Replace potentiometer in Boss FV500L to work with Line 6 Helix

[bsco]

That's a real problem if someone accidentally damages a newish pedal and no warranty repair is available. In any case, a lot of the newer pedals are very difficult and involved to repair and I've been saying for years that anyone buying a pedal should try to buy new to get the warranty.

either that or go buy pedals from the 70's...I have a few of those here.......at least those can be maintained......

[Mark Hammer]

If the OP wishes to use the FV500L with the Helix's expression-pedal input, the solution is actually quite feasible, quite cheap, and quite easy.

First, find out what the resistance of the control pot is. I'm guessing it is in the 25k-50k range for low-impedance source, but best to verify.
The Line 6 standard is, as correctly noted, a 0-10k variable resistance to ground. So, the second thing you need to do is identify which contact on the output jack is for the pot wiper, and which for pot input. We will want to use ONLY the wiper and ground in this application. Manufacturers will vary in which contact they assign to the tip and ring contacts of the jack/plug.
The plug you insert into the Helix should be a simple mono tip/shaft (TS) type. You CAN use a TRS plug, but only the tip and shaft will be used.

Having identified the pot and jack contacts on the FV-500L, and making sure that the pot wiper is connected to the tip of the plug you insert into the Helix expression jack, you now need to make sure it provides the right resistance. This can be easily achieved without changing the pot by simply soldering a selected fixed resistor between wiper and ground. So, if, for example, the pot is 50k, strapping a 12k resistor between the wiper and ground will make its effective resistance vary between 0-9.7k, with a 15k parallel resistor yielding 11.5k resistance.

Most foot-operated pedals that use a rack-and-pinion gear system to rotate the pot do not fully rotate it, lest they push the wiper past the end-point and break the pot. So, chances are pretty good that whatever the actual value of the pot is, toe-down is not going to produce the full resistance. I say this because my example of 50k with 15k in parallel might work out to 11.5k in theory. But if the pot only produces a wiper-to-ground resistance of, say 44k, then our combined parallel resistance will be a bit lower (44k and 15k yields 11.2k in parallel).

A little higher than 10k won't confuse the Helix, although the last bit of foot travel may be ineffective. But a substantially higher resistance might confuse it.

IN any event, 1) find out what connects to what in the FV500, 2) find out what the actual pot value is, 3) calculate what parallel resistance between wiper and ground provides the desired target of 10k, and 4) wire up a cable that connects the FV500 pot wiper to the tip of the cable.

[Trick]

If the OP wishes to use the FV500L with the Helix's expression-pedal input, the solution is actually quite feasible, quite cheap, and quite easy.

First, find out what the resistance of the control pot is. I'm guessing it is in the 25k-50k range for low-impedance source, but best to verify.
The Line 6 standard is, as correctly noted, a 0-10k variable resistance to ground. So, the second thing you need to do is identify which contact on the output jack is for the pot wiper, and which for pot input. We will want to use ONLY the wiper and ground in this application. Manufacturers will vary in which contact they assign to the tip and ring contacts of the jack/plug.
The plug you insert into the Helix should be a simple mono tip/shaft (TS) type. You CAN use a TRS plug, but only the tip and shaft will be used.

Having identified the pot and jack contacts on the FV-500L, and making sure that the pot wiper is connected to the tip of the plug you insert into the Helix expression jack, you now need to make sure it provides the right resistance. This can be easily achieved without changing the pot by simply soldering a selected fixed resistor between wiper and ground. So, if, for example, the pot is 50k, strapping a 12k resistor between the wiper and ground will make its effective resistance vary between 0-9.7k, with a 15k parallel resistor yielding 11.5k resistance.

Most foot-operated pedals that use a rack-and-pinion gear system to rotate the pot do not fully rotate it, lest they push the wiper past the end-point and break the pot. So, chances are pretty good that whatever the actual value of the pot is, toe-down is not going to produce the full resistance. I say this because my example of 50k with 15k in parallel might work out to 11.5k in theory. But if the pot only produces a wiper-to-ground resistance of, say 44k, then our combined parallel resistance will be a bit lower (44k and 15k yields 11.2k in parallel).

A little higher than 10k won't confuse the Helix, although the last bit of foot travel may be ineffective. But a substantially higher resistance might confuse it.

IN any event, 1) find out what connects to what in the FV500, 2) find out what the actual pot value is, 3) calculate what parallel resistance between wiper and ground provides the desired target of 10k, and 4) wire up a cable that connects the FV500 pot wiper to the tip of the cable.

Great info, thanks!