Cambridge Audio Discmagic/Isomagic project

Discussion in 'DIY Discussion' started by mjp200581, Jun 1, 2012.

  1. mjp200581

    mjp200581

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    Hi All,

    I'd like to share with you my Cambridge Audio Discmagic + Isomagic upgrade project.

    For those of you who aren't familiar with the S700 Isomagic is an unusual bit of kit in that it is both a standalone DAC and an isolation platform for your CD transport. The Isomagic is very slim and sits on 4 or 5 soft squishy vibration absorbing balls.

    You can see the overall set up here:
    http://s19.postimage.org/vlbywrfdv/Disc_Iso.jpg

    The Isomagic can be used with any CD transport with a coaxial digital or digital optical output but it is really designed to be partnered with the Discmagic.

    What makes the Discmagic/Isomagic combination so special is that the DAC can be 'clock locked' to the transport. As far as I understand it the DAC acts as the master clock and determines the timing of the data feed from the transport. This clock lock is via a toslink cable. By clock locking the two components jitter is significantly reduced resulting in superior sound quality. This is easily demonstrated as the clock lock function can be switched on and off with an external switch enabling you to make a quick A/B comparison.
    I believe a similar system was was used by Linn on the Karik/Numerik combination but using a coaxial cable.

    The digital audio output of the Discmagic can be connected to the Isomagic with either a coaxial or toslink cable. The toslink is the preferred option and gives a better sound, perhaps this is because ground loops between the transport and DAC are removed?

    The Discmagic is impressively well equipped and boasts two separate transformers for the servo and audio circuits. The audio circuit is also nicely screened with a copper partition and the build is functional and solid. Here is a pic of the internal layout:

    http://s19.postimage.org/bf8gxvjqb/Discmagic_overall_layout.jpg

    As an added bonus the Isomagic is also equipped with a HDCD DAC chip.

    Both units are John Westlake designs and John has been quoted several times as saying that the isomagic was his best ever design for Cambridge Audio (together with the CD4SE).

    So with a highly regarded designer, a great basic specification and the clock lock function I thought that the Discmagic/Isomagic had the potential to be tweaked into something pretty special or as one forum member on DIY Audio put it "formidable even by today's standards".

    The Isomagic was an ebay purchase and had clearly had a hard life (it reeks of fag smoke). As a first measure I therefore decided to replace the capacitors. I chose Nichicon Fine Gold for to replace the big electrolytics and Elna Cerafine to replace all of the smaller ones. I did however leave a number of small purple Sanyo caps in place as I think these are Oscons?

    Here are some pics:
    [​IMG]

    [​IMG]

    The capacitor change was well worth it and definitely added a bit of sparkle to the sound. They didn't even seem to need much burn in time and sounded better straight away.

    Well that's enough for part 1. I'll be added more posts over the next few days.
     
    mjp200581, Jun 1, 2012
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  2. mjp200581

    RobHolt Moderator

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    The little purple Sanyo caps do look like Oscons.

    Amazing they got all of that into a shelf!

    No reason why it shouldn't sound excellent with a refresh.
     
    RobHolt, Jun 1, 2012
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  3. mjp200581

    mjp200581

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    Well it's a quite day so here we go with part 2.

    The Discmagic has had the following mods:

    1) Replacement of all of the big electrolytic power supply capacitors. Again I used Nichicon Fine Gold caps here of 2200uF (sourced from HiFi Collective).

    2) Replacement of the bridge recitifier diodes on the audio circuit board with Schottky 11DQ10 types.

    3) I replaced the relay switch visible in the centre on the output circuit (yellow box approx 10x10x20mm). The original buzzed loudly when turning on the transport. I think this has something to do with the clock lock function.

    4) I covered all of the large open surfaces of the case with self adhesive bitumen roof lagging tape in an effort to dampen vibration.

    5) I replaced the two L7805 voltage regulators nearest to the toslink output with fancy Dexa Technologies Class D regs (sourced from HiFi Collective). You can see the blue LED on these in the pictures.

    Here are the pictures:
    http://s19.postimage.org/5tm1ttj1f/Disc_output_close_up.jpg

    http://s19.postimage.org/jyruvms2r/Votage_regs_close_up.jpg

    http://s19.postimage.org/bf8gxvjqb/Discmagic_overall_layout.jpg

    These mods have made a dramatic improvement to the sound. The voltage regs opened up much more detail, improved the transparency noticeably. I was also very surprised how much the bass was improved becoming much more 'solid' and textured. I must thank the staff at HiFi collective who were very helpful with advice on these. Overall a very significant and worthwhile upgrade but not terribly cheap at around £30 each.

    The Shottky diodes are a revelation to me, for such as simple and relatively cheap modification they make a surprising difference. To my ears the background noise was reduced significantly allowing you to hear much more detail in recordings. A great mod in the value for money stakes!
     
    mjp200581, Jun 1, 2012
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  4. mjp200581

    Tenson Moderator

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    I haven't heard the DAC but I like the DiscMagic, as you say it's very well built. The coax digital output is very clean, I've looked at it on the 'scope :)
     
    Tenson, Jun 1, 2012
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  5. mjp200581

    mjp200581

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    That's interesting info Tenson. I'd be interested to see how the Toslink output compares. When used with the Isomagic John Westlake himself recommends using the optical out in favour of the coaxial. Having tried both I agree with him although the difference is relatively subtle. I would say the presentation is a little more clear and detailed via optical but maybe also a little colder.

