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Need advice: chip amps + DSP

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  • #16
    Originally posted by neildavis View Post

    Nope--no filters at all on the main board. I've got one and traced the circuit. They might have filters on the I/O board, but I don't think so. It turns out that most class D amps have anti-aliasing filters on their input--at least, that is what several of the block diagrams show. So it's probably not a problem if you are using a class D amp. However, there are two others problems, as identified in this thread: http://www.diyaudio.com/forums/digit...-module-4.html. First, it uses a strange oscillator speed: 12MHz instead of the "standard" 12.288Mhz​. So instead of sampling at 48KHz, it samples at 46.875KHz. Second, the board is set up for 2V input, which results in 6dB insertion loss. Strange decisions on Sure's part, but maybe the newer boards are different.
    Well, that's a bummer. I guess at a $20 price point, 4 more caps and 4 more resistors for a passive filter are just too much to ask for . I need to look a little closer at the 1701. I've never used it before. I'm used to a chip that has an on-board oscillator, so the 12 vs 12.288 issue would be moot. But, it's good to know that the sample rate will be a little off, since I'll have to compensate for that in my FIR filters.

    Originally posted by neildavis View Post
    ​People are using SigmaStudio as a user interface for the DSP, but the program wasn't intended to be used that way. ADI recommends you use SigmaStudio to define the DSP architecture, and that you develop your own user interface. The approach I'm documenting only uses SigmaStudio to design the DSP flow. My user interface processes the SigmaStudio output files, and uses a microprocessor to load and control the ADAU1701.

    You don't really need that Sure programmer if you control the ADAU1701 with your own CPU. Since I'm using an Arduino board to load the DSP and update the Parameter RAM, my approach doesn't need that programmer. It's a much more flexible approach. My approach also doesn't require a PC for local control. You can select different crossover slopes and frequencies from an LCD display mounted on the speaker cabinet.

    The Arduino code is downloadable, so you don't need to understand the programming details unless you want to change the DSP on your own. Those articles and upcoming tutorials are intended to de-mystify that code and provide all of the tools needed to add new DSP algorithms. It's still going to require some computer programming skills, but the really difficult stuff such as loading DSP registers and understanding details of the hardware or microprocessor will all be hidden.
    Obviously, the technical details on Sure's website are VERY lacking... I'm planning to use this like a Ronco food dehydrator (set it and forget it) once I get the DSP load developed, so there's no requirement from me for an active user interface. I'll use SigmaStudio to develop it, dump it to the EEPROM, and let it self-boot. Sure doesn't specifically indicate that there is EEPROM on the board, but based on the fact they claim you can "turn the potentiometers on board to adjust main volume, treble volume, bass volume and cut off frequncy" right out of the box, it implies that it does have that present. Am I wrong in assuming that? I was actually excited to see they have a $10 version without the pots and reset button, but I'm unable to find where to actually purchase it.

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    • #17
      Originally posted by augerpro View Post
      How does a stereo input only end up as 3 channels out? Where would you "pick" the signal off the board for a 4th output?
      The board has all 4 channels out in the ribbon cable header. The Interface Extension board is intended to be used as a stereo input and stereo output with subwoofer out. If you're wanting to use it for 2-in 4-out, then you can forego the Interface Extension board. You'll need some way to get the signals to whatever cables you're planning to use. It may be easiest to just solder to the backside of the ribbon cable header.

      You'll need some way to program it. I ordered the "open-sourced programmer for SigmaStudio", but I can't recommend it yet as I haven't tried it out.

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      • #18
        Originally posted by 1100xxben View Post
        I'll use SigmaStudio to develop it, dump it to the EEPROM, and let it self-boot. Sure doesn't specifically indicate that there is EEPROM on the board, but based on the fact they claim you can "turn the potentiometers on board to adjust main volume, treble volume, bass volume and cut off frequncy" right out of the box, it implies that it does have that present. Am I wrong in assuming that?
        ​You are correct about the EEPROM. And yes, if you know exactly what code you need to run, the self-boot mode works fine.

        But for many speaker designers, it's nice to have some ability to tweak, and the local GUI provides that. But the other benefit of using a micro instead of self-boot mode is that the micro can respond to commands from a PC that has real-time modeling tools. The Active Speaker Designer tool lets you import FRD files and interactively tweak the crossover and EQ and other DSP operations. The PC program provides a math model of the DSP functions and allows real-time loading of the parameters into the DSP. It's a nice design tool that allows users to explore different DSP settings and configurations and evaluate them in real time. Once the desired performance is achieved, the settings can be stored permanently in the micro so you can return to "appliance mode". And it doesn't add a whole lot of cost, given how cheap the Arduino and display boards have gotten.
        Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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        • #19
          Originally posted by neildavis View Post

          ​What I'm using now is a stereo in/6 channel out. So feed it left and right and the output will be tweeter, woofer and sub for the left channel and tweeter, woofer and sub for the right channel. The volume, crossovers, EQ, delay and bass enhancement are all adjustable using that Nextion touch-screen display, which only costs $16. Since the display only requires 4 wires and the data rate is low, it can be mounted on the back of the cabinet.

