Output low from 260
Dra
Posts: 3,777
I found some interesting processes for setting limiters on PSW and thought I would give it a try. Basically using a volt meter to measure the actual voltage at the amps outputs (from just below hard clipping on the mixer) and using the limiter to scale the voltage back to match the voltage capacity of the speaker. In the middle of playing around using different sources (pink noise and sine wave tones from a computer program) I lost a lot of output at the amps. When I started, I was able to get 80 volts at full tilt and using the limiter bring it back to 54 volts (target was 56). I had a \"full range\" program loaded but wanted to switch to a x-over'd setup, so loaded one in. This is when I noticed that I have only line level voltages coming from the amp (less than 2v). I thought I had damaged the amp, or my volt meter was messed up (walmart cheapy). Then I noticed that I was still getting +18 on the 260's input meters (GUI) and about -18 on the output meters. I checked all limiters and they were all off. No compression, AGC, etc used. X-over gains were normal. I could get the output meters to move up to a respectable level by moving faders, gains, etc, but then they would fall back to the -18 range.
To confirm the meters, I connected the amp directly to the mixer and I was again able to get 80 volts out of the amp. The problem is definitely in the 260. Any ideas?
DRA
To confirm the meters, I connected the amp directly to the mixer and I was again able to get 80 volts out of the amp. The problem is definitely in the 260. Any ideas?
DRA
0
Comments
When playing music all seems well.
When playing tones (sine waves), oops I may have just figured it out...
Anyway when tones are played the input stays constant on the input meters but is up and then down on about 5 sec intervals. More volume then reduced, then more, then reduced. I didn't have a speaker connect before, so didn't hear what was actually happening
Here may be the oops. I did not have anything that would reduce gain on in any stage, but I bet the AFS was on with a 5 sec drop for the live filters. I bet the AFS was seeing the tone as feedback. The input must have been just above the point where the AFS believes that it sees feedback.
DRA
Wow... good detective work! 8)
The same kind of thing happened at the PSW amp shootout... they dismissed the Digam amps because they wouldn't reach full output with a tone...the amp has a high level feedback circute designed to see potential clipping, voice coil heating, resistance swings... in the load and would limit the output to protect the speakers... we actually hooked this 5000 watt amp up to a pair of Community loudspeakers (8 \" with a dome tweeter rated at 100 watts peak) and CRANKED the system, and amps... they got stupid loud but NEVER did blow a driver...this same amp is the one that drove 6 labsubs outdoors in stereo.. all day long with an impedance in the 3/4 - 1.5 ohm load... never even got warm and you could FEEL the bass a half mile away! (one rack space...17 lbs...stupid powerfull)
Well thanks for clearing up the mystery...
G
Technology is going to be the death of us. (but we'll be fat, lazy, and comfortable in the process) 8)
DRA
PS - I'm not getting error messages any more. But I am not getting e-mail notices since the server change.
Reading -0- in the input meters. Reading -0-, no... -6, no... -12, no... -18, no -12, no -18, no -24, and so on. Opened up the AFS module... there it was a shallow filter at 100 hz, and on top of that a deeper one, and a deeper one. Then one would go away and another one would take its place.
So there you have it. If doing gain structure or any test using tones (or sweeps) to indicate signal strength or output of a system...
TURN OFF THE AFS.
DRA
NICE use of superlatives! and a job well done! Troubleshooting of this nature takes years of screwing up!
Good to see your still out there mucking about...(that was for you Mark)
G