TU 18 Footswitch

Good to see someone else in there getting their hands dirty just as I love to do.  One tip I can give is that a lot of footswitch units use a cable clamp to secure the cable entry against being pulled.  If you remove that you can generally fit a panel mount jack socket in the same hole without too much fuss.  That way you can have a footswitch on your pedal board without a long cable permanently attached to it.  You then only need a separate cable with a TRS jack on each end carried around in your gig bag.

The stereo jacks thing is something I have recommended for other reasons before.  The idea of it suiting more amp switching systems is a great heads up.  In a speaker socket it allows you to reduce the contact resistance by soldering the Ring and Sleeve together as they both contact the barrel of a mono plug.  You MUST be careful to insert the plug before firing up your amp as inserting it with this wiring will actually briefly short out the Tip and Ring on the way in.  Some amps may not like that.  It's fine if it is already inserted fully when you switch on.

In your guitar it also helps to replace the usual mono TS open frame version socket with a stereo TRS version and also wire the Ring and Sleeve together.  It gives you two contact points for the ground which helps noise much more than crappy thin copper foil.  The usual "slip in sleeve" ground connection for that type of socket can cause intermittent problems when it ages as there is actually no sideways force pushing the plug barrel against the socket sleeve.  You can even sometimes feel them rattle slightly in the socket.  With an additional sprung ring contact there is a sideways force from the offset Tip and Ring blades which achieves this and gives that better ground security.

I'm not sure if you picked up on this from the original posts here bu just in case, if you are using your footswitch with the H&K setup you need an LED inside it in series with the switch without any resistor.  If you wire the LED across the switch you will make the amp think the switch is permanently closed as, when the switch is open, the LED then acts as almost a short to the line in place of the switch.  In series it will work in the same way as the LEDs inside the amp.  So you should wire it as:  Plug/Cable Tip in -> LED anode; LED Cathode -> Switch Contact 1; Switch Contact 2 -> Plug/Cable Sleeve.  Switch Contact 1 and 2 should be the centre wiper terminal and either outside one.

I'm not surprised you will get a response from your LED when you meter it for resistance.  The meter puts a voltage across the probes and measures the current that it takes.  If your LED happens to be across that you could well light it up slightly.  It's usually at a high enough impedance that it can't cause any real damage to normal circuitry.

In my day job, (retired now), I used to design electronic circuitry for the audio and then the seismic industry and I also programmed for the seismic and defence industries too.  Now I just make a nuisance of myself poohpoohing the lies, myths and legends of the music electronics business.  And there are MANY!  And it's a great pool of people wanting to desperately believe those lies, myths and legends.  Sadly, you can only make a few of those people think about it before believing.  All good fun.

“ I'm not sure if you picked up on this from the original posts here bu just in case, if you are using your footswitch with the H&K setup you need an LED inside it in series with the switch without any resistor.  If you wire the LED across the switch you will make the amp think the switch is permanently closed as, when the switch is open, the LED then acts as almost a short to the line in place of the switch.  In series it will work in the same way as the LEDs inside the amp.  So you should wire it as:  Plug/Cable Tip in -> LED anode; LED Cathode -> Switch Contact 1; Switch Contact 2 -> Plug/Cable Sleeve.  Switch Contact 1 and 2 should be the centre wiper terminal and either outside one.

I'm not surprised you will get a response from your LED when you meter it for resistance.  The meter puts a voltage across the probes and measures the current that it takes.  If your LED happens to be across that you could well light it up slightly.  It's usually at a high enough impedance that it can't cause any real damage to normal circuitry.”

Hey bud, I’m sorry for not responding back sooner. I was came back to post my findings and lo and behold, I think you may have answered the question to the problem I have been having! I wired the cable as explained in my previous post and I just couldn’t get it to work properly with the two external switches on the Carl Martin OCTA-Switch III no matter what. I couldn’t get the amp to go through the 3 stages like the FS-2 footswitch clean(no leds)crunch(1 led)and of course, lead(2 leds). The CM would turn on the lead led(red)on the amp but it was in reverse. I could switch it on with any preset as long as the external switch was in the off position but if it was in the on position and I hit a preset, the lead led would come on. Butttttt....I could never get the amp to go through the three stages ever. I could never get the blue AND the red leds to come on together giving me the full lead channel.

