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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Analog Switch Matrix questions
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macumbista



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PostPosted: Mon Aug 26, 2013 3:55 pm    Post subject: Analog Switch Matrix questions Reply with quote  Mark this post and the followings unread

I'm trying to wrap my head around the Analog Switch Matrix schematic:

http://www.cgs.synth.net/modules/cgs55_asm.html

I understand the the 4066 CMOS switch cannot handle negative voltages, and that is why there are reverse-biased diodes before and after it. However, wouldn't that remove the negative component of any bipolar signal you sent through the module?

I am looking for the place where the signal would get floated on a virtual ground, as in single-supply guitar pedal electronics for example, but I'm just not seeing it.

How does a bipolar signal pass through this module unaffected?

Thanks and best! D.

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PHOBoS



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PostPosted: Mon Aug 26, 2013 5:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm not seeing it either,. looks indeed like it only works with positive signals.
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macumbista



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PostPosted: Mon Aug 26, 2013 5:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

SOLVED!

Ken Stone wrote:

Quote:
The diodes only have any effect when the switches are open, so they can be
ignored.
When the switches are closed, both sides of the switch are connected to the
summing node, or "virtual ground" of the op-amp circuit, thus stay at zero
volts the whole time. From that point it is just a matter of understanding
the basic inverting op-amp summer circuit.

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PHOBoS



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PostPosted: Mon Aug 26, 2013 6:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

aha, I was allready wondering if the fact that the switch was placed between
the resistor and the opamp (instead of before the resistor) might have anything
to do with it. yeah that makes sense Very Happy (Now I need to remember it for future circuits)

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