dmbaer
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Is It Safe to Short Out Line-Level Sound Card Outputs?
The reason I'm asking is that I want to put a stepped attenuator (a fancy stereo volume poetntiometer, basically) in parallel to my monitor inputs. The monitors have 20K input impedance, so there's nothing to worry about there. However, in the simplest circuit configuration that I've seen, there's only the volume control in parallel with the monitor inputs. That means with the "volume knob" turned fully counter clockwise, the volume control is at (or very near) zero ohms. So, is this safe or will I risk damaging my sound card if I don't put some kind of resistance in series, just to be on the safe side. Educated answers only, please. 
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Guitarhacker
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/08 11:56:21
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I don't know if there is a danger in shorting the line level outputs, there's not alot of power there to heat things up... ... but then again the idea of a shorted output is not something I would seek to do... intentionally.... but my question is.....aren't there any volume controls on the monitors?
I don't know that this would work the way you want...for a variety of reasons.
There should be volume controls on the monitors, plus, there are the level controls in the DAW. I would use them as opposed to using a hardware device in the line level outputs. I set my monitor levels to 50% and adjust the sound level from the interface fader in my DAW.
Next question: is this attenuator designed to do that specific job or are you hoping it will do it when it was designed to do something else. Most attenuators are designed to work in a power circuit..... but the ZERO ohms thing is not a very good idea in any output circuit that I am aware of....
Does it wire in series? If so, there is no danger in using it. Worse that could happen is the results are not what you hoped for. In series, a high resistance would give a lower volume...whereas a short (zero ohms) would allow the signal to pass as if there was no attenuator on the line.
If it wires in parallel, the shorted or zero ohm position would be shorting the output, and I don't think that's how it's supposed to work. I might be wrong but that's what I'm thinking.
My website & music: www.herbhartley.com MC4/5/6/X1e.c, on a Custom DAW Focusrite Firewire Saffire Interface BMI/NSAI "Just as the blade chooses the warrior, so too, the song chooses the writer "
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/09 17:25:26
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Certainly there's a software (GUI based) volume control for the sound card. It's just that when you unintenally do something that blasts you out of your seat, you can react a lot more quickly if you can grab a physical knob within easy reach and turn the level down. It takes a lot longer with a mouse. The monitors have individual volume controls as well, but not within easy reach (and not one stereo control anyway).
The purpose of the stepped attenuator is that it (in theory) offers more accuracy in balance than even a quality volume potentiometer. At least that's advice I've picked up on several electronics forums. Audiofile caliber stepped attenuators cost $150 and up. But you can order what look to be quality devices on e-bay for about $45 including shipping. They are assembled in Hong Kong. Found this poking around electronics forums as well.
So why would I want to have a zero ohm load on the sound card outputs? No reason other than the electronics forums have circuit diagrams that do just that. I would suspect that maybe a 10 or 20 ohm load in series would be prudent (and would take essentially nothing away from the maximum level sent to the monitors). But the circuit diagrams I've seen (on multiple sites) never bother. That's why I'm asking the question. Thanks for your thoughts on this.
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Guitarhacker
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/09 21:09:52
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I understand the reasons you might want this device in the signal path..... However.... In a studio situation, it is rare that you would want to have the monitors set to "blast away". I like to mix at a very comfortable level. Even when the DAW output is at max.....(0db) the level is not loud. I keep the monitors on 50% and same thing with the sub.... Without seeing the schematic, it is difficult to determine if the device is in series or parallel. I would NOT want to short the output of any amp even line level in an attempt to control the volume. A shorted output would (in my mind with my understanding of circuit theory) cause maximum current to flow through the short which means less would go to the load, hence a lower volume. BUT, the maximum current flowing, lowers the voltage (it's a short) and I would assume that the combination of high current and low voltage would distort the output signal in some manner that would not be good for sound. This would happen if the device was a parallel device. In a serial device, turning the knob would introduce more or less resistance to the current flowing through it. A zero resistance would act like there is nothing in the circuit. As the resistance is increased, the volume would theoretically go down. It would act only as a device to add resistance to the current and in my mind, this would not present a major problem.... BUT, it's never as easy as simply adding a variable resistor to the signal path. BUT a pad or attenuator has other components in it to make it work properly and they introduce phase shift as you turn the knob. The thing you said about having a physical volume knob to grab made me think of something I saw earlier in the week. The KRK ERGO does what you want, and it does it the right way. With out any danger or damage to your system. It is a room correction system that also had a big volume control jump to 5:50 in this video...also the important thing is that with ERGO you don't change the tone character as you adjust the volume up and down. It is a bit more than a $40 chinese volume control but ..... you get what you pay for...... I would not put a cheap volume pad from china in my signal path. I think ERGO is close to $500 but only you can decide if you want to risk shorting out the sound card or doing it the right way.
