bitrex wrote:

In the mid 1980s, Roland had International Rectifier design a
custom chip called the IR3R05 for their analog synthesisers. I
think it was a 14 pin package...it basically consisted of 4 OTA
stages like the Lm13700 configured as a 24 db/octave resonant low
pass filter with inputs for voltage controlled frequency and
resonance, along with a VCA with both linear and exponential
inputs, all on the chip. The 4 filter capacitors were mounted off
chip on the board.

What kind of job would it be to design a chip or maybe a
daughterboard that performed an equivalent function? These chips
often fail in vintage equipment and there seems to be a decent
sized market for replacements that dont require scrounging for
NOS or cannibalizing old units.

I wonder it the required components could be squeezed into a
daughterboard that would fit the space available. Might require
some vertical mounting hack.

The amps in old Tek scopes also go bad, and there's a market for
replacing them too. I suggested years ago that somebody should make a
DIP module to replace them. Today's standard op-amps could do it I bet.