On Sat, 20 Aug 2005 12:14:53 +0100, 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.

snippage

Usually, two 100k resistors across the supply, their junction
connected at the non-inverting input, alows an op amp to run from a
single supply, the output floating at about half supply volts. This is
fine for my use, but will it work with a dual op amp? I've searched my
documentation, but found no reference to doing this for dual op amps.
If it will work, will say two 100k resistors (one to +12v the other to
ground, junction to pin 3) work? Does it need another 100k or so
between their junction to pin 3 to isolate the input audio from the
two 100k resistor potential devider?

Use two 10k and at least 100uf or more of filtering . Works in
designs I've built. Also insure the supply rails are well filtered
and the input and output capacitors are suitably sized.

The first op ampin the LF353 application notes is only a buffer in
the tone control circuit, so I guess I could avoid the problem and
use a single CA3130 or similar op amp and use the 100k devider trick,
and still use the tone control components. (I doubt the LF353 has any
special properties for this particular use.)

Use the buffer, the circuit will behave better with input sources of
unknown impedence.

The 353 is a nice low noise opamp.

If anyone has another three-control op amp circuit wthat runs from a
single 12v supply, I'd be interested.

There are but the one you have with an artificial ground point will
behave well.


Allison
KB1GMX