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DIY Studio Switcher/Attenuator Control Box???

Discussion in 'Recording Gear and Equipment [BG]' started by Projectile, Mar 13, 2009.


  1. Projectile

    Projectile

    Feb 5, 2009
    Okay, I'm not sure where to ask this question, but I thought I would see if anyone here could help. Basically, I have a set of active studio monitors and a separate headphone amp. My delta 1010 interface has multiple outputs and inputs so every time I need to switch between my headphones and monitors I just use the mixer inside my DAW to route audio to the appropriate outputs. As you can see, this is a major PITA. Also, I would like to be able to plug an mp3 player into my studio monitors without routing it through the computer. Finally, I want an external volume knob to control everything, so I don't have to reach for the mouse every time somebody comes into the room and I want to adjust the main level.

    I know a mixing board would solve my problems, but I really don't have the room or the finances for one. I'm also aware that mackie's "big knob" and presonus's "central station" are made to solve exactly for these home studio problems, but they are expensive.

    The solution:

    It seems like it would be very easy and cheap to throw together a simple passive control box that switches between two unbalanced stereo sources, and two stereo outputs, with a master volume attenuator. Here is a proposed wiring diagram I drew up:

    [​IMG]
    Mirror: http://img22.imageshack.us/img22/4493/deskcontroller.png

    So what do you guys think? Would this work? Seems too simple, but I don't see why it wouldn't work. Should I go ahead and build it? Thanks.

    EDIT: And what value pot should I use for the attenuator? 10K, 50K, 100K, 500K, 1Meg??? I have no idea.
     
  2. funkmuffin

    funkmuffin

    Aug 18, 2004
    Akron, Ohio
    Not a bad idea, and your diagram looks OK. The only thing I would suggest is for you to look into getting a stepped attenuator instead of the taper pot.

    I know the nice ones from DACT or Goldpoint are super expensive, but there's at least one guy on Ebay selling essentially the same thing much cheaper. You'll have MUCH better left/right balance. The taper pots (even the good ones) are known to be several decibels off between the channels -- not a good thing when you're trying to get a good stereo image.

    I'm currently building one myself using the Ebay attenuator, and a few 4PDT switches (my circuit is balanced all the way through). The 4 deck attenuator was $50 from the guy on ebay -- you'd only need a 2 deck version which are about half the price.
     
  3. It should work, but there are going to be impedance issues with the passive volume. That load won't have a constant impedance, and it will generally sound bad because it is going to be a mismatch at AF. I'd either yank the volume pot and just have a passive stereo switcher, or look into some kind of utility buffer to handle the job. Kinda seems like a lot of hassle to avoid having to move your mouse...
     
  4. Projectile

    Projectile

    Feb 5, 2009
    Thanks for the suggestion. I will definitely have to go with a stepped attenuator then. It looks like I can get one for $20 off of ebay. That's not too bad. What value attenuator would you suggest? 10K, 100K, 500K 1Meg??? I just realized I didn't even consider what range would be appropriate.

    I considered building a balanced box but it just seemed too expensive and complicated. I'm having enough trouble just trying to figure out how to deal with a stereo signal. I've been running my outputs to my monitors unbalanced anyway, and it seems to work okay. My headphone amp is also unbalanced, so it's just easier for me to keep everything unbalanced.

    Let me know how your switcher/attenuator box works out. I might come to you for advice again if I ever build a balanced version. Thanks. :D


    How exactly will it sound bad? I've seen other similar passive devices and passive mixing boards that seem to attenuate okay, but I'm not sure how their circuits were accomplished. What will the impedance mismatch do to the audio signal technically? Is it not possible to simply attenuate the signal to ground? Isn't this commonly how it is done? Help!!??? :(
     
  5. Attenuation, and flat, transparent attenuation are not the same thing. A lot will depend on the impedance of the potentiometer, the impedance of the source, destination... Hard to say since you have some question marks in there. Yes, there are some passive mixing devices that work, but they aren't transparent. I have one that I used to mix cheapo effects/sources, but it sounds like ^&* next to even a cheap buffered mixer. You want cheap, convenient, high quality switching and gain control... and it isn't going to happen (IMO) with that kind of passive setup. It is just an opinion... it isn't like I am going to build it and test it for you :ninja:
     
  6. Projectile

    Projectile

    Feb 5, 2009
    Thanks. I wasn't aware a passive device would color the signal so much. I have schematics for a few cheap opamp based buffers circuits lying around, but then I would have to use a power supply, and I would be getting in entirely over my head. Maybe I will just add a switch that will allow me to bypass the attenuation stage altogether for critical tasks like mixing. That would still allow me to use the volume knob for day to day casual listening and tracking.
     
  7. funkmuffin

    funkmuffin

    Aug 18, 2004
    Akron, Ohio
    As to the impedance question, what I read, and went with was that you should match the attenuator's impedance to the input impedance on your load -- your monitors. In my case, that's my KRK RP8's, which are rated at 10K Ohms IIRC, so I went with that. There's also a consideration for the impedance of the up-stream components, cables and such.

    Good stuff here: http://www.goldpt.com/diy.html

    ...and here: http://www.dact.com/html/technical_info.html

    Definitely check the second one. There's a calculator spreadsheet there that will show the different pieces of the puzzle.

    You also mentioned the balanced circuit -- I'm only going that way because I have balanced outs from my MOTU. Mine will also have a L/R Swap button and a mute switch wired after the attenuator. I also had planned on a Mono switch, but I couldn't figure out the wiring, so I scrapped that idea. Now I'm trying to figure out how to fit it all together, as the switches I found are PC mount, but have a pair of legs to power an LED, and they don't fit the standard spacing.
     
  8. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    On the cheap... how about an old 70's hi-end home stereo preamp, poweramp or integrated amp? I'd think some of these would function fairly well as a line-level monitor control panel for not much $.

    You'd need unbalanced RCA connections for both its inputs and outputs, but with many you get a mono switch/multiple line level inputs-outputs/volume-balance plus a headphone jack.
     
  9. Projectile

    Projectile

    Feb 5, 2009
    Thanks for the link. That's exactly what I needed.
     
  10. Projectile

    Projectile

    Feb 5, 2009
    Thanks, I hadn't considered that option.
     
  11. I'm just going to throw this out there:

    I had a similar problem (multiple inputs, multiple sets of monitors plus headphones) and I considered building something, but then decided that the $40 Behringer MON800 would take care of everything, and it ended up working out fine.
     
  12. Projectile

    Projectile

    Feb 5, 2009
    Wow, that's a lot of functionality for $49. I swore I would never purchase anything Behringer, but this is almost temping. Argghh! I think I'm going to have to sick to my principles, but thanks for the heads up.
     

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