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Old 12th May 2010, 08:25 PM   #1
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Default Volume pot

What type of volume pot do I need for chipamp.com,

50K, 100K, 25K? audio log?

How dose the K affect the choice?

What is the difference, many posts many different answers.
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Old 12th May 2010, 08:42 PM   #2
AndrewT is offline AndrewT  Scotland
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if your source can drive 10k load properly, then go for 10k log law dual pot. Audio and log law are similar/same.
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Old 12th May 2010, 09:01 PM   #3
infinia is offline infinia  United States
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Is this built and tested?
Make sure you use all the parts. The ones shown as "optional" are not, only unless you have a real good reason otherwise.
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Old 12th May 2010, 09:13 PM   #4
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Quote:
Originally Posted by AndrewT View Post
if your source can drive 10k load properly, then go for 10k log law dual pot. Audio and log law are similar/same.
I don't know what "your source can drive" what does that mean? it's a Briangt chipamp.

I use my tv for control now, and want to add a vol control now been working on the tv for 3 years.

Please explain what the different K's do to the amp.
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Old 12th May 2010, 11:02 PM   #5
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Default Lets try this again

If the LM3886 chipamp had a Dual Audio Taper Stereo Potentiometer, what Z would it be?

20K, 25K?

This question has nothing to do with the source just the chipamp.

Thank you
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Old 13th May 2010, 12:51 AM   #6
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by ppcblaster View Post
If the LM3886 chipamp had a Dual Audio Taper Stereo Potentiometer, what Z would it be?

20K, 25K?

This question has nothing to do with the source just the chipamp.

Thank you
Not to be rude, but the question doesn't make sense. You select the pot value based on the source it will be used with. I select the minimum value that will work so that the impedance is low enough that the input does not receive electrical noise or even oscillate from receiving it's own output.

For example, you could use 1M pot, but you must shield the input leads carefully or you can get hum from nearby electrical devices. If I was going to use the amp solely with my headphone music player, I would select a pot of low resistance because of the low impedance of the player's headphone output amp and the power amp would be pretty immune to electrical noise.

You see, it doesn't matter what chip amp I use, it is the source which determined the volume pot.

I should point out that if a particular chip amp has a lower input impedance might preclude me from using a higher value pot because the signal could be reduced too much.
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Old 13th May 2010, 01:06 AM   #7
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Since the amp has 22K input impedance, I usually use 25K pots, log of course.

10K will work fine too, but may be too low with some sources.
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Old 13th May 2010, 01:26 AM   #8
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Quote:
Originally Posted by Peter Daniel View Post
Since the amp has 22K input impedance, I usually use 25K pots, log of course.

10K will work fine too, but may be too low with some sources.
Thank You Peter,

Can you recommend a few pots and a few rotary non shorting selector

switches so I can add two or three RCA inputs?

I appreciate the other answers but the "sources" will vary from my sons protools Mbox to his Hauppauge TV card, or PC sound card.
knowing the sources will change, is the 25K pot the best choice?

I was told by Parts Express that the pot was to match the amp, perhaps a detailed explanation in the forum would help.
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Old 13th May 2010, 07:20 AM   #9
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The input resistance is not an isolated parameter. It is not determined by 'lower is better as long as your source can drive it'. As little as most sources have any problems to drive 10k or even lower impedances.

One of the goals is that both input pins see the same impedance for best CMRR and to cancel the input offset voltage as good as possible. A DC-coupled pot wiper is not a constant impedance so obviously not the best choice whatever its nominal value. You need to AC-couple the wiper or use a buffer stage in between for best results.
Another goal is that the filters between source and amp work best. With most sources being AC-coupled you would either want the highest possible impedance to bring the resulting high pass roll-off as far down as possible or the best matched impedance to form the optimal addition of the high-pass filters at the inverting and non-inverting inputs for your combination of amp and speaker. The latter is usually not possible, if you use varying sources, so you need to find a value that works with a range of sources. Usual input impedances of 10..100k on commercial amps hint at the direction to go.
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Old 13th May 2010, 01:21 PM   #10
AndrewT is offline AndrewT  Scotland
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John, Peter, Pacific and I all agree. Don't use a high value pot.
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