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Old 10th September 2007, 11:03 AM   #1
dejanm is offline dejanm  Austria
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Default Micromega Stage 2 Mod

Hi,

I came to the ideo to modificate a bit my old Micromega Stage 2 CDP. I already read somewhere that the output OPA NE5534 should be replaced with OPA627. Does anybody have some other ideas/experiences which might help to improve the sound of my oldy ? Does anybody have el. schematic, which will help a lot ?

Thanks in advance ...

Dejan
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Old 15th September 2007, 11:07 AM   #2
Mooly is offline Mooly  United Kingdom
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Hi Dejan
Your Micromega Stage 2 is IMHO one of the most musical players made and well suited to modification.I have modified my own Stage 2 as follows,
1. Replace NE5534 op-amps as follows,
For I/V convertor use OPA604.
For the output buffer use AD845JN. The multiturn pot next to the output buffer is used to null the output to zero volts with no disc playing.The value of 100k for original NE5534 is not ideal for AD845 but if offset can be reduced to zero then no problem.
2. Cut the P.C.B. track to the Left/Right outputs and insert 68 ohm resistor across the cut. This is to isolate the outputs from any capacitive effects of cables etc.
3. All electrolytics replaced with Panasonic low e.s.r. types.
4. 0.1 mfd surface mount caps added across all electrolytics.
5. I was lucky enough to obtain Japanese CDM12.4 mech a few years ago and fitted this 3 years ago.
Why this combination of op-amp? Because it sounds wonderful, the distortion produced is mostly even harmonic.
Good luck with any mods, you have player that is as good as anything available.
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Old 15th September 2007, 11:39 AM   #3
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You forgot the most important CD mod: the clock!
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Old 16th September 2007, 07:57 AM   #4
dejanm is offline dejanm  Austria
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Thanks guys for these ideas/experiences. Does anybody have schematic of the output stage ? That would be a great help ...

I would like to replace the coupling capacitors at the output, but I am not sure which one they are (I will have to open it and do some reverse-engineering).

How this clock mode should look like ?
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Old 16th September 2007, 11:08 AM   #5
Mooly is offline Mooly  United Kingdom
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There are no output caps.This is why it is important to ensure the output is nulled to zero volts as measured at the output sockets.This is best checked with 'scope set to D.C. coupling at around 1mv/division, alternatively use meter on most sensitive D.C. range.The clock on the Stage 2 is O.K. I.M.O not worth cost of upgrading as it's quite a reasonable design already.
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Old 16th September 2007, 02:11 PM   #6
dejanm is offline dejanm  Austria
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What do you think about the idea to put immediately after output OPA's Jensen transformers for RCA->XLR conversion ? And to use balanced outputs as analog outputs ...
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Old 16th September 2007, 03:33 PM   #7
Mooly is offline Mooly  United Kingdom
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Why do want balanced outputs? what are you feeding it into?
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Old 16th September 2007, 03:35 PM   #8
dejanm is offline dejanm  Austria
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Into TVC with balanced inputs ...
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Old 17th September 2007, 07:31 AM   #9
Mooly is offline Mooly  United Kingdom
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Have a look here. http://www.dself.dsl.pipex.com/ampin...d/balanced.htm
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Old 17th September 2007, 10:14 AM   #10
dejanm is offline dejanm  Austria
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Quote:
Originally posted by Mooly
Have a look here. http://www.dself.dsl.pipex.com/ampin...d/balanced.htm
Mooly, I see what you mean. There are though some other opinions about the same subject. But that is not so important at the moment. Thanks a lot for your support ...
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