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I am using a Re-audio SA 90.4 800W 4-channel class D audio amplifier (https://www.amazon.com/REAudio-SA90-4-4-Channel-Digital-Amplifier/dp/B00RE9EO7K) for some underwater piezoacoustics experiment. The setup is as follows:

  1. The piezo cylinder is mounted in a watertight shell with +ve and -ve cables connected to one of the amplifier output channels. Impedance varies from 50-500 ohm (depending on frequency as checked with a impedance analyzer)
  2. The amp is powered by a labbench 80W powersupply (yes I know it's not enough but I ensured the gain was limited using gain controls of the amplifier)
  3. The amp is fed by a 96 KHz DAC via RCA cable (left and right cable). It has two sets of RCA ports.

During the experiment, after ~10 minutes, one of the RCA ports gave out. I suspect it's the RCA port because when I connected the inputs to the other RCA port, the setup started working as normal, until that port gave out after 10 minutes. Now the amplifier turns on but there is no output. The piezo cylinder is fine (tested with another smaller pre-amp and impedance analyzer). Note that the amp is rated for 4-8 ohms at the output but no rating is specified for the input RCA channels.

I would appreciate if someone could help me narrow down the problem. I opened the amp and did not seem to find any damaged component inside.

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    \$\begingroup\$ At 63W per channel into 6 ohms you can expect about 8W into 50 ohms or nearly 1W into 500 ohms. Use it bridged; 32W or 3W into 50 or 500 ohms. But if you're blowing up inputs, what voltage are you driving them with?? \$\endgroup\$ – Brian Drummond Sep 4 at 22:24
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    \$\begingroup\$ Line level inputs are usually 1Vp-p. What were you inputting? \$\endgroup\$ – Aaron Sep 4 at 23:22
  • \$\begingroup\$ amazon.com/Syba-Headphone-Amplifier-Digital-Coaxial/dp/… The RCA output of this was being fed to the input of the amp. \$\endgroup\$ – Swapnil Saha Sep 5 at 0:52
  • \$\begingroup\$ What happens if you put a signal into the high-level input? \$\endgroup\$ – Bruce Abbott Sep 5 at 5:29
  • \$\begingroup\$ I tried using the hi-input but nothing happens. \$\endgroup\$ – Swapnil Saha Sep 5 at 6:25
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Beware of ultrasonic glitches on the DAC output.

Requires extreme slewrate to track, and serves as constant impulses that may trigger ringing internal to the amplifier and the combined amplifier_piezo load.

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How is heatsinking done? And how long are wires that bring in power?

If GROUND is shared between InputSignal, Power RETURN, and output RETURN, then inductive Kick will result.

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  • \$\begingroup\$ I checked the 96KHz DAC output on an oscilloscope and did not find any glitches. It produced the frequencies I wanted it to produce without any issues, with max frequency in my system being 30 KHz max (way below 48 KHz). Maybe the amplifier had issues with it. Can you point out to any specific component within the amp I should look at? \$\endgroup\$ – Swapnil Saha Sep 5 at 2:47
  • \$\begingroup\$ Read the amplifier's datasheet for its frequency response and its switching frequency. It may very well not be guaranteed to 30kHz and the closer the signal gets to the switching frequency, the less stable and efficient it may be. Was there any sign of stress or heating in those ten minutes? Did you measure its current consumption? \$\endgroup\$ – Brian Drummond Sep 5 at 10:12
  • \$\begingroup\$ Hi, there was no heating. Yes I measured current consumption. It reached ~ 1A max. \$\endgroup\$ – Swapnil Saha Sep 5 at 16:54
  • \$\begingroup\$ I still have no idea what went wrong. Now I am using my DAC for hours for experiments and it works beautifully, emitting ultrasonic pulses via the PZT cylinder while the hydrophone picks those up \$\endgroup\$ – Swapnil Saha Sep 5 at 20:50

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