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Old 6th January 2006, 06:35 PM   #1
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Default Musical Fidelity CD Pre 24

I am looking for schematics for Musical Fidelity CD Pre 24 and A308CR amp. Any help would be greatly appreciated. Thanks
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Old 7th January 2006, 12:47 AM   #2
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Any problem with them???
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Old 7th January 2006, 03:43 AM   #3
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Actually I have 2 reasons for wanting the schematics. The CD pre 24 causes the overload circuit in my power amp to activate - apparently there is a short in the pre-out or the output circuitry. Secondly I would like to perform some upgrades on my CD pre 24. For example, there is a company doing the following upgrade to this unit:

- 8 x oltra-fast soft recovery Vishay-Telefunken Fred diodes in the power supply
- 17 x Black Gate Standard, N,FK and C grade electrolytic capacitors around the coupling caps and throughout the power supply
- 24 x Riken Ohm 1% precision Carbon-comp 0.5-watt resistors with gold-plated leads in the signal path
- 12x Polystyrene film and foil caps in the analog filter
- 2 x REL-CAP TFT grade, 0.022uf Teflon film and tin foil bypass capacitors for the main coupling caps
- 6 x Burr-Brown OPA627-based opamp assemblies mounted on single-to-dual adapter PCB assemblies for I-V conversion stage, analog filter, output Buffer and preamp
- 6 gx old-plated machined 8-pin DIP IC sockets
- 2 x sheets of SoundCoat damping material to internal chassis
- 4 x large EAR compliant Sorbothane isolation feet to absorb vibration
- 1 pr. Vampire RCA jacks for pre-outs, OFC copper body gold-plated
- 2 ft. DH Labs pure 99.99% solid-core silver, foamed Teflon dielectric as preamp output wire
- TRT Wonder solder throughout

I would like to find a source of supply for these components and also determine what size each component is (notice the list above does not indicate capacitance or resistance).

Do you have any info that could help me? Thanks. Mike
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Old 7th January 2006, 04:00 AM   #4
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Hi devron12

It is not very likely you'll find these schematics. Nor are they really needed for such an upgrade. It is easy to identify important resistors/capacitors by just looking at the pcb. Input coupling/NFB caps should be the first to upgrade. Similarly positioned resistors as well.

Michael Percy and Partsconnexion carry most or all of the listed parts. Looks like a minimum $300 bill so you must like your MF components a lot

For the 627 opamps you should probably look at this forum sale section - a lot of forum members got those as free samples and seem willing to sell them cheap.
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Old 7th January 2006, 03:29 PM   #5
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Where can I find instructions/guidelines on how to perform these upgrades?
Are there more prefereable op amps to use than 627?

In a previous life (20 years ago) I was an electronics technician in the U. S. Navy where I taught soldering. I think the upgrade is something I can handle, but I have no experience working on high end audio gear. I know I don't want to pay someone $1200 to do it (as is the case for the company I referenced in my previous post) Right now I am in research mode to see what it will take to accomplish the upgrade.

Yes, I do like my MF pieces. I know there are better components out there, but not within my budget and certainly not within my wife's tolerance. I recently got these MF pieces to upgrade my 2 channel capability from a 7.1 B & K reference 21 and 5 channel B&K ref 7250 (hence the addition of the 2 channel amp).
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Old 7th January 2006, 06:01 PM   #6
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Good soldering and especially desoldering skills and basic electronic literacy (pin orientation of ICs, polarity of caps) is all it takes. Unless you have a desoldering station i would cut out all opamps before removing the leftovers of the pins.

It's all pretty simple and any electronics technician should be able to handle it with no worries.

Looking again at your component list i can see nothing objectionable - all solid, good sounding components. The opamp sockets are there to allow opamp swapping. I would ideally prefer no sockets but the effect from them is minimal compared to the fun of swapping

The Vampire RCAs and DH Labs silver hookup wire are btw my favourite.
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