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DIY: audio line selector w/ passive volume

Discussion in 'Miscellaneous [BG]' started by marantz10, Apr 29, 2010.


  1. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    I searched high and low and can't find a cheap effective solution to my problem so I'm going to build my own "passive preamp."

    My dilemma:
    I have two computers, a Playstation 3, and a MP3 player all at my "home studio" (aka my bedroom). I just got a really good sounding pair of M-Audio BX5a studio monitors. They require funky cable types (TVS and XLR) and each monitor has a volume knob. I wanted a solution that allowed me to connect all my devices to a switchbox and select which input I'd like to listen to and a master volume knob that does not need to be active. Turns out I'd have to get a mixing board to do the same stuff but I want something cleaner for my desk and something small.

    I plan on using a stereo potentiometer for volume control. I don't need it to be amplified, just limit the voltage going through it. Radioshack has a stereo pot for $3.50.

    I'm at a toss up on container to use. I was thinking of making a wood box and staining it. I am also considering a plain plastic box as well as some sort of metal box like stomp boxes are made from. Cost is variable depending on my choice and my resources.

    I'll buy all the input jacks I need. At the moment I need mostly pairs of RCA jacks (PS3, and MP3 player) although I could go for stereo 1/8" jacks if they are available for the computers. This is the time for me to also decide how many inputs. More could be better if I get more devices someday.

    Now here's what I'd like some of your guys' opinions and knowledge of selector switches. I could do push button switches, toggle switches (seems coolest to me at the moment), slider switches, etc. Now if you think of the input selector knob on your old home stereo (much like old 70's Marantz receivers if you've ever had the pleasure), any idea what they call those and where I could get one from? The reason I ask is I think that would be the coolest option AND if I used any of the other types of switches, I potentially could have multiple things on at once and if there are any electrical engineers out there, could you tell me what would happen? I don't think two sources will blend if they are both selected but not sure what could happen.

    The output can be either TRS or XLR for the monitors. XLR seems coolest to use but the cables might cost more. Any opinion on output type is appreciated.

    As mentioned, the whole thing will be passive and use minimal circuitry (most likely no capacitors, resistors, or op-amps although there are the pots if you want to call them resistors then you may) so it won't need any power. I think it could potentially be a very useful project for my scenario and then I get rid of my headaches of thinking of unplugging and plugging in wires and adjust the volume on each monitor if I want it lower.

    So what'd'ya guys think? I'll take your feedback into consideration and I'll post pictures as soon as I start rounding up parts.
     
  2. MIJ-VI

    MIJ-VI Banned Supporting Member

    Jan 12, 2009
  3. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    Well that's the thing, I don't need to mix the sources together just select the one I want to listen to. It's an interesting idea to do that but I'm thinking really simple source selection instead of mixing.
     
  4. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    Well I shopped around and purchased some parts online that enabled me to save money. Via parts-express.com I just ordered:

    5 pairs of gold plated RCA plugs - wanted them to be gold plated because they look cooler, and hopefully have a more snug connection.

    A 100k stereo potentiometer - allows me to turn only one knob and get volume change.

    5 toggle switches - decided on round toggle switches because I have a drill that can make holes that are circular like this. These toggle switches are also decent looking compared to a few and they were cheap.

    Things to get:

    Radioshack has project enclosures from $3 so I'm going to stop by there and pick one up. While I'm there I'll also shop for:

    A volume knob fit to my liking
    Two XLR jacks
    Two XLR cables

    The XLR is interchangible with TRS until my decision at the store. I'm going for the cheaper one but I found that TRS cables seem to cost more and XLR is pretty nice considering it locks into place.

    More to come later!
     
  5. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    Okay received parts in and started to build it. Problems I ran into:

    My switches will not suit the purpose that well. I need DCDP switches (dual throw) for stereo switching. I ended up sacrificing two switches so that I can have two working inputs today. I'm not sure if I will be replacing them--they work for now and I don't need more than 2 inputs really.

    The potentiometer I got really is not great. At full volume, sounds good. At no volume, nothing which is good. But anywhere between is terrible. To clarify, it's an Audio Taper 100k stereo potentiometer made by some no name company. When turning the volume down, it sounds muffled and like you put a pillow on top of a speaker rather than just turning it down. From the looks of it by looking online, I think I should be looking for an attenuator with many different steps.

    Can somebody point me in the right direction in terms of where to get an attenuator? Or plainly a stereo pot that won't muffle my sound so horribly?

    Thanks!
     
  6. RWP

    RWP

    Jul 1, 2006
    This thread is useful and could actually do someone good. Please get it out of OT. :D
     
  7. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    Yeah no kidding, I wasn't thinking right about which forum to throw this into :p

    Current status: I just purchased a 100k stereo attenuator off eBay. I shopped around and basically got discouraged from the $100+ units from DACT so I got a no-name company version on eBay for $13.

    At this point in time, I feel the switches are holding me back so I'm shopping around for a "rotary selector switch" with 4 positions. It'll need to be a 2-deck for my stereo needs and I can't figure out if 2-deck = 2-pole. Any hints would be nice. :p

    I'm basically thinking of purchasing a new enclosure and will transfer the inputs and outputs to the new one. Reason being is I drilled a lot of holes in this enclosure and they didn't even turn out in straight lines in the back or front. I'm also going for fancy looks since I will be spending a good deal on this one.

    More later, although send me what you know about rotary selector switches :)
     
  8. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    Okay I found a perfect 4 position, 2 deck rotary input by GaryHill on eBay for about 11 dollars which is exactly what I needed.

    Now to look for an enclosure and something to make it look nice :p
     
  9. RWP

    RWP

    Jul 1, 2006
  10. john turner

    john turner You don't want to do that. Trust me. Staff Member

    Mar 14, 2000
    atlanta ga
    i think this is sufficiently music related to go in misc as opposed to OT.
     
  11. marantz10

    marantz10 Master Bass Playa

    Oct 21, 2008
    Seattle, WA
    Thank you John! On a hunt for enclosure at the moment...
     

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