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Sili-Face II - Testing Some Mods

While I was off doing other projects, I was still at least pondering some mods to the Sili-Face fuzz.  And now I can try them out!

One item I was pondering is the name.  I need to give it a name.

When I first built it, I had the board wired up with no bypass switching - as a quick test to make sure it worked (which it did).  Now I need to wire it up with a bypass to see how much distortion/fuzz I get with different volume settings.  So I wired it up with a 3PDT and and LED, which you see in the picture.

This time I've decided to go with a white LED.  Actually kind of cool looking.  The dropping resistor is a 3K, and I may use an even higher value - it's a high-brightness LED and it's, well, really bright.

In the Sili-Face II circuit, there is a fixed amount of fuzz, which is set by the 1K resistor from the emitter of Q2 to ground, and the bypass capacitor, which is 4.7 uF.  When I had it wired up with no bypass, it seemed to me as if the amount of fuzz would go down or up with the setting of the volume control.  This is one reason I needed to connect a bypass - so I could compare the 'clean' guitar volume to the volume and fuzz with the effect on.

What I found was that the fuzz amount doesn't change with a change in the effect's volume.  The input of the amp may start to distort at a higher effect volume setting, but the effect itself is not changing the amount of fuzz no matter where its volume is set.  In rereading Aron Nelson's design notes, it's pretty clear that this is precisely what he intended.  And, frankly, it's a really good design.  It sounds pretty good, and there is something cool about just having one control.  I've never played a Fuzz Face before, so I'm learning a lot about its tone, its response, and the circuit and how it works.

I thought I would want control over the amount of fuzz, so I changed the emitter circuit to be more like the fuzz control on a FF.  And it's sort of disappointing.  The fuzz really doesn't happen until the last 20% of the range of the control, and most of the time, it sounds the best with the control dimed anyway.  This all lead me to realize that the Sili-Face II circuit is quite good as it is.  The one thing I messed with is the value of the bypass cap - it's way too distorted (for me anyway) with a 22 uF (stock FF value, btw), and it may be that Aron's choice of a 4.7 uF is perfect.  I'm going to try a 10 uF for the heck of it anyway.


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