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Old 5th October 2005, 09:33 AM   #1
jdunham is offline jdunham  United Kingdom
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Default Cambridge Audio IsoMagic & DisMagic problem - circuit diagram?

Can anyone help me with circuits digrams for either of these?

I am having problems getting mine to use the Sync Lock between the DisMagic transport and the DAC. The relay in the trasnport seems to be swicthing in and out intermittently and the DAC will not lock on to the signal.

Any suggestions?

Kind regards,

Jonathan
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Old 5th October 2005, 11:40 AM   #2
JohnW is offline JohnW  Hong Kong
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The most likely problem will be with the optical RX / TX modules on the clock-lock / SPDIF lines - these are very easily damaged by physical stress to there housings (during production or servicing). When physically stressed - the internal detector or transmitter diodes are displaced, causing the problems you described

John
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Old 5th October 2005, 01:42 PM   #3
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Default Re: Cambridge Audio IsoMagic & DisMagic problem - circuit diagram?

Quote:
Originally posted by jdunham
Can anyone help me with circuits digrams for either of these?
I have circuits drawings for the DiscMagic and some stuff on the clock link. Email me and I'll send them to you.
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Old 6th October 2005, 11:06 AM   #4
jdunham is offline jdunham  United Kingdom
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Dan - Many thanks for the diagrams for the DiscMagic, that's a great help!

JohnW - having done some searches before I posted this, I realise who you are - the designer himself!!

I really appreciate you taking time to respond directly to my post. Many thanks for the suggestion, I will look into this one first, and see if I can find some new TX/RX modules.

You don't happen to have a circuit diagram for the Isomagic do you?

With kind regards,

Jonathan
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Old 6th October 2005, 12:42 PM   #5
JohnW is offline JohnW  Hong Kong
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Jonathan,

Sorry over the years & the many changes in computer systems, I no longer have the circuits for the Isomagic. In fact I ask Dan to forward me the DiscMagic Circuits for my referance. If you like, once I get back to Europe (end of Oct) I can send you an old Digitial OP board from a Discmagic - could be good for spare parts - or replacement (with some work).

If you have no luck in fault-finding your unit, I will soon be launching a CD transport with Clock-Lock, which will also be compatiable with older Cambridge Audio designs.

Dan - thanks for the Circuits. As for your Drop-out problems due to external induced RF from mains and heating system, are you sure the units are correctly grounded? I understand parts of US & Canada often don't have Ground connected... You could also try optical link for SPDIF.

If you use Clock-Lock, then I recommend to use optical for both Clock (no Choice) & SPDIF - this helps Isolate RF between the units.

John
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Old 6th October 2005, 03:21 PM   #6
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Quote:
Originally posted by JohnW
If you have no luck in fault-finding your unit, I will soon be launching a CD transport with Clock-Lock, which will also be compatiable with older Cambridge Audio designs.
That's great news. The IsoMagic truly is magic when clock-synched. As I told you via email, I compared the DiscMagic/IsoMagic to a new Classe CDP-10 and there was really very little difference in sound.

Dan - thanks for the Circuits. As for your Drop-out problems due to external induced RF from mains and heating system, are you sure the units are correctly grounded? I understand parts of US & Canada often don't have Ground connected... You could also try optical link for SPDIF.

Thank you for the great design.

My stereo system is grounded, but I suspect my main house ground needs some cleaning up where it connects to the plumbing. I've been meaning to get an electrician in to fix that. I guess now's a good a time.

If you use Clock-Lock, then I recommend to use optical for both Clock (no Choice) & SPDIF - this helps Isolate RF between the units.

I tried that just now, and I dimmed the halogen lights. No dropouts, problem solved. Thank you! The optical connection doesn't sound exactly the same as the coax, so I'll have to see how I like it long-term.

BTW, I bought the DiscMagic before I bought the IsoMagic. I was very disappointed to find the Iso had no XLR connectors for data connection to the supposedly matching transport. What happened, did Cambridge cut your budget? And why was the DiscMagic discontinued at the same time as the IsoMagic was finally released in North America? That was very strange, considering what a fantastic value they were together. An IsoMagic without the clock link is rather ordinary sounding. With the clock-lock it's extraordinary.
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Old 6th October 2005, 06:10 PM   #7
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I have a circuit diagram for the Isomagic - I'll just have to find it (it's on paper)

The diagrams which I got from Cambridge were completely wrong in some places, so I had to buzz out parts of the circuit and correct the diagram.

