why things that drive
vco inputs have to be designed carefully. Assuming 100K input resistance
on the vco input (seems to be the standard) and 3 cent max error allowed
(@ 10 volts), 25 ohms is the max added resistance allowed. This can
loosen up if tracking to 10 volts isn't important.


On 2/19/2019 10:09 AM, chris wrote:
> On Tue, 19 Feb 2019 18:35:44 +0100 Florian Anwander <fanwander at mnet-online.de> wrote:
>> Am 19.02.19 um 11:06 schrieb Tom Wiltshire:
>>> The Prophet 5 managed to switch Oscillator B into low frequency mode about thirty years ago, so it must be possible.
>>> I had a look at the schematic and it doesn’t look like they switch an extra cap in though. Instead they switch an extra -15V into the CV. The Pro-1 uses the same trick.
>> Someone more knowledged may correct me, but I think this may work with a
>> coarse parameter change, but with tracking sensitive controls, the inner
>> resistance of the 4066 might become an influence.
>> Florian
> But once you're entering LFO range, IMHO tracking becomes less important.
> And I don't think an *open* switch will affect audio tracking.
> I agree that using a CMOS switch in tracking relevant areas requires at
> least some consideration. Switch resistance may be specified as foggy as
> "yes, it's there, and it's something around ^&@&%* ohms at room
> temperature".
> Christian
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--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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