12-12-2019, 03:29 PM
"Andy, let me know if you feel we should start a new thread for Tracy's amplifier" No need thanks Mark.
Had some interesting issues today, not with the amp, but when testing. I'd noticed there was some hum when the amps and preamp were connected to my main speakers, so put one monoblock and the preamp on the bench and scoped the OP of the preamp and OP of the poweramp. I was wandering if there was some HF oscillation or other deliterious interaction. First I scoped the OP of the poweramp at 0 volume and at full, result less than 10mV of N. Preamp, pretty much the same. Tested pre and power amp on two different speakers, no noise. So just to make sure I scoped the OP of the pre and OP of the poweramp, what the flegnog! Power OP only 1v RMS and after turning off and on and re positioning a probe the protection on the poweramp tripped.
After some investigation i found one BNC socket on the dummy load is iffy, a sinewave OP taken off this was dancing about like it was being modulated by 50hz, power OP down and other odd faults. I've had this on a few occasions and ended up tearing DUT's apart looking for faults whilst using this dummy load, so it needs to come down off the shelf and taken apart and looked at.
Apart from those shinnanigans I hooked everything up and played a few records through the setup, it sounds grand, happy with the result.
Andy.
Had some interesting issues today, not with the amp, but when testing. I'd noticed there was some hum when the amps and preamp were connected to my main speakers, so put one monoblock and the preamp on the bench and scoped the OP of the preamp and OP of the poweramp. I was wandering if there was some HF oscillation or other deliterious interaction. First I scoped the OP of the poweramp at 0 volume and at full, result less than 10mV of N. Preamp, pretty much the same. Tested pre and power amp on two different speakers, no noise. So just to make sure I scoped the OP of the pre and OP of the poweramp, what the flegnog! Power OP only 1v RMS and after turning off and on and re positioning a probe the protection on the poweramp tripped.
After some investigation i found one BNC socket on the dummy load is iffy, a sinewave OP taken off this was dancing about like it was being modulated by 50hz, power OP down and other odd faults. I've had this on a few occasions and ended up tearing DUT's apart looking for faults whilst using this dummy load, so it needs to come down off the shelf and taken apart and looked at.
Apart from those shinnanigans I hooked everything up and played a few records through the setup, it sounds grand, happy with the result.
Andy.
