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Question for the Crowd - Desire for a flexible active filter amp design

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  • Question for the Crowd - Desire for a flexible active filter amp design

    Guys,

    I've seen quite a bit of grumbling about the lack of good amplifiers for active designs or for 2.1 designs. With this in mind, and with the advent of the new TDA7492 amp that's been talked about recently, I've been thinking of designing a board to turn those TDA7492 amps into a very flexible design that can be used for mono or stereo designs and capable of high pass or low pass filtering. Here's the basic concepts of the design I'm contemplating (a marketing feature list, so to speak):
    1. Design will be a "base board" for the TDA7492 amplifier (or similar) found here: http://www.parts-express.com/tda7492...2x50w--320-606
      There's no need for the base board to be limited to connecting to this amplifier, but it will be designed to fit this amplifier.
    2. Entire design (base board + TDA7492 board) will be capable of fitting inside the Sure amplifier case found here: http://www.parts-express.com/aluminu...472-d--320-328
      The end user does not HAVE to place the amplifier inside this, but it will be designed to fit inside of it.
    3. The TDA7492 board will be capable of attaching to the base board with standoffs for permanent, secure mounting.
    4. The base board will be designed to handle a wide variety of power supply voltages (from 12V up to 26V)
    5. The base board will contain an analog potentiometer based volume control that will be designed to fit into the amplifier case listed above. The analog potentiometer will be bypassable.
    6. The base board will contain a power switch designed to fit into the amplifier case listed above.
    7. The base board will contain RCA inputs designed to fit into the amplifier case listed above.
    8. The base board will contain a 2.1x5.5mm DC input jack designed to fit into the amplifier case listed above.
    9. The end user will be able to connect the RCA input jacks together on the board to create a "mono" input. To save cost, this will be done with a solderable jumper.
    10. The end user will be able to choose a high-pass or low-pass filter for each channel.
    11. The end user can by-pass the filters for each channel, if desired.
    12. The high-pass and low-pass filters will support corner frequencies ranging from ~60Hz to ~600Hz or ~600Hz to ~6KHz. The range will be determined by a manual switch on the board or a solderable jumper.
    13. The user can select from LR2 (-12db/oct) or LR4 (-24dB/oct) slopes by using a solderable jumper.
    14. The filters will be controlled by using a Microchip PIC microprocessor which controls NON-VOLATILE digital potentiometers. Non-volatile must be used to preserve the settings even across power cycles.
    15. The user will be able to select from approximately 64 different corner frequencies inside each range (total of approximately 128 different corner frequencies for each filter).
    16. The base board will be designed for the standard QUAD op-amp package (TL074 or similar). There will be one QUAD op-amp for each channel (two quad opamps total).
    17. The volume control on the base board will use a standard DUAL op-amp package (TL072 or similar). If the end user chooses to bypass the volume control, this op-amp will also be bypassed.


    Anyways, I know that's a lot to digest. I'm hoping to get some feedback on the ideas that I've listed and to judge the actual interest in a board like this. All-in-all the end user can expect to be able to have an amplifier that can operate:
    • Two channels in high pass - or-
    • Two channels in low pass - or-
    • One channel in high pass - or-
    • One channel in low pass - or-
    • One channel in high pass and one channel in low pass simultaneously
    • Bypass all filters



    I'm not interested in making money off of this type venture. In fact, if we proceed, I'll probably loose a lot of money. I've already spent close to 2 days of research in a "concept" phase. The actual design would likely take upwards of a week for schematic capture and layout.

    In general, I'm thinking that I could build a few boards to start with, but the "buyer" of these boards would need to do a whole lot of soldering. I'd try and make everything through-hole if I can, but I know that the digital pots and the microcontroller are going to be surface mount. I can pick the "least hard to solder" package, but it would still be a surface mount.

    In a rough estimate of costs for the board, I'm thinking:
    • PCB - $12
    • Volume POT - $1.75
    • uController - $1.00
    • OPAMPS - $1.5 for TL07x quality
    • DC jack - $1.00
    • Digital POTS - $3.00
    • Power Swtich - $1.00
    • RCA jacks - $1.75
    • Miscellaneous - $5.00
    • Total cost ~ $28.00


    Now, bear in mind that this does NOT include an amplifier - only the volume control, filters, and some of the connection jacks. To complete the amplifier, you'd need to buy the case $10, amp $17, speaker connectors $5, and volume knob $3. That would total up about $65 or so.....

