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Christmas build project - Bedroom active 2.1 system

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  • Christmas build project - Bedroom active 2.1 system

    Here's my main request for Christmas, lovingly provided by my awesome wife:

    Click image for larger version

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    A SD215A-88, a pair of TDA7492 amp boards, and a Meanwell 24V supply to power them. Plus, bonus pair of active crossover boards I had made for my bass amp project this past summer.

    This will be destined for the business end of an active 2.1 system. One amp driving both coils of the woofer individually, the other for the highs out binding posts in the back. The active filter boards are textbook Sallen-Key third order butterworth filters set at a fixed 100Hz for both high and low pass. An adjustable filter would be nice, but these should do just fine. I'll have 3 level pots on the back, master, LP and HP.

    For enclosure I'm going with a simple trapezoid, ported in 0.88 cu ft net internal tuned to 32Hz with a 2" precision port. The box is minimalist, the back panel inset 2" to house the electronics and the front inset 1" to accommodate a protective grill. Where this thing will sit in the bedroom shoes are known to fly. All edges will get a 1/2" roundover, and the finish will be simple Duratex black with a smoothish roller.

    The backside will be covered by a metal panel to mount the power and I/O, with 1" slots at top and bottom for heat to convect out.

    Click image for larger version

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    The build will probably actually happen when weather permits, I'm currently in the deep planning phase. This system is destined for the bedroom where I have a TV and a pair of el-cheapo Dayton B652's providing speaker duty, which is a massive upgrade from the TV speakers. They do a decent job on general TV, but I desire bass, and with this I'm expecting a little music and movie action to be much more enjoyable.

    For power, I'm going to tap a 12V line from the PC that runs the TV and use a solid state relay to juice up the power supply, bypassable with a toggle switch if no remote signal is available. I'm pondering a second 1s delay relay to connect the speaker outputs, but would like to avoid the click if I can.

    Question for TDA7492 board users: Does that board have any turn on thump?
    Attached Files
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music

  • #2
    Should be a nice build. Looking forward to it...

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    • #3
      Cool Project! If someone wanted to duplicate it, would your active crossover boards be available to order somewhere?
      My "No-Name" CC Speaker
      Kerry's "Silverbacks"
      Ben's Synchaeta's for Mom
      The Archers
      Rick's "db" Desktop CBT Arrays
      The Gandalf's

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      • #4
        Originally posted by Kevin K.
        Cool Project! If someone wanted to duplicate it, would your active crossover boards be available to order somewhere?
        They're not a commercial product, but I'd be happy to send the ExpressPCB files. The trick in this application is I'll have to omit some parts and make other modifications. The original design was for dual power supplies (+-25V) while this has to run on a single 24V source.
        Electronics engineer, woofer enthusiast, and musician.
        Wogg Music

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        • #5
          Was just curious. Looks like a fun project, looking forward to the updates.
          My "No-Name" CC Speaker
          Kerry's "Silverbacks"
          Ben's Synchaeta's for Mom
          The Archers
          Rick's "db" Desktop CBT Arrays
          The Gandalf's

          Comment


          • #6
            No build updates yet.... but I finally plugged in the supply and an amp board to test for turn on thump. The answer is.. no, the TDA7492 boards don't thump at turn on with that PSU. Also, I measured 15.6VRMS on a meter at 100Hz before audible distortion creeped in, which should be at about 4 ohms on the SD215-88, which comes out to 60W RMS per channel from the amp board at 24V.
            Electronics engineer, woofer enthusiast, and musician.
            Wogg Music

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            • #7
              Still waiting for the weather and timing to permit a driveway wood cutting session, but I'm making a little progress on the electronics. ​I've assembled 1 of the 2 modified crossover boards to validate the design prior to building the other, and did some metal work on the custom plate amp today.

              Click image for larger version

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              ​The crossover, like mentioned above, is fixed at 100Hz using this schematic:

              Click image for larger version

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              ​I'm using the spare prototyped boards I had made for my integrated bass amp project, so if I were to design a new board I'd be able to fit stereo channels on a single board and change that input buffer to a non-inverting type in order to be able to get gain with lower noise. If anyone is interested in re-creating this I'd work on that. The prototype cost from Express PCB will use their mini board standard which gets you 3 boards for $41, so this isn't a super cheap option unless we can get 3 people interested to share cost. It is however, IMO, superior to the PE sub crossover in that the slopes are 18dB / octave and there's a high pass for true bi-amping.

