Volume Pot with 4 legs ?!!!

[gchrist]

I tried to change the volume pot on my fathers Kenwood amplifier (dated early 1980's) with a new pot. I bought a new 100K logarithmic pot with the same value as the old one. When I tried to install the new pot I found out that the old pot had four legs for each chanel and not 3. So the old pot had a total of 8 pins while the new pot had a total of 6 pins.

I intalled the new pot but it played to loud.

Does anyone know why the old pot had 4 legs/ch? Where can I get these pots today?

I will try to post some pictures tommorow.

Thanks
George

[Centauri]

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

[gchrist]

You are correct! If anyone knows where I can get a pot like this I would be much obliged.

George

[amb]

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

[cogsncogs]

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

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

[gchrist]

Thank you,

I will try to post a picture so that someone can tell me what type of taper I have, log or linear?

Thanks

[Frank Berry]

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

[sreten]

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.

[cogsncogs]

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

[sam9]

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.