    With all this in mind, is there any interest in me completing this? Would people be willing to "crowd source" some funding to help with manufacturing expenses? I could perhaps get the surface mount components soldered separately.....

    Let me know.
    DARPA Jr - 2015 InDIYana Winner - RS180-8 + RS100P-8 + ND25FA
    The Aria's - RS150-4 (or RS150-8) + XT25SC90
    The Mariposa's - TEBM65C20F-8 + ND16FA
    The Canzonetta's - RS100P-8 and ND16FA
    AudioSource AMP-100 Mods OR Pyle PAMP1000 Mods

  • #2
    Re: Question for the Crowd - Desire for a flexible active filter amp design

    Some further clarification - to accomplish a 2.1 design with this solution, the user would neeed 2x base boards and 2x amplifier boards. One would be set up to run two channels of high-pass, and another would be set up to run a mono channel low pass. That would allow for 2x50W on the stereo and 1x100 on the sub.

    Alternatively, one could use two of these amplifiers to drive an active stereo 2-way design.

    Finally, one COULD even use the high pass and low pass in series to create a band-pass design.

    Ultimate flexibility.
    DARPA Jr - 2015 InDIYana Winner - RS180-8 + RS100P-8 + ND25FA
    The Aria's - RS150-4 (or RS150-8) + XT25SC90
    The Mariposa's - TEBM65C20F-8 + ND16FA
    The Canzonetta's - RS100P-8 and ND16FA
    AudioSource AMP-100 Mods OR Pyle PAMP1000 Mods

    Comment


    • #3
      Re: Question for the Crowd - Desire for a flexible active filter amp design

      Hi Tyger, I'm very interested in anything you design, however,,,, this may be way over my head. I'm also a little leary of class D amps. I also am not sure how I would use it.

      With that said,,,, I'd be on board for the crowd sourcing thing if it would help you out. You have my email address. Let me know, Mark

      Comment


      • #4
        Re: Question for the Crowd - Desire for a flexible active filter amp design

        That sounds really nice. I'm interested, but shipping might be a deal breaker...
        My Statement monitors
        My Piccolatas
        My LM3886 amp

        Comment


        • #5
          Re: Question for the Crowd - Desire for a flexible active filter amp design

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          Tyger:

          I built a 2 way Linkwitz about 10 years ago using the AD5263(Analog Devices) dig pots,they worked great,they were volatile so I used an eeprom for saving settings,a Pic16F controlled the crossover via a serial interface.

          Have you considered making it a 3-way?,unless you are constrained by board size I think it would be a nice feature.
          The AD5206 has 6 pots but it is volatile,it also comes in a Dip package.
          You might as well add a PGA4311 volume control(4 Ch)....Just kidding...no I'm not :D
          You have a great plan and I look forward to your progress.

          Regards
          Bob C.
          NLA

          Comment


          • #6
            Re: Question for the Crowd - Desire for a flexible active filter amp design

            Sounds nice, I would be interested in this.

            Thanks

            Comment


            • #7
              Re: Question for the Crowd - Desire for a flexible active filter amp design

              It is really not a good idea to use quad op amps. There are not that many good ones compared to the number duals made especially for audio. Why design in a bottle neck to upgrading. I was going to upgraded my DBX active crossover and ran in to just this problem.

              Comment


              • #8
                Re: Question for the Crowd - Desire for a flexible active filter amp design

                I'm in. +1 for a 3 way version.

                Comment


                • #9
                  Re: Question for the Crowd - Desire for a flexible active filter amp design

                  I can do dual op amps. It just costs more and adds more soldering.

                  I realized that I can't let the user select between LR2 or LR4. It will have to be one or the other because the Q is different between the two filters. Given that Linkwitz recommends against using the LR2, then the LR4 is where I would put my focus.

                  Regarding a three way - I'll have to put some more thought into how I can do that efficiently. I'm concerned that it would virtually double the cost of the base board components. It would likely need 8 more op amps, 2 more quad digital pots, and likely a bigger microcontroller.

