Potentiometer with fixed center point

[mcs51mc]

Hi,
Any idea where to buy a 100k 2 gang linear potentiometer with fixed center point?

Between pins 1&2 always 100k
Between 1/4 & 2/4 always 50k
Between 1 to 3 normal 100k potentiometer

This part is used in an audio amplifier and needs to be changed.
No idea if this is the correct name of this part so rather hard to search the net.

Thanks for your inputs... ...

 

[alec_t]

If you can't source a replacement, then connection 4 could perhaps be taken from a pair of 50k (or higher) resistors in series across the pot.

 

[Nigel Goodwin]

Hi,
Any idea where to buy a 100k 2 gang linear potentiometer with fixed center point?
View attachment 119978
Between pins 1&2 always 100k
Between 1/4 & 2/4 always 50k
Between 1 to 3 normal 100k potentiometer

This part is used in an audio amplifier and needs to be changed.
No idea if this is the correct name of this part so rather hard to search the net.

Thanks for your inputs... ...

These were usually used for 'loudness' correction, basically increasing the bass and treble at low volumes - considering the lack of availability of pots in general now I would imagine it might be difficult to find, other than as a spare part from the manufacturer of the unit.

However, fitting a normal pot without the tap should be fine, and you probably won't notice any difference.

 

[gophert]

If you can't source a replacement, then connection 4 could perhaps be taken from a pair of 50k (or higher) resistors in series across the pot.

That might work but depends on how the connections are arranged in the circuit and the current draw of each. If pins 3and 4 are connected, the 50k divider adds an issue

 

[Pommie]

Wouldn't a standard 100k pot with two 50k resistors do the same job?

Mike.

 

[mcs51mc]

Thanks for the reactions!

Manufacturer is not an option, already contacted a few years ago for the “Balance” pot meter.
That one I replaced with fixed resistors.

I don’t think one can build such circuit with a few resistors and a standard pot meter.
At least I couldn’t think of any.

I’ll try as suggested by Nigel without using pin 4 at all.

 

[mcs51mc]

You asked for the circuit?
Well, here it is!
It’s RS09 in the schematics, the “VOL” pot meter.

 

[Nigel Goodwin]

Wouldn't a standard 100k pot with two 50k resistors do the same job?

No, I thought LONG and HARD about this MANY years ago, as such silly pots weren't ever available for very long. If you think abut it, adding two external resistors won't be affected by adjusting the volume, which is what the whole idea is.

However, the balance control could easily be replaced by a none tapped control, as it's not really doing much anyway. The Loudness control is switchable, so if he didn't have it switched ON anyway, it won't make any difference to him.

 

[crutschow]

If you examine how the pot functions with the external loudness RC circuit, you would see that adding two 50k ohm resistors across the pot will not give the same output as the tapped pot.

How about this pot.
It has a 40% loudness tap instead of 50%, but that should operate very similar to the original pot (difference probably inaudible).

 

[Nigel Goodwin]

How about this pot.
It has a 40% loudness tap instead of 50%, but that should operate very similar to the original pot (difference probably inaudible).

But again, if you don't use the loudness button, what's the point?.

 

[crutschow]

if you don't use the loudness button, what's the point?.

None, as long as the TS is okay with that.

 

[mcs51mc]

I'm ok wit that
Thanks for finding that one!