Re: Wattage Rating Of Pots Used In Volume Control

On Thu, 14 Feb 2008 04:10:13 -0800 (PST), "Dave.H"
<the1930s@xxxxxxxxxxxxxx> wrote:

I want to build I volume control for a battery powered amplifier I use
for my iPod, but I'm not sure what wattage value the pots have to be.
The amplifier outputs around 1 watt per channel.

The volume circuit I found was in a post on this newsgroup from 2001
by Beau Schwabe:

o------------->Right(+)
|
| o----o
+ | | |
Right(+)>----||----o----\/\/--o
100uF 1K Pot |
o-->GND
100uF 1K Pot |
Left(+)>----||----o----/\/\--o
+ | | |
| o----o
|
o------------->Left(+)

I plan on using two separate 1K pots, allowing me two adlust the left/
right channels separately, and the fact I can't get a dual pot of the
right value at *** Smith.

Do not use that circuit! Unless what I'm seeing is an ASCII art
translation artifact, it appears to have some serious problems.

A standard volume control has the input signal going to the top of the
pot (the contact that the wiper hits when the knob is fully
clockwise), and the output from the wiper. The other side of the pot
is grounded, the same ground for input and output signals.

If this is to go between the Ipod and an external amp, then
the pot resistance can be just about anything up to say 50K.
10K is a good value. On the other hand, if this is to go on the
output of a fixed-gain amp to reduce the volume, then you should
probably stick with 1K. But this is generally a poor choice compared
to controlling at the input.

Wattage is not an issue for input controls, and would only be an
issue on the output if the amp was to drive a speaker. If that
is the case, what you really want is a "fader", a low-resistance
wire-wound pot made for this purpose. Again, not recommended
in most cases.

You probably don't need the capacitor, depending on the Ipod output
and amp input circuits, but it shouldn't hurt.

Best regards,


Bob Masta

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