I tried a stereo cable with a ring/tip Y cable at the CM end for the two external switch jacks and that didn’t work either. So, am I understanding that I need to have the leds from the FS-2 wired into the mix to get the switching to work On the TM18? I am obviously doing something wrong here. What am I missing here?

Here’s a couple of photos with my rig set up at home. There is nothing currently plugged into the external switches mentioned which is on the left side of the CM. Also, I would normally have my old Arion stereo chorus at the end but it went south. Still, that CE-2 is no slouch but it isn’t stereo and the 8th loop on the CM has a stereo return. Fortunately, reverb pedal is stereo so I had to swap them around. I’ll be adding a new stereo chorus back to the end of the line. Anyway, I hope you can help me get this figured out. I would love to have the channel switching working with whatever preset I needed them to.

Sounds like you enjoyed what you did and actually in a sense, are still doing. Busting myths, eh? I’m glad there are people like you out there brother.

Please let me know what I’m doing wrong with this if you can. I am so close to achieving the rig I’ve dreamed of for years. This setup rocks! I just need less to do to so I myself, can do more. Cheers!!

I misread your post. I thought you were saying that you needed to have the leds that were on the FS2 footswitch itself. I read that too fast. ‍� I can still use the FS-2 like normal until I get this thing figured out.

Aha!  Clean, Crunch, Lead?  I think you mat be looking for the wrong thing here Rumworks.  The TM18 only has 2 true channels, Clean and Lead.  The TM36 is the model that has the three channel preamp.  One of your switches should toggle between the channels and the LED for that switch should show Off for the Clean and On for the Lead.  The other switch kicks in the Boost function for both the Clean or Lead channel depending on which is selected at the time and its LED obviously shows whether the Boost function is On or Off.  That should simplify the view of what you are seeing.  Try your amp out again with that in mind and see if it is performing as it should.

Well, what I mean by “clean, crunch and lead is that when both leds are off on the FS-2 pedal, the amp is in a clean mode. When you click the left #1 foot switch, it lights the left red led on the pedal and lights the blue led on the front of the amp and ignites the crunch mode. When you click the right #2 foot switch along with the left foot switch engaged, it lights the right red led on the pedal and also lights the red led “with” the blue led on the front of the amp. So both leds are on on the FS-2 pedal and both are on on the amp. That’s the normal operation which as you stated is just that. The foot switches are either on or off. The pedal works just like it should.

Enter the Carl Martin MKIII pedalboard. This is where I’m having my problem. “Supposedly”, the two external switches are designed to allow you to switch the channels on your amp the same way the FS-2 pedal works. It allows you to determine which of these two external switches will engage when you tap a preset switch that has the external switches programmed to do so. I have tried everything to make this work but the only thing I get to happen is the red led(lead channel)on the amp lights up when the external switch(Whichever one I’m trying) is actually turned off instead of when the dipswitch for it is turned on. It works backwards. I can’t get the blue led on the amp to engage at all. I can’t get the red and blue to work together to get me to the lead channel. All I’m trying to do is get the Carl Martin external switches to function just like the FS-2 does. According to CM, this is possible but it doesn’t work.

I can’t believe how difficult this simple procedure has become. I don’t want to take the CM apart. It sounds as if the CM external switches are wired backwards. I still don’t know if it would work if I reversed that inside of the CM. It would certainly VOID my warranty. lol

Something just doesn’t add up at all. ‍�

Ok, I've had a closer look at the Octa-switch manual. Here is the relevant portion. I've corrected the English!

"The Octa-Switch has two external switching jacks for changing channel on your amp, or other operational features. Operation is very simple as on the two corresponding DIP switches you simply engage which of the presets 1-8 you wish the amp to change channel or turn on reverb, boost or other operational features.

So, say, you wish to shift to a high gain channel on preset 6 via external switch 1. You simply engage DIP switch 6, so now every time you enter preset 6, the amp goes to the high gain channel. Please note that the different amps' switching systems vary so we recommend using a stereo jack and then trying to solder either the hot on ring or tip until the wanted result is achieved. The External switches are Latching. We suggest you check if your amplifier can work like this."