          The picture shows the ADAU1701 in the center, a teensy Arduino board toward the left, and the DAC for the subs at the upper right of the board. No working code yet for the display, but I'm getting there...
          An Arduino Nano?

          Just finished the last article ( I have to go 2 In 6 Out config. at some point )
          Any target date for completing this?
          "Not a Speaker Designer - Not even on the Internet"
          "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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          • #20
            Neil, you know I'm interested in your work ...

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            • #21
              Originally posted by Sydney View Post

              An Arduino Nano?
              ​Nah--I'm using the teensy boards from PJRC. They have more horsepower, as they use the 32-bit Cortex processors. The 8-bit AVR Arduino boards can actually do the floating point math for the biquad coefficient calculations, but they are slow. The teensy LC is $11.65, and it has a 3X clock speed and more efficient architecture for floating point. Also, there is a growth path to the teensy 3.2, which is even faster and has floating point capability. And, the teensy boards are 3.3V CPU's, which means you don't need a voltage translator to control the ADAU1701. These boards work fine with the Arduino IDE, so there is no software impact.

              ​I like the 2-in/6-out configuration. Most of the circuitry on this board is based on a prior 2/4 design that works fine, so I don't expect any problems. There's a lot of new software required, but most of the hard stuff was already done for the 2/4 board. I've got 3 boards built up, and I should know in the next 2 weeks whether there is a major problem. I've got a list of changes I need to make to finalize the board layout, and then I'll post the updated design. Software is going to drag on forever, tho...

              ​Getting back to the OP, this teensy board was also going to be used as a controller for the Sure DSP board, first as a subwoofer DSP. I don't see any easy way to use the Sure board for stereo active speakers, but it is perfect for a sub. It could also be used in pairs to make active speakers (one DSP board in each speaker), with two analog inputs and a sub output for each side. The teensy board will allow using an IR controller for volume control and input switching, and it could control the parameters for bass enhancement algorithms.
              Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

              Comment


              • #22
                Originally posted by 1100xxben View Post
                But, it's good to know that the sample rate will be a little off, since I'll have to compensate for that in my FIR filters.
                Could you explain the problem a little more in depth? How is this an issue for my use?
                ~Brandon

                Soma Sonus
                DriverVault

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                • #23
                  Originally posted by Millstonemike View Post



                  FYI: the 2x50 W limitation is a thermal power limit only.

                  I would ignore the 10% distortion figure on the 3340. That figure is with a 30 V PS into 4 ohms. The TPA3116 chip itself can deliver 70W rms per channel into 4 ohms with a 24V PS at less than 1% distortion. That's just before clipping sets in. But the thermal limit would be exceeded. With your 8 ohm configuration, you'll get 30 W rms per channel at 0.4% distortion with no issues.

                  I've worked with the TPA3116 chip amps and like them. Some say the TDA7492 is warmer in the mid-range but doesn't produce the low end as well as the TPA3116. But with your sealed RS-100s, you won't be getting that low for it to matter. Hence the TDA7492 recommendation.

                  Thanks for the feedback!
                  ~Brandon

                  Soma Sonus
                  DriverVault

                  Comment


                  • #24
                    Originally posted by neildavis View Post

                    ​What I'm using now is a stereo in/6 channel out. So feed it left and right and the output will be tweeter, woofer and sub for the left channel and tweeter, woofer and sub for the right channel. The volume, crossovers, EQ, delay and bass enhancement are all adjustable using that Nextion touch-screen display, which only costs $16. Since the display only requires 4 wires and the data rate is low, it can be mounted on the back of the cabinet.

                    The picture shows the ADAU1701 in the center, a teensy Arduino board toward the left, and the DAC for the subs at the upper right of the board. No working code yet for the display, but I'm getting there...

                    [ATTACH=CONFIG]n1323057[/ATTACH]

                    Where are you sourcing these parts?
                    ~Brandon

                    Soma Sonus
                    DriverVault

                    Comment


                    • #25
                      Originally posted by neildavis View Post

                      Second, the board is set up for 2V input, which results in 6dB insertion loss. Strange decisions on Sure's part, but maybe the newer boards are different.
                      How could this be an issue with the amps mentioned so far in this thread?

