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 Post subject: How does this work?
PostPosted: Fri Mar 18, 2022 12:45 pm 
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This is the clipping section from the Mouse documentation:

Attachment:
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Just trying to get my head around how this works. It looks like the LEDs are always connected to the circuit. When the switch is in one of the "on" positions, is it just counting on the Si and Ge [aren't they Schottkys?] diodes kicking in before the LEDs, thereby making the LEDs irrelevant?


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 Post subject: Re: How does this work?
PostPosted: Fri Mar 18, 2022 1:16 pm 
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The way I like to think about signal clipping is to consider the signal like flowing water and the clipping diodes like dams in the signal path. When the water level is high enough, it overflows the dam. So when the signal level exceeds the diode voltage threshold, it overflows and is lost to ground.

In this case, there are three diode "dams" and their relative heights are equal to their respective forward voltage thresholds--the LEDs are the highest at 1.5V or more; the silicons are about 0.6V and the Ge's about 0.3V. The signal path is like a channel carrying the water and the LED's are in this main channel, i.e. always active. The on-off-on switch serves to open one or the other of two additional channels, one with the silicons and the other with the Ge's. As soon as one of those channels is open, the "water" spills over that new dam instead of the LED dam, because the new dam is much lower. So the signal magnitude can no longer reach the threshold of the LED dam, and no further clipping occurs over it, despite that dam still being accessible through the main channel--the signal "overflows" exclusively at the lower Si or Ge dam, depending upon which side of the switch is engaged.

This also explains why the signal output volume varies between the different diode clippers. The lower the "dam" (voltage threshold), the more "water" (signal) is lost over it, so the magnitude of the remaining signal is reduced to a greater extent.

Hope that illustration helps....

P.S. No, germanium and Schottky diodes are different, though both have very low voltage thresholds.

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 Post subject: Re: How does this work?
PostPosted: Fri Mar 18, 2022 1:32 pm 
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I was typing this when I noticed that DVM had already posted an answer, but I figured I post it anyway.

As DVM says, the LEDs are always in the circuit. With the switch off the signal can only get to the LEDs which have voltage threshold of around 1.5-1.7V.

When you activate the switch to the 1N4148 Silicone diodes, they have a voltage threshold of around 0.68V. Since this voltage is lower than the LEDs voltage, the signal never gets to the LEDs.

This is also true for the Germanium Diodes with a forward voltage of around 0.33V. Once again the signal never gets to the LEDs.

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 Post subject: Re: How does this work?
PostPosted: Fri Mar 18, 2022 2:00 pm 
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Cool, thanks. That's pretty much what I was imagining.

I do know that Germaniums and Schottkys are different, I was just surprised to see Ge in the schematic since the text description talks about Schottkys.

Quote:
It also has a 3-way clipping switch. It has silicon clipping, like the original Vintage RAT, LED clipping like the Turbo RAT, and Schottky diode clipping for an even more saturated "fuzzy" RAT sound.


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