CA 3080 Tri to Sine converter question

[Paul Perry]

At 08:51 AM 20/05/98 -0700, John Speth wrote:

>My concern when implementing the Tri-Sin converter is "Just how pure is the
sine output?"  On the scope it *looks* good but I lack the instrumentation
to really measure the purity.  Can anybody quantify the purity of the sine
output for an optimized Tri-Sin converter using a 3080?
>
.....people do say around 3%, certainly close enough for rock&roll or dance ;-)

but, it occurs to me that by feeding a certain amount of input (possibly
inverted?
possibly rectified?) to the bias input on the 3080 it would be possible to
cancel
out the error term to a first approximation...
if you are building one of these and have a differential scope (yeah, right)
or make
a little differencing ckt you can look at the ERROR, by running the output
signal into a low pass filter to purify it and give a good sine which you
then difference with the 3080 output.

paul perry melbourne australia

btw you might not 'hear the difference' between a sine and triangle lfo as
such, but you sure will
when you use it to eg modulate a VCA.. that 'instant reverse' on the
triangle stands out like dogs balls.