My website & music: www.herbhartley.com MC4/5/6/X1e.c, on a Custom DAW Focusrite Firewire Saffire Interface BMI/NSAI "Just as the blade chooses the warrior, so too, the song chooses the writer "
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/10 13:39:39
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Guitarhacker
In a studio situation, it is rare that you would want to have the monitors set to "blast away". I like to mix at a very comfortable level. Even when the DAW output is at max.....(0db) the level is not loud.
I'm mostly messing around with synth sound design right now. It's really easy to accidentally get into a "blast away" situation. I agree, if I was doing routine mixing for long periods, volume adjustments would not be something I'd be constantly doing.
Without seeing the schematic, it is difficult to determine if the device is in series or parallel. I would NOT want to short the output of any amp even line level in an attempt to control the volume. A shorted output would (in my mind with my understanding of circuit theory) cause maximum current to flow through the short which means less would go to the load, hence a lower volume. BUT, the maximum current flowing, lowers the voltage (it's a short) and I would assume that the combination of high current and low voltage would distort the output signal in some manner that would not be good for sound. This would happen if the device was a parallel device.
I'm not trying to stubbornly advocate this approach, and I hear everything you're saying about the downside of shorting an output. However, in researching how to approach this, I came across multiple variations on this design in various places, so I have to believe there's some validity to the approach. Here are four links I found in case anyone is curious: http://www.hometheaterhifi.com/volume_10_1/kimber-dact-volume-control-2-2003.html http://www.suite101.com/content/use-a-passive-preamp-for-excellent-sound-quality-a128047 http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=cmoy7_prj.htm http://sound.westhost.com/project01.htm I think ERGO is close to $500 but only you can decide if you want to risk shorting out the sound card or doing it the right way.
Well, I'm just a hobbiest with too little time to devote to this right now. And if I had 500 bucks to blow on new toys, I'd probably pick up Omnishere. 
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Guitarhacker
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/10 13:47:13
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OK looking at the schematics to the passive gizmo's.... there is a variable resistor (pot) that is 100k ohms to ground.... the wiper contact comes off the center and it has another resistor (22k ohms) to keep it from a dead short to ground. that should be OK. Worst case scenerio would be that it won't perform like you would hope it would. At radio shack the parts with the box might be $20 (inflation these days) so go and pick up a few parts, remember it's stereo so you want a double 100k pot.... and grab your soldering iron and build it to see if it does what you want.
post edited by Guitarhacker - 2011/03/10 13:51:10
My website & music: www.herbhartley.com MC4/5/6/X1e.c, on a Custom DAW Focusrite Firewire Saffire Interface BMI/NSAI "Just as the blade chooses the warrior, so too, the song chooses the writer "
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wogg
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/10 15:17:41
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You're misreading how a volume control looks to the input circuit (the output of your soundcard). With the wiper at 0, the output (to your monitors) is shorted to ground while the input (from the soundcard) continues to see the full value of the pot. The smallest impedance the soundcard will see is actually at full volume, when it has to drive the value of the potentiometer in parallel with the input impedance of your monitors. http://woggmusic.com/WP/?p=474
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/10 19:15:09
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wogg
You're misreading how a volume control looks to the input circuit (the output of your soundcard). With the wiper at 0, the output (to your monitors) is shorted to ground while the input (from the soundcard) continues to see the full value of the pot.
The smallest impedance the soundcard will see is actually at full volume, when it has to drive the value of the potentiometer in parallel with the input impedance of your monitors.
http://woggmusic.com/WP/?p=474
Aha!!! Now it finally and fully makes sense. You're absolutely right that I was misreading the schematic. With your explanation it's completely obvious what's going on and it's embarrasing I was being to dense. Many thanks!
post edited by dmbaer - 2011/03/10 19:24:04
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/10 19:22:11
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Guitarhacker
OK looking at the schematics to the passive gizmo's.... there is a variable resistor (pot) that is 100k ohms to ground.... the wiper contact comes off the center and it has another resistor (22k ohms) to keep it from a dead short to ground.
Actually, if you read the text accompanying the schematics that have the second (fixed) resistance, that extra resistor is there so that a linear tap pot which is not suitable for volume control but costs less (this has to do with loudness and dBs and all of that stuff that I sometimes understand but only on a good day) will behave a bit more like a audio tap (or maybe it's called log tap ... don't recall).
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johnnyV
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/10 21:20:54
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It has been my observation to not try and mess with electronics without 100% understanding of what is happening to your equipment as a result of home made gizmos. Most interfaces have a handy monitor control right on the front. If not, I would then use a mixing board to control monitor level. Your right about the "panic " of trying to find a computerized volume control. There will be smoke in the room first. Passive circuits may seem to work but personally I would not subject a pair of $500 speakers to anything questionable. They do make control boxes thet control mutiple monitor set ups as example http://www.mackie.com/products/bigknob/
post edited by johnnyV - 2011/03/10 21:23:14
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/11 13:34:28
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johnnyV
It has been my observation to not try and mess with electronics without 100% understanding of what is happening to your equipment as a result of home made gizmos.
