In article , Trevor Wilson
wrote:
On 31/05/2016 9:13 PM, Dave Plowman (News) wrote:
In article ,
Phil Allison wrote:
** The simple solution is to add a DPDT relay to mute both inputs of
the 405 whenever there is no AC power.

Ideally, a miniature sealed type with gold contacts powered by
rectified AC from the secondary of the transformer - plus a suitable
series resistor.

You can use the contacts to either ground the two signals or open
circuit them.

Snag is this squawk happens immediately at switch off. So the relay
would have to operate extremely quickly.

**Phil's idea is a good one. I used exactly that solution a short time
back with a Sony integrated amp. The preamp section was going unstable
at switch-off. The job was rapidly becoming unviable, so, after
consultation with the client, he agreed that a fast operating relay
would be acceptable. I used it to short the output of the preamp to
earth at switch-off. Perfect solution. Not ideal, but it does work well.

IIRC The Quad 34 has a circuit that clamps the output to ground as soon as
the rails start to fall when you switch it off.

Jim

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