Official M2 schematic

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#3,583
Good evening, friends

I completed an M2 build this weekend but apart from the one Edcor transformer having broken wires the left channel suffers from DC offset drifting. It drifts as much as 200mV as a slow tempo - let say taking about 1 minute to do a full swing and bobbing back. Could this be the Opto-coupler? I have replaced the bias diode string. The DC offset pot does adjust the offset as well as the right channel. I have compared the voltage measurements between the channels on all points and everything checks out.

I have also scoured the thread to see if someone experienced the same issue but could only see the issue with the transformer wires that's broken.
 
#3,586
KevinHeem said:
@deltavektor

Just to clarify...you're talking about two seperate issues? (1) A broken wire on one of the Edcor's windings (which you repaired?) and (2) DC offset is slowly drifting in one channel. Is that correct?

I would think the transformer should go back to the factory for replacement.
Click to expand...
Both these problems are on the one channel. The transformer is now fixed but the DC offset is doing a very slow see-saw drift. Too slow to be called a subsonic oscillation but I guess the term fits.
 
#3,592
no damage

I asked for gate resistors, there is a chance that you have slightly misbehaving mosfet , on the verge of collecting HF in gate, so slightly increasing gate resistor could help

only one way to check that

btw. bad opto should result in wandering Iq, not output offset

so, if you trust that everything is decently soldered, try gate resistors first
 
#3,594
Zen Mod said:
no damage

I asked for gate resistors, there is a chance that you have slightly misbehaving mosfet , on the verge of collecting HF in gate, so slightly increasing gate resistor could help

only one way to check that

btw. bad opto should result in wandering Iq, not output offset

so, if you trust that everything is decently soldered, try gate resistors first
Click to expand...
I will certainly have a try at the gate stoppers and report back.
 
#3,595
Cinco said:
In my M2 clone, I added a 1R3 ohm resisitors in parallel with the original 0R47 source resistors to lower them to 0R345.
I simply removed them from the R2 positions and zeroed the output offset to try favoring the P-ch. It raised H2 to about the same level as H3 as seen in the measured spectrum.
I like the sound, more relaxed and spacious was my impression. I'll leave it like this for a while.
I need to get a twin-T notch filter built to look at the residual distortion in real time.

Cinco
Click to expand...
After what felt like YEARS of trial and error, I finally got my old sound card to talk to the DiAna s/w thru ASIO4ALL. So here's the residual distortion as seen in DiAna at 1W into 8ohms. Finally a way to confirm H2 (and H3) phase in vivo... yep it's negative.... cool
 

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  • M2 more 1W P ch1 H2 phase.PNG
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  • M2 L-Ch 1W 1kHz more P-ch.png
    M2 L-Ch 1W 1kHz more P-ch.png
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