Great, would really like to try it before swapping the m2 boards for the sissysit. Sissysit for witch I’m still waiting patiently for the cinemag’s to show up! 😱
How to Schade your beloved M2 amp
Step 1 :cut trace between pin 4 of optocoupler and R7-R9 common node , insert new (Schade) resistor ; best to place two 1pin sockets , easier to change resistors ; once you make up your mind , solder resitor in sockets and that's it ; start with 3K6 ;decide by ear - go up for more sugar , go down for less sugar ; of course - power down amp while changing resistor
Step 2. desolder positive output speaker wire from pcb , solder it to other end of R14 , practically on drain of IRFP9240 or whatever you have in its place
Step 3. power up the Beastie , input shorted , no load ;check Iq ( voltage across any of source resistors , 0R47) , fiddle with P1 to set 0V of output offset ; if you can't ( trimpot on end ) , DC offset is most probably still negative - solder additional resistor across existing R6 , say that 150K is bingo , from top of my head
Step 4. let it cook for a while , re-set DC offset in temp equilibrium , re-check Iq , connect speakers and enjoy
don't forget top re-set DC Offset every time you change Schade resistor value
Step 1 :cut trace between pin 4 of optocoupler and R7-R9 common node , insert new (Schade) resistor ; best to place two 1pin sockets , easier to change resistors ; once you make up your mind , solder resitor in sockets and that's it ; start with 3K6 ;decide by ear - go up for more sugar , go down for less sugar ; of course - power down amp while changing resistor
Step 2. desolder positive output speaker wire from pcb , solder it to other end of R14 , practically on drain of IRFP9240 or whatever you have in its place
Step 3. power up the Beastie , input shorted , no load ;check Iq ( voltage across any of source resistors , 0R47) , fiddle with P1 to set 0V of output offset ; if you can't ( trimpot on end ) , DC offset is most probably still negative - solder additional resistor across existing R6 , say that 150K is bingo , from top of my head
Step 4. let it cook for a while , re-set DC offset in temp equilibrium , re-check Iq , connect speakers and enjoy
don't forget top re-set DC Offset every time you change Schade resistor value
Attachments
really interesting amp: the sound is between M2 and DefiSIT, rather like M2 on steroids.
tube like sound, with strong separation and deep stage, a bit sofr, just enough to be intriguing.
Or if you have been semi-clever and socketed your 6-pin critter, you may lift pin 4 and solder the Schade resistor directly to the leg. Classic rework- even IBM shipped early PC motherboards that way.
Something else to try when I’m back in my workshop.
Something else to try when I’m back in my workshop.
few lines more needing to stay in contact with Pin4 of Opto , so no go soldering resistor ditto to leg
I have tried the sef mods on my m2 with teabags boards. I have found an easy to try it without taking out the board or cutting traces.
I have listened to the amps for 2 days and it was not conclusive for me. I have tried with 2k5 and 3k9 schade resistor. For me the sound was a little bit more blurry especially in the hi end of the spectrum. Little bit less authority in the low end too. Maybe would be different with the cinemag instead of edcor?? Now I’m back to stock m2 and I’m quite happy again.
I have attach some picture of how I have done the mods if somebody want to try it. 30min max to unsolder one side of r7 r9 and to attach the schade resistor and to recalibrate offset.
Hubert
Attachments
Oh I forgot about that... 😎
I’m not sure I understand this concept.. If you reverse the polarity at the speakers, not only the harmonics flip polarity but also the fundamental? Why does that change something to the sound?
I said - it's more sugar 🙂
everything else you can conclude from measuring graphs
btw - did you moved LS + output?
everything else you can conclude from measuring graphs
btw - did you moved LS + output?
Yes I did, you can see on he second picture the added socket directly on q2.
By the way I always enjoy trying different topology/mods even if I go back to previous version. For me it’s part of the process of finding what my ears like/don’t like! 😉