I ran some tests on my amps recently. I was surprised to find one amp was fake balanced the other (not surprised) was an honest xlr only single ended amp and the other was something else. I have a question about that last one.
The test was two things:
1) with amps off checking continuity between pins on the xlr inputs. If any of the two pins beep (usually 1 and 3) there's a pin tied to ground (1)… (probably)
2) I made a thru board XLR in and out and had pin 1 (ground) connected thru at all times. Then I was able to connect pin 2 in to pin 2 out or 3 only or both and read the output on a 4" driver.
the amps and results:
Adcom 555se = fake balanced. pin 3 connected I got nothing. pin 2 only and I got full signal. Both 2 and 3 connected thru same full signal.
Yamaha P2050 = honest single ended XLR only amp. Same results as the Adcom.
Cerwin Vega CW-1800 = Strange. With pin 3 only connected there was nothing. With pin 2 only connected I got 76.8 db out of the driver. With both 2 and 3 pins connected thru I got 82.8 db out of the driver. On this amp I connected a XLR cable up to the input (amp off) to do test 1 and put the leads in the other end of the cable to test continuity. This amp has those XLR / TRS combo jacks and I didn't want to miss. It beeped when connecting pins 1 and 3. hmm?
This is kind of a two part post what have you seen? Any other weird results from a "balanced" amp? What is true balanced supposed to do in test 2? And what could be going on with the CV-1800?
The test was two things:
1) with amps off checking continuity between pins on the xlr inputs. If any of the two pins beep (usually 1 and 3) there's a pin tied to ground (1)… (probably)
2) I made a thru board XLR in and out and had pin 1 (ground) connected thru at all times. Then I was able to connect pin 2 in to pin 2 out or 3 only or both and read the output on a 4" driver.
the amps and results:
Adcom 555se = fake balanced. pin 3 connected I got nothing. pin 2 only and I got full signal. Both 2 and 3 connected thru same full signal.
Yamaha P2050 = honest single ended XLR only amp. Same results as the Adcom.
Cerwin Vega CW-1800 = Strange. With pin 3 only connected there was nothing. With pin 2 only connected I got 76.8 db out of the driver. With both 2 and 3 pins connected thru I got 82.8 db out of the driver. On this amp I connected a XLR cable up to the input (amp off) to do test 1 and put the leads in the other end of the cable to test continuity. This amp has those XLR / TRS combo jacks and I didn't want to miss. It beeped when connecting pins 1 and 3. hmm?
This is kind of a two part post what have you seen? Any other weird results from a "balanced" amp? What is true balanced supposed to do in test 2? And what could be going on with the CV-1800?
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XLR only in that it only has that kind of input. Honest because it’s printed right on the back that pin 3 is tied to pin 1. It’s a single ended amp from pin 2 on.
Take any battery like AA/AAA and check whether amp rejects or accepts common mode at pins 2+3 without DC protection alarm.
