alfonso

Bal.I/O Volume control for soundcard to act. mon. connection
« on: September 26, 2004, 05:34:00 PM »
Hello :)

I need a high quality volume control between my soundcard's balanced outs and the balanced inputs of my ADAM monitors.

I don't need many I/O's , talkbacks etc., just a quality device for this single task.

Suggestions?

Thanks in advance.


Rochey

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #1 on: September 26, 2004, 07:00:09 PM »
are you diy'ing or buying a unit.

If you're diy'ing - take a look at teh PGA2310 or PGA2311 digitally controlled volume control. I think they are already used in devices which fit what your doing.

cheers

R
Expat Audio Home: http://www.expataudio.com

Bjorn Zetterlund

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #2 on: September 26, 2004, 07:14:19 PM »
I'd go with a balanced pad.  Something like two 1k resistors in series with both the pos and neg signal, and a 10k pot that connects between the pos and neg input on the speaker input.  A dual neg log pot will do both left and right.  I'm assuming the speakers have a normal 10k or above input impedance.  Quick and simple and should work ok!

Bjorn

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #3 on: September 26, 2004, 07:29:37 PM »
I'd say go unbalanced by grounding the negative input signals, feed positive inputs to a 10k stereo pot (went with TKD for my unit), then out to the positive inputs of your monitors. You'll lose -6dB by unbalancing, but there's no detriment to the sound at all if you keep your cable lengths as short as possible. Made a HUGE improvement compared over the Furman SRM80 which it replaced in my mix room. Also used a Greyhill 6-way rotary switch for selecting inputs, and added a mute/mono toggle switch after the volume pot. Under $200 including chassis and 18wag wire. Rawk on!
--
J.P. Sheganoski
Recording/Mixing Engineer
www.RisusProductions.com
www.Purevolume.com/risusproductions

Rochey

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #4 on: September 26, 2004, 07:31:27 PM »
bah -- i thought you wanted something alittle more complex :)

 :razz:
Expat Audio Home: http://www.expataudio.com

NewYorkDave

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #5 on: September 26, 2004, 07:52:28 PM »
Many balanced output stages will not tolerate one side of the line being shorted to ground. The simplest solution that is safe in every case is a balanced volume control. Here's an easy balanced volume control that I've used with success, and it's similar to the type Bjorn is describing:



The 3dB minimum loss figure assumes that the following input impedance is much higher than 10K. Under real-world conditions with the usual 10K to 20K inputs, the minimum loss will be more like 5-6dB.

If you could find a dual pot with perfect matching between the sections, you could build a lossless balanced volume control; but such a pot does not exist in the real world, at least not in a non-stepped form.

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #6 on: September 27, 2004, 12:19:50 AM »
The only downside to a balanced system like the one described is finding a quality dual-stereo potentiometer. I spent $60 on the TKD which was a simple stereo 10k pot, for a balanced rig you'd need a dual stereo, which would be near twice the price. Of course you could spend less, but then you're getting what you pay for. I started off my monitor control with the idea of staying balanced and going for a stepped attentuator like DACT or Goldpoint, then i realized the part alone would run over $300. Not worth it for me personally. Unbalanced with the TKD stereo pot has been fine with various sources feeding it (console main outs, masterlink, various DACs).
--
J.P. Sheganoski
Recording/Mixing Engineer
www.RisusProductions.com
www.Purevolume.com/risusproductions

SonsOfThunder

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #7 on: September 27, 2004, 04:01:13 AM »
Digital pots are annoying if you ask me, Rochey.  They NEVER have enough steps, in my experience.  Some of the bad ones 'click' when changing, though I'd guess the ones you recommend are pretty good.

I have another idea on this that I'm not quite ready to share just yet.  Working on the proto...along with too many other projects.  I really need this function for monitoring myself so this one is going to move to the top soon.

Peace!
Charlie
"The sow would rather have her ear than a purse." - PRR

Rochey

Bal.I/O Volume control for soundcard to act. mon. connection
« Reply #8 on: September 27, 2004, 04:36:56 AM »
Heya Charlie...

I assume some of the clicking is down to gain changes when the signal is non-zero. The TI one's (PGA231x) have a function where the gain only changes when the signal is zero-crossing - this should begin to avoid some of the 'zipper' noise associated with gain changes when the signal is non-zero.

Cheers

R
Expat Audio Home: http://www.expataudio.com

 

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