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Old 1st February 2001, 03:37 PM   #1
JkL is offline JkL
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I'm building an ic-amplifier and I would like it to have volume control... I don't need tune/balance...etc... I just want to build simple volume control... Any ideas how I could do it...?
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Old 1st February 2001, 10:09 PM   #2
blmn is offline blmn  Brazil
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Hi,

The SGS-Thomson site (www.st.com) has datasheets and application notes of many IC power amps, from 1 to 50 watts.

Some of them have built-in gain controls and these controls are usually out of signal path circuits. It means less trouble with noise and other problems.

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Old 1st February 2001, 10:12 PM   #3
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I once built a variable DC power supply. It uses a pot to adjust the output. So, I bet that would work for an amp. You simply use this to increase or decrease the power supply.

Anyone see a problem with that?

I can't remember what it used. It's a small transistor looking thing. Variac, triac... anyone know what I'm talking about? This was 12 years ago.

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Old 1st February 2001, 10:36 PM   #4
blmn is offline blmn  Brazil
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Pixie,

I think there are at least two problems with this solution:

- DC levels and polarization (worse in discrete designs);
- efficiency of power supply (if it is a linear design).

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Old 1st February 2001, 11:16 PM   #5
blmn is offline blmn  Brazil
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Pixie,

Usually an amplifier is a linear device (Vout=K*Vin). Where
K is a constant (ideally), not dependent on Vcc. If you change Vcc you will only "clip" the output voltage.

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Old 5th February 2001, 06:41 AM   #6
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This is usually done with a potentiometer. Alternatively a multiplying DAC could be used if you wanted computer control.
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Old 6th February 2001, 08:06 AM   #7
JkL is offline JkL
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Quote:
Originally posted by thespeakerguy
This is usually done with a potentiometer. Alternatively a multiplying DAC could be used if you wanted computer control.
Hmmm... What does potentiometer do? I mean what effect it has... ? ( This might be stupid question... but... =)
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Old 6th February 2001, 09:29 PM   #8
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A potnetiometer is a three terminal resistor. Two terminals are across a fixed resistance, while the third is an adjustable connection anywhere along this fixed resistance. When you turn a knob on a pice of equipment, chances are you are turning a potnetiometer.

It is connected in a circuit like an adjustable voltage divider. Alternatively it can be used as an adjustable gain resistor in an opamp feedback.
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Old 6th February 2001, 10:10 PM   #9
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Thanks, "thespeakerguy".
Now we all know what a potentiometer, sorry, a potnetiometer is, and how it works.

JkL: Read my post in the "6-way volumn control"-thread.
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Hoffmeyer ;0)
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Old 6th February 2001, 11:00 PM   #10
grataku is offline grataku  United States
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Hoffmayer,
you have little to be joking about, thespeakerguy was sincerely trying to be helpful. Personally, I think this website needs to crank-up it's level a couple of notches. A multiple choice admission questionnaire is in order in my opinion. If you don't know what a potentiometer is you probably shouldn't be building any audio stuff, if you think that is ok to shorten the output of your zen amp at startup in order to prevent transient noise you probably should not be building any audio stuff, either. That is for your safety and the safety of your loved ones, too.
It seems that some people are expecting to be spoon-fed the knowledge they need by asking the stupidest questions rather than trying to open a book and teach themself something.
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