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Old 25th May 2005, 02:42 AM   #1
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Default musical-fidelity-a3.24 mods

I have done some mods to the MF A3.24 which some of you with some electronic experience may wish to try. These mods greatly improve the transparency and bass tightness of the unit. Which truly makes it one of the best dac's around. The output stage of this dac is awesome, fully discrete and capable of driving a speaker direct, up to 6wrms!!!!!!!

1/ Direct coupling to the outside world, instead of going through a very average coupling electro. I tried a Blackgate instead of what they used, it was better but nowhere as good as direct coupling (removing the cap altogether). But you CANNOT just remove the cap as you'll get large amounts of DC offset at the output, and you will blow you pre or power amp.

This is how it's done

A/ Remove and short or just short out the output caps 470uf/63v C101 and C201.

B/ Find the 2X 2.2kohms resistors R108 and R208 (around 3inches from the back of the board) remove these resistors and replace them with 2x multiturn 5k cermet mini pots set at 2.2k to start with (Spectrol are good and avalible at most good electronic shops) You only need to use the centre and one of the outside legs the spare outside leg can be left in the air or attached to the center leg.

C/ put a digital multimeter on the output and earth and set the sensitivity to dcmv 200mv, powerup the unit and let it warm up and adjust the mulit turn pots for zero (0dcmv) offset. you can get it to stay at zero it will drift +1mv -1mv.

2/ For the very keen ones this will make it sound even better again.

A/ Find the i/o opamps 2x NE5532 after the dac and replace them with 4x AD825's these are smd singles and have to be mounted on 2x Brown dog boards. 2x ad825's for each Browndog board. They now replace the 2x NE5532's This jobs takes some patiences and care as the NE 5532's are through the hole plated on both sides.

Now you have a dac that is truly awesome to listen to.

Note: these mods will definatly void your warrenty

If you do a search i have posted the diagrams of both the circuit and power supply somewhere in this forum, should you need them.

Cheers George
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Old 25th May 2005, 12:37 PM   #2
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I've been asked by a number of members by private email to post the circuits again as they cannot find them in previous posts that I've put them on, so here's the links. I cannot email them as they are A3 and I do'nt have a scanner that big. This is as sharp as I can make them. All the components are marked on the circuit board so you should'nt need the diagram to do the mods.

Front stage:
http://www.diyaudio.com/forums/attac...amp=1109562245

Rear stage:
http://www.diyaudio.com/forums/attac...amp=1109372290


Power supply: minus transformer
http://www.diyaudio.com/forums/attac...amp=1109570483


Cheers George
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Old 25th May 2005, 06:45 PM   #3
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any more mf circuits George, very interesting. thanks
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Old 26th May 2005, 09:28 AM   #4
Ruach is offline Ruach  Singapore
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Thanks George. The diagrams are very interesting. I used to own a A3 24 myself.

I was looking at the power supply pic and some of the wordings are not clear. Can you tell me what are the values for the following?:

i. Choke at CH1
ii. Capacitors at C110, C112, C210, C212


Thanks
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Old 27th May 2005, 05:00 AM   #5
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All chokes are 8.6mh 2A, and C212, C112 100uf/16v C112
C210 C110 .1uf/100vpolyprop.

Cheers George
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Old 30th May 2005, 01:23 AM   #6
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I finished mods on MF A3.24 CD Player two weeks ago, so couple of hints might be helpful…

Both analog and digital board are done very nicely, i liked the ground topology a lot, but I wasn't impressed with the ribbon cables connecting two boards, nor with the length of the same type membrane cable connecting mechanism and digital PCB. Even worse, parts quality is very bad. Using a lot of 0.01uF disk-ceramics for the local decoupling brought-up the highs in this CD Player - but also completely removed the natural sound character. NE5532 as current to voltage just can not perform this duty properly. Buffer - maybe, but rather not.

I have installed a lot of Black Gates, used 2134, 275 and 826. The end configuration: first two IC's 2134, second two IC's 826. Silver ribbons were used as well, and 4.7uF V-Caps for sound coupling.
Both oscillators got their separate low noise power supply. The output pulse transformer was replaced.


The end result was very, very good.

Regards,
Extreme_Boky
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Old 30th May 2005, 01:28 AM   #7
Ruach is offline Ruach  Singapore
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Hi, can you post some pictures of the A3 cdp? Thanks
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Old 30th May 2005, 01:32 AM   #8
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Sorry, long gone back…
Regards,
Extreme_Boky
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Old 27th November 2008, 02:54 AM   #9
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Hi Georgehifi, I have just registered and also cannot send you a PM ^^. I'd like to ask a few questions about your Musical Fidelity A324 DAC mods.

1. How did the AD844 compare to the OPA627 or AD825 ? (I have some OPA627 that I can use and I don't fancy soldering expensive chips SMD). Will a PDIP-N package of the AD844 fit the Brown-Dog adapters to convert 2x single op-amp to dual? Is it worth doing the mod to use the OPA627?

2. Are you able to recommend a part number for the mini-pots?

Something like a Vishay Spectrol 064W502 (Digi-Key part number SP064W-100K-ND ) or a 63M type?

Thanks a lot for any advice you can give. I wasn't sure where to post to get your attention.
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Old 27th November 2008, 04:15 AM   #10
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Not the correct forum for this so this is all she wrote, this was a while ago but the AD825's were used in place of the 4 x NE5532's for their great sound (for an opamp) and because of it's fet input it had close to zero dc offset in this circuit, just a little tweak with the instaled 5k Spectrol timpots in place of the 2.2k resistors, and it was adjusted down to .1mV offset at the rca outputs. This was important now that the whole shebang was now dc coupled from the dual dif outputs of the dac through the opamp I/V stage and then through the discrete output stage, and it could drive 6watts, pretty impressive for a dac, it could almost drive a speaker direct.

Cheers George
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