Mods to Line6 DL-4 tap tempo?

[drfrankencopter]

Hi All,

Great forum you have here. A while back I bought a Line6 DL4 delay modeller and expression pedal. While the pedal has some pretty cool sounds inside, it frustrates me because while the expression pedal has so much potential, it always changes my delay time, making it useless for delays that need to be in time with the music.

I'd like to make a mod to this pedal to make the tap tempo maintened throughout the range of the expression pedal. Without having see the schematic (and without too much luck in searching) I was thinking of something like this:
- install a switch that allows standard/stock tap tempo functionality or replaces the tempo switch with a second circuit
- build a tap tempo circuit that outputs a pulse  in time with the tapped tempo...the output of this circuit will be routed through the aforementioned switch, and then to the tap tempo points on the PCB.

Basically, this would be kind of like what would happen if you kept tapping on your tap tempo switch all the time, but kept the timing consistant.

Would this work? Has anyone tried this.....or is there a more elegant fix to this issue.

Cheers,

Kris

[chokeyou]

those line 6 units are really tough to mod well. Its my understanding that the tap tempo stuff isnt really in the circuit at all...all the delay time parameters are set using the EPROM on the board (that way they can use the same board for all the **-4 pedals over at line 6 and just flash a different eprom for the different models) so adding hardware to it is kind of out of the question unless you can figure out a way to hack the tap tempo switch and hook it up to some kind of sequencer. like i said, its complicated and kind of useless.

You know, the expression pedal doesnt have to change the tempo at all...you could just reset your patch and then when you put the exp pedal in the opposite position, just dont move the delay time knob at all and you're good to go.

another thing I've done is I created a little addon to the DL4 that uses the expression pedal input as a means of switching between "presets within the models" this can be done by having a stomp switch switch between 0ohm and 10K+ohms. You can't use an expression pedal anymore...but you get consistent presets...

otherwise I think you're asking a little too much of the DL-4

[Processaurus]

The rhythmic delay model on the dl-4 maintains tempo with the expression pedal, as long as you have it set to the same tap tempo subdivision at the toe and heel position.  The only bummer is that model is a really plain sounding digital delay, unlike the other more exotic sounds... 

[drfrankencopter]

You know, the expression pedal doesnt have to change the tempo at all...you could just reset your patch and then when you put the exp pedal in the opposite position, just dont move the delay time knob at all and you're good to go.

What do you mean by "reset your patch". If I dial in the tempo using the delay time knob with the expression pedal say full down, the time is still changed when I go full up, except if I tweak the delay time again when the pedal is full up. If there was a fast and consistant way to do this I'd be set, but as it is I can't do this live....

Cheers,

KRis

[Transmogrifox]

I don't have a DL4, so I'm not clear on the issue...

But any mods you do will have to be  as you suggessted about "tricking" the tap tempo input.

The problem is that those Line6 pedals are not mod-friendly at all.  You will likely have to do some very cosmetically ugly things to the pedal to accomplish what you want, since you would have build a seperate sequencer type pedal using a programmed chip to interface with the tap tempo input.

I don't say this to put a wet blanket on your idea.  It's just that these digital pedals are very hard to deal with.  Mechanically speaking, they're typically designed to fit their own components and no more.  The real workings of the pedal are programmed.  There's nothing in hardware that can be changed.  It's like taking a soldering iron to your computer's circuit board to make the scroll button on your mouse to function as a pan and zoom on an html site.

The best you can do is to trick the software in any way it can be tricked...or go visit the Digital & DSP section of this site and learn how to program the chips.  Then you could develop your own DL4 and program a DSP pin-for-pin replacement...then you could desolder the existing DSP and put your own custom DSP in there and it would do whatever you wanted.  Unfortunately for you, this would take years to accomplish on your own, and by then it wouldn't matter any more because your band would have left you since you stopped playing guitar when you got into the programming thing.  Bummer Line6 doesn't openly distribute source code, eh?

[drfrankencopter]

I understand that most of the DL-4 happens in software, not hardware....I write real-time DSP code for a living, so I am no stranger to the routines, but wouldn't dream of even attempting to write my own DL-4 type software since I cannot take advantage of the economies of scale that Line-6 have. Anything I could do would cost me 100X what a DL-4 would cost.

All that said, I did find a work around last night. Here's what works:
- If you set up a delay patch with the expression pedal in say the full down position, unplug it, and then re-plug it in you can move it to full up and not change the delay time. Maybe this is what the previous poster meant by 'resetting the patch'.
- If you wire a momentary switch in line with the expression pedal, you can then re-set the expression pedal on the fly, without changing the delay time. Bingo, problem solved. It's an extra button tap, but I think it will work.

Cheers,

Kris

[Dave_B]

It's like taking a soldering iron to your computer's circuit board to make the scroll button on your mouse to function as a pan and zoom on an html site.

Now that's clarity.  Nicely phrased.   

[drfrankencopter]

I don't think there's any reason to fear modding a digital pedal....you just need to know that some things cannot be changed. You also need to know a little about how computers and DSPs function. Something like the tap tempo switch is in all likelyhood a digital I/O signal (5V TTL) that sends an edge trigger to the processor chip to start a timing cycle. It's not that difficult to duplicate this sort of signal with another circuit. I believe that this sort of mod is quite 'do-able' without requiring any software mods.

The ideal way to do it, of course, would be to have access to the software and to make a simple code change that assigns tap tempo as a global variable for the patch instead of local to the two expression pedal extreme positions. But, there's no chance of that happening without Line-6 deciding to do it...

Cheers,

Kris