Micromega Stage 2 modification - and incorrect info... - diyAudio
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Old 10th February 2009, 03:31 PM   #1
jono799 is offline jono799  Sweden
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Default Micromega Stage 2 modification - and incorrect info...

Hi,

My first post here. I've been mildly audiophile for many years, and have done minor electronic tweaking (output stages, caps, power supplies) in the past but remain pretty clueless about the digital world.

My system (a few years old...)
-Micromega stage 2 cd player
-Audiolab 8000P+C amps
-PSB stratus silver speakers

The Micromega is either leaving or getting updated. Mine has always worked flawlessly, so I must have been among the lucky few.

Possible updates are:
-Tentlabs or D-clock (www.newclassd.com) clock, with dedicated power supply
-separate power supply for analogue section (transformer, caps and regulators, like the Tentlabs shunt regulator)
-new opamps (NE5534N originally)

Any feedback/suggestions on these? Will it improve the sound, or should I go for an other player? Rather like the sound though...

One possible show stopper: Several references online suggest the stage 2 is equipped with saa7321 converter, which appears to be of rather nice quality. I opened mine, however, and underneath the mother board i found 2x TDA1305T, as I understand a budget DAC found in Cambridge DACMagic and others.

Question remains then, how much further can I go, sonically, with this converter?

Any feedback/hints/suggestions are most appreciated!

Cheers!
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Old 10th February 2009, 05:43 PM   #2
jitter is offline jitter  Netherlands
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I'm not so sure that the TDA1305 is a "budget DAC". I have a Micromega DAC1 which IMHO sounds great (as good as my Primare D20 with 24 bit/96 kHz DAC). The analogue section may be a bit more state-of-the art than in the Stage 2, though. You won't find 5532/5534 in a DAC1 and the single ended (RCA) outputs are DC-coupled; it also has balanced outputs (XLR). And yes, the DAC1 also has the TDA1305.

My suggestion would be to start with the analogue section (the attachment is the analogue section of the DAC1).
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Old 10th February 2009, 05:47 PM   #3
Mooly is online now Mooly  United Kingdom
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I have a Stage 2... wouldn't swap at the moment for anything. Owned from new and modded as follows. The "first" Op amp from the DAC is the I/V convertor, I replaced this with OPA604AP and the buffer with AD845JN. The output from pin 6 to the muting relay, cut the print and added a 68 ohm series resistor to isolate the output of the Opamp from any cable capacitance. Add a 0.1mfd across the supply pins of the OpAmps soldered on the pins, not supply to ground. I also replaced ALL the electroylitics in the whole unit, adding 0.1mfd surface mount caps across most of these on the print side. They fit perfectly, looks factory original. I also added a TOSLINK output ( fitted to the removable aluminium plate ) on the rear for connection to a Mini Disc recorder.
It's an amazing player even after all these years. I was lucky, got hold of a new Japanese CDM12.4 mech which I fitted recently.
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Old 10th February 2009, 05:54 PM   #4
Mooly is online now Mooly  United Kingdom
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One other thing, the multiturn pot sets the output at zero volts dc, and this limits your choice of OpAmp unless you mod that part of the circuit. The AD845 will work as is and sounds great. Worth doing IMO. Also the board is not easy to work on as all the holes are plated through vias so you will have to cut each leg of the IC to remove, then use braid or a sucker.
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Old 10th February 2009, 05:56 PM   #5
EUVL is offline EUVL  Europe
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> The "first" Op amp from the DAC is the I/V convertor....

Isn't it true that the TDA1305 has built-in IV converter and is therfore a voltage-output DAC, at least according to the Datasheet ?


Patrick
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Old 10th February 2009, 06:02 PM   #6
Mooly is online now Mooly  United Kingdom
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There is an inbuilt OpAmp yes, I even looked at eliminating this but decided it wasn't worth the hassle, it just sounds so good as is. Have listened to stuff like the new Sugdens etc, and the Micromega can still hold it's own.
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Old 10th February 2009, 07:48 PM   #7
jono799 is offline jono799  Sweden
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Thanks for replies and tips!

Feedback like this is exactly what I need, the feeling I had about keeping the stage 2 is definitely reinforced. But it will not go unaltered (the player, that is...) !

I'll definitely look into the analogue stage. AD845 could be an option, and I have seen others recommending OPA627 or AD797. Hard to know which is best, I've never listened to any of them, haven't checked availability either.

jitter: Thanks for the DAC 1 picture, I tried to see what kind of opamps that were close to the multiturn pot in your picture, as I guess that would be the buffer, but I'm not able to read the text on it. It could look like LT1227, is that right?

I'll still check out the clock upgrade though, no fortune and fun to fiddle with.
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Old 11th February 2009, 06:24 AM   #8
Mooly is online now Mooly  United Kingdom
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The AD797 will require modification to the circuit for the offset null to work correctly. I would definitely try the opamps first before even thinking about any clock mods. The clock is closely integrated into the PCB design and adding a separate unit may make things worse, it's as much to do with layout as anything, sending the clock signal down an inch or two of wire can negate any benefits. I chose the opa604 because it has even harmonics as the predominating distortion, which is the most pleasing to the ear. Beware of using any ultra hi bandwidth opamps, they are just not needed for CD. I also don't like sockets, and please don't underestimate actually removing the devices to begin with. You will have to cut them out and clear each hole separately, the PCB is of extremely high quality but some of the print is very fine... beware. But it's all worth it !
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Old 13th February 2009, 09:32 PM   #9
jono799 is offline jono799  Sweden
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So out went the AD797. I'm not wanting to fiddle with the rest of the output circuit.

Talked to Guido Tent yesterday though, he recommended OPA134 over the AD845. I'm not gonna let this descend into an opamp thread, but does anyone know if the 134 can be used directly in the Stage 2? I might want to install sockets and listen to both.

Mooly: You mean you just added the resistor across the cut in the print?

thanks!
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Old 14th February 2009, 12:38 AM   #10
jitter is offline jitter  Netherlands
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Quote:
Originally posted by jono799
jitter: Thanks for the DAC 1 picture, I tried to see what kind of opamps that were close to the multiturn pot in your picture, as I guess that would be the buffer, but I'm not able to read the text on it. It could look like LT1227, is that right?
LT1227 is correct.
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