Class D Bass Amp

Discussion in 'Shock Brother's DIY Amps' started by Rock_Glenn, Mar 16, 2017.

  1. Rock_Glenn

    Rock_Glenn TDPRI Member

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    I've been intrigued by these cheap power amp modules all over the internets like these:

    http://www.ebay.com/itm/New-TDA7293...453807?hash=item212065a7ef:g:6SkAAOSw-itXqBqT

    http://www.ebay.com/itm/YJ-IRS2092-...610289?hash=item41a74b64b1:g:Z44AAOSw7ThUmTXS

    I'd love to pair them with one of Runoffgrooves preamps and test the waters in solid state amp building.

    I see one of these would take AC direct to the board, and the other would take true DC + and - with a separate ground directly to the board.

    I happen to have a 250VA non-center tapped 50V transformer kicking around, and also a 100VA 24V non center tapped transformer. I've tried wrapping my head around the power supply, I can easily rectify, filter, voltage divide, and put a regulator in for the preamp, but what do I need to know about using either of these power amps with the transformers I have on hand? The lack of the center tap has me nervous about attempting to rectify for the larger module. And sending the 24VAC directly to the smaller board seems to good to be true. Any suggestions?
     
  2. printer2

    printer2 Poster Extraordinaire

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    The first one is not class D but class AB. That is why the big heatsink in one of the pictures. The following,

    Power input: Double AC 12-32V,100W

    makes me think you need a split power supply also. Actually pretty sure of it, you need one if you use either amp. The second one is probably better for your application. Just need to get the right PS.
     
  3. Rambs83

    Rambs83 TDPRI Member

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    Class D is a whole other beast compared to class AB, tubes or transistors for that matter. don't be fooled by the '200W' number, distortion numbers won't be nice at that output level. I don't have first hand experience, but spent some time researching a class D power amp to combine with a tube preamp for bass. (I currently lug a round a Yamaha P3500s which sounds great, but could use a diet :-D)
    What i found is that the best route to success would be using a ICEpower or Hypex module, that's what's actually being used in some high-end brands like aguilar, there are usually matching power supplies offered, and if you pick the right module, its all-in-one power supply and power amp, just hook up 220/110V :)
     
    Last edited: Mar 17, 2017
  4. printer2

    printer2 Poster Extraordinaire

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    How will he be fooled? The class AB amp in the upper EBay add lists the 100w at 10% distortion. So what output level would it be nice? 250W as is one of the ICE modules? When you have the hifi community accept the above amp I doubt a bass will sound poorly through it.
     
  5. reddesert

    reddesert Tele-Meister

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    I haven't played with any of these modules yet, but if you're going to, the first step is probably to google up the IC name and read the datasheet or application notes. These will typically contain answers to many questions about implementation. For the first one, TDA7293, http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00001887.pdf

    Figures 14 and 15 show that the IC power is rated pretty clean up to about 70 or 80 watts (at 4 or 8 ohms resp.) and then the THD shoots up. Figure 19 shows what power you can expect to reach as a function of supply voltage.

    Edit: clarified that I meant the THD shoots up after 70 or 80 watts (similar shape to the curves posted for the other amp, below).
     
    Last edited: Mar 18, 2017
  6. Rambs83

    Rambs83 TDPRI Member

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    OK, maybe i was a bit fast in my reply, i was thinking 200W, that's in the gigging-range for bass, so u assumed that was the intention. but hey, i don't know that do i :).
    Usually power output claims of amps not intended for bass guitar can't be compared as equals with wattages you find on bass amps, that's all. 10% distortion is in my ears a whole lot, and not realistically usable.
    To be a bit more constructive, i found this chart on the IRS2092 chip here:
    upload_2017-3-18_10-2-58.png
     
  7. printer2

    printer2 Poster Extraordinaire

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    The power device used with the chip in the chart is a IRF6645. Using a different device and depending on the PS voltage the above curve would not be valid. The sheet you referenced does not say what the voltage used was and the rated power. It does say that into four ohms with the IRF6645 the range could be 120-200W. The IRF6645 has a limit of 4.5A and the Ebay amp lists that it can use 8A. I am guessing they are using a higher spec'd part. Mind you the power rating might be inflated. But for under $20 not a lot to loose to try it. And as far as the curve shown, I might assume they used the same PS voltage for the two circuits. In that case I prefer an amp that does not draw a straight line distortion curve at clipping.
     
  8. Rock_Glenn

    Rock_Glenn TDPRI Member

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    The only reason these caught my attention is the price, and I thought the heatsink was huge on that first one so I was inclined to use that particular one. The price point on the module makes a whole lot more sense than trying to build a circuit using the chip from scratch.

    I started looking at spec sheets on the chips themselves, and that led me to ebay and the modules. I'm impressed by the high power some bass amp manufacturers are fitting into small packages, and I figured I'd try my hand at that. I don't mind tinkering a bunch to get it to work, but these modules are probably pretty picky about power supplies, and I imagine it will be a crapshoot as to whether the power amp will sound good in the end.
     
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