Announcement

Collapse
No announcement yet.

Building a subwoofer amp from an amp board (for Digger8 sub, maybe)

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Building a subwoofer amp from an amp board (for Digger8 sub, maybe)

    After doing some research, I'm thinking about building the Digger8 subwoofer. (Regardless of the sub build, the questions below are pretty general.)

    The goals of the Digger8 were to reach low 20s, be very small, be inexpensive relative to comparable commercial subwoofers. However, with the limited supply of the original driver recommendations and the Bash 300 being $155, the price is quite a bit more than back in 2012.

    It could greatly reduce the price (for this or any sub build) to build an amp from one of the modern Class-D amp boards. I can buy a driver and build a cabinet. Now I need to have an amplifier, a power supply and a crossover. So, my thoughts/questions:
    1. Buy a plate-amp. Pros: Amp/power supply/gain/adjustable crossover all included. Cons: Relatively expensive.
    2. Buy a power amplifier like a Behringer iNuke with DSP. Pros: Amp/power supply/dsp built in. Cheaper watts/$ than plate-amp. Cons: Not as convenient, especially if space is limited.
    3. Build an amp from an amp board. Pros: Cheaper watts/$. Convenience/size. Cons: DIY. Need the right power supply and a cross-over.
    a) If I went with the Digger8 with the Infinity 860w driver would this $40 Sure 1x300 amp (320-3361) be a good choice?
    b) If so, would this $20 buyout Qualtek 320w power supply (36V, 8.8A)(129-148) be a good choice?
    c) Would the Sure $50 1x500 amp (320-3363) be better (the amp in (a) is only going to give me 225w at 1% THD @ 3ohms), and if so, would the power supply in (b) still work? (I don't need the full 500w, just 300w at less distortion(?))
    Assuming I get the right amp board and power supply for whatever sub build, what about the crossover?
    d) Can I just use this $7.50 variable low-pass filter board (320-670)?
    e) Can I just build a passive non-adjustable low-pass filter given the specific speakers that I have and be done with the crossover?
    f) If I get a Denon x.1 amplifier with Audyssey, do I need to worry about the crossover?
    Thanks in advance for any advice.


  • #2
    Great questions... I wish I had an answer, but I've actually thought about these specific scenarios in the past. I too will be eagerly waiting to see what the experts say.

    Comment


    • #3
      a) That amplifier is only rated to take a 42V amplifier. Assuming you have a 4-ohm speaker, the highest power that amplifier could deliver would be ~200 W (with a 42V supply)
      b) That 36V power supply, with either amplifier, will only be able to deliver ~150 W to a 4-ohm speaker.
      c) That amplifier has the potential to deliver ~300 W to a 4-ohm speaker, but would require a 50V supply. Again, with the 36 V supply mentioned in b), you'd only get 150W to the speaker.
      d) Yes, this would work, but is not the steepest filter. I believe there is a thread somewhere discussing using this board. You will also need to either regulate your main supply down, or use another power supply to power this board.
      e) Yes, you can, but it would likely need to be an active solution, not a passive one.
      f) I have no experience with the Denon you speak of, or Audyssey, so I can't comment.

      Comment


      • #4
        Originally posted by 1100xxben View Post
        a) That amplifier is only rated to take a 42V amplifier. Assuming you have a 4-ohm speaker, the highest power that amplifier could deliver would be ~200 W (with a 42V supply)
        b) That 36V power supply, with either amplifier, will only be able to deliver ~150 W to a 4-ohm speaker.
        c) That amplifier has the potential to deliver ~300 W to a 4-ohm speaker, but would require a 50V supply. Again, with the 36 V supply mentioned in b), you'd only get 150W to the speaker.
        d) Yes, this would work, but is not the steepest filter. I believe there is a thread somewhere discussing using this board. You will also need to either regulate your main supply down, or use another power supply to power this board.
        e) Yes, you can, but it would likely need to be an active solution, not a passive one.
        f) I have no experience with the Denon you speak of, or Audyssey, so I can't comment.


        +1. Ben's analysis is correct. The amp rating is the max it can deliver. However, the power out is determined by two factors: (1) The PS voltage and (2) The driver impedance. For DC amp's (in BTL mode), the equation is W rms = (Vps2 / 2) / Driver impedance.

        d) Here's the thread on the mod's to 320-670 to correct it shortcomings. The filter is a 2nd order LP. A little analysis and it can be made steeper by altering the two cap mod's in the thread.

        http://techtalk.parts-express.com/fo...re-amp-exposed

        Comment


        • #5
          Thanks Ben and Mike.

