someone please point me to a basic footswitch schematic

[onusx]

hi, i have never done any pedal building, but am planning on trying a couple of simple projects soon and am learning to read schematics. recently my (now ex-)roomate threw away my mesa mkIV footswitch because it was in a brown paper grocery bag along with some other stuff i was taking home for christmas, that he thought was trash. this is the 5 button switch with the special jack on the back and i assume some kind of chip inside. since replacements are $250 through mesa, but there are normal 1/4" external switching jacks also on the amp, i decided it's time to learn to make a footswitch.

i know this should probably be self-explanatory, and it's probably just a matter of buying a SP/ST footswitch and mounting it to a piece of wood then sending a 1/4" jack out, but if someone could show me where to find a simple on/off footswitch schematic, that would be great. i need to build separate switches for rhythm 1, 2, lead, and effects loop, and have the option of externally switching power options and other stuff that might be cool, but figure i'll just build the essentials. it would be nice to put three switches in the same box, i figured i could probably order such stuff through mouser or something.

alternatively, if anyone knows definitely that it will be a lot cheaper and easier for me to buy a slew of random one-button switches off ebay, i'll use those. it's not my first choice partly because i'd like to learn to build my own anyway, but also because they tend to be large and not guaranteed to work well and many have multiple buttons but only one cord out, and i'm pretty sure i need to send a separate cord to each external switching jack on my amp.

all help would be greatly appreciated.

thanks a lot,

brian

[Mike Burgundy]

okay, day-um. This is not a really basic setup (well, lessay more than one switch and MB are kind of partial to putting out wrong info) but it's do-able.
Rules:
#1 Hit roommate.
#2explain reason for hitting is he's an idiot.
#3 (Okay, I'll stop here
I have no idea *as yet* what that switch could ('cuse me, *would*) contain exactly, but I haven't really seen anything really new from MB either. (Patent on something that has been CK since the early fifties??)
I'll have a look, and I'm sure some other people will at least experience some sensation of challenge

[onusx]

hi, thanks for the reply. i didn't hit my roomate, but i did move out; things were already weird.

anyway, i should clarify-- on the one hand it's frustrating that i lost that switch because M/B made it with some weird set of pins so that you can't just plug something else in where that original switch was.

however, the good side is that the MK IV also has a SEPARATE set of jacks on the back panel (6 of 'em) for switching between channels and options using any standard remote footswitch, as i understand it. it's a pain in the ass because to use them all i'll have to run 6 separate cords to the amp, but at least it will work. so basically mesa designed 2 ways for you to switch the amp remotely, and i lost one option, so i need to go with the other by default.

also, i really don't want to try and build a big complex multi-button switch with a bunch of LEDs to make up for the one i lost. all i need is a plan for a basic one button switch; if it can have an on/off LED, so much the better, but i won't die without one. i was thinking that maybe i would just make a box that had three or four of these exact same circuits in the same box, but they wouldn't be connected together at all. i would just have a separate line running out from each one. i just thought that might be easier or cheaper than building 4 separate little one button switches and velcroing them together or something.

i hope i'm being a little more clear this time. i don't think i would know what i meant either if i hadn't looked at the back of the amp myself. anyway, thanks, and all help is still appreciated.

brian

[smoguzbenjamin]

What did the original footswitch connector look like? Maybe it's a 6-pin cable like some MIDI interfaces.

[Mike Burgundy]

I can't find anything on MkIV switching as yet, but since M*sa have a tendency for switching one heck of a lot of components in and out of the schem with various "channel-selections" I'd say this amp will have LDR and/or FET switching, which has it's own electronic control. This means it's entirely possible that the switching system uses *momentary* switches with a flipflop or something to remember the new state it's in after you let go of the switch. On the other hand, there's sort of a standard that says external FS'es (like the extarnal jacks you mentioned) are regular SPDT. If this is the case it's very easy. A LED would also be possible with this: either in series (although that might affect the switching function, plus it's rather unlikely for other reasons) or in parallel with a DPDT switch and a limiting resistor. Note: This depends on the switching voltage!!!!
Measure the pins on the original connector, see what voltage (DC) is on them. Might shed some light.

