[sdiy] Chorus unit

[Mike I.]

Paul and DIY,
These units tend to be very noisy due to the ultrasonic clock signals 
generating audio beat notes as the the clock frequencies momentarily 
cross over. Need to decouple the individual BBD's  + drivers as much as 
possible.
Probably easiest to modify an existing board like the KLM-368. The 
KLM-368 board uses MN3004 512-stage BBD's clocked by CD4013B dual D-type 
F/F chips. Each CD4013B does double-duty as both a VC clock and 
two-phase driver. Could use 1024-stage BBD's such as MN3007 (same pinout 
as MN3004 maybe?) clocked at twice the rate of the MN3004 to get more 
bandwidth - with filters changed accordingly. Probably could improve the 
treble end a bit by using buffers on the CD4013B outputs to improve the 
rise and fall times. The SAD1024 has a reputation of providing better 
treble response than the MN3x chips.  Part of this may be due to the 
SAD1024 having a much smaller clock line capacitance than the MN3x BBD's 
and being easier to drive from unbuffered CD4013B outputs. With suitable 
buffers I've run the MN3207 at clock rates as high as 2 MHz. The chip 
doesn't even get warm. 
Mike