Thanks to all who have replied. I've certainly got some ideas now.

On Wed, 24 Aug 2005 23:14:02 -0700, "Dana H. Myers"
wrote:

Ian Liston-Smith wrote:
I'd like to build a tone control circuit using the LF353 dual op amp.
The circuit has bass, mid range and treble adjustments.

The problem:
The circuit (see
http://www.ece.ucsb.edu/courses/ECE0...remi/lf353.pdf
circuit on page 7) uses dual voltage rails of +15 and -15 volts,
though for line input levels, this will probably work down to +8 and
-8 volts. But I want to run it from a single +12 volt supply.

Usually, two 100k resistors across the supply,

What is magical about 100k?