Wattage Rating Of Pots Used In Volume Control

[Dave.H]

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 Dick Smith.

 

[default]

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 Dick Smith.

Looks like you are running the pots to ground the signal at one
extreme of the travel? That won't fly. Hard on the pot and hard on
the amplifier.

The wiper from the pot taps off part of the signal the way it is
normally done, and then the amount of power involved is usually
minimal - as for how much exactly, that depends on the type of output
drive you have but with an Ipod I can't see it dissipating enough
power in the pot to be a concern - not with a 1K or higher pot . . .

So signal goes to one end of the pot (full clockwise), ground to the
other, and the wiper takes single off to the amp you are adding -
along with a separate ground connection to the amp.

So wire it the right way and don't worry about it. Most pots of a 1"
size are rated from 1/2 to 2 watts depending on construction - but use
it the way you show and that becomes meaningless since the rating is
for the entire pot element not the bit at the end that will burn out
if wired incorrectly. When that is something you must do you look at
the current capacity of the pot and don't exceed that.

Your 1 watt pot becomes a 1/2 watt pot at its midpoint if you use it
to short the signal. Or your 1K, 1W pot can't exceed about 30
milliamps anywhere in its range.
--

 

[Bob Masta]

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 Dick 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

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[Dave.H]

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

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

Here's a link to the amplifier schematic, to make this easier. I
would probably use the volume control on my computer with my
headphones also, so i want to build one that will work with that and
other devices.

http://s222.photobucket.com/albums/dd237/ozguy89/?action=view&current=1WattAmplifierSchematic.jpg

 

[Dave.H]

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.

I've done this just now with a 5K log pot I had on hand, and I have it
playing now. I know what to do now, thinking of sticking with 5K so I
can reuse this pot.

 

[Dave.H]

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.

I've done this just now with a 5K log pot I had on hand, and I have it
playing now. I know what to do now, thinking of sticking with 5K so I
can reuse this pot.

 

[Dave.H]

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.

I've done this just now with a 5K log pot I had on hand, and I have it
playing now. I know what to do now, thinking of sticking with 5K so I
can reuse this pot.

 

[John Larkin]

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:

Ghastly! That's desighed to kill ipod batteries, cause distortion, and
fry pot wipers.

Just do this. Pot wattage doesn't matter.

o------------->Right(+)
|
Right(+)>--------------\/\/--o
1K Pot |
from ipod o-->GND to amplifier INPUT
1K Pot |
Left(+)>---------------/\/\--o
|
o------------->Left(+)

John

 

[Dave.H]

I've done this just now with a 5K log pot I had on hand, and I have it
playing now. I know what to do now, thinking of sticking with 5K so I
can reuse this pot.

The only problem with the 10K pot (incorrectly called it a 5K pot
previously) is that the volume barely increases until the shaft's all
the way clockwise.

 

[Eeyore]

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.

With the voltages and resistance values involved, ANY pot will have a
large enough rating ( typically it'll be around a milliwatt ).

Graham

 

[default]

The only problem with the 10K pot (incorrectly called it a 5K pot
previously) is that the volume barely increases until the shaft's all
the way clockwise.

You are expected to use an "audio taper" pot for audio. The
resistance is non-linear and compensates for the perceived volume to
the human ear.
--

 

[Eeyore]

You are expected to use an "audio taper" pot for audio. The
resistance is non-linear and compensates for the perceived volume to
the human ear.

In this application you'd need a REVERSE log pot actually.

Graham

 

[Bob Masta]

Here's a link to the amplifier schematic, to make this easier. I
would probably use the volume control on my computer with my
headphones also, so i want to build one that will work with that and
other devices.

http://s222.photobucket.com/albums/dd237/ozguy89/?action=view&current=1WattAmplifierSchematic.jpg

You can replace the 10K resistors to ground on the inputs with 10K
log-taper pots. Just connect the amp chip inputs to the pot wipers
instead of to the top of the pot.

If you can't find a log-taper pot, you may be able to "fake" one
by tying a fixed resistor between the wiper and the top leg.
Experiment with different values... it's been a while since I've
done this, and I've forgotten which value gives the best fit to a
log curve. (I think something in the 3K range.) You won't get
a log taper, but at least it will be better than linear.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!