[sdiy] Aztec MkII Schematic

[Michael Ruberto]

Here's a peek at what's working so far.

http://i108.photobucket.com/albums/n13/somnium7/Aztec%20MkII/AztecMkII_REV2.gif

This is just a preliminary draft since the circuit isn't finished yet. 
What's on paper so far is working good but I am wrestling with a few things. 
I have also made a sort of AGC-type circuit to limit the output level to a 
certain range. I'm performing some tests to determine if it is worth the 
extra parts to include it or just leave the manual control circuit in place.
One thing that keeps hampering my tests is my signal generator. I have a 
Fluke 6011 and it's output amplitude seems to vary quite a bit with 
temperature. This is very annoying with a circuit that is sensitive to input 
voltage.
The other add-on I am working on will allow 4 or more octaves to be 
generated from the input signal. So far this waveshaper is already quite a 
powerhouse of interesting sounds but as usual I like to push things. The 
octaves would be controlled by the bit depth or "Width" control. As the 
Width increases it would add more octaves. I believe I can accomplish this 
with a single IC and some diodes. The hang up with this is I have run out of 
breadboard space. I have some more on order and will resume the work once 
they arrive.

The harmonic sweeps I can generate are many times smoother than with the 
original Aztec design. The abrupt shifting heard in the original only occurs 
in this design at a Width of 5 bits or lower. The amount of harmonic control 
can be very subtle or suprisingly wild depending on how the slope is set.

The bad news is that I may have to AC couple the output. This will make the 
unit useless for processing CV signals. The problem lies in the Slope 
control which can add a huge amount of offset as it's rotated towards LOG 
response. My thinking is the unit is more versatile with the slope and no CV 
than with CV and no slope.

M. A. Ruberto

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