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Old 12th January 2007, 04:18 PM   #1
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Default Musical Fidelity A3.24 repair

Hi,

I have a MF A3.24 DAC with a failure of the coaxial digital input. The Optical input work OK and the DAC works and sounds great. My only problem is the coaxial input.
Anyone has experienced this problem? Can you recommend how to approach this repair?

If someone on the forum has the schematic for the A3.24 DAC that would be great.

Thanks,
Ronen
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Old 12th January 2007, 07:15 PM   #2
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I would guess that the problem is the IC10 the DS266L532CM as it it the only active device that would stop the coax input as the optical comes in after this.
Also are you sure it's not the coax output of your transport before you start ripping into this?
Cheers George
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Old 12th January 2007, 07:58 PM   #3
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I have the same unit. Sometimes the signal fails to "lock" unless one cycles power. As you probably know, the bright blue LED in front indicates signal lock. Is it on?

If cycling power does not fix the problem, you'll need to get inside the unit to troubleshoot. For that you'll need a #10 Torx security wrench/bit.

As far as the schematics ... good luck. I've tried to obtain these myself but this company -- like many "high-end" audio/video companies -- are highly protective of their designs and only supply circuit schematics to official dealers or repair facilities. (Check MF's web site for more info on this.)

Frankly, my disgust with companies like this -- and all the high-end magazine kiss-*** politics that promote their so-so over-priced products -- is why I pretty much went DIY. It's way less $, way more fun/rewarding, the camaraderie/support (via DIY forums) and open availability of info and schematics is unparalleled, and (IMO) the end product actually performs better. An example of this is mod'ing one of the latest Toshiba CD/DVD players (see this page for more info)). For about $90 -- that includes the price of a new player ($40), readily-avail. schematics ($20), and a few upgrade parts ($30: op-amp, rope caulk, etc.) -- I have attained Red Book playback that sounds better than the A3-24. I also have a decent DVD player, whose performance also improved via the mod. And I don't need a special $10 bit to get inside it!

Okay I'm stepping off my soapbox, now
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Old 12th January 2007, 08:24 PM   #4
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Quote:
[i]
As far as the schematics ... good luck. I've tried to obtain these myself but this company -- like many "high-end" audio/video companies -- are highly protective of their designs and only supply circuit schematics to official dealers or repair facilities. (Check MF's web site for more info on this.)

Frankly, my disgust with companies like this -- and all the high-end magazine kiss-*** politics that promote their so-so over-priced products -- is why I pretty much went DIY. [/B]
Maybe it's the way you ask, I receieved it (see previous post) this is only part of the circuit I have the rest if needed posted at other threads do a search under my name and you'll shall find all.
Also this dac is very good sounding out of the box, and if you do my dc coupling and I/V mods also in previos threads, it is so far unbeatable.

Cheers George
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Old 12th January 2007, 08:32 PM   #5
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Quote:
Originally posted by georgehifi
I would guess that the problem is the IC10 the DS266L532CM as it it the only active device that would stop the coax input as the optical comes in after this.
Also are you sure it's not the coax output of your transport before you start ripping into this?
Cheers George
Quote:
Originally posted by hollowman
As far as the schematics ... good luck. [/B]
Thx for posting the circuit schematics. I've TRIED to obtain them from MF several times, but they always refused. Ditto experience with Theta and other commercial "high-enders". I guess I should've asked here!
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Old 12th January 2007, 09:02 PM   #6
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Quote:
Originally posted by hollowman
... For that you'll need a #10 Torx security wrench/bit.

.....And I don't need a special $10 bit to get inside it!

Does this DAC have the Torx security screws with the hole in it ?!?
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Old 13th January 2007, 12:24 AM   #7
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Quote:
Originally posted by jean-paul


Does this DAC have the Torx security screws with the hole in it ?!?
Yes: TR10.

Click the image to open in full size.

I ended up getting
this Security Torx Fold-Up Keys Sets , which actually cost more than the $10 I noted earlier. I think the $10 tool was/is avail at Lowe's or Wal-Mart.
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Old 13th January 2007, 12:24 AM   #8
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Quote:
Originally posted by georgehifi
Also this dac is very good sounding out of the box, and if you do my dc coupling and I/V mods also in previos threads, it is so far unbeatable.
I assume this is the thread you're referring to. Although I've already played around with swapping op-amps -- using AD8620, OPA627, etc. -- and still think the moded Toshiba sounds better, I did not remove/replace-with-better/short-out the output caps. To that end, some Q's...

- In the aforementioned thread you wrote "put a digital multimeter on the output and earth". Do you mean put one lead of meter on the output JACK (hot side)?

- Would you recommend this same mod (one that uses 5k cermet mini pots) for DACs in general?

Thx
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Old 13th January 2007, 12:57 AM   #9
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Quote:
Originally posted by hollowman



- In the aforementioned thread you wrote "put a digital multimeter on the output and earth". Do you mean put one lead of meter on the output JACK (hot side)?

- Would you recommend this same mod (one that uses 5k cermet mini pots) for DACs in general?

Thx
No the mod for DC coupling the output, only applies to this (A3.24) Dac as this DAC has a very powerfull low impedence discrete output stage.
The IC change is for the I/V stage which changes out the two NE5532's for 4 AD825's smd.
The DC coupling mod greatly enchances the sound, as does the I/V IC mod to a lesser degree.
Cheers George
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Old 13th January 2007, 01:56 AM   #10
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Quote:
Originally posted by georgehifi
No the mod for DC coupling the output, only applies to this (A3.24) Dac as this DAC has a very powerfull low impedence discrete output stage.
The IC change is for the I/V stage which changes out the two NE5532's for 4 AD825's smd.
The DC coupling mod greatly enchances the sound, as does the I/V IC mod to a lesser degree.
Thx for your reply.

I'm not sure if you addresed my first question so I'll repeat it again:

In the aforementioned thread you wrote "put a digital multimeter on the output and earth". Do you mean put one lead of meter on the output JACK (hot side) and the other on ground?
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