This seems simple enough but I may have this wrong as there isn't too much info in the manual to expand on it. They don't tell you for example whether LEDs on your FS2 will switch on with correct polarity as this depends on how the switching of the Occta-switch has been implemented. My guess is that you plug a switch into say External 1. This allows you to turn on the Lead channel select from the switch but only for those Octa-switch selections for which you have it enabled. Effectively there are two switches which have to be set correctly to access the channel select.

By setting up the DIP switches on the Octa-switch near each of the external switch sockets you are meant to define which of its selections will offer control through the FS2 to turn the Lead channel on. Let's look at that DIP switch. It has 8 bits to set. Each one of those bits represents a switch channel on the Octa-switch. If you set bits 3, 4, 7 to On then each time you select 3, 4 or 7 on the Octa-switch the Lead channel should be enabled to work via the FS2. For all of the other bits and their associated switches, that's 1, 2, 5, 6 and 8, the Clean channel should be selected and the FS2 can do nothing about that. If you want to control every OS selection via the FS2 then I think you have to simply set all of the DIP switch bits to On.

The other complication you have is the wiring. The Octa-switch uses mono (TS) sockets in order to connect to a single switch. The complications of that is that, if you plug in a Stereo (TRS) plug such as your FS2, the socket will simply short out or ignore the Ring connection on the plug and respond to the Tip connection in the case of both sockets. You can use your FS2 but whichever external switch socket you plug into will use the Channel switch as that is the one attached to the plug tip. That is where your splitter cable will come in as it takes the Tip and Ring and breaks them out to the Tip of two separate cables.

Try just this. Attach the FS2 to the socket of External Switch 1. Switch ALL of the DIP settings for ES1 to On. See if all of your 8 selections on the Octa-switch now respond to the FS2 Channel switch. Don't worry if not everything works as you want yet, just let me know what happens.

I was just writing a query to Martin Support asking for technical info regarding their sockets when it occurred to me that I may have the wrong end of the stick for those External Switch sockets.  They are NOT there to connect to a FS2 type switch unit directly.  They are simply to run cables directly to the amp to control its Channel and Boost functions.  I don't think you can use the FS2 in conjunction with the Octa-switch at all.  I don't think you really need to

The idea is simply to connect the amp directly to the OS2 and control its channel selection from the DIP switch for that socket.  Let's say you connect the socket on the amp to Ex1 on the OS2 by a simple mono TS lead.  You should then be able to set the DIP switch on the OS2 for Ex1 to whichever Banks you want the Lead channel selected for.  You can expand this by having a TRS type lead to the amp which is then plugged into the OS2 via a Y-splitter to take the Ring and Tip out to separate TS plugs.  That way you can control the Channel and Boost separately on EX1 and Ex2.  You will then have to set up separate Banks for each combination you need to use.

However, if that is correct there is another way!!!!

The H&K amps have their Lead Channel selected and Boost turned on by shorting the Tip or Ring of the lead to the Sleeve which is ground.  The amp circuitry then responds to the grounded line.  If you REALLY need to have the Lead channel only engaged on some Banks on the OS2, and you want to then be able to change the Channel selection on the fly independently of the OS Bank setting you will need to put the FS2 switch and the OS2 switch in series.  You cannot do this with the wiring as it stands. You will need to mod your FS2 to be able to carry cables from both the OS2 and the H&K amp.  If you are ok with this then I can show you the wiring which will be pretty simple.  You should use the OS2 to ground the signal and put the FS2 switches between the amp and the OS2 sockets.

Let me know what you think.

Here is an idea of how it can work.  Bear in mind this will make the switching action to be:

Overriding control sits at the Octa-Switch DIP switch.  Enable the FS2 switch here for particular banks.  All unset Dip wafers (banks) will be forced into "Clean only" mode.  It will be impossible to engage the Lead Channel on the FS2 if the DIP switch is set Off for the selected bank.

If the switch is enabled at the Octa-Switch then the FS2 switch becomes the controlling factor.

The FS2 LEDs will keep their present action, i.e. matching the amp.  I cannot guarantee what the Octa-Switch LEDs will show at the Ex1 and Ex2 sockets.

It is just possible that we run out of voltage and the LEDs may be too dim to be of use but I wouldn't think that would be likely.

How does this fit with what you want?

So, are you saying that I keep the FS-2 in the loop between the CM OCTA-switch and the Tubemeister and wire one stereo jack from the FS-2 to just one of the external switches on the OCTA-switch? Then keep the switches both in the “on” position on the FS-2? Will this setup allow me to be able to go between all three channels of clean, crunch and lead using just one of the external switches on the OCTA-switch for any preset? In the normal operation of the FS-2, I have to have both pedal switches engaged to get the lead channel on and only the left pedal switch on to get the crunch.

I’m really sorry for all the questions brother. I just don’t understand this very well.
I just realized you had two other posts above this. Thank you for spending so much time in trying to help me get this right. I’m not sure I have it figured out just yet but I’m sorting through all of this at the moment.


‍�‍�‍�

My apologies Rumworks.  I posted there what was the concept without thinking it didn't reflect the finished setup.  I have replaced the original pic with one that shows what you spotted, that the Octa-switch needs to have the two separated lines, one to each of its switches.  I hadn't taken into account in the diagram the Y-Splitter which you have to add at the OS2 end to give you those two TS lines from the single FS2 TRS one.

Check out the updated pic and see if it makes more sense now.

"Will this setup allow me to be able to go between all three channels of clean, crunch and lead using just one of the external switches on the OCTA-switch for any preset?"

No it won't!

You are still missing this point and it is important to see clearly what you are doing.  The TM18 does not have three channels which are all selectable, it only has two, the Clean and Lead.  There is no Crunch channel.  Channel selection with its own dedicated switch can only swap between these two channels Clean and Lead.  It has a Boost function which can be applied to both of those channels.  The Boost function is nothing to do with the channels, they are both totally separate functions. The Clean/Lead selection is handled by one switch and the Boost On/Off is handled by the other.  The FS2 cannot operate both from one switch keeping them independent, nor will the OS2 be able to.  You effectively get four combinations by using the two switches:

FS SwA	FS SwB
Clean	Boost Off
Clean	Boost On
Lead	Boost Off
Lead	Boost On

Your only other option would be to use both wafers of a single DPDT switch, one for each function, and toggle both selections at the same time every time you hit the switch.  That way you could go between two of those options but never between all three.  You cannot step between three distinct states with a single two way stomp switch or even the OS2 internal relay switch.

Here is the thing.  I think I'm right in assuming what you are calling the Crunch channel is actually the Clean channel with Boost engaged.  As I said, there is no Crunch channel in the TM18, you can only swap between two.  The only way to access that is via two switches to change both Channel and Boost functions.  Your OS2 can handle that however as it does it by controlling both the switches.  Assuming you then wanted individual control of both functions with the FS2 overriding the OS2 you would still have to toggle both switches to go from Lead Boost Off to Crunch (Clean Boost On).  One switch must change from Lead to Clean and the other must turn the Boost function On.  It is possible to design switching units to select between three different states but it would involve a PCB and a fair few logic chips to generate the switching controls.  Here we have two independent conditions intertwined and controlled separately from each other.

If I have the picture of what you are looking for correct you want to be able to do just that, step cyclically between the three states which you are thinking of as channels:-  Clean Boost Off;  Clean Boost On; Lead Boost Off.  That must entail hitting two switches to go between the last two.  Your OS2 can make that automatic for you but when you want to extend the control to include on the fly switching with the FS2 the change between Clean Boost On and Lead Boost Off will require a press of both switches.  There is no way round it that I can see without building a pretty major piece of logic electronics.

My first H&K amp was a TM36.  That has 3 channels.  These were controlled via their own FS2 2-button footswitch.  They had an unusual action.  The first switch swapped between Clean AND (Crunch OR Lead).  The second switch then swapped between Crunch OR Lead.  This meant some unusual thinking but it was possible to do almost anything with a single stomp.

Left switch = Clean / NOT Clean (effectively swaps between Clean and one of the other channels set by Right switch)
Right switch = Crunch OR Lead (even when Clean is selected with the Left switch the Right switch will set up one of those channels for when the Left switch is pressed next.

Clean <-> Crunch   Left switch 1 press (with Right switch already set to select Crunch)
Clean <-> Lead   Left button 1 press (with Right switch already set to select Lead).
Crunch <-> Lead  Right button one press (with left button already set to select NOT Clean).

It is possible to set up this sort of action with your existing FS2 if it has double pole switches (6 terminals and not just 3) and leave out the OS2.  (EDIT: Just checked it out and it doesn't even need double pole switches, the cheaper single pole will do it).  You would also lose the ability to control the Boost function independently as both switches would be used for channel selection set up as Clean (Clean Boost Off), Crunch (Clean Boost On), and Lead (Lead Boost Off).  One switch would swap between Clean and Drive (Crunch or Lead) while the other switch swaps between Crunch or Lead when allowed by the first switch setting to Drive.  Also any LED action would be a little unusual to match the switching action.  I solved that by designing a bit of logic circuitry which switched the LEDs between Red/Yellow/Green according to the channel but remember, mine was a TM36 with 3 definite distinct channels and I am used to designing and building circuitry and PCBs.  Your TM18 is not the same channel setup.

How does that idea suit?

Bert, yes... you are correct in assuming how I was defining the actions of the footswitch operation. It isn’t clean, crunch and lead. It is exactly how you described it. All I have been trying to do is make the OCTA-Switch’s external switches operate exactly like the FS-2 does normally. I wasn’t trying to change that at all. I’m sorry for not being more clear in my description in the beginning.

So it looks like by your “updated” drawing that I am in fact keeping the FS-2 in the “loop” so to speak and depending on which presets I want to engage either of the two FS-2 switches will be dictated by the dipswitch selected as it should. In other words, if I want preset 1 to engage the boost only, (if I’m using the foot switches respectively with the external OCTA switches hence fs-2 switch 1 with external switch 1), Then I would have the dipswitch for external switch 1 set to on and I would leave the fs-2 foot switch 1 on all the time. Same for the lead channel. Basically, I will leave the fs-2 switches on all the time and depending on what preset I have programmed to turn either of these on will kick them on accordingly. So, I can in turn have let’s say, preset 7 to activate both external switches which should give me the boost/lead channel. Either way though, the FS-2 is still being used between the OCTA-switch and the TM18? If this is correct, I will wire that up ASAP.

Man, thank you so very much again. If I were near you, I’d be buying you pints of Newcastle! I have a set of Newcastle pint glasses here at the house that I’ve had for years. It’s not a bad brew at all!

One question regarding your new updated image. If I want to use the CM’s external switch 1 for the clean boost, do I need to reverse your wiring chart as far as the FS-2 is concerned? I would think the TM18 will only work one way correctly right, or does it matter?

I’ve lost my mind Bert! I don’t have to reverse the wiring at all. I can just swap the jacks at the external switch inputs. ‍�

Bert, I wired it exactly how you showed it with the updated diagram and well sir...it worked!!! It is working exactly like it should. The LED’s all function properly as well. I can’t thank you enough mate, seriously. I’m glad you didn’t throw in the towel.

Wow! I didn't think things would move as quickly as that!!! Full marks to you for getting your hands dirty straight away and I'm really glad it's doing what you want right off the bat, (and a little surprised if I'm honest ). Anyway, for now get some good use out of it. I will say that I think your idea of setting the amp up so it effectively has expanded the TM18 2x channels to a pseudo TM36 3x channels with the same TM36 switching process is a really neat one. I wouldn't have thought of that.

You know where we are if there is anything you need!

I had a good feeling about it and you nailed it. I’m guessing that was pretty basic stuff for you, eh?

Believe me, if I have another technical question, I know where to go!

Here are a few photos of the LED’s lighting up correctly. Of course, the LED’s on the TM18 correspondence with them too. Me tips me ...

Bert...


I hope all is well. Everything is working fine here. Thanks again.

I have a question. It might sound crazy but here goes...is there a way to measure the output of a particular effect pedal that would allow you to adjust the volume(or output)? In other words, say I could adjust the output knob on each pedal to be the same so that they’re all putting out the same level so to keep the effects at the same level? For example, when you changed presets on the pedalboard, you wouldn’t be able to notice a difference in volume when you changed to possibly a different effect that wasn’t on on the preset you’re switching from. Does that make sense? Is there a way to use a meter attached to a cable with a mono quarter inch jack that you could plug into the output of a effect pedal, then measure that output while adjusting the level on the pedal? Is that even possible? To do it with a meter instead of balancing by ear so to speak.

Rick

I think I get what you are saying but it is a difficult thing to set up.  Your suggestion seems to be that different combinations of pedals are difficult to balance against each other which we all know is true of course.  Setting a Modulation pedal and a Distortion pedal to output levels where they sound right individually does not guarantee that the level will stay the same when you kick them both in together.  That's always a problem for me too so if anyone has a real solution we would love to hear it!

The problem is that an individual pedal used alone is being fed your guitar signal and it puts out its own processed signal at a different level according to the processing it performs.  This can usually be adjusted with an output level control so let's say you set its output so that it gives a slight boost to the processed signal because that sounds best for the individual pedal.  Another pedal which can follow that now has two situations to deal with where, when it is used alone, it has your plain guitar signal fed into it, or when both pedals are used it could have the signal from the previous pedal fed to it which is now amplified by that first pedal.  Without adjusting levels for each case it is inevitable the second pedal will sound different under both options and the amp will be hit with two different levels of signal depending on selections.

The only think I can suggest is that you set up all of your pedals to give your tonal choice into a clean amp by adjusting the pedal input level.  When the sound is right, adjust the output level of the pedal so it gives the same perceived loudness when it is in or out of the signal path.  Do this for every pedal in turn individually so then each pedal is giving out the same signal level as the guitar itself, as much as is practically possible.  When you switch a pedal in or out it should then not affect the overall volume level.  If you use a Boost pedal this should then be at the back end of the setup otherwise it would affect the level of signals fed to the other pedals after it.  That may not sit well with some peoples' ideas of how to get the best out of their pedals so bear in mind, I am not suggesting this is the way things should be done, only that it helps with your own problem.

On the tech side of this...  The volume we hear is not just a feature of the voltage level of a signal so measuring the peaks of a very spiky shaped signal, which would be fairly easy, would not necessarily be of use to us here.  The other alternative is to imagine the signal voltage on an oscilloscope as a curve almost like a graph with the x-axis left to right representing time and a y-axis up and down for voltage.  Our perceived volume of the signal when we hear it is more based on the amount of area between the signal and the x-axis.  The larger that area is the louder we perceive the level.  A clipping type distortion pedal does not sound much quieter as it comes into action even though it is removing some of the signal level from the highest points.  It is actually removing more of the thin spikes with not too much effect on the overall area.  It is possible to build a unit which would measure that area, it is the equivalent of integrating the signal, but it would be an independent piece of specifically designed and built kit as complex as another pedal on the board.  Even having the ability to measure this it would not be of too much help over using your ears in this case.  (You won't find many areas where you will hear me say that!  )

I do think that, even knowing what the levels would be, you would still have the same problem of balancing as that measuring unit would not be making any changes dependent on selections.  It may tell you what the levels are but it won't adjust them for you.  I have to also say that I run a very simple pedal board by modern standards.  I have my own designed and built flat response buffered input switching unit to swap quickly between two guitars on stage, an Origin Effects Sliderig CD Mk2 Compressor used only for slide work, a Blackstar Dual HT valve preamp pedal which I use mainly for Boost and to add clean bite and an occasional bit of "Strat feel from a LP" which it does fairly well, and a venerable Marshall Bluesbreaker pedal for basic boost and lead overdrive.  I do have boost/overdrive/distortion pedals of my own design and build which I swap in from time to time but I'm not a tone freak and I find I can live with any of these distortion pedals really.  Yes they do sound different, but it isn't of too much real importance in a live setting.  Have you already tried the basic practical procedure I described?

I'm hoping someone has some insight on my problem. I followed the simple schematic (led, resistor (1K), spdt footswitch, in series) and converted a Fender double footswitch to work with my Tubemeister 18. It switches the LEDs on the pedal and on the Tubemeister, but it doesn't change channels or engage the boost (again, only the LEDs on the front panel change.) When I remove the cable (it's a stereo, TRS) the pushbuttons on the TM18 work as expected. I researched and found that the square (5x5x7mm) LEDs on the footswitch have a slightly higher Fv drop (about 3.4VDC) so I took a generic two switch DPDT pedal (no LEDs,) added the series resistor (1K) and LED (standard T-1) and tried it. Same results.  Any thoughts?

You are adding in the 1K resistor and that is the problem.  The TM18 switching is achieved by simply grounding the coil of the reed relays.  Their supply voltage is 22V and they have 12V coils so there is a resistor in there in series with them to take up the other 10V.  There are also the internal LEDs in series with them too.  That resistor is 220R or 470R depending on the number of LEDs.  If you think about it you are dropping the voltages across these devices with your switch LED but if you use a sensible LED with a low Von you will not make too much difference.  Put a 1k resistor in there too and you have a problem!  That drops the current through the whole thing down to below the striking level of the relay.

You are absolutely right in your thinking, that an LED MUST have a current limiting resistor to control its current.  That resistor is already in place inside, the 220R/470R.  Try just using the LED in the footswitch without your 1k resistors and it should work.




EDIT:  I think I can see where the confusion has come from lousaad.  It looks like you picked up on the diagrams from early in the thread. Try looking at my Post17.  You will see there that I revised my original diagrams with the resistor in them once I had the schematics of the TM18 and could see exactly how it had been set up. My original advice was based on the idea of controlling this via the voltages involved. With the simpler (and more effective) TM18 approach of grounding the coil directly it actually works around current. Hence the controlling resistor is already fitted.

THANK YOU BORDONBERT! You are correct. I didn't notice the updated diagram. I removed the CLR and it worked fine. I knew there was a voltage drop issue, but was looking in the wrong place. I didn't consider there was another CLR in the amp, thinking 'I can't remove the CLR in the circuit!" Anyway, THANK YOU for your guidance!!

bordonbert wrote:You are adding in the 1K resistor and that is the problem.  The TM18 switching is achieved by simply grounding the coil of the reed relays.  Their supply voltage is 22V and they have 12V coils so there is a resistor in there in series with them to take up the other 10V.  There are also the internal LEDs in series with them too.  That resistor is 220R or 470R depending on the number of LEDs.  If you think about it you are dropping the voltages across these devices with your switch LED but if you use a sensible LED with a low Von you will not make too much difference.  Put a 1k resistor in there too and you have a problem!  That drops the current through the whole thing down to below the striking level of the relay.

You are absolutely right in your thinking, that an LED MUST have a current limiting resistor to control its current.  That resistor is already in place inside, the 220R/470R.  Try just using the LED in the footswitch without your 1k resistors and it should work.




EDIT:  I think I can see where the confusion has come from lousaad.  It looks like you picked up on the diagrams from early in the thread.  Try looking at my Post17.  You will see there that I revised my original diagrams with the resistor in them once I had the schematics of the TM18 and could see exactly how it had been set up.  My original advice was based on the idea of controlling this via the voltages involved.  With the simpler (and more effective) TM18 approach of grounding the coil directly it actually works around current.  Hence the controlling resistor is already fitted.

No problem lousaad.  Glad it worked out ok.  And I'm glad to see you actually already have an idea of how LEDs work.  They are NOT bulb substitutes as most people want to treat them.  It's absolutely essential to realise they are current controlled so you can't do without the resistor setup to define that, (or sometimes even better but more complicated constant current configurations).

The guys at H&K might not always see eye to eye with us as to what to design into their amps but they sure as heck do their design work correctly once they are implementing it.  That area of footswitch control is flexible the way they have done it.  The only thing I can add is that it is even possible to design and build a multicolour LED switching system if you can remote power the footswitch, perhaps from your pedal board supply.  I've done that in the past and it means then you can easily define your colours and brightness just as you wish.  Just a thought.