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Old 6th August 2011, 06:41 AM   #21
Mooly is offline Mooly  United Kingdom
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Hi Richard,
Think I've got that... so the resistors are only applied at power off to shunt the rails. If it works then there is no technical problem with that.

Yes the resistors are in series with the rails.

The caps... you already have them in place... you could mount the zeners on the preamp pcb across the "unregulated" rails. So that is straight across the reservoir caps on that board (before the regulators). You then feed the - and + 36 volts via a series resistor to the AC input side of the bridge. The polarity is important but only in that it won't work if you get it wrong. The bridge prevents it entering the PCB incorrectly.
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Old 6th August 2011, 08:12 AM   #22
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Look at datasheet for upc1237, I think you can parallel two relays, with adjustment of the voltage dropping resistor, use one for the preamp side , one for speaker output, it has a built in power on delay during which it first checks DC status before activateing relays.
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