                  One could best accomplish a stereo version of a three way by using three of these base board/amp combos. The lows/Mids/highs could be handled one board each.
                  DARPA Jr - 2015 InDIYana Winner - RS180-8 + RS100P-8 + ND25FA
                  The Aria's - RS150-4 (or RS150-8) + XT25SC90
                  The Mariposa's - TEBM65C20F-8 + ND16FA
                  The Canzonetta's - RS100P-8 and ND16FA
                  AudioSource AMP-100 Mods OR Pyle PAMP1000 Mods

                  Comment


                  • #10
                    Re: Question for the Crowd - Desire for a flexible active filter amp design

                    It sounds like an interesting project? Out of curiosity I wonder what the best solution is going to be for the power supply? I remember reading in the other thread that's it's not a good idea to drive multiple class-D amps from the same power supply due to them not syncing or something. So is this box going to have to have 3 laptop power supplies inside of it? Or is there a cheaper and/or more elegant solution?

                    Comment


                    • #11
                      Re: Question for the Crowd - Desire for a flexible active filter amp design

                      subscribed.

                      regards,
                      asmd.

                      Comment


                      • #12
                        Re: Question for the Crowd - Desire for a flexible active filter amp design

                        Originally posted by tyger23 View Post
                        One could best accomplish a stereo version of a three way by using three of these base board/amp combos. The lows/Mids/highs could be handled one board each.
                        Once you go to multiple channels, a DSP solution makes more sense. You are welcome to use a design I drew up recently. It's got what amounts to a miniDSP, plus two Analog Devices SSM3302 stereo amp chips plus a stereo DAC for woofers/subs. That's a total of 6 channels of output, with 4 channels of very high quality amplification, plus an almost endless supply of biquads and audio effects. Obviously, it is not solder-gun friendly, but if you know of a way to get it made, you could sell an assembled board.

                        The SSM3302 amps are very high quality, with lower distortion than the TDA7492. Running on 16V they can output a good 15-20W. So you can use them for the mids and tweeters, and send the bass through the DAC's to an external TDA7492 board (that was my plan in making this...). The SSM3302 amps work fine with 4-ohm loads (in fact, you can parallel the outputs for 2-ohm loads). There are two woofer outputs, so with a TDA7492 board this amp could be used as a 2.1, 4.1, 4.2, or many other configurations. Or, you can just send the output to a powered sub. There is a lot of flexibility with this design.

                        There are two versions--one was done using ExpressPCB and the other was done with DesignSpark. The ExpressPCB version is "low-risk", as I just added the DAC to a previously working board. This is the first DesignSpark board I've ever designed, so there may be lots of surprises in that version. The DesignSpark version is 64mm by 96mm -- a bit too large to fit in that chassis, although I could probably make the board a bit smaller without too much effort. The ExpressPCB version is 64mm by 64mm.

                        If you want more details on this approach, PM me and we can discuss it.

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                        Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

                        Comment


                        • #13
                          Re: Question for the Crowd - Desire for a flexible active filter amp design

                          I'm very interested in an amplifier system for my desktop audio.

                          My plan is to run a stereo pair of active 2-ways plus a sub, so five amp channels total. I don't know much about amp design, so the others comments above regarding using the lowest distortion/highest SQ amps appeals to me. This is my "critical" listening system.

                          For a total investment of ~$250 or less including power supplies I would be all over this. MiniDSP interests me also, but it's a higher cost solution and once set up its easy USB interface and software package is no longer useful. Solder bridges would work perfectly.

                          Comment


                          • #14
                            Re: Question for the Crowd - Desire for a flexible active filter amp design

                            Originally posted by evilskillit View Post
                            I remember reading in the other thread that's it's not a good idea to drive multiple class-D amps from the same power supply due to them not syncing or something. So is this box going to have to have 3 laptop power supplies inside of it? Or is there a cheaper and/or more elegant solution?
                            This

                            Comment


                            • #15
                              Re: Question for the Crowd - Desire for a flexible active filter amp design

                              Originally posted by superspeeder View Post
                              This
                              It depends on the amp, but for a fixed-clock modulator like the TDA7492, multiple amps should be synchronized to use a common clock. That's advice straight out of the TDA7492 ST datasheet. The SSM3302 class-D amps use a spread-spectrum modulator, and for that chip there is no need to synchronize the clocks.
                              Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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