At 11:23 AM 10/25/2011, Bob Blick wrote: >Plugging an audio cable between two devices that are powered by AC can >put a lot of stress on opamps, whose inputs can sometimes be almost >directly connected to the input jack. > >Is there a device that is preferred for clamping audio inputs, like a >bidirectional surge absorber is used for power input, but suitable for >this application? My preference has always been to use a pair of signal diodes from the=20 op-amp pin to the supply rails (assuming single-ended / unbalanced=20 input). This, of course, requires an appropriate resistor between=20 the input jack and the op-amp / diodes junction. If this is something that you are modifying rather than building from=20 scratch, varistors designed for telcom use are useful. The ones that=20 I have are about the size of a fat 1/2 resistor and made of green=20 epoxy or similar material. The markings on them are "V120-2" and=20 they clip at about 1Vp-p. These are nice because the onset of=20 clipping is soft and rounded - they are significantly less audible=20 than 4- 1n4148 diodes in series / anti-parallel at the onset of=20 clipping. Obviously, these varistors are bi-directional. I purchased probably about 1000 of these green varistors about 30=20 years ago and often wish that I had purchased the whole (large)=20 cardboard box - I'm pretty sure that the ones that I didn't take=20 eventually made their way to the landfill. Anyway, I'm pretty sure that the 1Vp-p is a fairly standard telcom=20 varistor spec and should work nicely at the nominal -10dBu or -10dBv=20 level that your consumer-grade audio equipment is running at. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .