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Line level volume control without opamp?

Hello,

I am attaching a set of computer speakers to a 20 foot lead from a television set, that come off of a set of line level RCA jacks at the television. These speakers will enable a person near the speakers to have a local set of speakers that they can adjust independantly from the main television volume.

In the effort to build a volume control near the auxillary speakers, while I realize that I could use a unity gain op amp to control the line level volume, this would require building a circuit and piping in voltage.

What I want to know is if I could just use a potentiometer on the line level connection to control the volume. In other words, would placing a 100k Ohm resister in series with the line level connection be enough to significanly reduce the volume?

Thanks for any suggestions,

Jon

Reply to
Jon Danniken
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It depends on the impedance of the line but 100K pot should make a difference.

Kal

Reply to
Kalman Rubinson

If the speakers had their own amplifier, you could probably get quite good results with a potentiometer wired as a voltage divider on their line in, because the relatively high impedance of the amplified input will not draw much power from the resistor and will not vary too badly with frequency.

However, if you are powering the speakers from the line output, you are probably not getting designed frequency response anyway. If you now go and add a resistor in series (not a voltage divider, just one end and the wiper) the frequency response of the system will change depending on the setting, as the inductance (and whatever else) of the speaker will interact with the resistor in different ways at different frequencies.

Practically, it may work fine for your application anyway.

However, one thing that will make a big difference in either circuit: buy an "audio taper" potentiometer to use (though you will wire it as a variable resistor in the second case). Your ears perceive loudness on a logarythmic scale, which means that you will not get a satisfactory range and smoothness of variation of out a linear pot. For direct connection inline with speakers, you probably also want a fairly small resistor, maybe only a few hundred ohms if that.

Reply to
cs_posting

"Jon Danniken"

** Most powered PC speakers have a volume control on the front anyhow.
** The PC speakers have a supply of power don't they ?
** This is not on the level.

Are you PC speakers self powered or not ?

If not, the get some that are.

............ Phil

Reply to
Phil Allison

Yes.

I'd suggest a 10k pot actually. No need to use 100k. When you wire a pot as a voltage divider, the absolute value of the resistance isn't the big issue.

Graham

Reply to
Pooh Bear

level

Ohm

significanly

Thanks CS, I hadn't thought of using the pot as a voltage divider. That looks like it will work perfectly for this application, thank you for that. BTW, they do have a powered amplifier, or at least they will, when I find a decent set of cheap speakers.

Thanks,

Jon

Reply to
Jon Danniken

level

significanly

as a

Thanks, Graham, this looks like the solution I will be using. I only mentioned 100k because that was what I saw at RatShack the other day (for dual ganged pots), but I'm going to the other local electronics store first that I'd rather give my money to. I'll keep in mind your suggestion as to a

10k pot as being applicable.

Thanks,

Jon

Reply to
Jon Danniken

Yep, use pot (MaryJane).

Reply to
Robert Baer

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