Soundcraft UI12 Vol Pot

[Davebassman]

Hi,

I need to replace one of the Main Mix potentiometer ( encoders? ) because they don't respond correctly and the touch it's to hard compared to the others. Anybody can help me to indentify this pot?



Thanks.

[Greg Robinson]

Looks like an Alps Alpine RK12 series dual 10k audio pot. You'll have to confirm dimensions with the datasheet.

[Davebassman]

Looks like an Alps Alpine RK12 series dual 10k audio pot. You'll have to confirm dimensions with the datasheet.

Wow, amazing! it's a 103C = 10KC pot not a encoder!

Thanks a lot.

[J M Fahey]

Take care of getting a "C" curve pot, which is the opposite of an Audio (A) one.

[Greg Robinson]

I believe in this case the code AE103c, the first digit refers to A=audio taper, as that would make most sense for a conventional level control. If it were a mic gain control reverse taper would make more sense.
I think here the trailing c references the vertical format of the pot, but who knows without knowing who the actual OEM is and having the correct datasheet - I think this is a generic clone of the Alps Alpine style I linked above.
Make sure to measure the existing pot to confirm either way.

[Davebassman]

Yes, I think it's a A pot, it's from main out control. And Alps doesn't have any C pot in the datasheet,

[J M Fahey]

Maybe.
Easy to check, set it to 5 and measure both halves, from 0 to wiper and from wiper to 10.

Linear will be 5k - 5k
Audio will be (roughly) 1k - 10k
C/antilog will be 10k - 1k

C/antilog/reverse_Audio curve is not common in the Guitar or Hi Fi world but quite common in mixers as an input stage Gain control which I suspect here (hint: it IS a mixer)

Also used as Distortion/Gain control in MXR pedals and in a few Fender SS Guitar amps.

But in any case measuring rules

[Davebassman]

I changed the pots, and the new ones fit perfect. But when I turn up the right level, a lot of pops starts. So I dissasembled again the board and I found IC 8068 that gets so hot! The advantage is that I can compare the voltages between left and right channels and the right channel has strange voltages on it. I traced this voltage and I found a short on another 8068 opamp. I dessoldered this one and the short was gone and this opamp out the board still have the short. Do you recommend me change both opamps? or only the one that fail?

Thanks.

The opamp is JRC 8068. I found this one: NJM8068G-TE2


https://ibb.co/DY9JQzJ
https://imgbb.com/bbjKVMN

[Greg Robinson]

So for posterity's sake, were the pots audio taper, or reverse audio taper?

I changed the pots, and the new ones fit perfect. But when I turn up the right level, a lot of pops starts. So I dissasembled again the board and I found IC 8068 that gets so hot! The advantage is that I can compare the voltages between left and right channels and the right channel has strange voltages on it. I traced this voltage and I found a short on another 8068 opamp. I dessoldered this one and the short was gone and this opamp out the board still have the short. Do you recommend me change both opamps? or only the one that fail?

Thanks.

The opamp is JRC 8068. I found this one: NJM8068G-TE2

Short circuit to what? To ground? It's important to be explicit about these details. Probably best to change U37 given it was getting hot as well as U34? (designator obscured by your notes in the picture, the bottom right). They're cheap, and better to avoid having to open it back up again if there are further problems. Make sure to carefully check for any stray solder, and check for short circuits to the power pins 4/8 before reassembling and applying power.

[Davebassman]

Pins 3 and 4 was shorted on u34 also when it was de-soldered from board. This short injected a -8V to pin 7 of u37 and this was the cause that this opamp was get hot.

Thanks.

[Greg Robinson]

So were the pots audio taper or reverse audio taper?

[Davebassman]

So were the pots audio taper or reverse audio taper?

Audio taper.