PL2000 S2 Balance pot.

[marcok]

A question related to PL 4000 series 1 .
The volume pot is a 100k linear with a 39k across center and ground to
have a log pot . But the pot is not connected directly to ground but via a 56 Ohm resistor .
Why ? What's the reason ? Never seen in other applications .
Ciao
Marco

 

[Gepetto]

A question related to PL 4000 series 1 .
The volume pot is a 100k linear with a 39k across center and ground to
have a log pot . But the pot is not connected directly to ground but via a 56 Ohm resistor .
Why ? What's the reason ? Never seen in other applications .
Ciao
Marco

Nothing in the circuit that is obvious that would drive the need for it.

 

[George S.]

You replaced a dual log pot with a single linear pot correct? Did you measure in ohms where each pot measured to its ground terminal when the knob was centered on the original pot?

Correct, had 3 of them. 100k single gang. All measured very close to 98k ( and change) total resistance. With wiper very precisely centered, 49k (and change) from wiper to each leg. Amazingly accurate for such a cheap pot.
Took extreme care to cut the shaft to "D" shape at correct clock position.
Nothing on the board needed changed that I could see, just jumpers put across each channels solder pads with the pot legs to the channel jumpers and wiper grounded. So I decided no need for "jumpers" if I wired it as in photo. I maintained the correct wire colors.
On the dual channel scope, each channels wave form aligns over the other perfectly at 12:00, fades equally, gains or diminishes equally with volume.
I'm very satisfied with the results.

 

[George S.]

Oh, and the original dual gang is clearly logarithmic. The new single gang Bourne's is linear. The linear works fine, I think better. Better as in one has a finer ability to adjust the balance out near the pots limits.

 

[Gepetto]

Oh, and the original dual gang is clearly logarithmic. The new single gang Bourne's is linear. The linear works fine, I think better. Better as in one has a finer ability to adjust the balance out near the pots limits.

The likelihood that positional matching between 2 ganged log pots has to be much smaller than a linear pot is.

 

[George S.]

I agree, when I plotted the values on the two gang there was a clear clocking discrepancy between the two gangs. A single gang eliminates that potential issue.