MOTM

> Is there an easy way to shift an AC signal by 90 degrees?  In principal,
it
> seems like such an easy thing.  However, I understand how principal and
> reality often differ.  In principal, it should be easy to live with a
woman
> that you love.  In practice, they make it very difficult at times (like
> mine, right now).

Try these links (for AC signals, not women):

http://www.synthfool.com/diy/hjfs6_df.gif
http://www.synthfool.com/diy/hjfs_phd.gif
http://www.synthfool.com/diy/hj_fs.html

JH.

A filter can shift one frequency a set amount. BUT...for a anything-in,
anything-out circuit, you cascade
a zillion *all-pass filters* (also called a PDN: phase-differencing
network). Electronotes had a good
issue on the proper design of these. You need a 90 degree shift from say 20
to 20kHz: takes something
like 14-16 filters in a row. This is what Bode called a "dome filter".

Paul S.