AMP Channel Switching, Will this work?

[craigmillard]

Hi Guys,

Been looking into ways to switch amp channels with relays and been reading Merlins book on the subject:)

Im looking to switch 2 channels in a simple amp, clean and lead. it will use 2 DPDT relays to do the switching but i would also like channel indicators for BOTH channels, ie Green and Red.

Would this work:



When the switch is made then Q1 pulls the base of Q2 to ground turning it off meaning the Green LED no longer sees ground, when the switch is then released the Green LED can see ground again so lights..

What ya all think?

[PRR]

> What ya all think?

I think it could be simpler. Why? Maybe not for cost, but less labor and less ways to wire stuff wrong.

Q3 does the SAME thing as Q1. Discard Q3, wire K2 coil right across K1 coil. Not only saved a transistor and resistor, you can use one diode for both relay coils. (But please use a beefy diode like 1N400x; the 1n914/4148 series are fast but fragile.)

The relay specification is incomplete. They may be 12mA or 50mA or something else. 2N5088 is good for 100mA, maybe; if you push it, the transistor heats very fast. 2N2222 is a popular part for higher current.

The base current shown is (assume 12V supply 0.6V Vbe) around 10mA. The relay current could be not a lot higher, perhaps 25mA. One wonders what the transistor brings to the show. SW1 could probably switch a couple relays directly. (And without the D1 D2 diodes.) Or the base (and switch) current could be a lot less with a larger R1.

To go totally 1947 again, do the LED switching with a relay pole. (Does lead to a third relay.)

Or if the LED current may be much less than the relay current, put the one LED+resistor across the relay coils, put the other one from there to ground.