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Modded Behringer Powerplay IEM (build report, DIY)

Discussion in 'Live Sound [BG]' started by Fredde, Oct 5, 2016.


  1. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Hi,

    I wanted to share my latest build, in case someone else is looking for a similar solution. I've been using In-Ear monitoring for a few years now, but none of the ready-made solutions that I know of have exactly the features I need. The optimal solution IMO is:

    - Only a single cable between myself and the pedalboard
    - The bass should be heard in the IEM even when she signal is tuner-muted (allows for last minute practice between songs...)
    - Belt mixer with separate controls for my bass and the main monitor feed
    - No batteries

    Now, I built a first version of this system a couple of years ago, but it wasn't perfect, and I'm not going to share that here. But this second version turned out pretty good, so maybe it can be of value for someone else as well.

    Instead of building the system ground-up, I chose to mod an existing belt pack this time. This way you don't have to design the mixer circuit, and you get some built in features like a protective limiter and the ability to drive low impedance headphones. I chose the Behringer Powerplay P1 for this purpose because it's cheap and has easily accessible innards.

    The setup looks like this:
    monitor_mixer_setup.png

    So, to the point, opening up the Behringer. Looks promising, standard connectors, lots of space inside:

    P1_open.jpg

    Replaced the connectors to XLR/plug combo and a 5-pin XLR. The combo connector allows for accepting a standard XLR monitor feed if I should want to use this for something other than bass playing at some point.

    connectors.jpg

    The connector board with molex connectors to plug in the Behringer's board, power cables and my buffer-splitter board:

    connector-board.jpg

    The main circuit's job is to split the bass signal so that a dry (but buffered) signal goes to the pedalboard, and an amplified signal goes to one channel of the belt pack. The buffer is needed to prevent crosstalk, a passive Hi-Z signal will not keep its integrity when led through the same cable as the main monitor feed.

    The circuit is designed around op amp OPA2134. The trimpot controls a Lo-cut filter, I don't like boomy bass in my ears. The gain resistor (far right) is socketed until I'm sure about the correct value.

    buffer-splitter.jpg

    The board is made to fit in the battery compartment:

    buffer-splitter-in-compartment.jpg

    Connections:

    P1_open2.jpg

    Done:

    [​IMG]

    The connection box on the pedalboard receives and distributes signal and power. It also has ground lift and phase revers switches to deal with common problems. (The phase reverse is needed in case you also have the bass (post effects and amp) in the main monitor feed. If its phase is reversed somewhere along the way, the two bass signals might cancel each other out.)

    5-pin XLR-male to the belt pack, XLR-female to receive the main monitor feed.

    connbox-inside1.jpg
    connbox-inside2.jpg
    connbox.jpg

    Installed on the pedalboard:

    [​IMG]

    I haven't tested this one on stage yet, but everything works great at home. The design is very silent (at least with my power supply), hiss and hum are negligible. The only change I might need to do would be the gain resistor for the amplifying stage, to match the levels of the main monitor feed and keep the gain as small as possible.

    The thing is, as the volume is controlled after this circuit, the op amp stage will always amplify everything, including possible supply noise, up to set gain first (in a normal application, you would put the volume pot before the amplifying stage). The 68k used here is probably a bit much, 47k should be enough. But this depends on the output level of your bass and the impedance of you headphones. Still, I can only hear a slight hiss/hum with the 68k, and that's with the levels cranked. Also, filtering caps are used pretty sparingly to save circuit board real estate, maybe there's room for improvement here.

    I anyone want's to build this, och just steal some ideas, feel free! Here's the schematics:

    monitor_mixer_behringer-FINAL.png

    monitor_mixer_behringer-CONNBOX.png
    EDIT: Add pull down resistor 1M
     
    Last edited: Oct 16, 2016
  2. Radio

    Radio

    Jan 8, 2010
    New Haven, CT
    Wow! What a great project and a beautiful presentation, Fredde. I think I've found my next project! Thanks.
     
  3. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Thank you! If you build it, please tell me how it turned out, and about any changes/improvements you've made!
     
  4. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    Looks like a cool mod.. but got a couple of questions about the setup - based on the signal flow diagram at top.
    You have:
    1. raw bass output going modded P1 - with output going to IEM's and pedalboard
    2. conn box on pedal board splitting signal to mixer and board.
    3. pedalboard output goes (w/ effects) to amp.

    Based on that approach, I have to ask why are you NOT monitoring the output side of the pedalboard?
    With the config above, the "dry" signal is what you monitor (via P1) in your ears and also send to the mixer.. you'll NEVER hear what goes to the amp!
    Is there a reason for that?
    I would think one would want to monitor what your audience hears ??
     
    Last edited: Oct 5, 2016
  5. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Sorry, my drawing was probably a bit unclear, I've updated it now. The bluish cable is the main monitor feed FROM the mixer to the conn box, which sends it to the IEM, in which I can mix between the main feed and the dry signal.

    The post-effects, post-preamp bass signal is part of the main mix which I hear in one of the IEM channels.

    But yes, there are some reasons for using the dry signal in the IEM:
    - As I said above, the bass should be heard in the IEM even when she signal is tuner-muted. This is more important to me than getting exactly the right sound. Getting both would be possible, but too complicated to be worth it.
    - To get some other than dry signal from the bass, I would need a cable with more conductors (probably 7-pin XLR). Also too complicated to be worth it.
     
    s0c9 likes this.
  6. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    Thanks for the reply - was just curious about the layout.. I know I'd want to monitor what goes to FOH.
     
  7. WayneP

    WayneP Supporting Member

    Oct 11, 2004
    Corpus Christi, Texas
  8. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Thanks WayneP!
     
