Stereo volume attenuation - diyAudio
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Old 16th May 2013, 03:11 AM   #1
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Default Stereo volume attenuation

Hi there,

Read a few other similar threads but would appreciate opinions...

I am outputting audio from a soundcard via a mixer to some monitor speakers in my studio. Problem is, both the soundcard and mixer are on the other side of the room, and so I don't have volume control when I'm sitting at the desk where the speakers are.

I want to build a stereo volume control device that will receive input from XLR and output as XLR.

Would it be best (in terms of sound quality) to build a pre-amp or just throw a volume pot on the line to change output level?

Will I risk damaging my monitors if I use a pre-amp? Will sound degradation become an issue if I don't?

Cheers
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Old 16th May 2013, 11:01 AM   #2
Loren42 is offline Loren42  United States
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You could just use an L-Pad on the speaker lines if you are not throwing a lot of power into them.

If that does not work...

By XLR am I to assume you mean balanced line?

If so, then an active circuit may be best, which requires something like a pair of INA134 and DRV134 Texas Instrument chips to convert to unbalanced, insert the stereo volume control, and back again to a balanced line out. You will also need a 15 or even 18 VDC power supply. That seems like a lot of hoops to jump through, but a good solution if sound quality is important.

You can try to simply attenuate the balanced line with a low impedance 4-gang volume pot, but any slight imbalance will create additional attenuations between left and right channels.

There may be a IR remote control you could make or just buy to do the same thing, but balanced lines make it more complex.

Is the input to the power amp also a balanced line or are they powered monitors?

Last edited by Loren42; 16th May 2013 at 11:07 AM.
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Old 16th May 2013, 11:21 AM   #3
AndrewT is offline AndrewT  Scotland
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Do you need balanced impedance connections?

If your answer is yes, then you must go and educate yourself about what is required to allow a balanced impedance connection to operate to it's potential.
Balanced impedance connections are very different from unbalanced. You NEED to understand this DIFFERENCE.

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Old 16th May 2013, 11:33 AM   #4
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About sound degradation :
The potentiometer may act as a low pass filter
Because of the Rseries introduction, together with next stage ( amp's input)
input capacitance. So it's better to have lowish pot value, like 10 K- 20 K Ω .
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Old 16th May 2013, 03:53 PM   #5
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The xlr in and outputs were described in my original post because I understood that balanced lines carry better sound.

I could very well be wrong.

I can run a regular unbalanced signal (RCA in, 1/4" out) if that is a better (more economical) way to do things.

The monitors are powered.

I guess I am tossing up between re-amplifying signal to a powered speaker (will it blow the speaker amp?) or reducing voltage through the input line to reduce signal strength (will degradation become an issue at lower volumes?)

The output is a 4 channel mixer. On line 1 and 4, turntable in/out. Line 2, computer. Line 3, mic.

Into powered monitor speakers.

Cheers.
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Old 16th May 2013, 04:03 PM   #6
AndrewT is offline AndrewT  Scotland
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Are any of your sources or receivers using Balanced Impedance in/outs?
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Old 16th May 2013, 04:39 PM   #7
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by fishparty View Post
The xlr in and outputs were described in my original post because I understood that balanced lines carry better sound.

I could very well be wrong.

I can run a regular unbalanced signal (RCA in, 1/4" out) if that is a better (more economical) way to do things.

The monitors are powered.

I guess I am tossing up between re-amplifying signal to a powered speaker (will it blow the speaker amp?) or reducing voltage through the input line to reduce signal strength (will degradation become an issue at lower volumes?)

The output is a 4 channel mixer. On line 1 and 4, turntable in/out. Line 2, computer. Line 3, mic.

Into powered monitor speakers.

Cheers.
Balanced lines are great when signal runs are long (i.e., longer than 15 to 20 feet).

However, you must convert the signal from unbalance to balanced, then to unbalanced to the volume control, then back to balanced, then unbalanced again at the speakers.

A better solution probably would be to search for a remote volume control or a servo driven volume control that you could implement between the preamp you have now and the powered speakers.

Placing the volume control physically at your desk will be expensive, so I would be looking at off-the-shelf components you can buy to do the job.
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Old 17th May 2013, 05:42 AM   #8
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Something like this?

I would prefer it to be a passive solution if possible.

What if I output in unbalanced from the mixer, then run that into a pot, then output from the pot to the monitors to control the signal level passing through.

Will that work?
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Old 17th May 2013, 08:43 AM   #9
AndrewT is offline AndrewT  Scotland
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All unbalanced will work.
Which bits of your kit will only accept balanced impedance?
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Old 21st May 2013, 08:19 AM   #10
tomcc is offline tomcc  Australia
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You can run a balanced output through a passive vloume control and keep the whole path balanced. Its much cheaper to do this than unbalance and then rebalance signals.
Here is a link to one I built only last week with a cheap pot just to make sure it works. I have actually got a stepped attenuator coming to build into a more complex setup.
http://www.proharmonic.com/articles/AT78_OTB.pdf
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