Cambridge dacmagic (current version)

Discussion in 'DIY Discussion' started by rsand, Nov 19, 2010.

  1. rsand

    rsand I can't feel my toes

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    Anyone had a fiddle with one of these?

    Are there any off the shelf power supplies to replace the noisy wallplug?
     
    rsand, Nov 19, 2010
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  2. rsand

    Captain

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    These not cheap, but Brent always delivers LINK
     
    Captain, Nov 21, 2010
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  3. rsand

    Tenson Moderator

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    I borrowed Rob's DACMagic. He lost the PSU so I'm using one of these - RS Stock No. 361-6197

    www.rswww.com

    Just connect a mains lead to one side and the thin wire with plug from the original PSU to the other.
     
    Tenson, Nov 21, 2010
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  4. rsand

    RobHolt Moderator

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    Something worth considering is dropping the AC voltage a little.

    Not something I've checked but there are reports the internal regs run quite hot and that there is enough headroom to reduce the AC input slightly.
    I mention this as I know many 12v ac transformers actually deliver 13-14v on light loading. Might be worth trying a 9v ac transformer that typically delivers 10-11v.
     
    RobHolt, Nov 21, 2010
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  5. rsand

    sq225917 Exposer of Foo

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    They work fine with the Maplins high current 9v transformer, and at £15 a damn site cheaper than anything else that delivers nothing more.

    If you want to do anything to it replace the power supply diodes with decent low noise Schotkys. 11DQ10's will be fine.

    If you really want to give it a clean power supply then remove the AC input, the diodes, the smoothing caps and the two internal regulators on the front end of the power supply and pipe it directly with the two dc rails it actually needs from high quality linear supplies.

    Giving it a £180 power supply to feed the Ac input is an utter waste of time, utter and absolute.

    Either go cheap, or go utterly balls out, there is no measured improvement to be gained from the middle ground
     
    sq225917, Nov 21, 2010
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  6. rsand

    rsand I can't feel my toes

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    Would there be any benefit to buying the maplin 9v plug and play over the 12v transformer Simon mentions?
     
    rsand, Nov 22, 2010
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  7. rsand

    sq225917 Exposer of Foo

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    It runs a little cooler internally, which may prolong the life of the unit, other than that it'll sound just the same.
     
    sq225917, Nov 22, 2010
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  8. rsand

    rsand I can't feel my toes

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    thanks!
     
    rsand, Nov 22, 2010
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  9. rsand

    Tenson Moderator

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    Doesn't it already use Schotkys? I think that was at least the case with the phono stage.

    I used the RS transformer because I already had it in on a shelf. The Maplin one seems better value and ready to use I take it.
     
    Tenson, Nov 22, 2010
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  10. rsand

    sq225917 Exposer of Foo

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    Sadly, not the case for the phonostage, which i was disappointed at, low noise fast recovery types though.

    The maplin is plug and go.
     
    sq225917, Nov 22, 2010
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  11. rsand

    rsand I can't feel my toes

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    What are the benefits with this option over the £15 maplin plug and play
     
    rsand, Nov 22, 2010
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  12. rsand

    sq225917 Exposer of Foo

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    I have no idea as to the audible benefits. But if you want to give it the best power supply possible then you need to bypass the crappy onboard regulators and rectifiers.

    Alternatively you could just attack the power supply further inside the unit, replacing any monolithic regs with low noise discrete regulators, S-power, Tentlabs Shunts, Newclass D regs, there's loads available. Giving best regulation rigth next to the clock and the DAc chips themselves.

    That's what I did to my 840c, new clock, and reg, new regs for each dac chip and rebuilt the power supply with better caps and diodes. It's easier due to the large case on the 840, hence most companies trying to sell external supplies for the dacmagic, but that's missing the point.
     
    sq225917, Nov 22, 2010
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  13. rsand

    rsand I can't feel my toes

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    How did the 840c respond to these mods?
     
    rsand, Nov 23, 2010
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  14. rsand

    sq225917 Exposer of Foo

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    it bought me a birthday card... ;-)







    I did most of the mods in stages.

    First off I damped the case with Dynamat, using one solid piece where possible, with multiple layers on the sides and lid and lots of smaller pieces damping the webbing extrusion that the transport is mounted on. That made a noticeable difference when playing back CD's, tighter bass with more definition. Made bugger all difference when just using the DAC inputs. (£20 well spent!)

    The diodes and caps for the power supply were done next. I can't really say exactly how it sounded different. Just a bit better overall, less 'hash' at the top end, smoother-but not less detailed if you get my drift. (£30 of parts + a fe hours time)

    Then I had the clock replaced and a tentlabs shunt added. Honestly that did SFA, i really couldn't hear any difference when that came back (£120- not wasted I guess but certainly not something i could recommend).

    Then i had a few things done at the same time.
    1. Paul Hynes regs added to the DAC chips- right on the DAC chips and some additional local decoupling with Oscon caps.

    2. The balanced section of the output stage was cut out of circuit, it draws power even when not being used and I'm never going to use it.

    3. I then had selected op-amps in the output stage replaced with a variety of different ones and the whole output stage re-biased into Class A. Some of the cheaper op-amps were replaced with LM4562 (these are renamed now) and some odd Burr Browns were added as well, the number alludes me.

    This made a big difference, in several areas. There seemed to be an obvious reduction in what I call digital hash- the thing that makes cd's sound like digital, I'm not sure what the artifact/distortion is, but it was greatly reduced/removed giving my player a much more analogue sound- or allowing it to better express the qualities I like from good analogue replay.

    The tonal quality of the player improved, the overall impression of real instrument sounds was improved, more like live music when the recording is of that nature.

    Lastly it seemed to improve the acoustic, the sense of space within the recording and of musicians being within a real space. overall a worthwhile set of changes.

    I'd like to think that the clock changes were made audible by the improvements to the dacs chips and output stage, but I probably just wasted £120 in reality.


    I'm very happy with the way it sounds and it gives my SME10, SME V, Benz LP vinyl front end a good run for its money for about 1/5 of the cost.
     
    sq225917, Nov 23, 2010
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  15. rsand

    rsand I can't feel my toes

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    Thanks for taking the time to explain that

    Rob
     
    rsand, Nov 24, 2010
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