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Howdy,
I have an 8 knob laney AOR with an intermittent output problem.
A little back story; we were rehearsing and something happened leading to both my amp and the bass amp cutting out. The bass amp wouldn't come back on (although it was fine the week after) and my amp would sound odd when turned up, like it was cutting in and out with poor bass response. No smoke or funny smells.
Initial testing (copied from another forum)
I've just run the thing up pretty much near dimed and clean without too much to report, there was a little bit of a hiccup with the volumes all up and the bass (with boost) on full. My neighbours might think otherwise however. The OT was cold and the PT was only just warm and it had been running for 10's of minutes.
I set about trying to replicate the fault, so into the high input I go and the gain boost was added with the gain and level controls all pretty high to dimed (the AOR has a very odd preamp and effectively have 3 gain controls in this mode!) and everything is fine until the master gets to about 1 o'clock and then the problem starts. I put down the guitar and periodically hit the low B (yes B, I'm childish) while poking about with a meter checking voltages and then there is a serious drop in output and I think "oh, thats done it, bugger." I turn off the amp and reset the dials. A short while afterwards I get brave and turn it back on, still quiet, maybe a few Watts output with the levels all high enough to strip paint. I then pull the bass boost out and there is a short crackle and then its obnoxiously loud again which was quite the surprise. I went back to running it clean and it would run full tilt with no complaints.
Additionally I poked about with a chopstick and didn't find anything that was obviously loose or significantly microphonic. The biggest offenders seem to be the high input jack and one of the gain pots. Interestingly the problem still occurs with no input and the jacks are shorting.
Upon suggestion I replaced the inputs as they were noisy which may explain some of the noise, however, the amp still isn't putting out anything near its full power which should strip paint from walls with ease.
I did a sweep of the preamp from the low input onwards, measuring the plate and cathode voltages. I also scoped the output from the plates.
All the voltages looked sensible or tallied with the ones from the AOR100H schematic where given (attached). Plate for V103B was slightly high, 158V, when 142V was specified which isn't a kick in the pants from 10% tolerance so I doubt a problem.
I input a 370Hz sine wave at 1Vpp from my audio interface using NCH yielding the following outputs throughout the preamp:
V102A 4.5Vpp plate
V102B 65Vpp plate
V103A (CF) 65Vpp cathode
Tonestack all at noon, no boosts
V103B 78Vpp plate (The AOR has an odd topology!)
I then checked the PI with the master on 2 where both outputs were about 14Vpp. I dimed the master and got ~125Vpp. One of the plates is at 183V when 200V is specified. Cathodes both at 35V.
This leads me to believe that the gremlins lurk somewhere in the power amp. Any suggestions on how to proceed? Could this be a shot OT? What is the best way to check this? It does return to normal volume on occasion for reasons unkown. Bias is -42V.
I have an 8 knob laney AOR with an intermittent output problem.
A little back story; we were rehearsing and something happened leading to both my amp and the bass amp cutting out. The bass amp wouldn't come back on (although it was fine the week after) and my amp would sound odd when turned up, like it was cutting in and out with poor bass response. No smoke or funny smells.
Initial testing (copied from another forum)
I've just run the thing up pretty much near dimed and clean without too much to report, there was a little bit of a hiccup with the volumes all up and the bass (with boost) on full. My neighbours might think otherwise however. The OT was cold and the PT was only just warm and it had been running for 10's of minutes.
I set about trying to replicate the fault, so into the high input I go and the gain boost was added with the gain and level controls all pretty high to dimed (the AOR has a very odd preamp and effectively have 3 gain controls in this mode!) and everything is fine until the master gets to about 1 o'clock and then the problem starts. I put down the guitar and periodically hit the low B (yes B, I'm childish) while poking about with a meter checking voltages and then there is a serious drop in output and I think "oh, thats done it, bugger." I turn off the amp and reset the dials. A short while afterwards I get brave and turn it back on, still quiet, maybe a few Watts output with the levels all high enough to strip paint. I then pull the bass boost out and there is a short crackle and then its obnoxiously loud again which was quite the surprise. I went back to running it clean and it would run full tilt with no complaints.
Additionally I poked about with a chopstick and didn't find anything that was obviously loose or significantly microphonic. The biggest offenders seem to be the high input jack and one of the gain pots. Interestingly the problem still occurs with no input and the jacks are shorting.
Upon suggestion I replaced the inputs as they were noisy which may explain some of the noise, however, the amp still isn't putting out anything near its full power which should strip paint from walls with ease.
I did a sweep of the preamp from the low input onwards, measuring the plate and cathode voltages. I also scoped the output from the plates.
All the voltages looked sensible or tallied with the ones from the AOR100H schematic where given (attached). Plate for V103B was slightly high, 158V, when 142V was specified which isn't a kick in the pants from 10% tolerance so I doubt a problem.
I input a 370Hz sine wave at 1Vpp from my audio interface using NCH yielding the following outputs throughout the preamp:
V102A 4.5Vpp plate
V102B 65Vpp plate
V103A (CF) 65Vpp cathode
Tonestack all at noon, no boosts
V103B 78Vpp plate (The AOR has an odd topology!)
I then checked the PI with the master on 2 where both outputs were about 14Vpp. I dimed the master and got ~125Vpp. One of the plates is at 183V when 200V is specified. Cathodes both at 35V.
This leads me to believe that the gremlins lurk somewhere in the power amp. Any suggestions on how to proceed? Could this be a shot OT? What is the best way to check this? It does return to normal volume on occasion for reasons unkown. Bias is -42V.
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