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    TU 18 Footswitch

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    Eighthnote

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    TU 18 Footswitch

    Post by Eighthnote on Tue Oct 13, 2015 9:25 pm

    Hello all.............new to this forum. I own a Tubemeister 18 and need to be able to use the foot switch. Not much luck so far. I'm going to post two pics here. One is of a std. 2 button (stereo plug with LED) foot switch. The next pic is the schematic of the same switch. I know why a Am7 and a Cmaj6 is the same but I don't know why this F&*^%$#$ pedal doesn't work. If someone with the electronic thing going on can explain it to me I would very much appreciate it.
    Let be clarify what I mean by the foot switch doesn't work. It works, the LEDs on the pedal light up and turn off. However as soon as I plug into the head it activates the lead channel. When I press the right foot button the clean channel (yellow light) comes on but the lead channel light stays on. The amp does not go to the clean only channel. I would think that when I plug this foot pedal in nothing would happen until I press one of the buttons. No clean channel with the foot switch is possible even though the yellow clean light is lit. HELP............Thanks......... bounce

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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Wed Oct 14, 2015 7:49 am

    For that switch to work it depends on the way the unit responds to the signal levels. You have a situation where the control signals on the tip and ring are being fed from an output impedance. You have switches which short it down to ground on the sleeve or leave it open. But when they leave it open there is a LED and 1k resistor across it. If that is a low enough impedance the amp may still detect it as a short in relation to its own impedance! So you would have both signals shorted in any switch position.

    Are you able to temporarily disconnect the LEDs to try it with just the switches?

    I remember posting something about the signal logic and levels in a previous thread. I'll have a look when I get a minute and get back to you.
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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Wed Oct 14, 2015 7:58 am

    Have a look at this thread when you can.  There is info in there which might help.  We can go forward from there.

    Control Voltages
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    Eighthnote

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    Rats

    Post by Eighthnote on Wed Oct 14, 2015 1:53 pm

    bordonbert wrote:Have a look at this thread when you can.  There is info in there which might help.  We can go forward from there.

    Control Voltages

    Well, that's slightly over my comfort level without some help. Having to disconnect the LED's is disappointing but it is what it is. I'm posting a pic of the wiring inside. If you could step me through what I need to do I do have some soldering ability. I just do not have the electronic background. If you could give me an option for leaving the LED's working that would be great. If it's just a matter of taking the resistor and LED's out of the loop then it is what it is. Thanks for the guidance.

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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Wed Oct 14, 2015 6:43 pm

    No, you misunderstood what I meant.  I was saying just disconnect them temporarily to prove it is the LED current which is the problem.  Once you have disconnected them, (at one end only and it looks as though breaking where the resistor and LED join may be the easiest spot), you will be able to see whether the switches then work without them attached.  That way we have proved that it is the LED current draw which is false triggering the system.

    If that proves to be the case then we can try to simply increase the resistor value to a point where it does not cause the problem.  I would guess about 10k though you may get away with less.  Unfortunately that will probably mean a noticeable decrease in the light output of the LEDs.  You may be able to get away with a not very high resistance and still maintain a sensible light output.

    Did you catch the part where I mentioned that with the type of switch setup you have you cannot get the LEDs to function like the ones on the amp.  If you can get these to work you will have the following indications.

    LED1: Clean / Drive
    LED2: Crunch / Lead

    Clean: LED1 ON / LED2 ON or OFF (as currently selected by switch 2)
    Crunch: LED1 OFF / LED2 ON
    Lead: LED1 OFF / LED2 OFF

    Without powering the unit and adding a LED control circuit block you can't do better than that I'm afraid.

    EDIT:  Wait a minute, you may be able to do better.  If we find we can make the LED work without triggering the control switching we can add a second LED for the Crunch/Lead selection.  Then we can set one side of the Crunch/Lead switch to work with one LED and a high resistor value without shorting, and the other to work as it is now with a low value resistor to short.  That way you have an LED for every selection.  The resistor values are the key thing there.  LEDs will not necessarily be balanced in light output though and you still haven't solved the problem of the Crunch/Lead selection LED being on when you are on the Clean channel.

