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Custom analog 2.1 crossover board for the electronically adventerous

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  • Custom analog 2.1 crossover board for the electronically adventerous


    This schematic is a dedicated design for this purpose. The master volume may be connected before the gain buffers, or after. If the master volume is connected after the buffers as shown in the schematic, there will be a risk of clipping the gain block given sufficient input signal. With 21dB of gain and a 24V supply, the op-amp will clip with just over 1V peak input, which may be a concern. In the schematic, R5 and R7 can be altered to change the gain setup using standard op-amp non-inverting calculation Av = 1+R5/R6. The advantage of putting the volume after the gain block is an improved noise floor, however the potential to clip may be a larger problem. When built using a volume control in front of the filter board, simply install jumpers where the master volume connections would be. A complete design package is available for those that would like to prototype this design themselves.In the ZIP file is a BOM for purchasing parts, and the files required to purchase the boards. To open the schematic and board layout files you'll need the software from ExpressPCB, sorry no standard format gerbers for other software. Total cost for building these yourself is just under $60. That is a premium over pre-built 2.1 boards, but still cheaper than DSP options and worth the cost to provide that true bi-amplification in my opinion.
    The BOM spreadsheet also has some formulas that will let you re-calculate values for a different crossover frequency, gain, sub and ultrasonic cutoff etc. Change the values up top and the affected parts will be re-calculated. You'd then need to adjust the values purchased to be as close as you can get.
    Last edited by wogg; 06-04-2017, 08:57 AM.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music

  • #2
    Is there a reason why you decided to use a half-wave rectifier over a full-wave bridge for the power supply?

    Never mind, looking closer I see that the input of the diode is DC, rather than AC.
    Don't worry, if your parachute fails, you have the rest of your life to fix it.

    If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

    Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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    • #3
      Double post.
      Don't worry, if your parachute fails, you have the rest of your life to fix it.

      If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

      Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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      • #4
        Yup. What that does is keep the crossover board running for a few seconds after the power supply is shut off. I found in my build that I had a hell of a turn off thump that was originating from the op-amps as they lost power. Keeping them powered for a few seconds cleared the problem.
        Electronics engineer, woofer enthusiast, and musician.
        Wogg Music

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        • #5
          The diode with the capacitor behind it. I figured that out after realizing that the input to the diode is DC coming from a regular power supply rather than AC. I at first thought that this was the (rather crude) rectifying and smoothing part of a power supply until I looked closer. I guess my eyes are not what they used to be. It sucks getting old!

          I have actually used this type of circuit myself a lot to create a delayed drop-out of relays in control circuits.
          Don't worry, if your parachute fails, you have the rest of your life to fix it.

          If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

          Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

          Comment


          • #6
            Wogg how would you feel about designing a simple generic Signal Processing circuit using one or two op-amps on a small standard PCB. Something like Neil Davis is designing, but much simpler and analog rather than digital.

            Functions like Bass Boost/Cut, Treble Boost/Cut, Subsonic Frequencies Cut, Amp, etc. A circuit would be for one or two functions, but could be daisy-chained. It could be fixed with a table for component values or use a dip switch.

            Uses for example would be a a boost in low end for sealed subs with a plate amp that does not have boost built in. A bass boost for a boombox, a cut-off for sub-sonic frequencies, a pre amp if signal is low, etc, etc. Cost could be under $10.

            I think this would be tremendously popular in the DIY community.

            I have thought about this for some time, but am somewhat rusty in my electronic knowledge (I am retired) and have a disabled son who keeps me very busy. I personally don’t have the time or at my age the inclination to do this, but thought some "Young Buck"” may.

            There are some others on this board who have sufficient electronic knowledge you could collaborate with if you want.

            What do you think?
            Don't worry, if your parachute fails, you have the rest of your life to fix it.

            If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

            Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

            Comment


            • #7
              That's not a bad idea. The limiting factor is the PCB build, the prototypes are costly. ExpressPCB does a specific size set of 3 for $41. At 3.8" x 2.5", that is pretty big board for these little circuits. I may be able to fit 3 modules on a single board that could be cut up. Perhaps a mono low pass / high pass and a stereo gain block and another one for bass boost or other contours. I could fit a lot more if I went SMT, but then they're more difficult to assemble without additional tools like solder paste and a heat gun.

