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Mono Amp Using NAP180 Board

Discussion in 'd.i.y.' started by Suffolk Tony, Nov 6, 2019.

  1. Suffolk Tony

    Suffolk Tony pfm Member

    Hi folks,

    I've got a spare NAP180 board, so I'm contemplating using it in a small mono amp to power the centre speaker in an A/V setup. I want to keep the case as small as possible, so I'm after suggestions on how to make the power supply very neat. I've still got some of the generic CAP boards kicking about, but what's the smallest transformer I can get away with, and what CAPs? (Still got some Q-Speed diodes etc.)

    All help and suggestions much appreciated!
     
  2. a.palfreyman

    a.palfreyman pfm Member

    Centre channel is all voice isn't it and little else i.e. no explosions or really loud stuff. I would think that an 18-0-18 traffo of about 50VA would be ample. You certainly wouldn't need more than 80VA. This will give you about +/-24V DC and about 25W max output. One 4,700uf cap per rail will be enough.
    Hope this is useful.
    Best,
    Andy P
     
  3. MJS

    MJS Trade: Consultant at WH Audio

    For centre use in an AV setup your speaker is going to be quite close to the amp board I presume. It'd be very worthwhile putting an inductor on the output of the amp. Use the NCC200 method: 16 turns of 1mm copper on a 1/4" former will do it. Put a 16R resistor inside it.
    Pay attention to earthing arrangements and make sure you don't forget the signal and the zobel 0v connections. These boards are notoriously picky regarding stability.
     
    Suffolk Tony likes this.
  4. juz400

    juz400 pfm Member

    I used to think the centre was all voice but as I have tried a few centres and amplifiers over the years, something close to your left and right in size, amplification and speaker works the best.
    There are quite a lot of effects coming from the centre channel, quite a bit of bass too. Im not sure if my vintage Yamaha DSP-E800 with a coaxial to a Sony Bluray running 6 channel DolbyDigital compares
    to modern TrueHD rig as to where it sends Bass but the opening tones on Edge of Tomorrow come more from my centre and sub channels than left/right.
    I havent tried a Hackernap 500VA on my centre yet but I imagine it should give the Yamaha amp some competition
    The Zobel is probably a good idea, I think a hungry boa constrictor would be easier than trying to wrestle 3m of Naca5 out of sight behind the telly.
     
    Suffolk Tony and Mynamemynaim like this.
  5. Suffolk Tony

    Suffolk Tony pfm Member

    Indeed juz. I'm currently using the on-board amplification from my Denon 7200 A/V amp, which is pretty decent but given how important the centre channel is, I thought I'd try something a bit better, only because of the spare NAP 180 board I happen to have. I use the main stereo system for the left & right channels, in a 7.1.4 Atmos system.

    OK folks, I realise I've got a redundant DIY "Hi-CAP" power supply wot I made a few years ago, using two STRs, in a half-size case. I've just changed the generic rectifier board to its positive and negative default output, with six Vishay 3300uF 63V caps, & producing 37V. Will this be OK please? (minus the STRs, obviously...). Maybe a bit overkill.

    Thanks for the tip re. the inductor MJS. I notice there's a 22R resistor on the 180's output - can I maybe use this through the inductor?
     
  6. misterc6

    misterc6 Wasted and wounded, it ain’t what the moon did

    That all sounds fine except that the output resistor on the NAPA circuit is 0R22 which means 0.22 ohms, not 22 ohms!
    Replace it with a 15 ohm resistor with a similar power rating inside an inductor as previously mentioned.
     
    Suffolk Tony likes this.
  7. Suffolk Tony

    Suffolk Tony pfm Member

    Thanks Malcolm, resistor duly ordered (I've probably got one somewhere...)

    Before I put this all together, is there anything else worth changing on the NAP180 board?
     

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