Improving a delay audio relay circuit

It is a pretty basic circuit, but it works...

In more refined circuit designs K1 can be eliminated so that only one relay is used. The circuit must be arranged such that the relay operates on delay but releases instantaneously.

In all delayed-on or anti-pop circuits I have encountered, even in high quality professional audio systems, the good old electro-mechanical relay is still preferred as the speaker isolation device. There is as yet no solid state device that I know of which will duplicate the function as well as a relay.

In message , dated Wed, 23 Aug 2006, snipped-for-privacy@videotron.ca writes

If asked to do that job today, I would still use relays. It IS possible to do it solid-state, but it's not all that easy to switch loudspeaker-level currents with negligible voltage drop, no noise and low distortion. Metallic contacts do it easily.

A better solid-state solution would be to fix the power supply design 'feature' that causes the problem.

Relays have always been my preference.

With a single supply, there's no solid-state solution. Slow slewing invites other issues with the local feed back loops.

Dual supplies are hard to power up perfectly balanced.

...Jim Thompson

In message , dated Thu, 24 Aug 2006, Jim Thompson writes

Not too bad for sufficiently relaxed values of 'balanced'. Phono equalizers (remember them?) are notorious for creating thumps, because of the high gain at low frequencies. In a rash of optimism, I designed and prototyped a precision EQ (frequency response correct to less than 1 dB), and fed it from an AC wall-wart. In the box were +ve and -ve half-wave rectifiers with big (1000 uF) filter caps compared with the value indicated by the current drain followed by bootstrapped 78/79LO5 regulators. No thump. OK, the filter caps came from the same batch, but....

The last time I hand-built a power amplifier (admittedly some 30 years ago) I used a grotesque mechanically-delayed mercury-wetted-contact relay that connected a resistor load on power-up and then switched to the speaker two seconds later ;-)

...Jim Thompson