I made some mods to the clock circuitry too, which really improved the sound.

-Mark.
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Old 6th October 2005, 06:41 PM   #8
jdunham is offline jdunham  United Kingdom
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This thread has getting better by the minute, thanks guys!

Brussell Sprout - it would be great if you could scan and email this - there are three of us here that I'm sure would bite your hand off for a copy!!

JohnW - many thanks for the offer of the Digital OP board, that would be great to have. Do you want me to email you in early November on this? Are you coming to the UK at all?

Regarding the fault on my units, a friend is actually doing the fault finding so perhaps Tom, you might post with more details on what you have found so far? And maybe you or others might be able to shed some further light on things.

With kind regards,

Jonathan
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Old 6th October 2005, 07:13 PM   #9
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I'll do that, and I'll be sure to wear my chail mail gloves... I've moved house since I last saw the papers, but I have a pretty good idea where they are Give me a couple of days though.

The Isomagic really is rather nice once it's been tweeked a bit.


-Mark.
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Old 6th October 2005, 08:08 PM   #10
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Default Troubleshooting the Discmagic

Hi all,

I've been trying to get my Discmagic to work in clock locked mode so that Jonathan can use it with the Isomagic he recently acquired... that is due to undergo some... shall we say, substantial modifications.

John - I tried replacing the RX176 optical block, but to no avail. I've also tested the removed unit, and it appears to be in perfect working order - connecting my frequency counter to the output pin gave a stable 5.644673MHz (or thereabouts), so the Isomagic appears to be outputting a decent clock, and is also being received okay.

I tried connecting the frequency counter to R11 (which should be giving the tripled clock, AFAIK), but I was just getting rubbish, regardless of whether the clock was connected to the receiver block or not.. jumped from an average of around 300kHz to around 1MHz when the lead was plugged in, but no stability at all.

So I disconnected the coupling cap C34, so the relay/LED driver circuitry was taken out of the equation... this made R11 show a clock of around 16.3MHz when the clock from the Isomagic was fed in... not rock solid, but not terrible either.

I thought C34 might be dodgy, even though my DMM measured it as around 120nF out of circuit, so put in a nice 100nF C0G. Unfortunately, this had no effect on the intermittent relay problem.

The relay/LED circuit is something I find quite peculiar... I was wondering whether it would be feasible to replace it with a different circuit using a HC126 chip, LP cap, gain stage, and an NPN transistor to drive the relay. My best guess right now is that some of the gates of the HCU04 are damaged (U6: D in particular), but it is proving hard to make sure of this without a scope...

I have ordered a replacement HCU04 in case it is broken, but I don't understand how such a thing could occur (VCC is fine). R13 and R16 both measure around 10K in circuit. What about C46? Or am I clutching at straws?

One thing I haven't tried yet is removing D5 and seeing whether it's already messed up at pin 12, but as it already seems to be messed up at pin 13 when it is in circuit... hmm...

Beyond trying to figure out what is wrong with the unit, I saw something that struck me as odd in the power schematic... the centre tap of the transformer is shown as being connected to common ground... as is the -12V (which becomes ground for lower common mode noise after the CM choke, it seems)...

I would have thought the centre TX tap would be only connected to the pre-regulators and decoupling before L2? I'm not claiming to know, being a relative novice, but I just thought better CMRR would be obtained that way...

Audiobomber - I've also had trouble with losing S/PDIF lock over the coaxial output of the Discmagic. When I brought in a AT PC PSU and plugged it into the same power strip to demo the problem, the salesman in the Richer Sounds listening room seemed unphased... even though my JE510 was losing lock several times a second...

With clock lock, the optical should (in theory!) be fine, but there may be other factors at work. You might want to try using the positive pin and ground (pins 3 and 1) of the XLR to an unbalanced plug - I used this for a while, and never suffered a music glitch when I switched a light on or some such thing...

One major reason why the Isomagic doesn't have an AES/EBU input is probably because the connector would be physically too big to fit on the back panel! Besides which, it is not regarded as a particularly good connector from a HF impedance POV.

- Tom.
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