              ​Another option, perhaps a board with multiple circuit blocks on it that can be populated for whatever you need. The downside would be wasted board area and it may end up too big for a smaller project.
              Electronics engineer, woofer enthusiast, and musician.
              Wogg Music

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              • #8
                ExpressPCB is premium manufacturing. Try one of the offshore companies for a significant break in cost.

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                • #9
                  I actually thought more of a generic prototype board to keep costs down, but a dedicated PCB would be easier to use, especially for those who don't have much experience with electronic builds.

                  Actually even ExpressPCB's price would not be bad with your 3 modules per board idea. The cost would be $4.56 per module. That is not bad. Price would go down for a production run, even more so using an offshore company as Envision suggested. I also like your second option used maybe for more elaborate builds. I may not have the time to devote to this, but I am willing to fund some of the initial costs.
                  Don't worry, if your parachute fails, you have the rest of your life to fix it.

                  If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

                  Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

                  Comment


                  • #10
                    That looks like a useful and simple board; maybe you could keep a batch of them available for anyone doing a 2.1 project.

                    One note I would recommend adding is that the board requires its own (isolated) power supply, otherwise the signal ground derived on the board (halfway between the power supply rails) could conflict with the source device.

                    You can use "PCBShopper.com" to quickly identify offshore PCB manufacturers with the lowest cost. For small boards, OSHPark (a domestic service) does pretty well. But with all of these low cost options, you have to wait a while for your boards to arrive.

                    I've built speakers using a generic analog crossover platform and I can share more information if it would be helpful.

                    Michael

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                    • #11
                      Originally posted by Michael P View Post
                      That looks like a useful and simple board; maybe you could keep a batch of them available for anyone doing a 2.1 project.

                      One note I would recommend adding is that the board requires its own (isolated) power supply, otherwise the signal ground derived on the board (halfway between the power supply rails) could conflict with the source device.

                      You can use "PCBShopper.com" to quickly identify offshore PCB manufacturers with the lowest cost. For small boards, OSHPark (a domestic service) does pretty well. But with all of these low cost options, you have to wait a while for your boards to arrive.

                      I've built speakers using a generic analog crossover platform and I can share more information if it would be helpful.

                      Michael
                      The in and out signals should be referenced to the power supply negative (PSU Gnd on schematic). The board layout uses 0.1" pin connectors that reference the PSU Gnd. They're all capacitively coupled, so no problems there.

                      I like PCBShopper.com, there are a lot of lower cost options overseas, looks like they'll start at about $20 to ship in low quantities. Obviously no matter where you go getting larger quantities cuts per board cost dramatically. I'd have to get some other CAD software that can generate gerber files for generic board houses though. Not that hard to do I suppose... just more time.
                      Electronics engineer, woofer enthusiast, and musician.
                      Wogg Music

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                      • #12
                        Originally posted by wogg View Post
                        The in and out signals should be referenced to the power supply negative (PSU Gnd on schematic). The board layout uses 0.1" pin connectors that reference the PSU Gnd. They're all capacitively coupled, so no problems there.
                        Interesting, so it sounds like it's not isolated at all. I'd be a little worried about this approach too, since the op amps would see the power supply ripple in addition to the driven input voltage. Is your supply regulated? How are the output hum/noise levels? In any case, this is just my speculation based on reading the schematic; if it isn't broken, don't fix it.

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                        • #13
                          Yup, requires single ended regulated supply, like one you'd use to run a class D chip amp setup. It'll take up to 36V before endangering the op-amps and run under 12V if needed.
                          Electronics engineer, woofer enthusiast, and musician.
                          Wogg Music

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                          • #14
                            Shouldn't be a problem with the signal isolation caps on the input and output. I use my desktop PC to drive a class D amp with a similar voltage divider and Op-amp filter on board. It has isolation input caps on the inputs. Both the PC and amp are using switching power supplies (non isolated). I haven't had any issues.

                            They're may be some DC current flowing between the signal ground planes via the PS divider resistors. The amp's 24 V PS is higher than the PC's internal 12 V rail. Their half V+ reference ground's will be different. I'v never tried to measure / confirm this. Just a hypothesis.

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