  9. Radio

    Radio

    Jan 8, 2010
    New Haven, CT
    How could other band members connect to the mixer monitor feed?
     
  10. WayneP

    WayneP Supporting Member

    Oct 11, 2004
    Corpus Christi, Texas
  11. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    You assume correctly. Most modern (digital) mixers have great features for this, but with an older/cheaper mixer it could even be something as simple as the main output mix shared to everyone. Whatever works for you.
     
  12. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Tried out this system live last night, everything worked perfectly!

    ...that is, after soldering in a pull-down resistor to the conn box jack. I had forgotten this in the initial design, DC offset from the buffer circuit caused switch popping. Schematic above is updated with this addition.
     
  13. Motioneso

    Motioneso

    May 4, 2007
    Dallas, TX
    This looks absolutely awesome. How are you finding it after a couple of months? Picking up an XR18 for in ear control for shows and this looks like a fantastic alternative to cheaper wireless rigs.
     
  14. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Thanks! I've only done two gigs using it so far, but it works great (after adding the aforementioned pull down resistor.) No problems, clear sound, no noise. The belt pack is a bit (top) heavy, the belt clip is too low down. Not much I can do about that, though.

    But before warming up your soldering iron, remember this is designed to fit the very specific needs listed in the first post, so don't go wasting your time and money if these needs don't match yours.

    Having said that, please report back when (and if) you're finished, or if you have any questions during construction!

    Funny you should mention the XR18, btw, we use the same one. Being able to completely control your own monitor feed, real time, using your smart phone, is fantastic. (Behringer haters may grumble, I used to be one myself, but this is a really awesome product.)
     
  15. Ulf_Hansson

    Ulf_Hansson

    Apr 15, 2014
    Must admit I had some doubts about relying on Behringer, but these mixes really shine. I even like the preamps!
     
  16. Motioneso

    Motioneso

    May 4, 2007
    Dallas, TX
    So say I wanted to monitor the bass only from the XR18, does this setup allow me to just turn down the bass signal on the P1 and use the monitor in only? My primary goal is to be able to run a single cable from the pedal board to my bass/ears, so I love that part.
     
  17. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    To hear only the XR18, just turn the balance knob all the way to R and the P1 bass monitor will be muted.

    If this is how you're mainly planning to use the monitor, and the only need for modding is the one-cable-only setup, you could do with a simpler mod (or even just assemble a dual purpose cable and use the P1 as is). There would be no need for a separate on board bass preamp. This would, of course, remove the ability to hear yourself while tuner-muted between songs.

    I play in a covers band, and we have around 50 songs on our repertoire. I don't like to have any sheets on stage, and sometimes (ok, quite often) I need to refresh my memory before playing a song. With the hear-while-muted ability, I can quickly rehearse the bass line during the speak or guitar intro. So for me, this is a very important feature.
     
    Red Planet and Motioneso like this.
  18. Motioneso

    Motioneso

    May 4, 2007
    Dallas, TX
    Ahh ok, thanks! Yes, the primary use is to just have one cable for monitor/bass. Would it essentially be swapping out the XLR connectors with a combo jack and XLR 5-pin (I also like the idea of having power come from the pedal board)?

    Or, if I can pick your brain, would you propose a different way to do it? I've seen some of the multi cables, but none that quite fit the bill. I'm not afraid of attempting to hack one together myself, something along the lines of a mini 1/4"/XLR snake?

    Thanks again!
     
  19. Fredde

    Fredde

    Oct 21, 2010
    Helsinki, Finland
    Yes, you could use the connectors I have in my design, but omit the whole preamp board, and just wire the jack input of the combo straight to the 5-pin XLR in order to get the bass signal to the pedal board.

    Sure, that wouldn't be too difficult. Just get some multi-conductor cable and fork the ends with all the connectors you need. As I see it, you would need XLR, 1/4" and Boss-style DC-plug in each end. This could be a bit pf a tangle, though.

    The biggest problem with discarding the buffer board is that a hi-impedance bass signal will travel in the same cable as the monitor-signal, and will be very vulnerable to cross talk. You'll have to keep the cable as short as possible. The ideal would be a cable with individual shields for all conductors, but I haven't been able to find one that's not too thick. Technically a Cat-7 network cable would be perfect but these, in turn, are way too stiff.
     
    Last edited: Dec 28, 2016
    Motioneso likes this.
  20. NicovanHeck

    NicovanHeck

    Feb 13, 2017
    Fredde, thanks alot for this!
    I was just looking for about the same solution and this fits my needs!

    Though, I don't need the 'Bass to IEM' - signal but I would like a stereo feed for my headphones.
    Since my requirements are a tiny bit different I have a question about crosstalk.

    I did some testing to figure out how signals behave in cables and this is what I found:
    - Shared grounding in a single XLR cable gives huges crosstalk (Pin 1: Ground, Pin 2: Bass, Pin 3: IEM Mono)
    - A dual mono jack cable gives no crosstalk, but still gives a mono IEM signal. Each conducer is shielded, which in turn works amazing! (A solution might be to use dual-XLR cables, but now I'm curious as to how cabeling/grounding/buffering affects crosstalk)

    This leads me to the following questions:
    I can see you're using the balanced Right signal for the IEM which makes it possible not to share the Ground for both bass ánd IEM. Did you do this to reduce crosstalk, or just because it was easier?

    Will it be possible to use the 5 wire cable in the following configuration without crosstalk?
    1: Bass signal
    2: Bass ground
    3: IEM Left signal
    4: IEM Right signal
    5: IEM ground

    And what can I to reduce crosstalk if there is any? How much will buffering the Bass signal help?
     

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