    I'd definitely recommend the mods outlined in my previous post. They made quite a difference.

    Well here is my final instalment of progress so far; the power supply.

    The factory power supply for the Isomagic is a power 'brick' thing which connects to the DAC with a DIN type connector. Inside the 'brick' is a smallish E-core transformer a bridge rectifier, two 2200uF electrolytic filter caps and two small bypass caps.

    Well inspired by a thread on the DIY Audio forum I launched into making my own (hopefully better) power supply.

    In the end I opted to buy 3 separate P05 printed circuit boards from Elliott Sound Products of Australia which I then built following the recipe on the ESP website. The three separate boards provide the following:

    +15v / -15v for the left audio channel
    +15v / -15v for the right audio channel
    +15v and 0v for the digital circuit.

    Each circuit is regulated with LM317 / LM337 voltage regulators mounted on home made heat sinks.

    The left and right audio circuits are powered by a 30VA toroidal transformer and the original E-Core is used to power the digital supply.

    I included an on/off switch a fuse and a power on LED light which is powered by the aux pin of the circuit board which feeds the digital supply.

    The whole thing is built into an aluminium case which I bought from Maplin and the case is fitted with an IEC socket so I have the option to use a higher spec power cord in the future. The case is sprayed satin black to match my other components.

    Here are some pics:
    http://s19.postimage.org/tr4mvifmr/PSU_internal.jpg

    http://s19.postimage.org/tajf92rvn/PSU_closeup.jpg

    http://s19.postimage.org/co1uzzyxv/PSU_external_2.jpg

    It's far from the most sophisticated bit of audio equipment but since it is my very first DIY build I'm quite pleased with it.

    So the question now is what next? I've already ordered some more Shottky diodes to replace all of the ones in the PSU and I'm also going to rewire the PSU with some Teflon insulated silver plated copper wire.

    After that I'm really getting out of my depth as I have virtually no knowledge of electronics.

    I'd be really interested to what other forum members suggest as the next stage of modifications for this project. Suggestions very much welcome!
     
    mjp200581, Jun 1, 2012
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  6. mjp200581

    Tenson Moderator

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    Actually I tested the AES output. When I believed such things mattered, I thought it sounded better than a Chord Blu £4k cd transport (which I then broke). These days though, I don't think anything makes much difference before the DAC chips outputs (unless something is plainly done wrong).

    Be aware that the psu's should join the player ground in the optimum way, or all sort of poo can get into the audio stream.

    I can't tell you the best way to do it as it really needs trial and error with lots of measurements of the audio outputs to check for noise and distortion products.

    That said if the DAC has a star ground point, this is a good bet, as is the ground point of the RCA jack. You might be better asking someone more expert than me, I just try lots of stuff and measure the results. Things have been destroyed along the way! ;)
     
    Tenson, Jun 1, 2012
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  7. mjp200581

    mjp200581

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    Thanks again Tenson.

    I've been asked to post the other thumbnails of the pics. Here you go:

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
    mjp200581, Jun 2, 2012
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  8. mjp200581

    Puffin

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    Seems I joined this forum in or around Sept 2009 and forgot!

    I have a Discmagic which had a Trichord Clock 3 mod some years ago. I only recently got round to adding a separate PS for it, which IMO has taken it to a new level. The T3 clock was a worthwhile mod, but the PS has really made a difference. The PS is based on the TeddyRegs (PFM)

    I also had an IsoMagic for which I made a new PS. Is sounded great. It was transformers and bits of wire everywhere waiting to be boxed up. Yup, you've guessed it, something got dislodged and killed the DAC:eek:
     
    Puffin, Nov 4, 2012
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  9. mjp200581

    mjp200581

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    Yesterday I got a P.M. from a Guy called Walter who lives in Austria telling me that he is now the proud owner of my old Isomagic and D.I.Y PSU!

    Amazing!

    So it's time to start this thread up again.

    Here is his message:

    Your S700 now in Austria!
    Hi mjp200581,

    just for your information: your ISOMAGIC shown in the thread, belongs now to me (from italian ebay - what else), i am Walter from Austria and use your nice modified S700 instead of my old DACMAGIC1. To continue yor way, i will put the well modified PS in an Italian 43,5cm 2U case: http://www.modu.it/pesante.html
    You are right, the S700 smells a litte smoky, i tried to clean it and fixed a broken leg of one 2200µF! Only one of the four blue rubber-connectors - holding the pcb - is now dead.

    Best Regards, Walter
     
    mjp200581, Nov 8, 2013
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  10. mjp200581

    mjp200581

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    I have learnt a lot since building the Isomagic PSU and I have some suggestions for Walter about how to improve it.

    Hi Walter,

    One of the best simple upgrades you can make to the PSU is to add a capacitor in parallel across the voltage set resistor(s) on the adjust leg of the voltage regulators. This is a trick which I learnt from Martin (aka Felix) on this forum.

    You need to use 10uF or higher. I suggest something like 33uF 63v electrolytic.

    If you don't have room above the PCB you can squeeze them in on the underside of the PO5 board. I did exactly this when I built a PSU for my phonostage.

    Like this:
    [​IMG]
    image hosting sites

    Another possible upgrade would be to substitute the voltage set resistors for zener diodes. From memory I think the PSU is set to give +/- 15v supplies so 13.6v zener would do the trick here.

    I used the same modifications on my Arcam Alpha 5 CDP and D.I.Y phono stage PSU. I suggest you read both of these threads as they detail most of the information you need.
     
    mjp200581, Nov 8, 2013
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