outoftune

pm1000 oscillation / motor boating problem
« on: August 02, 2008, 05:26:13 PM »
i am just finishing up racking 4 pm1000 modules in a 1U rack.

the first 2 channels (built from master modules) are working fine and sound great.

the 2nd two channels (built from the echo modules) have some problems. when i turn the gain up all the way, they will oscillate/motor boat and spew squealing noises. i have tried a few different things with the grounding but haven't had any luck. they sound good until they get turned up and start to go wild.

it is strange because i have them wired exactly the same way, same signal path.

anyone have suggestions on what to look for? is there something with the grounding? i have it connected in a star ground and am using the external PSU for some other pm1k's I have (they work fine).


PRR

pm1000 oscillation / motor boating problem
« Reply #1 on: August 03, 2008, 03:47:11 AM »
Motorboating is usually power supply related.

The preamps used in PM-1000 can be unstable if the inputs are not terminated in a low impedance (the reverb bus).

I'm not sure what use a PM-1000 reverb bus amp is, outside a PM-1000.

outoftune

pm1000 oscillation / motor boating problem
« Reply #2 on: August 03, 2008, 11:39:29 AM »
the echo module has the "almost" the exact same gain block as the mike preamps/master section etc....i just realized now that it has a few value changes for the gain block in the master section...maybe this is my problem...i will try that.

when you say that is is a power supply issue, as far as motorboating, is there anything in particular to look for/check?

when i checked the boards with the scope/function gen before I install them in the rack, i didn't see this problem. which leads me to believe it's something from the hook up.

thank you for the reply PRR.


 

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