Passive volume control (POT VALUE)

[japmn]

If I wanted to put a passive volume control between my Powered monitors and Sound card (+4 dbV), What value Stereo Pot should I look for and does anyone know a good place to get it (Mouser?)

Thanks yuns,

Jap

[brianroth]

What you need is a dual-section (for stereo) *audio taper* pot. I would suggest 5K Ohms (but that is an oddball value) to minimize any chances of high frequency loss between the output of the pot and the powered monitors. 10K is a much more common value, but you will need to keep the shielded cables between the output of the pot and the monitors as short as possible, and/or use low capacitance cable.

One thing about inexpensive audio taper pots that can be a problem is the matching between the two (left/right) sections. In a bad case, the output levels won't match well as you vary the setting of the pot, causing the image balance to shift left and right as you vary the control's setting.

Bri

[japmn]

Thanks Brian,

As far as inexpensive pots go, I would pay the cash to get something better.
Is their a better way that you suggest that I do this, rather than a Pot? Would a Spare fader form a console work just as well or better? I see Ward Beck faders on Ebay all the time. Or, is their going to be a bunch of har-de-har-har about op-amps and stuff.

I just want to be able to turn my Monitors down without getting up and reaching behind them and trying to balance both speakers.

[brianroth]

Ohhhhh boy, this can be a can o' worms! That is, channel-to-channel tracking on a stereo pot, be it rotary or a slidewire.

Looking at page 2 of this spec sheet from Penny & Giles, one of the best slidewire manufacturers:

http://www.pennyandgiles.com/docGallery/76.PDF

...you see that the spec is +/- 1 dB left-right tracking accuracy on their best pots over the upper 40 dB of the control range, and typically a P&G beats any of their published specs. A new P&G slidewire ain't cheap (well over $100), but my friend Dale Manquen keeps them in USA stock for small quantities (tell him I sent you, even though I *don't* get a commission! <g>, just connecting a friend who is the USA distributor back to you):

http://www.manquen.net/png/

As far as rotary pots go, ALPS sells some "high end" units that seem to have decent channel-channel tracking specs, and those pots are sold by higher-end "hi fi" DIY websites.

Many of the "removed from service" slidewires from Ward-Beck, etc. broadcast consoles MAY or MAY NOT include onboard opamp buffers, which in-turn can require DC powering, etc.


Bri

[RodC]

Thanks Brian,
Is their a better way that you suggest that I do this, rather than a Pot?

Now Ill open another can o worms, do some searching for stepped attenuators.

Using a standard pot will affect your sound as the impedance will change for what ever is driving your monitors. You will also loose your balanced signal, if its balanced now.

[brianroth]

Yes, a stepped attenuator is a good choice, but can be quite expensive. For this unit (a controller I built for a mastering studio):

http://www.brianroth.com/custom/monitor-control.jpg

...I used a Shallco stepped attenuator:

http://www.shallco.com/attenuators.html

Bri