EV 2.0kw class H high rail oscillation? - diyAudio
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Old 30th May 2015, 12:47 AM   #1
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Default EV 2.0kw class H high rail oscillation?

hi guys,

im currently working on a EV 2.0kw amplifier from the 90's
its a dual switch mode power supply class H amplifier.

it had all the output fuses on the smps blown for channel B. ive successfully replaced those and i get my voltages to my output module (+/-60v & +/- 120v)

the problem is now the amp pulls way too much from the wall at idle (over 400w if i let it go) since its a switch mode supply i cant variac it or pass it thru the light bulb limiter so i switch it off as soon as i see it pass the 300w range.

my troubleshooting has gone so far: (channel B)
-if i disconnect +/-60v & +/-120v from psu B to output module B, amp does not pull more then 100w from wall at idle.(no signal output)

-if i disconnect only +/- 120v rail from psu B to output module B amp does not pull more then 100w at idle ( does pass audio without distortion until maxed out rail)

- if i disconnect only +120v rail from psu B to output module B, amp does not pull more then 100w at idle (audio passes, maxes out rail, does not engage - high rail)

-when i reconnect +120v rail from psu B to output module B amp DOES pull over 400w from the wall ( no audio passes)

-when +/-120v is disconnected audio passes cleanly , output transistors get warm at low volume.

-when +/-120v rail disconnected, looking at the bias voltage of the output transistors with a scope, there is a 41khz noise signal reaching maybe 1v

-when both rails plugged in, the signal before the speaker protection relay on a scope jumps positive(rail voltage) then quickly negative and quickly to 0v with some noise on it,

i now suspect an oscillation on that channel, but ive never dealt with oscillation before, so im not sure.

could anyone point me something out that im missing?
its oscilating but with the high rail out it still plays?

the schematics can be found on the complete last page of the user manual >here<

thank you for your help!

Last edited by Salomon102; 30th May 2015 at 12:50 AM.
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