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how do I?

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New Member
this is my second post since nobody wanted to even view my first

Hi all, here's the deal...

I am building myself a foot controler for a "swr mo bass amp"
see: (http://www.swrsound.com/products/proseries/mobass.html)
I only want the bottom 6 switches with led's.
It hooks up the the amp via db9 connecters.
the pins do the following.(hang on this is about to get long winded, but I like to be thurough)
pin# disc.
1 +
2 drive (on/off)
3 synth (on/off)
4 chorus (on/off)
5 dual mode (on/off)
6 (I don't know)
7 subwave (on/off)
8 eq (on/off)
9 -

now... the switching occurs like so (pin 1+ pin 2=drive on)
(pin 9+ pin 2=drive off)
OR... (pin 1+9)+pin 2= effect on/off via a momentary switch.
ie. push the switch once the effect goes on, press it again the effect goes off.
see?? Great!!!
Now HERE is where I am stumped!!!!\
How do I wire up an LED into this mess so that the led lights up when the effect is on and shuts off when the effect is off?
If I hold an led to pin 1 and pin 9 it will light up but I have no Idea how to get the whole thing to work together.
So far I have eliminated the option of using a on/off type switch as that would mean I would have to push the switch 2 times to turn any given effect on or off...
Any help would be very much apreciated and once again I appologise for being so long winded. lol



New Member
I want it yesterday

in 3 hours I got 2 views of my first post.... in 1 hour I got 7 on this thread
I appologise if it seems impatient but I am very anxious to get this issue resolved.

I just needed to revise my subject line to get a little more traffic that is all...
once again sorry if I offended

do u have any ideas regarding my pedal?


Sounds to me, like you need a flip-flop... schematic to come a bit later (after I think about it a bit :!: )


I'm not quite sure I understand the switching. Are pins 1 and 9 power rails (positive and ground)?

(pin 1+9)+pin 2= effect on/off via a momentary switch.
Do you mean that you are shorting pins 1,9 and 2 together? Not possible if 1 & 9 are power rails (dead short between rails = KABOOM)

Can you explain this switching a little more thoroughly?


New Member
that is exactly what I am doing

It is exactly like I said, pin 1 and 9 spliced together and momentarily touching pin 2-8 to THAT lead switches the effect on or off.
What also works is pin1+ pin 2-8 will switch the effect on and pin 9 + pin 2-8 will switch the effect off.
Yet another way that also works is touching pin 2-8 to the housing of the db9 conecter I am using which I would assume is ground.

I appologise there are no values I can give you... I am after all not an electrician, Just a bass player trying to get a foot pedal constructed ecause some louse stole the one That came with the amp.

I apreciate any and all input,Phasor
thanks for taking the time!


Where did you get the pinout from? like phasor said if 1 and 9 are part of the supply shorting these out could knacker the amp - although maybe a current reg or resistor has so far prevented this!
Anyhow, looking at the 'mo control' if that is the correct unit looks like to me as if there is definately logic control in there - especially considering you can 'group' the effects and seeing also that the buttons appear to be simple contact switches - my approach being so inclined would definately be microcontroled as I think this would be the simplist way to implement such asystem. DPDT switches like so...
Not sure if this would work without knowing more but sounds to me like logic 1 on logic 0 off you may also need resistors before the output.



Also if you shorted supply out that suggests to me that it can't source much current so maybe up the resistor to 1k for the leds.
I forgot to mention that you would need to copy that circuit for each effect.


New Member
Thank you so much!

I will try your circut and post results here.

Wish me luck!



New Member
is it complete

I came across this thread while searching for a Mo Control foot pedal..they can't be found.

did you ever finish the pedal you were making? if so..i'd like to hear about or see your final schematic...

aside from being a bass player, i am also an electronics engineer..

i would like to build a pedal as well.
I was wondering,(as was someone else), where you got the pinout for the db9 connector.

hope you read this...

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