Stereo amp EMF protect

Hello Klaus,

Hard to say without any schematic. Large diodes to the rails could help some. However, if it is a pnp/npn pair that is driven from a hard source exceeding base current or reverse Vbe limits could already blow the transistors.

Maybe you should find good spare transistors and keep a whole lot of them in a bin for replacement ;-)

"Klaus Jensen"

Only by having a series resistor of at least 4 ohms from the output AT ALL TIMES could a domestic audio amp be expected survive driving low such impedance and saturating magnetic loads.

If the amp has VI limiting protection built in for its output devices, then it will also have clamping diodes from the output to each supply rail. These are needed for use with ordinary loudspeakers.

....... Phil

Or a great big series resistor.

I have seen 60Hz resonant electromechanical loads driven by a regular old Archer PA amplifier -- this is a load that consumes 60W at 12Vrms during 'normal' operation, and has an instantaneous impedance that's well below the apparent 2.4 ohms, and that will bite you if you ramp up the amplitude too fast. AFAIK the amp is still in working condition, buried in a lab someplace, ready to be dug out and used when it's needed.

There is a long and deep tradition of using home audio equipment in scientific experiments.

When I got started, tube based consumer amps were being used to drive everything from voice coil shake tables to piezo transducers.

At the ultrasonic end, it didn't matter what you put in, what you got out didn't look like it :-). And the shake tables were at the other extreme.

When (not IF) they blew up in the lab, I got to fix 'em :-).

For the cost of a single output transformer back then, you could buy a dozen brand new solid-state amps of ten times the power capacity, any of which will do a much better job at driving the bizarre loads than the old tube/transformer amps (especially outside the AF range).

Tim.