Re: Covox Voice Master

From: Gerrit Heitsch <>
Date: Tue, 11 Oct 2016 19:34:45 +0200
Message-ID: <>
On 10/11/2016 06:10 PM, Jim Brain wrote:
> The SID POT ADC circuitry needs to drag the line hard to ground for 256
> cycles.  NMOS would easily handle this, but it must be a pretty hefty
> transistor to ensure it can overcome the current coming from the paddle
> resistor.  I don't see such a transistor on the 6581 die shots, but it
> must be there.  What should I look for?

When looking at

the paddle inputs should be the 2nd and 3rd pad from the bottom on the 
left side of the die. Between them is a mirrored structure which should 
be the measuring circuit.

Close to each pad, I can see something that looks like a transistor that 
connects the pad to the GND line. But it's a lot smaller than the 
drivers for the data pins.

The paddle resistors are 500K max, but I don't know what their minimum 
value is. The schematics suggest that it's zero, but that would be more 
than any NMOS driver can handle...


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Received on 2016-10-11 18:00:24

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