Volume Pot with 4 legs ?!!!

These pots were quite common on old stereo amps, and were quite often associated with a "loudness" switch, which gave a bit extra bass/teble boost when activated. The extra connection is a tap on the main resistive element (can't remember now around what %, but not half-way), which with associated circuitry, gave reduced loudness boost as the volume was turned up.

This idea has dropped out of favour, and I don't think you will get this type of pot anymore - unless you happen to find surplus stock or genuine spare part.

Cheers

The "boutique" stereo pots like the Noble and Alps have the loudness taps on them. They are somewhat pricey and the physical size is a bit large too. If that is not a concern, then you can get that... Try here:
Michael Percy Audio. Look at his PDF catalog.

HTH.

-Ti

The extra connection is a tap on the main resistive element (can't remember now around what %, but not half-way)

Click to expand...

Most are 40%, a few were 50% and even some with dual loudness taps at 40% and 60%!
Most Kenwoods from the 70's and 80's used a dual 100k (B) linear taper pot with a 40% loudness tap. Radio Shack may still sell an Alps dual 100k (A) audio taper (log) w/40% loudnes tap.
Make sure you get the right taper!
100k A = log or audio taper
100k B = linear taper

Wayne

Almost all audio level control pots are "audio taper" log.
There are a few exceptions.

I agree with FB regarding passive volume controls.

But active volume controls (control is in the feedback loop)
and active loudness controls complicate matters considerably.

So to modify FB's statement - nearly all passive controls are
logarithmic / audio taper, nearly all active controls are linear.

So you do need to make sure you get the right taper, but if
you know whether the control is active or passive you can
presume the type of taper required.

sreten.

In my experience most SS amps/recievers that used a passive form of loudness circuit used a linear pot. With a cap and resistor from the tap to ground with a switch across the cap (I'm ignoring the treble boost, most good loudness circuits do). In that configuration the linear pot behaves close to a log taper. Using a 100k log taper would make it difficult to get sufficient bass "boost" without using low resistor and high cap values and the resulting loss.
It's very easy to tell what you have as I stated earlier. If it says this: 100KB it's a linear pot, 100KA it's a log/audio taper. As I have owned 6 Kenwood sand amps, a couple recievers and repaired quite a few of them (I mod'ed a KA 5700 last month, the loudness circuit in particular!), so if you post the model number I might be able to tell you what you need.

Cheers
Wayne

A bought a couple of very inexpensive 4-leg pot at Radio Shack a week or so ago. ~$2.00 The pot had the word "ALPS" stamped on it.

Rat Shack 100K Alps pot

A bought a couple of very inexpensive 4-leg pot at Radio Shack a week or so ago. ~$2.00 The pot had the word "ALPS" stamped on it.

Click to expand...

Yup, that's the one! Good ALPS pot for 2 USD. Channel balance isn't very good at lower volume settings though. It's a 100k audio taper with 40% loudness tap. They used to sell the ones with detents, I still have a few of them lying around here somewhere!

Cheers
Wayne

it's a linear pot!

Hi gchrist

Yup that's a 100k linear taper! I may have one for you. I'll look in my junk/spare parts bin. Rat Shacks 100k pot is an audio/log taper and wouldn't be a good match in your case. You'll find your self having to use more of the upper part of the Vol. control's rotation to reach the same vol level and the bass boost will be a little less. But you may or may not find the result more to your liking.
And by the way, what's wrong with the original pot? If it's noisy you may just need to clean it! Caig makes some excellent stuff just for that. Also Silicone Lubricant spray made by Prestone works good because it doesn't contain acetone which will eat the plastic parts of the volume control, too aggressive! Some people have used WD-40 with ok results. I don't like to use it for that, the oil in it attracks dirt and dust and doesn't last long.

Cheers
Wayne

gchrist said:

I found out that the Noble AP25 pot has a center tap on a fourth pin. Is this pot ok? Is this the same thinhg as a loudness tap?

George

Click to expand...

Yes it is.

-Ti

M. Percy will ship to international destinations, according to his catalog. Why don't you send him an email to inquire? His email address is michael@percyaudio.com

-Ti

Have a look here:

http://members.aol.com/sbench/freqres3.html

I have used some sprays with good results but only for a short while. It is difficult to open the lid now and then and spray the pot!

Click to expand...

I've used Caig DeoxIT D5 and CaiLube MCL on my dirty controls and so far I've gone almost two years without having to respray! Just make sure you get the spray inside the pot and rotate the pot back and forth about 20 or more times and repeat. Use DeoxIT first then follow with CaiLube.
I have an Alps 100K linear pot w/40% loudness tap that came out of an old Marantz amplifier, but it's in poor condition (dirty) which may or may not fit shaft wise. The solder pins will fit though you will have to solder wires to the loundness tap. I dont' think it's worth the cost of shipping to you. I'd suggest emailing Micheal Percy

Wayne

Edit: spelling