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Need advice: chip amps + DSP

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  • #31
    Originally posted by neildavis View Post
    So here's your chance to quit your job and make up to $100 a year selling DSP boards ​.
    Does that job come with any benefits?

    But thanks for mentioning the hot air station. I'm an old thru-hole guy and didn't have a clue about SMT fabrication / repair. You tube solved that. Since the chip amp boards I'm evaluating / modifying have moved to mostly SMT, I may need to get a station.

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    • #32
      Originally posted by Millstonemike View Post
      I'm an old thru-hole guy..
      ​I used to do a lot of thru-hole designs, but I find SMD much easier. I get the Kester EP256 solder paste in a syringe, and you just have to dab a little on the pads, drop on the component, and then hit it with air at 250C. I can assemble an SMD board a lot faster than a comparable thru-hole board, because that lead-forming and clipping slows you down. The boards are harder to debug because of the tighter spacing, but the trick there is to keep building prototypes with only a few new sections in each new board. So you end up having working sections of boards that you can reuse. The boards are only about $45 for a round of ten, including shipping, so if you make mistakes the penalty isn't too severe. Low cost board fab houses like ITEAD have opened up a lot of new possibilities for the hobbyist.

      ​What I really have trouble with is cables. And that's where using those boards like the Sure DSP gets complicated. For example, it looks like the 4 analog outputs of the ADAU1701 are available on one of the connectors, but that connector is a right-angle SMD connector, with the pins on the inside of the board, where they are hard to get to. And the connector that has the I2C and self-boot lines is the same way. So you either need to make your own cables or else find preassembled connectors to bring the signals out to your amps or CPU, and do some jury-rigging to connect everything. It's nice having low-cost modules, but unless there are easy ways to connect them, they can be a pain.
      Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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      • #33
        It took me awhile to find pre-built cable assemblies for the Sure 1701 board. I ended up buying Digikey H3CCH-2018M-ND (1.5 ft. long) for the 20 pin connectors and 455-3140-ND (6 in. long) for the 6 pin connector. Both have connectors at each end so you can cut them in half and use both connectors.

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        • #34
          Originally posted by ernperkins View Post
          It took me awhile to find pre-built cable assemblies for the Sure 1701 board. I ended up buying Digikey H3CCH-2018M-ND (1.5 ft. long) for the 20 pin connectors and 455-3140-ND (6 in. long) for the 6 pin connector. Both have connectors at each end so you can cut them in half and use both connectors.
          ​I think I saw a previous post from you and bought the 6-pin cable assemblies from Digikey. That's going to be a big help, but the other end still needs termination.

          I usually use the .1" headers on my boards and crimp each terminal with needle nosed pliers and then solder it. It works, but it's a slow, tedious process. There are specialty crimp tools but they are expensive and there are too many types of connectors in use to make them worthwhile for hobbyists. If you are trying to connect a DSP, CPU, Bluetooth, WiFi, or extra DAC and amplifiers you end up with a lot of cabling and different types of connector pins and headers. At some point it makes more sense to make your own boards that consolidate the various components and minimize the connectors.
          Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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          • #35
            Originally posted by neildavis View Post
            ​I used to do a lot of thru-hole designs, but I find SMD much easier. I get the Kester EP256 solder paste in a syringe, and you just have to dab a little on the pads, drop on the component, and then hit it with air at 250C. I can assemble an SMD board a lot faster than a comparable thru-hole board, because that lead-forming and clipping slows you down...
            Definitely - Had an early 70s job assembling Avionics with SMD ( prior to Hot Air ).

            The boards are only about $45 for a round of ten, including shipping, so if you make mistakes the penalty isn't too severe. Low cost board fab houses like ITEAD have opened up a lot of new possibilities for the hobbyist.
            I get the impression that there is a bit of interest to see where this goes.

            What I really have trouble with is cables. And that's where using those boards like the Sure DSP gets complicated. For example, it looks like the 4 analog outputs of the ADAU1701 are available on one of the connectors, but that connector is a right-angle SMD connector, with the pins on the inside of the board, where they are hard to get to. And the connector that has the I2C and self-boot lines is the same way. So you either need to make your own cables or else find preassembled connectors to bring the signals out to your amps or CPU, and do some jury-rigging to connect everything. It's nice having low-cost modules, but unless there are easy ways to connect them, they can be a pain.
            As a habit I strip out electronics prior to a trip to Recycling center - do you have pics of what to look for?
            Thanks!
            "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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            • #36
              Originally posted by Sydney View Post
              As a habit I strip out electronics prior to a trip to Recycling center
              You do that too, huh? You call it habit... my wife calls it sickness. My bone pile of circuit boards is getting a little out of hand, but when that one component I'm looking for is right there, at hand, for free... it's totally worth it.

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              • #37
                RE: Sickness
                The vindication is in moments when it just so happens that I have a part that can repair something or be reused - without having to spend time and $ finding and buying.
                One person's junk is another person's repair kit.
                "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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                • #38
                  Back to chip amps: I generally prefer the TPA3116/3118 chips over the TPA749x series. Here are some distortion measurements for the Sure AA-AB32178 TPA3116 amp, PE Part # 320-3342. This is advertised as a 2 X50 W amp, but that’s at 10% distortion. I consider it a 2 X 25 W amp, its 1% distortion value using a 24 VDC supply.

                  The first graph is a loopback test to show the baseline distortion in my system. All amp tests are into 4 ohms (a 50W 1% power resistor) using a 24 VDC, 5A wall power supply. This amp has 26 dB gain which matches up very well with ADAU1701 output.

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                  • #39
                    Here's the 1W distortion plot from PE's "Sure AA-AB32178 2 X 50W Class D Amp Board Manual" and my 1W distortion graph for comparison.
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                    • #40
                      More on chip amps: A mono (PBTL) 1 X 60W TPA3118 amp board called the “Sanwu” board has gotten a lot of positive reviews on a different DIY audio site. This tiny (about 35mm X 40 mm) board is available on different auction sites and runs about $6.50 or less. There are many cheaper knock-offs, so if you purchase the board make sure the advertisement has a picture with “Sanwu” on the bottom.

                      All amp tests are into 4 ohms (a 50W 1% power resistor) using a 24 VDC, 5A wall power supply. This amp has 32 dB gain which is a bit high for the ADAU1701 board, but workable. I do plan on modding it to 26 dB later.


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                      • #41
                        Originally posted by neildavis View Post

                        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.
                        But the I/O board has only three outputs, so I can not "pick" that 4th channel off the board as you suggested earlier, correct? At least if I wanted to drive the ADA to full resolution? Now that I think about it, how would I match the gain of the I/O board if I did pick that 4th channel off the board in the first place?

                        emperkins> thanks for the plots!
                        ~Brandon

                        Soma Sonus
                        DriverVault

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                        • #42
                          That's the big drawback of the I/O board - it uses one DAC output (DAC2 IIRC) for the sub output and simply runs DAC3 to signal ground. I'm personally planning to use the 10-pin connector for all my inputs and outputs. If the 2 Vrms input is a problem then many affordable pre-amps are available in the $5 to $10 range. It's pretty straightforward in SigmaStudio to create code that lights an LED when the 2V input limit is approached. Then a one time calibration can be performed: have your source play a 0 dBFS signal (or whatever limit you want) and adjust the pre-amp until the LED starts to flicker. This will allow using the full 2V input range w/o having to worry about clipping.

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