              ​Here's the rear plate layout, fitting the boards, power supply, and all input / output connections.

              Click image for larger version

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              Attached Files
              Electronics engineer, woofer enthusiast, and musician.
              Wogg Music

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              • #8
                Mains and DC power section all built up for the plate amp. The power device strapped to the top of the power supply is a solid state relay, that enables the remote turn on signal which I have setup to accept a wide range of input. My intention is to use a USB cable to turn the amp on when the host PC turns on.

                The LED power indicator is blue, for optimum sound

                Click image for larger version

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                Electronics engineer, woofer enthusiast, and musician.
                Wogg Music

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                • #9
                  Originally posted by wogg View Post
                  No build updates yet.... but I finally plugged in the supply and an amp board to test for turn on thump. The answer is.. no, the TDA7492 boards don't thump at turn on with that PSU. Also, I measured 15.6VRMS on a meter at 100Hz before audible distortion creeped in, which should be at about 4 ohms on the SD215-88, which comes out to 60W RMS per channel from the amp board at 24V.
                  Your losing up to 1.0 V in the TDA7492's PS reverse polarity protection diode. Personally, once everything is buttoned up, I replace those diodes with a jumper. You likely can't hear a difference in SPL but it gets you a little extra headroom.

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                  • #10
                    Originally posted by Millstonemike
                    Your losing up to 1.0 V in the TDA7492's PS reverse polarity protection diode. Personally, once everything is buttoned up, I replace those diodes with a jumper. You likely can't hear a difference in SPL but it gets you a little extra headroom.
                    Nice tip, thanks! Every volt helps when I'm trying to get the most of them into 8 ohms.
                    Electronics engineer, woofer enthusiast, and musician.
                    Wogg Music

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                    • #11
                      Nice work!
                      .

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                      • #12
                        Originally posted by mzisserson View Post
                        Nice work!
                        ​Thanks man! I can't match your woodworking, but I can get OCD on wires
                        Electronics engineer, woofer enthusiast, and musician.
                        Wogg Music

                        Comment


                        • #13
                          Here's the audio boards in place, all wired up and tested. I'm waiting on another RCA jack to fill that last hole, that's a line level sub out for expansion to a second sub.

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                          Everything seems to be working pretty well, there may be a bit much noise through the crossover boards from the switching supply and or amps, the scope showed switching noise coming back on the input and it was audible against the test speaker with the pots all the way up. Backing the pots down immediately killed the noise, we'll see how the gain structure works out in place. I definitely would improve the crossover board if re-designing instead of using existing boards, but prototyping boards is expensive so I'm sticking with what I've got.

                          ​Now I just have to wait for the weather to realize it's supposed to be spring so I can build the woofer for this thing's home.

                          Electronics engineer, woofer enthusiast, and musician.
                          Wogg Music

                          Comment


                          • #14
                            Originally posted by wogg View Post
                            Here's the audio boards in place, all wired up and tested. I'm waiting on another RCA jack to fill that last hole, that's a line level sub out for expansion to a second sub.

                            [ATTACH=CONFIG]n1324670[/ATTACH]

                            Everything seems to be working pretty well, there may be a bit much noise through the crossover boards from the switching supply and or amps, the scope showed switching noise coming back on the input and it was audible against the test speaker with the pots all the way up. Backing the pots down immediately killed the noise, we'll see how the gain structure works out in place. I definitely would improve the crossover board if re-designing instead of using existing boards, but prototyping boards is expensive so I'm sticking with what I've got.

                            ​Now I just have to wait for the weather to realize it's supposed to be spring so I can build the woofer for this thing's home.
                            It might be from two amp chips in proximity that are not sync.'d. I would try powering only one amp to verify/eliminate that issue as the source of noise. Could you get a good read on the noise switching frequency?

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                            • #15
                              Originally posted by Millstonemike
                              It might be from two amp chips in proximity that are not sync.'d. I would try powering only one amp to verify/eliminate that issue as the source of noise. Could you get a good read on the noise switching frequency?
                              I'm getting 55 - 60kHz on the scope. I measured the output with the gain pots all the way down, got single digit mV. There's a whole lot more noise when I crank up the level after the crossover, same frequency range though.
                              Electronics engineer, woofer enthusiast, and musician.
                              Wogg Music

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