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Old 19th March 2003, 04:15 AM   #11
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Like this:
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Old 19th March 2003, 04:20 AM   #12
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Here's a nice one for cheap.
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Old 19th March 2003, 10:24 AM   #13
OliverD is offline OliverD  Germany
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This won't cure the pops.

While at it, why not bypass the relay contacts with a nice 20W resistor, put the power switch back in series with the relay contacts and use a secondary rail to power the relay. This will make a nice "soft start" circuit - your caps and rectifiers will live longer.

To cure the popping sounds during power up and shutting down, you can add a speaker protection circuit with a second relay.
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Old 19th March 2003, 11:07 AM   #14
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Quote:
Originally posted by AMT-freak
This won't cure the pops.
Maybe you can show me where I said it would...

You're talking about one problem, I'm talking about another.

However, soft turn-on would be a good addition. Draw something up there Freak..
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Old 19th March 2003, 07:28 PM   #15
OliverD is offline OliverD  Germany
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Something like this. Relay coil series resistor calculated for voltage drop of Vrail-Vrelais.

BE CAREFUL WITH MAINS VOLTAGE
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Old 20th March 2003, 12:35 AM   #16
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I like that. A larger resistor could even be used to add a longer delay before the relay turns on. If I was going to do this I'd increase the resistor to 10-15 Ohm or somewhere in that neighborhood.

Simple is good.
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Old 20th March 2003, 02:24 AM   #17
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My last post on this since KevinLee seems to have lost interest.

This circuit does as you described AMT, but adds a capacitor discharging resistor (the 150-ohm 10W at top) for when power is removed (as long as the power switch is at least a DPDT, this can be used).

All Elecronics has a 70-amp 24VDC relay here. It draws around 80mA, so I thought it wise to steal the voltage from both the pos and neg rails, as well as increasing the series resistor to 100 ohms since taking voltage from both rails means that the relay will turn on too fast with a 3-ohm resistor. The unknown resistor value of course will be determined by the rail voltages.

The 100-ohm 20W and 150-ohm 10W can both be had very cheaply from Parts Express. If I was going to do this, I might even try a 680-ohm 20W resistor and see what kind of delay it gives me. Probably too much, but PE selection of 20W resistors is kinda lean. Other values would have to be sourced elsewhere (Digikey).
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Old 23rd March 2003, 10:15 PM   #18
OliverD is offline OliverD  Germany
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Sounds good, although a longer delay is not necessarily better - the series resistor might easily be overloaded, even if its rated for 20W. The circuit above or varations thereof is used in many commercial amps with toroids (Accuphase and others).

Btw, we both forgot about the flyback diode across the relay coil.
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