volume control problem

[bristan]

I am replacing a volume control pot on a sangean prd4 radio.
The original unit has four pins and a pcb mount. I have found it difficult
and expensive ($44) to get an original replacement.
The fourth pin comes from a centre tap of the pot resistance and is taken to
earth via a 2.7k R and a 473 cap in series.
I assume this is to give the 50kb linear pot a log response but I don't
know.
I would like to replace the pot with a 3 pin 50k pcb mount pot from jaycar.
I was thinking I could I use a 50kA log pot and ignore the fourth pin or
possibly use a linear pot and connect the centre pin to the fourth pin
connection as well.
Alternatively, does anyone know where I could obtain a suitable four pin
pot?

 

[Doug Jewell]

On 28/10/2010 8:09 PM, bristan wrote:

I am replacing a volume control pot on a sangean prd4 radio.
The original unit has four pins and a pcb mount. I have
found it difficult and expensive ($44) to get an original
replacement.
The fourth pin comes from a centre tap of the pot resistance
and is taken to earth via a 2.7k R and a 473 cap in series.
I assume this is to give the 50kb linear pot a log response
but I don't know.
I would like to replace the pot with a 3 pin 50k pcb mount
pot from jaycar.
I was thinking I could I use a 50kA log pot and ignore the
fourth pin or possibly use a linear pot and connect the
centre pin to the fourth pin connection as well.
Alternatively, does anyone know where I could obtain a
suitable four pin pot?

The pot you describe sounds like it has a "loudness" tap.

Basically at low volumes it cuts the treble a bit, making
the bass a bit stronger in relation to the other
frequencies, so it sounds a bit fuller. A standard pot
should work just fine, but may sound a little tinny at lower
volumes. Dunno where you'd get a replacement loudness pot
these days. A decade or so ago they were common as dirt.

--
What is the difference between a duck?

 

[bristan]

Thanks for the reply doug
I have seen an idea where the centre tap can be simulated with two equal
series resistors in parrallel with the pot resistance, so I will try that.

"Doug Jewell" <ask@and.maybe.ill.tell.you> wrote in message
news:rcadnYj8-qhBylTRnZ2dnUVZ_i2dnZ2d@westnet.com.au...

On 28/10/2010 8:09 PM, bristan wrote:
I am replacing a volume control pot on a sangean prd4 radio.
The original unit has four pins and a pcb mount. I have
found it difficult and expensive ($44) to get an original
replacement.
The fourth pin comes from a centre tap of the pot resistance
and is taken to earth via a 2.7k R and a 473 cap in series.
I assume this is to give the 50kb linear pot a log response
but I don't know.
I would like to replace the pot with a 3 pin 50k pcb mount
pot from jaycar.
I was thinking I could I use a 50kA log pot and ignore the
fourth pin or possibly use a linear pot and connect the
centre pin to the fourth pin connection as well.
Alternatively, does anyone know where I could obtain a
suitable four pin pot?

The pot you describe sounds like it has a "loudness" tap. Basically at low
volumes it cuts the treble a bit, making the bass a bit stronger in
relation to the other frequencies, so it sounds a bit fuller. A standard
pot should work just fine, but may sound a little tinny at lower volumes.
Dunno where you'd get a replacement loudness pot these days. A decade or
so ago they were common as dirt.

--
What is the difference between a duck?