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Old August 20th 05, 12:14 PM
Ian Liston-Smith
 
Posts: n/a
Default Op amp supply-rail question


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, 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?

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.)

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

Thanks...

Ian