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converting channel fader to rotary pot
converting channel fader to rotary pot
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Old 28th February 2020, 02:23 AM   #1
arteom is offline arteom
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Default converting channel fader to rotary pot

Have a Allen and Heath Xone 02 dj mixer. It's a 2 channel mixer, each channel stereo. I want to add pots to it to control each channels volume. I took it apart, The channel faders sit on a pcb, with 4 pin connector on it. What I don't fully understand is how the channel fader works with 4 wires, instead of the normal 6 wires that are standard on like a ALPS RK27. Can anyone help me make sense of that?



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Old 28th February 2020, 11:49 AM   #2
MAAC0 is offline MAAC0  Portugal
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Does it have fader start ? Perhaps it isn't analog but VCA controlled. Pioneer mixers and DJ consoles use VCA control. It's time to hunt the service manual.
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Old 28th February 2020, 01:40 PM   #3
arteom is offline arteom
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It doesn't have fader start. From what I've gathered from various sites that have it listed for sale, they do seem to be VCA faders "Every fader is a deluxe VCA design, they’re all reversible, they all have contour controls and they can all be easily replaced by removing the steel faceplate.".

Is it that there is no L&R wired to the line fader? Rather it's just one input, output, but would the other two just be grounds? Also FWIW, I have briefly seen a dismantled Rane Empath Rotary version, that had ALPS RK27's each sitting on a pcb, but again only four wires coming out from that pcb.
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Old 28th February 2020, 03:47 PM   #4
arteom is offline arteom
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Reading the marking just below the line fader would have been another clue that it's a VCA fader .
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Old 28th February 2020, 11:16 PM   #5
MAAC0 is offline MAAC0  Portugal
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I believe those are stereo pots. You have 4+2 connections. 2 IN 2 OUT 2 Wiper
Remove the fader from the pcb or try to measure between pins actuating the lever to find out the pin-out, for each channel and then test with an identical resistance pot.
On a VCA, You usually vary a voltage on the pot, (3-5V) That goes to a microprocessor. So, on the molex there should be a fixed voltage on one or two pins. The wiper could be connected to one side, so it acts as a variable resistance and not as a regular pot. That leaves us with 4 connections 2 for each channel which You have on the connector.
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Old 2nd March 2020, 02:52 AM   #6
arteom is offline arteom
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Thanks for writing, I'm going to take the mixer apart again in the next few days. I will get back to you with progress.

Last edited by AllenB; 2nd March 2020 at 03:04 AM. Reason: Remove excess quoting
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Old 13th March 2020, 01:45 AM   #7
arteom is offline arteom
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so I again had access to a rotary empath. this time I used a voltmeter to test for continuity on the pins on the alps pot and the connection going to the board. Only the front 3 pins are used! I think it's an input for the channel (both L+R), wiper, and ground. What do you think? If this is correct I only need a mono pot.

It's the same on the A&H, there are four wires going out to connection terminal but only three traces from the circuit board of the channel fader. I think I should be able to get by with a 100k rotary pot just fine.

I want to do a proof of concept. The A&H alpha fader pots have 0100knx2 inscribed inside the fader casing. So it's a 100k pot. I want to do a proof concept before I purchase a nice 100k pot to use in there. My question, can I test with a 50K pot?

Another idea I had in mind was to install a switch to be able to switch between the fader pot and the rotary pot. Would a DPDT be sufficient in this application?
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Old 13th March 2020, 09:38 AM   #8
turk 182 is offline turk 182  Canada
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0100knx2 wouldn't that make it a 2 element or dual gang fader?
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Old 13th March 2020, 10:42 AM   #9
MAAC0 is offline MAAC0  Portugal
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Krank up the master mixer pot
What happens if You touch the connectors on the PCB with a finger ?

Leds begin to dance ? Humming ? Those are Your summing amp inputs. The others are the channel outs.

If nothing happens, I believe it's VCA controlled and a mono pot would make sense since it controls both channels. But for example the Pioneer Ergo uses stereo pots wired in parallel and is VCA controlled.
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Old 19th March 2020, 03:22 PM   #10
arteom is offline arteom
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Quote:
Originally Posted by MAAC0 View Post
Krank up the master mixer pot
What happens if You touch the connectors on the PCB with a finger ?

Leds begin to dance ? Humming ? Those are Your summing amp inputs. The others are the channel outs.

If nothing happens, I believe it's VCA controlled and a mono pot would make sense since it controls both channels. But for example the Pioneer Ergo uses stereo pots wired in parallel and is VCA controlled.
It's definitely VCA, no doubt about it. So, I poked around a bit and got it working. I wired in a spare stereo pot I had lying around. It seemed to work just fine, up until smoke started to come out of the mixer!! I toasted a resistor. I think it was because the pot I was testing with was 50k, instead of 100k. It all is working fine still, but will be swapping a new untoasted resistor.


So the way the stereo pot is wired three pins are used - input, output, and ground. If this is the case, and I want to switch between two potentiometers (one line fader and one rotary), can I only run the output of each to a SPDT switch, and run output of that to the mixer pcb? Does this make any sense? Input and ground pins would be wired from pcb to one pot, then to the other.
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