    EDIT EDIT: Just had a brainwave.  Yes you can solve the problem of the Crunch/Lead LEDs lighting up when Clean is selected.  The switches are DPDT types and have a whole spare section which is just currently paralleled up.  We can use that to short down the Crunch/Lead signal from the jack ring while the Clean is selected on the Clean/Drive switch.  That way the Drive side LEDs are extinguished until Clean is deselected then the short is removed and their own switch controls their action.

    This depends on you finding out about your switch working without the LED attached.  Be careful when you disconnect the LED.  Make sure to have the heat applied for only a couple of seconds otherwise you will burn out the LED.
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    Eighthnote

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    Re: TU 18 Footswitch

    Post by Eighthnote on Sun Oct 18, 2015 5:34 pm

    Hello, thanks again. Here's where we're at with getting the FS to behave. I took my soldering iron and simply heated the joint where the 1K resistor was soldered to the lead off the switch. Both switches of course. Pedal works exactly like it should. No LED's but the lights on the amp head and my ears can tell me everything I need to know. Next I will track down some higher value resistors starting at 10K and if I understand your electronic lesson correctly I can re-introduce a resistor into the circuit. Am I on the right track here? Thanks again.
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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Mon Oct 19, 2015 2:27 am

    Haha! I love it when a plan comes together! Well done Eighthnote, exactly what was needed. You have proved that the problem is the LED and resistor drawing current and the TM interpreting that as a short and a sign that it needs to switch. What we now need to do is to get a higher resistor in there and reduce that current until it doesn't see it as a short. We can then see if the LED will still give enough light at that current to be useful. If you can hold off for a couple of days I will dig out my own TM and check it out here as I have a full range of resistors to test with and can then tell you what works.

    Incidentally, as well as the LEDs, be very careful with the amount of heat you put into those switches. I have worked with that type and can tell you they are soft and delicate! The whole unit softens and distorts very quickly and the terminals move around making them unserviceable with just a little too much heat.

    Just as a final observation for now, it ALWAYS pays to take a logical engineering approach with guitar kit. It is just another arm of engineering and the whole concept of "mojo" is simply "engineering that we haven't explained yet". Except that most of it HAS been explained but the die hard mojoists don't understand it and insist that things are down to "just knowing". If you train yourself to look at every problem with an engineer's eye along with your musician's ear you will not only fix it faster and more reliably and often cheaper, you'll also understand it and be able to fix more complicated issues in the future. You get better and more able that way, not just appear to be cleverer.

    I'll get back to you with some findings when I've had a chance to try it out.
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    Eighthnote

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    Re: TU 18 Footswitch

    Post by Eighthnote on Mon Oct 19, 2015 2:46 am

    Perfect. I look forward to what you find. FYI.......I really didn't have to apply heat directly to the switches. Whoever designed these things actually soldered a separate short wire from the switch terminal so the resistor is actually soldered to this short wire. Looking at the wire into the LED's off the resistor though looks problematic. That wire appears to go right into the small LED's without any real access to where they connect. One thought is to simply cut those wires near the LED's and use them to solder the new resistor into the circuit. Just like the short wires near the switch. Right now I'm just happy the switch works and my amp head responds as it should. Cheers..............
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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Tue Oct 20, 2015 11:13 am

    I've talked to H&K service team about this and they are more confused than we are. geek They are trying to convince me that we need a smaller resistor rather than a larger. That doesn't work either in theory or in practice! I've tested this here on my own TM36 and in fact I get perfect functioning with a LED + 1k resistor, yours must be a tad more sensitive than mine or the LED choice makes a difference. Either way you can't be far out with that 1k.

    I have perfect working with a 1k5 resistor, though the LED is a little duller. I would start there. As resistors are so cheap try to get 1k5, 1k8, 2k2, 2k7 and select the lowest value which works for you out of them. You could test just the resistors manually by holding one without the LED across the stereo jack plug tip to sleeve until you select one where the channel doesn't change. The addition of the LED would then give you a little safety margin.