Certainly agree (thus this thread being posted in the first place). Thankfully, with Wogg's response above, I now know how to proceed with 100% comfort that no damage will ensue. Assuming this works out, I'll report back on how it was done. Thanks to all for your inputs.
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Bristol_Jonesey
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/11 14:05:49
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I'm with Johnny.
I have a console between the compuer & my monitors.
Interesting also that you're primarily wantin this as a result of synth design.
Whenever I'm browsing for a patch in any of Sonar's bundled synths, I ALWAYS insert a really fast limiter on the master bus just to prevent overloading the monitor chain. Some patches are just so damned loud, how they made it past QC is a mystery, and potentially damaging.
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Beagle
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/11 14:40:06
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johnnyV
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/12 12:47:09
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Most excellent suggestion. And for 2x the $$ you can even get 3x as much! A mixer is something I would never be without to set up my signal paths.
Sonar X3e Studio - Waiting for Professional Scarlett 6i6Yamaha Gear= 01v - NSM 10 - DTX 400 - MG82cx Roland Gear= A 49- GR 50 - TR 505 - Boss pedalsTascam Gear= DR 40 - US1641 -Mackie Gear= Mix 8 - SRM 350's i5 Z97 3.2GHZ quad 16 Gig RAM W 8.1 home buildTaylor mini GS - G& L Tribute Tele - 72 Fender Princeton - TC BH 250 - Mooer and Outlaw Pedals Korg 05/RW
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tarsier
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/14 15:01:48
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I daresay a cheap Behringer mixer wouldn't pass dmbaer's quality check. See post #3.
If all that dmbaer wants is to quickly shut off an inadvertent big blast, then maybe a panic button would be better than a stepped attenuator? Just a simple switch you can slap when the sound gets out of control--which has happened to us all, I think. Even after all the precautions we might take.
A panic button would just cut off the signal and you can then stop the noise at your leisure. It wouldn't be a messy potentiometer or a complicated stepped attenuator. But if you want more than a panic button, then by all means proceed.
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chuckebaby
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/14 15:15:52
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thats what the audio engine buttons for.do you use it?
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/14 15:39:17
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tarsier
I daresay a cheap Behringer mixer wouldn't pass dmbaer's quality check. See post #3.
Quite right. One thing I discovered early on in my web investigating is that stereo potentiometers are apperently difficult to manufacture such that the resistance on both channels is consistent throughout. This is allegedly true in even the more expensive units. The idea behind a stepped attenuator is that it uses discreet reisistors on a rotatry switch assembly. The resistors used are typically 1% accuracy, so consistency can be achieved at all level settings. The inexpensive Behringer, while a marvelous small bundle of capabilities, almost certainly uses inepensive pots.
If all that dmbaer wants is to quickly shut off an inadvertent big blast, then maybe a panic button would be better than a stepped attenuator? Just a simple switch you can slap when the sound gets out of control--which has happened to us all, I think. Even after all the precautions we might take.
A panic button would just cut off the signal and you can then stop the noise at your leisure. It wouldn't be a messy potentiometer or a complicated stepped attenuator. But if you want more than a panic button, then by all means proceed.
Well, it certainly would have been cheaper solution. But the attenuator is being shipped as I write this.
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Guitarhacker
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/14 17:59:04
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Be sure to let us know if it works like you are expecting.
My website & music: www.herbhartley.com MC4/5/6/X1e.c, on a Custom DAW Focusrite Firewire Saffire Interface BMI/NSAI "Just as the blade chooses the warrior, so too, the song chooses the writer "
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/14 19:09:51
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Guitarhacker
Be sure to let us know if it works like you are expecting.
I will indeed. If I can finally insert jpg-s into posts with my new W7/IE8 setup (some some can do but I could not with XP), I'll even include pictures.
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Beagle
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/29 11:04:01
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david - did you ever get this working?
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dmbaer
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Re:Is It Safe to Short Out Line-Level Sound Card Outputs?
2011/03/29 14:32:31
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Beagle
david - did you ever get this working?
Yes, I did. But I'm still experimenting with optimizing the solution. I bought an expensive ($45 w/ shipping) 10K stepped attenuator. It works fine, but only the highest 6 positions out of about 22 are worth using ... the others are too quiet. I just picked up a cheapo 100K stereo volume control at Radio Shack, just to see if I shouldn't have started out with that value stepped attenuator. I will report back with full details and assembly hints when I've finished my additional testing.
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