[sdiy] Really obscure OTA question

[harrybissell]

While studying a circuit (the PV-1 based on the design by Bob
Moog...used
with permission  ;^)... I noticed that his OTA current source had one
input
at ground, and the other at +6V (divider of two 22K resistors)...

now we all know the differential voltage limit is 5V for this part.

Question 1:  What would be the possible benefit to driving the input
this hard ?

Question 2:  If you see the CA3094 OTA with buffer output... the spec
sheet says
differential input voltage 5V... but no device damage will occur if
input current is limited
to 1mA or less...

no such disclaimer on the CA3080...  otoh I have used these in higher
differential voltage
apps without damage.

Observation:  I tried a PV-1 running on +/- 15V supplies (now that
voltage is 7.5V)...
with a NATIONAL LM13600, or 13700... circuit operation was normal. With
the
NJR 13600, or 13700... the OTA would not shut off when the bias current
was reduced
to zero... output current continued to flow.

I found it was very sensitive to that higher input voltage. Making the
input 7V or less made it
resume operation...

Now what's with THAT do you think ???

Theories, please...

H^) harry