    So you don't need to go to a really high value to sort this out at all, just a slight increase from your 1k should work.
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    Eighthnote

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    Re: TU 18 Footswitch

    Post by Eighthnote on Tue Oct 20, 2015 11:59 am

    Thanks for the info. I had you until you wrote " You could test just the resistors manually by holding one without the LED across the stereo jack plug tip to sleeve until you select one where the channel doesn't change." ....... I've got the "across the stereo jack plug tip to sleeve" but I'm missing something. The stereo jack plug would be inserted into the foot switch jack. I do not understand how I could place a resistor tip to sleeve while the stereo jack is in the socket. I could do that inside the switch box by removing the 1K and manually hold higher values incrementally where the 1K was located. Straighten me out here.........what am I missing? Thank you again for your help.
    Another variable I see when buying resistors that there a 1k8 1watt and 1k8 2watt. Can you enlighten me on why or why not I should use one or the other? Again thank you.........
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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Wed Oct 21, 2015 3:51 am

    Sorry, I should have explained a bit more. I use two double footswitches on my pedal board and I've put my footswitches on it with my other pedals. I fitted a small sheet aluminium panel at the back to carry two jack sockets. I cut the switch leads short and fitted the two jack sockets in p[lace of the plugs and mounted them on the panel so the switches are now an integral part of the board. I then just set up the board with the usual connections plus two stereo jack leads to the amp carrying the switching, one to the channel switches and the other to the effects/loop switches. It just makes the whole thing more portable.

    I meant that with the stereo jack inserted in the amp you can work on the other bare end. For the test you can use either use a stereo jack lead if you have one or just a plain old mono guitar lead. Just insert the jack lead into the channel switch socket on the amp. If it is a normal mono plug, the Crunch/Lead switch on the ring will be permanently shorted out selecting Lead but that isn't a problem at the moment as the Clean/Drive switch will still work perfectly on the tip. Do your testing across the tip and sleeve of the bare plug at the outer end of the lead.

    The resistor you want is the smallest you can handle. There is absolutely no power worth worrying about being dissipated in these resistors so 1W or 2W would be wildly oversized for your needs. 1/8W or 1/4W will be perfect.
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    bordonbert

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    Re: TU 18 Footswitch

    Post by bordonbert on Wed Oct 21, 2015 9:38 am

    And the penny has dropped and I have the answer to this puzzle!

    From a user review of their FS-2 footswitch I found that H&K use the following indications:  Clean = No LEDs;  Crunch = 1 LED;  Lead = 2 LEDs.  Now that is different to what your footswitch would produce.  And the answer is because H&K wire up their LEDs differently.  They don't put them across the switch, they put them in series with it.  To set it up like H&K you need to change your setup to be something like this:

    " />

    That shouldn't take too much doing.  The 1k resistors are totally optional!  The circuit will work without them being there at all with a higher light output.  If you want to remove them just bridge across them in the schematic.  You will need to try it to see what the LED light level turns out like.  I would wire them up with the 1k in there and just short across it with a short piece of wire to see the difference.  If you prefer it just solder the wire across.  That way you have a handy dimmer switch if it gets irritating by just removing it again.  Be careful with overheating the LEDs and switches as I mentioned before.

    Now this will mean that your LED indications change!  You now get the following logic: Clean: No LEDs;  Crunch: 1 LED;  Lead: 2 LEDs.  If you think about it that's logical.  Increased drive means more LEDs come on.  Or you could replace the Reds with any other colour you want and have a Yellow for Crunch and a Red for Lead to kind of match the panel lights.

    (Or you could go the whole hog and do what I did, build a little driver and logic circuit and power it from my pedal board supply and have them exactly the same as the panel lights, one on at a time for each channel and Blue, Yellow and Red. cheers )

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    Re: TU 18 Footswitch

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