Excellent post by Kijanki. I agree completely.
The specifications at the ARC website do not appear to indicate either full power bandwidth or slew rate for your VS-115, so there isn't enough information to answer your question. As Kijanki indicated, though, high power levels are not required at ultrasonic frequencies, so small signal bandwidth is a more meaningful number than full power bandwidth.
Returning to the question of ultrasonic intermodulation distortion, I'm not sure that bandwidth limitations are directly relevant to the issue, although they might play a role. What is relevant is non-linearity. As long as the amp's output amplitude is linearly proportional to input amplitude, at each of the frequencies for which an ultrasonic spectral component is present, there won't be a problem. Perhaps there will often be a tendency for linearity to degrade at frequencies where the amplifier's small signal frequency response is rolling off, in which case bandwidth would have some relevance to the issue. Or perhaps not; I have no particular knowledge on that question.
Best regards,
-- Al
04-22-12: BifwynneMy understanding is that unless otherwise stated frequency response and bandwidth are usually specified under "small signal" conditions. I believe that for power amplifiers "small signal" is commonly defined to mean 1 watt or 2.83 volts (2.83 volts corresponds to 1 watt into 8 ohms). Full power bandwidth will sometimes be considerably less, in part because in some designs it will be limited by what is called slew rate, which isn't a factor under small signal conditions.
... do you know what the power bandwidth is on ARC amps, particularly the VS-115. Freq. response is approx. 100K, but I don't know if that is the same as power bandwidth.
The specifications at the ARC website do not appear to indicate either full power bandwidth or slew rate for your VS-115, so there isn't enough information to answer your question. As Kijanki indicated, though, high power levels are not required at ultrasonic frequencies, so small signal bandwidth is a more meaningful number than full power bandwidth.
Returning to the question of ultrasonic intermodulation distortion, I'm not sure that bandwidth limitations are directly relevant to the issue, although they might play a role. What is relevant is non-linearity. As long as the amp's output amplitude is linearly proportional to input amplitude, at each of the frequencies for which an ultrasonic spectral component is present, there won't be a problem. Perhaps there will often be a tendency for linearity to degrade at frequencies where the amplifier's small signal frequency response is rolling off, in which case bandwidth would have some relevance to the issue. Or perhaps not; I have no particular knowledge on that question.
Best regards,
-- Al