PAiA 9700 now midi2cv8 mods

[Tony Allgood]

>Tony, in an earlier post of yours you mentioned reducing the supply
voltage for this chip (to bring it closer to its prefered 15V) but I
don't understand why you didn't just tie the negative rail to ground
rather than using -0v6. Any chance of a hint for the hard of thinking
amongst us?

Hi Conrad and all,

The theory is that the DAC-08H is used in conjunction with an op-amp to
give a voltage output from zero to some multiple of the reference
voltage. The DAC itself is a passive device as far as the digital to
analogue functions go, ie. a bunch of resistors and switches. However,
the op-amp is not, it is liable to generate offsets at its output. Thus
the voltage of the DAC/opamp combination may well give output voltages
of less than zero to some positive value. By making the supply to
4051 -0.6V, you cater for the odd time it does go below zero, and still
be able to switch it reliably. The odd small negative fluctuation will
not kill the 4051, but it does mean that the input voltage is well
within the input specs. And I like to play safe... especially for the
sake of one diode and one res. Running it across the split rail is
madness.

Regards,

Tony Allgood, Cumbria, UK

Rack mounted moog filter and the TB3030 SuperBassline projects:

http://aupe.phys.andrews.edu/diy_archive/schematics/oakley/