Relays as input switch?

[Nisbeth]

gilid: I would very much like to see your circuit. Once you have found a way of displaying it, could you post it here or e-mail it to me at Nisbeth@hotmail.com ??

Thanks for your help!
/Uffe

[Alex M]

I was going to supply a pointer to my preamp project, but then I noticed that Jake already had...

The idea of using the normally closed contacts is a good one, but in the case of my project to actively deselect all the unused inputs would require over thirty relays to be powered at once, and at 15mA for each relay this would require about half an amp, which seems to me pretty wasteful!

Don't relays have a magnetised element in them even when unpowered? I'm not sure whether the solenoid core uses a permanent magnet or not. The 53W/1 relays I use have a magnetically assisted switch to reduce power consumption when they are on.

I would be very interested to hear of any technical explanation for a change in sound quality in the presence of a magnetic field. I guess it could be something to do with the Hall Effect, but I recall from my undergraduate lab work that this was generally related to a large magnetic field.

Alex

[gilid]

Nisbeth,

I am attaching a zip file of my circuit. I have a total of 6 inputs, one tape output, and one mute function, for a total of 8 relays. The 'active' input relay is powered on. I use sealed, internally shielded relays to get around the magnetic problem. A well-designed DC power supply with minimal ripple will also reduce any magnetic effects. The relays can also be mounted on a double sided PC board, with the top side used as a ground plane. Sounds simpler to me than powering mutliple relays.

I use 4 pole relays - the schematic only shows the three active poles. One pole is used for the LH channel, one for the RH channel, and one for a LED indicator. That way, the LED indicates actual relay position, not just commanded position.

If you have any questions, I will be glad to reply.

[seangoesbonk]

Originally posted by Alex M
The idea of using the normally closed contacts is a good one, but in the case of my project to actively deselect all the unused inputs would require over thirty relays to be powered at once, and at 15mA for each relay this would require about half an amp, which seems to me pretty wasteful!Alex

Actually, maybe NC relays are a bad plan. One thing I've learned from programming PLCs is that you have to incorporate failsafes. What happens if the logic circuit holding the relays open loses power(for whatever reason)? Then all your sources are shorted together. And, what about when your preamp is off? Your sources are all shorted together. This could be bad thing...
Also Alex makes a good point about wasting power(as well as shortening lifespan...)

just something to consider...

[mlloyd1]

I managed to find a few of these Omron GS6-2F DC5V relays. Can anybody say anything good or bad on their behalf as used in a preamp for volume control functions and as input source selection functions?

For those that want to see the specs

Thanks!
mlloyd1
p.s. The leads on mine actually bow out away from the relay body, making DIY soldering a little easier

[sam9]

If I read it right the question is how to be sure that only one input source is connected at one time and hoe to be sure that when pushing the button for another source the prior one is disconnected.

I don't know if there are limitations on the tytpe of switch but assuming that is fexible/open I'll interjec6t that I have seen "interlocking" push button switches in eithe the Digikey or Mouse catalog (don't remember which). This would make the circuit logic simplistic as the logic is in the mechanical action of the switches.

I din't know if this helps or not.

[jleaman]

you should use some murcury wetted ones im using 50 of them for my volume control and for my speaker protection's for my amp.

j'