[onusx]

i like the 'very easy' part of your reply. i've never done any of this stuff before. i have biased my marshall successfully following really careful instructions, know how to solder decently, and more or less how to use a multimeter. i'm still trying to get a handle on switches and reading schematics. i need some instructions like 'buy the kind of metal switch you step on, a little LED, an output jack, and solder a red wire to this lead and a white wire to that lead and put it all in a box and you're done. that would be perfect. maybe some helpful mouser part numbers or at least what the things i'm looking for are called would be great too. i saw somewhere online that someone had made an A/B box out of a sewing machine pedal, which i could also probably handle, since i know how to use a drill.

could you please explain the difference between putting an LED in series with a SPDT (this means that it's only got one position when you step on it, but the double throw means it turns on and off?) switch vs putting it in parallel with a DPDT switch? what would i do with a resistor in there? do i need a power source anywhere in this? what will generate the current that will let the switch turn functions on the amp on and off? if i do need a power source like a battery or something, how woud i connect that? and how could i possibly use the same battery to power more than one switch? i've used a lot of switches that didn't seem to need any power, but i don't know why.

thanks, please keep the information coming,

brian

[Mike Burgundy]

The amp is likely to detect the switch state through having a certain voltage on one connection (this is the "detection-pin"), and mass on another.
If these two are not connected, the detection pin sits at, say, 5V. This is reghistered as the "high" state, or "1", or ON.
If you throw the switch and connect the two together, youre clamping the detection pin to mass, so it will have to be 0V, or "low"/"0"/OFF - but a current will flow because you're still feeding in 5V somewhere, but it's bled off to mass. Got that?
Depending on the circuitry it's sometimes possible to tap that current and run a LED from it. The catch is the voltage drop across the diode. If that drop is something like 3.5V (hi-efficiency white light LED) the detection circuit only has 1.5V to play with when the supply is 5V. Plus the resistor thats needed to limit current...There's still 5V there, so you need something apart from the LED to drop that extra voltage or you will have waay too much current and a fried LED.
Actually quite tricky come to think of it.
If the amp is in OFF mode when the switch is closed, then youre best bet is to hook up a LED with current limiting resistor from the detection pin to mass, and *parallel* that with an SPST or SPDT. The detection circuitry should be able to deliver 20mA without really sagging though.
switch open: 5V over LED plus resistor, little bit of current, LED lights.
switch closed: conductive path between detection pin and mass, 0V 0over LED, so it's off.

Carefully and find out what the voltages are on the connections and what reacts to what if you start connecting things together.

[smoguzbenjamin]

Why don't you email the manufacturer and ask them for a schematic?

[Mike Burgundy]

With M*sa?
Well. I guess you could attempt it, you never know. I have a MkIV schem, but with no switching. M*sa tend to deliberately %^&* up that bit of the schem as well, but it will tell us what techniques are being used, probably solving the problem as well.

[smoguzbenjamin]

If you look at it from Mesa's point of view it makes sense though, it's a product they're selling and it would suck for them if people started making clones.

[Mike Burgundy]

Don't get me wrong, I *understand* it  - I was quite stumped when KittyHawk (Roy Electronic) readily sent me a factory schem simply because I showed interest.
I't just annoying me a little at times that they've patented some quite public domain stuff.

[Gearbuilder]

Hi ,
Look at this schematic ,it's my  Mammoth II pedalboard ,First swith is Clean or disto channel(with red and green lights!),second switch allows to have a rhtymic  or a solo (you can use a MXR + for rhytmic and a full volume Fuzz-Face for soloing)in the disto channel,third switch is the effect loop in the disto channel ,the first  switch upside is a general bypass, the next is for the effects in the clean channel.Mammoth features too a system wich takes to me some time .You could choose and prepare your effects before engaging the FX loop on and when you switch on the selected channel for your next song ,the fx are on .For exemple you'are playing in clean mode with a chorus ,during this time you choose the flanger in the FX disto loop ,when you 'll push disto channel the loop  is going on and you will have the sound you prepared before.
But all of that is not a simple pedal-board
Here's the schematic link:
ftp://zepfloyd93.no-ip.info/Photos/Pedal%20Board%20and%20Main%20Rack/schematic%201.jpg

Regards
Bruno