Replace output opamp NE5532

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#2
OPA2604 Give it a try, I have used to very good effect to replace NE5534 in my Micromega Stage 2 (Used a OPA604 of course). I believe the distortion spectrum has even harmonics as predominating, which is more pleasing to the ear. I know some swear by some of the latest op-amps on the market but I would urge you to try these first.
Regards Karl
 
#8
Op Amp Tweaks?

Hi All,

Are the OPA2604 and LM4562 dual Op Amps?

I know there are tweaks putting a small ceremic cap across pin 4 & 8, and also putting resistors across pin 1 & 4, and 4 & 7 to have a class A bias.

Do these 2 tweaks work for OPA2604 and LM4562?

I am thinking of modding my newly acquired Micromega Stage2 (used).
 
#9
Hi, I too have MM Stage 2 and can recommend following. Replace the four NE5534 Op-Amps as follows. For the output buffers, they are the ones nearest the output sockets use AD845JN, for the I/V convertors use OPA604AP. You will find the I/C,s VERY difficult to remove due to the plated through vias, and I would recommend using very small sharp snips to cut each I/C out (cut as close to the package as possible), then use braid to clear holes which is also made easier if you use a thin piece of stainless wire to help clear the hole. I also cut the print to each output (the track that goes to pin 6 of the buffers) and bridged this with a 68 ohm surface mount resistor. This ensures total stability with any capacitive load. You probably would not need to do this though. The small multiturn trimmer next to each buffer is used to null any D.C. offset and you need a meter on its most sensitive D.C. voltage range to adjust. Set for ZERO volts on outputs NO disc playing. You will not be disappointed. There are other mods but these have the greatest gain in my opinion.
Please let us know how you get on,
Regards Karl
Edit The Op-Amps you mention are dual. Micromega uses single.
You may feel happier using socket,s if so recommend neatly soldering small bypass cap directly across pins 4 and 7 of the I/C - observe polarity if electrolytic.
 
#11
MM Stage 2 Help

Hi Karl,

Thanks for the info. What do you recommend for single Op Amps to be used in MM Stage2?
Do you think biasing to class A will be a good idea?

I just open up the MM Stage 2 and I suppose the digital section and the analogue section are seperated with different board.
On the analogue board, I see a lot of red and blue caps. However the print on all of them are very blur.

I suppose the red ones are 150pf and the blue are 100pf.
If that is the case I plan to change these to polystyrene caps which sounded great when I did that for my old Marantz.

I'm searching for better elec caps and will bypass them with poly caps once changed.

Thanks for all your help.

Cheers.
 
#12
Hi, Use OPA604AP to replace I/V convertor, AD845JN to replace output buffers (the two nearest the sockets). The offset null pot is not configured correctly to work with the OPA604s or you could use these all round (you would need to reconnect the wiper of the pot to the negative rail rather than the positive as now). I would not recommend changing any caps at the moment, try the opamps first, and be careful unsoldering parts as I said earlier. It looks easy, but unless you are use to working on double sided boards, those plated through "vias" will cause difficulties. You can bypass the electroylitics as you say, I replaced all mine with low "ESR" types (Panasonic and Elna) and bypassed each one underneath with a 0.1mfd surface mount cap which fits perfectly the 5mm lead pitch. The Op-Amps run in class A anyway for all small signal conditions, and adding a resistor or current sink/source will just increase dissipation as the Op-Amp is forced to counter the extra load. Sorry, I know some will disagree on this point ! Anyway above all ENJOY and do let us know how you get on with this.
Karl
 
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