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Electronics ideas for 12V amplifier?

Discussion in 'Modding' started by Munterofamodder, 9 Dec 2003.

  1. Munterofamodder

    Munterofamodder What's a Dremel?

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    Hi. I'm building a computer-hifi in an old Marantz amplifier box. I want to add an amplifier which can run off the 12V lines of the PSU. I'm going to be pretty pushed for space (at the moment, I have a mini-ATX mobo with slot celeron processor :wallbash: , standard AT (!) psu and two hdd in there.
    No pics im afraid, but basically with current setup im already a bit pushed for space, and I have got an optical in there yet.
    I basically have a space about 2" deep, 8" long and 2.5" wide (5cm*20cm*6.5cm) above the PCI slots to fit in a hifi-ish quality stereo amplifier, for driving 8ohm speakers. I will squeeze in active (fan) temperature-controlled cooling. I was thinking a car style booster amp IC might do the job nicely. The current PSU is only 230W, I will replace this with appropriate ATX PSU when built, but I'm looking at a circuit which draws say 4A max on 12V. I may replace the mobo with ITX (this will obviously free up loads of space).
    So, does anyone a) Know any good ICs (ideally with circuits) b) Tried anything similar (any tips?)
    Any ideas appreciated...
     
  2. cpemma

    cpemma Ecky thump

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    I've used the TDA2004 ic for a couple of 12v PA systems, it's a 6.5W/4R single-rail stereo chip but can be bridged for about 24W mono.

    Maplin do the TDA2005M which looks similar. TDA2003 also single-rail mono chip worth looking at.

    I used pcbs RS were selling at the time, don't know if they still do, but I think the datasheets have designs.

    edit: RS still do the pcbs, bargain @ £1.50, stick TDA2004 in the search box for details

    The power outputs I quoted above are in a car with the engine running, around 14V supply. 12V power will be around 4W stereo, 15W bridged mono, as good as you'll get without an inverter.
     
  3. tomek

    tomek What's a Dremel?

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    All You need is ... TDA 1555Q (4x10W or 2x20W BTL)
    To build In BTL mode You will need only 2 capacitors!!!
    You can't connect amplifier to the same PSU as the rest of the computer!
    Distortion in these configuration is pretty audible.
    The power amplifier is fully protected, werry small package bla bla bla...
    Greetings
    Sorry for my english
    Tomek
     
  4. Munterofamodder

    Munterofamodder What's a Dremel?

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    cheers for the ideas guys. will be looking into them both, especially the 204 (those cheap pcbs sound like just what im after! :)
     
  5. eaterofpies

    eaterofpies What's a Dremel?

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    quick q are we talking full on amp or just an earphone amp? i made a floppy bay earphone amp a few years ago before i got a live drive
     
  6. fump

    fump What's a Dremel?

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    why not just get a car amp and convert it to run with a computer (not extremely hard 2 do but it needs som guess/bodge work) They run at 12V and can b like 500W+

    it is easy with old amps that have relay on/off switches, all you need to do is connect that to the 12V line and the left right to a jack plug and it should work well. Mute lines are a different story.....
     
  7. dfhaii

    dfhaii internets

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    computers use switch mode powersupplys so u will need to do sommat to clean the power line up a little, and also hooking up a 500+ watt car amp may not be the best idea as they like pulling alot of current hence the 0 guage power wires ;).
    there are some push pull mosfet designs floating about the net which would give enough for some small efficient speakers.


    Col
     
  8. Munterofamodder

    Munterofamodder What's a Dremel?

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    i'm after somethings in the region of 5W to 10W rms, stereo out into 8 ohm speakers. Ideally 4 ohm speakers would be fine too. I'm after a hifi-ish quality amp, that is say 0.1% THD or less at 5W out. Assuming an efficiency of 50% (reasonable for class AB amplifiers) were talking a peak power of 50W drawn from PS, at 12V. Please do correct me if I'm wrong here, but this will be a 4.25A current. Lets say 5A to be safe. The computer currently works fine on a 200W PSU, with 12V rated at 8A. If I replace this with ATX PSU, true 380W, with 15A rating at 12V, it should be able to supply the current necessary. I know large transients can cause a sudden high current draw, but with suitably large capacitors on the circuit and this extra headroom I should still be ok shouldn't I?
     
  9. Munterofamodder

    Munterofamodder What's a Dremel?

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    tomek, where can I source this IC? I cant get it at Rapid. I will check RS and Farnell when I finally find the catalogue cds...
     
  10. Munterofamodder

    Munterofamodder What's a Dremel?

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    cpemma - just checked RS and those ics look like just the thing im after. I think i might use two both in bridge mono configuration. I can't see info about the extra components needed though - trying to find datasheet to see if there on that.
     
  11. tomek

    tomek What's a Dremel?

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    Last edited: 11 Dec 2003
  12. cpemma

    cpemma Ecky thump

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    RS do their own version of the datasheet with the dual-purpose (bridge or stereo) pcb circuits included. Think its in the general audio one. Board is also printed with component values. You need to register to get datasheets but its painless & spam-free. ;)

    Official ST datasheet doesn't show the bridged version. :duh:
     
  13. Munterofamodder

    Munterofamodder What's a Dremel?

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    guess i'll register with RS then. how do you rate them for prices\delivery? (I'm used to Maplins so i guess they'll be good!)

    what sort of heat sink do i need for the pcb? ideally, i'd like to use one of those angle heatsinks and bolt\thermal epoxy old PC heatsinks onto that (I have a couple of large slot A heatsinks lying around). i guess this would be satisfactory with the 20W or so dissipation (I'm probably going to make it semi active - turn on a couple of 80mm fans when hs temp rises above 50 degrees or so)
     
  14. cpemma

    cpemma Ecky thump

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    RS are often a lot cheaper than Maplin on prices (as is everybody else), delivery is fast but a painful £5.82 (inc VAT) so get a big order worked out to justify it. ;)

    They've got a truly massive range of heat-sinks, all shown in profile with ratings and dimensions, so you'll find wot u need to fit the case. :thumb:

    Don't forget this is an audio IC, you can fry eggs on the sink without it missing a beat...turns itself down at 150°C :rock:
     
  15. Munterofamodder

    Munterofamodder What's a Dremel?

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    cheers cpemma. informative and helpful as ever :) .
    guess i'll have to get a lot of leds to make the postage worthwhile... :hehe:
     
  16. cpemma

    cpemma Ecky thump

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    Why not a TSOP1738 for an IR remote control receiver (286-1419, 86p), a DS1621 or two for a task-bar temperature gauge (218-3826 @ £3.20) and the low-quiescent 5v regulator to go with it? :D
     

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