Official M2 schematic

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#3,063
Russellc said:
Sorry, not making myself clear, What I mean to ask is the use of the 220uf that mark's design contemplates wont end dc at the speaker taps will it? The original pot from PAPA's schematic will have to bring that to zero, right? or No?

Russellc
Click to expand...

Yes. My understanding is that 220uF cap will just remove any DC at Edcor input. You still have to use the original pot to bring the offset down to zero at the output of the amp.
 
#3,066
My M2 clone

More images here: Do It Yourself Audio Projects | First Watt M2
It plays music and sounds great, first impression - very dynamic with strong bass. I hear a bit of buzzing with my ear by the speaker, will have to put some screening around transformers...
 

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#3,072
Hi, I am thinking to modify the M2 schematics to serve as a preamp. The target output voltage will be about 6VRMS and 2VRMS (two candidates for different system setups and final decision will be made after comparison).



What fets would your kindly suggest to replace the orignal M2 fet complementary pair to suit my need? J310? 170BL？ Or anything great and easily available? Thanks.
 
#3,073
If you're starting over you could consider replicating the stage1 function ("unity gain buffer capable of driving 600 ohm load") using a different circuit design. One possibility that has worked for me, is an IC opamp configured as a unity gain buffer, with or without a current booster. {Norwood and Tucson respectively}. Or you could try a BJT diamond buffer {Austin}, or perhaps a J112 source follower with a current booster {Mountain View}. I've used them all and they got the job done beautifully, in my opinion.

Since you plan to "modify the M2 schematics" keep in mind that you do have the option to discard complementary JFETs entirely.
 
#3,074
Hi, Mark,


Thanks. Yes I am open to all voltage follower possibilities. But I suppose that the complementary source / emitter follower gives lower distortion? So I thought maybe I would simply look for FET replacement in the M2 circuit and then do some simulation.



Anyhow, I will look into the circuits you suggests. Thanks again.





W. YAN
 
#3,075
wyan said:
...What fets would your kindly suggest to replace the orignal M2 fet complementary pair to suit my need? ...
Click to expand...
Originals were from Toshiba but matched replacements manufactured by Linear Systems currently available from diyAudio Store perform adequately.
wyan said:
... But I suppose that the complementary source / emitter follower gives lower distortion? ...
Click to expand...
Not necessarily correct. When lower distortion is desired, either the Tucson or Norwood input module that Mark Johnson designed for the M2X shows high potential to deliver. Sonic impression and your personal preference however, obey different set of rules altogether.
 
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#3,076
Hi, Indra1,



Thanks for the advice. I did a search and there are a lot of preamp circuit involving 170/74 pair as the final stage. However, the replacement price by Linear Systems is not really favorable. Therefore I am still looking for more affordable replacements. I will look into the Tucson and Norwowd module. Cheers.





W. YAN
 
#3,078
I had a catastrophe because of a dry joint on the optocoupler, I saw smoke coming up from the board but can't figure which component it was. At that time, the voltage across the source resistor went up to about 1.7V. After doing a solder reflow, I managed to get the channel up and running but at a lower voltage, 0V555 versus 0V572 on the other.

I know its working somewhat, but for the long term reliability and ease of mind, what should I think of replacing with new parts?
 
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