Solved - Help with TL Audio 5001 (SSM2017 IC) Gain Pot Replacement

[chilidawg]

Howdy,

I need to replace the gain pot (RV9) but local vendors in my country are selling only single 5K log or dual 10K log pot.

I understand the schematic says it's a single 5K pot, but the board wants a dual because the front pins of the pot are used for mechanical support and also because if I put in a 15mm shaft length single pot instead of a dual, then the shaft will no longer protude enough for the collect knob to grab it. A 20mm shaft length log pot is even impossible to buy.



So my stupid question is, do I need to modify the circuit, or can I just drop in that 10K pot and be done with it?

because according to SSM2017 datasheet; with a 5K gain resistor, the lowest voltage gain is 3 (around 10 dB)

G = (10k/5k)+1

therefore with a 10K, that would be 2. No idea what's the equivalent in decibel, but it shouldn't matter much???

Please correct me if I'm wrong.

Thank you!!!

 

[elskardio]

The gain pot needs to be Anti log (C taper).

The 10k will work, but the gain vs % of rotation will be different. You’ll have a steeper gain curve by the end of rotation.

 

[chilidawg]

The gain pot needs to be Anti log (C taper).

The 10k will work, but the gain vs % of rotation will be different. You’ll have a steeper gain curve by the end of rotation.

It is as you say. When I measured the resistance, at CCW it's 4.9K (reverse log), so I'm not sure why the pots have A5K stamped on the front wafer and printed on the sticker.

Good news is that dual gang C5K pots are easier to get.

 

[elskardio]

looking at the schematic from the 1998 version, it’s written 5k Alog for the pot…
I guess it stands for Anti Log

 

[gyraf]

If you have a dual logarithmic pot of the type where the tracks face each other, then it's possible to swap the two and make a (dual) neg-log pot out of it..

http://gyraf.dk/gy_pd/calreq/magnus_j/index.htm

A dual 10K in parallel is more-or-less a 5K

/Jakob E.

 

[chilidawg]

Thank you all.

Pots replaced, tho unfortunately local vendors only sell common 18T shaft pots, so I had to get a bit creative by wrapping the shaft with a heatshrink so the collets can bite into it better.

 

[chilidawg]

If you have a dual logarithmic pot of the type where the tracks face each other, then it's possible to swap the two and make a (dual) neg-log pot out of it..

http://gyraf.dk/gy_pd/calreq/magnus_j/index.htm

A dual 10K in parallel is more-or-less a 5K

/Jakob E.

I believe that's exactly what Alpha and the manufacturer of the pots that I use as replacements, did. Hence they have A5K wafers, except the A5K marking is redacted with a black marker pen and a C5K sticker is added.