"Eiron" wrote in message


Have we all stopped arguing? May I ask a question?
What's the best way to check if a power amp is likely to
be stable into a capacitive load such as an ESL?

Hang capacitors across its output.

However, presuming that an ESL is necessarily an unusually capacitive load
is not always correct.

I could put a 2uF cap on the output and look at the
output on a scope while feeding it with a square wave.
But is it likely to damage anything if the amp fails the
test?

If there is damage at all, it is likely to damage the amp, and also the
capacitor if it is too frail. Signfiicant currents can pass through the
capacitor.

IME if an amp is going to be actually unstable, the worst case capacitance
is likely to be far less than 2 uF. 0.01 uF +/- a factor of 10 would be my
recommended values for fishing for instability.

Remember, there are two ways to mess up an amp with capacitive loads. One
involves frying the output transistors if they lack adequate SOA and SAO
limiting. The other involves actually instability. Furthermore, both
inductive and capacitive loads can cause problems.


One old Rotel amp has a warning in the manual against
capacitive loads, which is a pity as it is a nice,
low-power amp and not likely to make sparks if the kids
turn it up to 11.

IME, most modern amps are both stable and durable.