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logonwheeler 14th September 2006 10:16 PM

Chip Amp Power Relay
I know that there have been previous threads posted on this before, but I still feel a little confused....

I would like to use a momentary push button switch to power on and off my LM3875 and realize that I am going to need a bistable relay in order to provide continuous power to the circuit.

I live in the USA so I do know that I need a 120 VAC relay, I am just confused on what size is required. 10 amps, 20 amps? Any suggestions and suppliers with links would be greatly appriciated.


bushroot 14th September 2006 11:42 PM

I used a small 12v power supply which I constantly power. I built a flip flop using a timer which fires a SSR powering the transformer. I delay the outputs using a timer circuit I purchased .

They don't seem to have the supply I purchased, but something cheap like this would be fine:

I used this SSR mounted to the heatsink that my diodes are attached to:

I jused this relay for my speaker output:

I threw it on an octal socket I found somewhere
I used this for a timer:

Flip flops are easy:

I know it's not very elegant, but I'm a controls engineer and I'm used to more "industrial" things.

Anyway, you probably won't need the big SSR. I built an Elliot P101 using a 1.2kva toroid and a bunch of computer grade caps. Hope I could help and good luck!

maxw 14th September 2006 11:48 PM

I wanted the exact same thing as you because there are no good looking 240V switches. Here is what I made:

logonwheeler 14th September 2006 11:54 PM

I was hoping not to build one as I dont have the capabilities (or the time really) to build one and etch a PCB for all this. A little over my head so to speak as well (I am a mechanical engineer, dont blame me).

Is there something similar that I can order or get someone who builds these relays?



bushroot 14th September 2006 11:57 PM

I never etched a PCB myself. What kind of voltage does your chipamp work at? You may not need the power supply at all. I built the little flip-flop on a radioshack perf board.

logonwheeler 15th September 2006 12:56 AM

As of right now, I am still getting all the parts together so I still need to get a transformer. I was thinking of getting around 120 VAC in and 22 VCT out.


bushroot 15th September 2006 01:11 AM

If you have a tap somewhere around 12v, you could do away with the extra power supply. If you're looking for some decently priced toroids around that voltage, check this out:

If you just want a cheap and dirty (but very simple) solution:

logonwheeler 15th September 2006 01:28 AM


Thanks for the second link, I think that is what is needed. Let me review:

120VAC in going to a 3 amp slow blow fuse that in turn goes into my Bulgin swith (very nice looking) and then on to the relay that you posted the link to and on to the transformer.

Now for how to wire up the relay. I had a look at the datasheet ( ) and need to know what terminals are the input and which ones connect to the transformer.


bushroot 15th September 2006 02:51 AM

2 Attachment(s)
Here's something I drew in CAD and converted to .jpg. Should get you started!

If you need a better image or more info, feel free to E-mail me.

logonwheeler 15th September 2006 03:08 AM

Tried to email you - didnt work - must have permissions set...

As for the diagram, I think I see what is going on (the picture isnt totally clear) but would you mind walking through what is going on there?

Sorry for my limited schematic experience!

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