Audio pot with tap

[brucetassin]

New to me. Maybe not to you.

Restore old amp with loudness tap.

https://www.radioshack.com/collecti...nged-stereo-volume-control?variant=5717293381

 

[Wigwam Jones]

I happened to see that one listed online as well, and like you, I have no idea how it is supposed to work. I'd love to know if anyone actually has the info on that.

 

[Eli Duttman]

Those Fletcher/Munson loudness compensation circuits used to be commonplace. A switch, resistors, and caps. were used, along with the volume pot. tap to provide the feature. Bass was boosted at low listening levels, when the feature was engaged.

One example should be as good as another. Dig up the schematic for either the Fisher 500C or the H/K FA3000X. Many other units have the feature too. I just happen to remember those models, off the top of my head

 

[rayma]

Restore old amp with loudness tap.
https://www.radioshack.com/collecti...nged-stereo-volume-control?variant=5717293381

Those are very good, inexpensive Alps pots. I've used them for years to restore older equipment.

 

[Wigwam Jones]

As an aside, is it OK to ignore the loudness tap and simply use the pots as volume controls?

 

[brucetassin]

wigwam
I know how to use the tap. Whats new to me is the supplier.
Here is an example of the "loudness" feature in use

 

[rayma]

As an aside, is it OK to ignore the loudness tap and simply use the pots as volume controls?

The taper is best if you still use the external resistor from tap to ground,
just without the capacitor.

 

[Wigwam Jones]

The taper is best if you still use the external resistor from tap to ground,
just without the capacitor.

Thanks!

 

[rayma]

Thanks!

With these pots, the shaft is metric (a little under-sized than 1/4" in diameter),
and also it is a little longer than usual. If you use some washers between
the pot and the panel, so there are still enough threads left to tighten the
panel mounting nut, this will shorten the excess shaft length a bit, so you
may not have to cut it off.

 

[Wigwam Jones]

With these pots, the shaft is metric (a little under-sized than 1/4" in diameter),
and also it is a little longer than usual. If you use some washers between
the pot and the panel, so there are still enough threads left to tighten the
panel mounting nut, this will shorten the excess shaft length a bit, so you
may not have to cut it off.

Good to know, I do plan on picking a few of these up soon.

 

[brucetassin]

If this type pot is used as a simple volumn control, I would not use the loudness tap, just leave it alone. If a resistor were put to ground that would mess with the lower volumn range settings.

 

[DeathRex]

If the tap is in the middle, not just to the side, it is the newer version made in China.

 

[rayma]

If this type pot is used as a simple volumn control, I would not use the loudness tap, just leave it alone.
If a resistor were put to ground that would mess with the lower volumn range settings.

Pots with a loudness tap are designed to use a resistor to ground on the tap for normal operation.
A capacitor is connected in series with the resistor to give bass boost for loudness compensation.

 

[brucetassin]

I measured the pot with my DVM.
Across the pot, 109.6K ohms
Tap to one end 18.01K ohms
Tap to other end 91.5K ohms
Looks like tap is at about 20%