Converting Ibanez Soundtank to true bypass

[slowpogo]

I hope DIY mods are okay to discuss here. I have an Ibanez TL5 tremolo from the Soundtank series. This series is notorious for having unreliable switches that often take multiple tries to turn on/off. The tremolo is actually very good though so I decided to replace the small, cheap internal switch with a standard momentary SPST footswitch and see if I could remedy the issue.

The new footswitch works, but nothing has changed. It still often takes multiple tries to turn on/off so the problem is apparently not with the switch but with the transistor-based switching circuit.

I've found a lot of stuff on the internet about rehousing this series or replacing the switch as I did. But nothing about actually converting it to true bypass with a 3PDT switch. Anyone have an inkling of how to do this?  I found a schematic here:

https://www.dirk-hendrik.com/temp/ibanez_tl5.pdf

[bartimaeus]

are you sure there's  space in the original enclosure for a 3pdt? that could be the reason nobody's done it.

but even if there is space, rehousing is probably the best option for this sort of thing. you have a full schematic, so you could even just build a clone without the transistor switching circuit.

[antonis]

[slowpogo]

Beautiful, thank you! There is enough room for the switch, you just have to Dremel out a ton of plastic under the pedal portion. That's already mostly done for the SPST, I'll just have to do a little more on either side to fit the 3PDT. This will be a bit of a project though for sure, I'll need to either cut the input/output traces or desolder the jacks if that's not possible.

[slowpogo]

The other part of this is to remove the transistor switching system.  For this pedal that means removing TR2, TR3 and TR4 completely.  Then, wire together the outer leg pads of TR2, and the same with TR3, and leave the middle leg open for both. TR4 will remain totally open.

Now the pedal will be always on, and the true bypass wiring will take care of the rest.

I also found I needed to remove the LED completely from the board circuit and wire it directly to the DC input with a resistor in-line. Although it still seemed to be running through a current limiting resistor even with the mods, when I wired as above the LED would be fine for a few cycles and then burn out for some reason. Luckily I had a bag of 50 (pink naturally).

[antonis]

I also found I needed to remove the LED completely from the board circuit and wire it directly to the DC input with a resistor in-line. Although it still seemed to be running through a current limiting resistor even with the mods, when I wired as above the LED would be fine for a few cycles and then burn out for some reason. Luckily I had a bag of 50 (pink naturally).

Wire LED cathode on RED wire (marked LED-) on plug 3 od 3PDT switch as shown above..
What value of current limiting resistor did you use..??

[slowpogo]

Wire LED cathode on RED wire (marked LED-) on plug 3 od 3PDT switch as shown above..
What value of current limiting resistor did you use..??

That is how I wired it and that part hasn't changed. However I did end up moving the LED anode as discussed and the black wire on 2. I first ran the black wire back to the original cathode pad of the LED, which I thought was ground.  Something over my head may have been going on there because that pad had continuity with ground when I first tested it, but later after removing the FET switching it did not (?).  In any case I also ended up moving the black wire to one of the switch ground pads instead, just to remove that variable.

I ended up using a 4.7k resistor on the LED and it's been fine for a while now, so hopefully it's all good.

[antonis]

4k7 resistor counts for about 14mA (for a pink led) so I presume it will be fine for some time..
(your LED probably is a 20mA device so it should be better to use 5k6 resistor for a long-life healthy item..)

[slowpogo]

There's another artifact of this mod to mention. The volume knob now acts like a "blend" control instead of a regular output attenuator. Fully right is 100% wet, and fully left is a weak dry signal (kind of like having a second Depth knob, in essence) It's not really a problem because the effect volume matches the input volume (close enough for me anyway) when kept fully right.

But, what if I wanted to get the regular attenuation back? My first thought is to move the Volume pot past Q1 and Q2 which are part of the EFF_ON/OFF system (which has been disabled).  What about placing it between R42 and TR6?  Wouldn't be too hard to cut & jumper the appropriate traces and wire the pot into the new position.

[antonis]

What about placing it between R42 and TR6? 

Crackly/Scratchy pot..

Anyway, I can't see the reason for Level pot not working it's supposed to do..