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Maxhawk 9th October 2004 02:28 AM

FS: Kit for amp power soft switch
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I've designed a small board that's used as a soft power switch in my Leach amp. I had to order a minimum of five boards so I'd like to offer 3 of them for sale.

The PWB contains a PC mount AC transformer, JK flip-flop, switch debouncer, and relay to switch 115VAC to a device(s). I use the output to drive a solid state relay that powers the main torroid transformer.

I'd like to offer the kit for $20 shipped with all parts except for the switch, relay, and transformer. The switch I used is pretty fancy and has a built-in blue ring to indicate power is on.

Here is a list of parts you will need to order/provide. Vendor part numbers are in parentheses:
1. DIGIKEY: Relay (Z105-ND) $4.68
2. DIGIKEY: Transformer (TE70000-ND) $9.34
3. MOUSER: Switch (117-MPI002/28/BL) $19.40
4. MAXIM: Debounce IC (MAX6816) $0 -- free sample

You can choose to use a cheap momentary switch but this one gives a very high-end look.

I've got pictures on my webshots page:


fcel 9th October 2004 03:08 AM

I've just send you an email.

Kelly McDonald 9th October 2004 05:50 AM

Any chance for a group order? I would be interested in couple of these

Maxhawk 9th October 2004 01:05 PM

If there's really enough interest I can order more boards. The switch and transformer that I used makes this sort of expensive for what it is, but it's done in a very neat package and looks nice.

Since I didn't mention it before, the PWB measures 2.0" x 3.5".

If I can get a total of atleast 8 orders (3 PWB's that I want to sell + minimum order of 5 PWB's from vendor) then I'll order more boards. After the 3 are gone, I'll order more if there's enough interest.


JTT 10th October 2004 07:25 PM

I don't want to be a killjoy, but if switch-on thump is the problem, the Leach amp will power-up with no significant disturbance if the input is held at ground potential for two or three seconds after switch on. A 'normally closed' pair of relay contacts will do this,
relay operation being delayed and energised by a simple SCR/thyristor circuit with CR charging on its gate. This arrangement requires no significant additional power components, and leaves nothing attached to the signal path after power-up. The relay de-energises immediately on switch-off, and again results in no output disturbance as the power rails decay.


Maxhawk 10th October 2004 07:37 PM

Nope, that's not at all what this circuit is intended for. I wanted a momentary push button for my power switch with an LED "ring" to indicate that power was on. I was prepared to make a lightpipe around a regular push-button switch when I stumbled an off-the-shelf switch that did exactly what I wanted. I'm using a JK flip-flop to toggle power on and off, clocked by the switch. The switch needed to be debounced and I also needed some drivers for me LED. So to simplify things I made a PWB that contained all this as well as the power transformer.

Hence the name soft power switch.

jean-paul 10th October 2004 07:55 PM

Hello Rob, can you show a schematic ? Too bad you did not include a jumper for use in 230 V areas ( I saw you used a transfomer with dual 115 V primaries ! ) ;)

fcel 10th October 2004 08:01 PM


I have installed a Vellerman kit in my BOSOZ pre-amp to solve the turn-on thump problem. I have wired the output relay the way you have described it. I was wondering which circuit are you referring to. Can you post a schematic too?

jleaman 10th October 2004 08:06 PM

um i like these boards. is there any way we can get a schematic or a board layout. ? Id like to get some. for my aleph 2's and mypre amp's

Maxhawk 10th October 2004 08:13 PM

All the source files are on my PC at work. I can post the schematic tomorrow.

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