                      Sorry for all the dumb questions, but I've had no experience with this sort of thing so trying to figure what is the most accessible and issue free route is taking some time.
                      ~Brandon

                      Soma Sonus
                      DriverVault

                      Comment


                      • #26
                        Originally posted by augerpro View Post
                        Where are you sourcing these parts?
                        ​The 2/6 board is made by ITEAD--the boards are about $4.50 each, shipped, with a minimum quantity of 10. The design is done with DesignSpark, which is free. The design and the Gerber files that get sent to ITEAD will be posted once the design is finalized. Most of the parts are from Digikey. You can get the CPU boards from PJRC, Adafruit or Sparkfun. The Nextion displays are available at ITEAD.

                        It isn't hard to assemble the boards if you have a $120 hot air soldering station and a few good tools like tweezers, a magnifying head loupe and precision cutters. With those tools just about anyone with reasonably steady hands can build these boards. I can't take soldering this stuff too long anymore, so I usually work as long as it takes me to drink two bottles of beer. It takes me about 4 or 5 of those work sessions to completely assemble 3 boards.


                        How could this be an issue with the amps mentioned so far in this thread?
                        ​The Sure DSP board is designed for 2VRMS input to achieve full resolution of the A/D converter. Since "line level" for most consumer equipment is .3VRMS (see this link), the DSP will not be using the full resolution of the A/D converter. And unless the digital gain is increased somewhere in the DSP code, the output will be 6 or 7 dB below the input level. If you look at page 20 of the Rev C datasheet, there is a chart that shows the resistor values required for different input levels. The Sure board uses 18K resistors for ADC0/ADC1, which is good for professional audio. However, for consumer audio levels the resistors should be 7K. The miniDSP has jumpers to select between pro and consumer input levels, but the Sure board doesn't have those jumpers. However, the I/O board has a gain stage to bump the level back up. So as long as you are using the I/O board, the 2V input shouldn't be too detrimental...maybe a little extra noise, but not that much. However, if you don't use the I/O board, you will need some extra gain somewhere to drive any of the amps mentioned in this thread to full output.
                        Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

                        Comment


                        • #27
                          Originally posted by neildavis View Post

                          It isn't hard to assemble the boards if you have a $120 hot air soldering station and a few good tools like tweezers, a magnifying head loupe and precision cutters. With those tools just about anyone with reasonably steady hands can build these boards. Kinda takes the fun out of it, no?

                          I can't take soldering this stuff too long anymore, so I usually work as long as it takes me to drink two bottles of beer. Ok, fun back in.

                          there is a chart that shows the resistor values required for different input levels. The Sure board uses 18K resistors for ADC0/ADC1, which is good for professional audio. May loosely correlate with a few known issues on other Sure modules - designed for where the volume / money is, not necessarily us.
                          .

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                          • #28
                            Originally posted by neildavis View Post
                            ...It isn't hard to assemble the boards if you have a $120 hot air soldering station and a few good tools like tweezers, a magnifying head loupe and precision cutters. ....
                            Unfortunately inability to find/borrow or purchasing a Soldering Station isn't an option for me.

                            "Not a Speaker Designer - Not even on the Internet"
                            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                            Comment


                            • #29
                              Originally posted by Sydney View Post
                              Unfortunately inability to find/borrow or purchasing a Soldering Station isn't an option for me.
                              ​Bah! I don't remember exactly where you live, but if I remember right it's within 100 miles of our cabin in Western Maryland. You tell me when, and I'll bring the tools to the cabin. The hot air station I use is the CSI825a, which currently sells for $115. Spread out over many projects, it's a worthwhile investment. I also use a 40-year old Weller iron (TC202) for the 64-pin chips. I use the solder-bridge-then-wick method, and all you need for that is a temperature-controlled iron with a fine tip. I'm 64 and usually filled with beer while I'm assembling these boards, so I know that anybody with good hobby skills can build these boards if they try.

                              ​But I'm not actually encouraging people to build their own boards. One reason I'm showing pictures of this stuff is to encourage someone to get some of these boards made. ITEAD offers assembly services, but I've never looked into the prices. I'm not interested in selling hardware--I prefer to stick to designing and always be moving on to new projects. But if someone wants to gets some boards fabricated and assembled, I'll give you all of the information you need to made that happen. So here's your chance to quit your job and make up to $100 a year selling DSP boards ​.
                              Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

                              Comment


                              • #30
                                Haha,,, I believe you could fabricate in your sleep Neil - 1 beer mellows me , 2 beers and I'm about ready for bed.
                                ( Coincidentally, Just turned 64 a week ago ).
                                Intriguing offer - Thanks. Been a looong time since I soldered up a board ( w a Weller and not "modern" Hot Air SMD ).
                                However if someone does decide to seize on this opportunity to make that big money....
                                Last edited by Sydney; 03-12-2017, 12:17 PM.
                                "Not a Speaker Designer - Not even on the Internet"
                                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                                Comment

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