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Topic: Really confused over volume control "Potentiometers". (Read 246 times) previous topic - next topic

marine_hm

I'm making my own Bluetooth altoids tin amp to play music from my iPhone without any cords.  I ordered an LM386 board from ebay that has a tiny plastic looking 10k potentiometer.  I want to desolder it and replace it with one I can mount to the side of the tin.  Since I'm not an electronics expert...  I googled 10K audio potentiometers.  Can someone please explain the difference between type A, B and linear potentiometers and recommend what would work best for my application?

Thanks.    Nick

Runaway Pancake

An audio amp volume pot needs to be of the audio (log, logarithmic) taper sort.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

MarkT

Modern pots are marked A for log and B for linear.  As in A10k or B4k7 etc.

In fact a 'log' pot has an exponential response - the output voltage will be an exponential
function of position.  Its the position that is a logarithmic function of the resistance, rather
a backwards way to name it in my opinion, but I guess the justification is that you mark
the scale in dB, which is the logarithm of audio power or voltage.

The ear's subjective response to loudness is very closely a logarithmic response as far as
people can actually measure something subjective...

The net result is that with a log pot the position of the pot and the perceived loudness seem
to be linearly related (which is definitely not the case with a linear pot).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Paul__B

In fact, in previous discussions, it is noted that "log" pots are usually not logarithmic or taper at all, but simply have two (possibly three) sections of track of different resistivity.

jremington

#4
Jan 17, 2016, 01:33 am Last Edit: Jan 17, 2016, 01:34 am by jremington
It is possible to add one resistor to a linear potentiometer and have a roughly "audio" taper. See this informative article http://www.geofex.com/article_folders/potsecrets/potscret.htm


marine_hm

What affect would it have on sound or volume quality if I used a 50k pot instead of a 10K?  I'm looking for a dual volume control with switch.  The only ones I've found were 50k?  Edit:  Maybe because I was searching for linear instead of logorythmic.

Question still stands.

Maybe for an audiophile...  What would make a better housing for my setup:  Wood cigar box or acrylic tube?

Thanks.  Nick

jremington


DVDdoug

Quote
What affect would it have on sound or volume quality if I used a 50k pot instead of a 10K?
The input impedance of the LM386 is 50K.    With the pot at less than maximum, you'll get slightly more voltage drop across a higher impedance pot, so the volume will be slightly less at the same setting.   But, you'll still get full power at the maximum volume setting...  So no big deal...

There is also a chance of more hum/noise pickup with the higher resistance pot.     But, once you connect something to the input, that source is usually low-impedance so there shouldn't be any difference once something is "plugged into" the amp.

JimboZA

Modern pots are marked A for log and B for linear. 
Well they say it's a bad day when you don't learn something and it's not 7am here yet.

In was looking at a pot just last night and wondered why it said "B10k".... now I know.
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Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

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