Foot Switch in MSZW Marshall Zakk Wylde Mini Stack Head

[sikaudio_com]

--> Enzo...
after all your guidance, just wanted to confirm that you agree with
Mr Steve C....that the "Mini PCB DIL 12v Relay" (in image above)
is the go for the Marshall ?

Looking forward to getting this little project over with...in a good way

Cheers

[Enzo]

Sure. This is not a critical application, but there is no point in getting something overly large. Larger contacts may not be the best for the tiny signal current, as Steve points out. Plus the coils on the larger relays typically draw more current. Your existing power supplies probably are not stressed for current, but why draw more than you have to? Excess current potentially drags down the rail, and the added ripple currents could induce some hum.

Get a couple relays, so when you melt one, you have a backup.

[sikaudio_com]

Just one other thing....will I be needing a little 12v regulator to feed the Relay power as well? If so will a +12v 1A be ok ?

Cheers.

[Enzo]

I wouldn;t bother. The 12v relay is just a nominal rating. The thing will work on 10-14v easily. Look at that PV Audition schematic I posted earlier. See the coil circuit? it runs that 12v relay off a 15v supply. They added a resistor to drop some voltage.

In fact, I wouldn't be surprised if the relay worked on a 9v battery.

If you have regulated 12v already, no reason not to use it, but the relay certainly doesn't need regulated. I bet the voltage suply in the amp won;t be dancing all over the voltmeter. Just get close.

[sikaudio_com]

Here's the latest:
I have finally got the little relay & started soldering on the wires to the back
of the Original Front Panel push switch (on the board....see below)



Now I am a little stuck, I have found 15v running pretty much all over the
board & to the original on board switch. Just not sure about the exact wiring &
guessing I will need a little resistor to drop the 15v down to the relay too.
Maybe I am a little over my head here....

[Enzo]

You must have it mis-wired. there is no reason for 15v to be on any of the signal pins.

Did you remove the push switch before soldering those wires in? You should.

Look at the side of the blue relay. The bottom of the side is a drawing of the bottom, identifying each pin. The two pins on the left end are the coil leads. They do not solder to the old switch points. One coil pin goes to the + power supply, and the other will go to your footswitch jack, with a resistor added. The footswitch should then click the relay off and on.

In the existing switch, the center pin on each side is the common, and it is switched either to the top or to the bottom leg on the same side of the switch. Now look at the relay, the common contact is the second leg from the left. Then the 3rd and 4th legs are the two throws. So your green wires connect to the #2 leg of the relay, top an bottom.

Then the blue wires to the #3 pins and the red wires to the #4 pins, #4 being the end opposite the relay coil pins end.

[sikaudio_com]

....yeah cheers Enzo.
I thought it was a little weird that there is 15v to the push switch...
that's why I mentioned it.
I did not do anything to the amp before I measured the Voltage.
Just opened it up & started poking with the multi metre.
And ..no I did not remove the push switch...I just tacked onto the bottom
of the pins on the board.....
I will get in & have a go today with your instructions....
Thanks again mate.

[Enzo]

Did you wire up the coil of the relay? That unwanted 15v is coming from somewhere.

[sikaudio_com]

The Relay Switch is doing its job & the
Amp is now channel changing with
the Channel Select Foot Switch. HAPPY Happy, JOY joy!!


Just one thing I cant work out....
I am running the 12v Relay on the 15v line from the Board....
I Put a 330 ohm resistor in the orange wire between the
15v+ source on the board .... to the coil on relay.
Tried to drop the voltage a few volts....But no change???

Check out the image below....



Also, this link here has all the images of the mod so far
www.sikaudio.com/marshall.html
For anyone else how wants to tackle this footswitch mod.
[I know one other Lad who has this amp & wants to do this mod as well...]

Hope this helps!

[Enzo]

Ohm's Law - voltage will only drop across a resistor if current is flowing. MAke sure the relay is energized when you make your voltage readings. When the relay is off, the one side is still connected to the +15v, so there will be 15v on everything. No current flowing means no voltage drops.

If you are connecting a resistor to the +15 and expecting the other end of the resistor to measure less voltage, that is what is wrong.

[sikaudio_com]

Yep...you got it! I thought I had the relay powered up the last reading I did....but the
jack to foot-switch was not connected properly....no power to relay....woops.

So thats it then....Finished, Sweeet!


Thank you so much for your time & Expertise....your a very giving Man.
I know where to come for my next project...that is for sure!

Now, back to my Ohm's Law studies.....

Cheers mate,
Nath
www.sikaudio.com