          So, I think the solution to the amp/PS is to buy the amp that can produce the watts I need (given the driver impedance) at the level of distortion I'm willing to accept and buy the power supply that is needed, based on the amp board specs and the math above, and not risk getting a significantly under-powered PS because I tried to save $10 or $20.

          Mike, to check my understanding of your equation: A hypothetical 36V power supply with 4 ohm driver will get me 36*36 / 2 / 4 = 162w RMS and a 50V PS with 4 ohm driver would produce 50*50 / 2 / 4 = 312.5w RMS ?

          Comment


          • #6
            Originally posted by a4eaudio View Post
            Thanks Ben and Mike.

            So, I think the solution to the amp/PS is to buy the amp that can produce the watts I need (given the driver impedance) at the level of distortion I'm willing to accept and buy the power supply that is needed, based on the amp board specs and the math above, and not risk getting a significantly under-powered PS because I tried to save $10 or $20.

            Mike, to check my understanding of your equation: A hypothetical 36V power supply with 4 ohm driver will get me 36*36 / 2 / 4 = 162w RMS and a 50V PS with 4 ohm driver would produce 50*50 / 2 / 4 = 312.5w RMS ?

            That is "hypothetically" correct. In reality, you lose some PS voltage due to semiconductor losses in the amp's chips. You also have to look at the distortion characteristics on the amp chips as they reach max rated output. But the theoretical math gets you fairly close, probably can't hear the difference.

            And yes, getting a PS with the highest voltage the amp can handle and extra amps will afford you headroom for dynamic peaks. Going with a higher rated amp will never hurt (unless the users don't hear/understand over-driven drivers).

            Comment


            • #7
              So I'm going to attempt to build the subwoofer amp.
              I'll buy one of the Sure boards, an appropriate power supply and the variable crossover board and mod as needed.

              Another thing I have read several posts on is the high pass filter. It sounds like the plate amps (and Behringer iNuke) include this, something around 20Hz. Is this something I need to worry about? (Looking at WinISD for the Infinity 860w it looks like I do.) If so, what are the options? I think there are cheap inline HPF's and a more expensive option would be miniDSP 2X4. Any comments on those and/or better options?

              Comment


              • #8
                Originally posted by a4eaudio View Post
                So I'm going to attempt to build the subwoofer amp.
                I'll buy one of the Sure boards, an appropriate power supply and the variable crossover board and mod as needed.

                Another thing I have read several posts on is the high pass filter. It sounds like the plate amps (and Behringer iNuke) include this, something around 20Hz. Is this something I need to worry about? (Looking at WinISD for the Infinity 860w it looks like I do.) If so, what are the options? I think there are cheap inline HPF's and a more expensive option would be miniDSP 2X4. Any comments on those and/or better options?
                If you mean the PE sub-woofer pre-amp board (PE # 320-671), be aware that the "new and improved" board most likely has significant problems, worse than the nearly identical module it was meant to replace (no longer available # 320-670). Another member asked me to evaluate a different, but similar module. I am waiting for it to arrive and put it through it's paces.

                i don't see the issue with XMAX unless your providing sound for a drive-in movie with LFE. In a WinISD model, Xmax begins to be a problem below 25Hz and at 250 W rms. that won't happen with music, only (sub)audible movie LFE material (explosions, et. al). At that's just Xmax, not Xlimit.

                But if you require huge, LFE output, an INuke might a better option ...

                Sub.png

                Comment


                • #9
                  I think my normal music listening won't be a problem. However, I will be using a record player with lots of old records bought of eBay. My understanding is that minor warp can cause problems (significant cone movement) at very low frequencies. On the other hand, I still won't be cranking it super loud. I did do a lot of searching and didn't find many threads, so maybe it's more of a theoretical problem than a practical problem in typical applications.

                  Comment


                  • #10
                    Originally posted by a4eaudio View Post
                    I think my normal music listening won't be a problem. However, I will be using a record player with lots of old records bought of eBay. My understanding is that minor warp can cause problems (significant cone movement) at very low frequencies. On the other hand, I still won't be cranking it super loud. I did do a lot of searching and didn't find many threads, so maybe it's more of a theoretical problem than a practical problem in typical applications.
                    That's my bet. The small sub pre-amp boards have decoupling caps on the input. The value of the caps (in conjunction with the op-amp circuit) form a 1st order high pass. This high pass can be tailored to needs by replacing the stock caps with select values (e.g., 15 Hz, 23 Hz, 33 Hz)

                    But given the price of higher power amps, and the PS and all the misc. stuff required to build a usable amp, an iNuke 1000 at $150 seems like price parity and offers more functionality in a proven design. Of course, that analysis omits any DIY gratification factor. Up to you ...

                    Comment

                    Working...
                    X