MX50 LAST VERSION - probably the best

[Stee]

hi
before was a perfect CFP amp
now is a quasi-complementary masterpiece
Assembled Stereo MX50X2 CLASS-AB Power Amplifier Board For Audio Project | eBay
better with output transformer

[kenpeter]

Sure works, but not even close to compliment, quasi or otherwise.
Q13 and Q17 without emitter degeneration will determine Voltage.
Q12 and Q16 with emitter resistor will determine outstage current.
SRPP behavior is what you got...

R27 and R22 in series with collectors are doing absolutely nothing.
If you can't be bothered to monitor currents through them? DNI...
But I would be watching them in quadrature to shape a class and
define a quiescent in some manner that forces a compliment.

I swear I seen and fixed this schematic before, where was it???
Even marked where to cut and jump the layout to get collector
resistors functioning as proper part of the quasi equation.

[Stee]

I swear I seen and fixed this schematic before, where was it???
do you have?

[kenpeter]

Regarding collector resistors:

I tried the ebay MX50 DIY Kit, Class AB 100W+100W; Worked but problem.

I tried the ebay MX50 DIY Kit, Class AB 100W+100W; Worked but problem.

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Someone else noted that Q2 is (was) drawn backward in an earlier schematic.
But kit included a non-standard pinout version of 5551 transistor to correct it.
Looks like your version, Q2 orientation in the drawing appears to be fixed?
I wonder if Q2 pinout and layout on the PCB are now oriented properly?

[ljm_ljm]

MX50X2 does not mean MX50. They are two different.
MX50X2 music derived from the MF X-A50 Musical Fidelity models, it is a quasi-complementary circuit, have a good musical.
MX50 is a CFP output circuit with low distortion.
Their circuits are correct, but some parts are not standard. Can not change parts instead.

[kenpeter]

If this was a faithful clone of Musical Fidelity, the original might
also have same mistake? I'm not saying it isn't musical. Only that
CFP degenerated by emitter resistors on pull side, but not in any
way similarly degenerated or protected from runaway by useless
collector resistors on push, is not how a quasi-compliment works.
Low distortion SEPP it might be, fine music alone does not prove
quasi-compliment behavior claims have been achieved.

If schematic (LJM LJM) is same as shown at Stee's link to Ebay?
The disputed collector resistors are implemented incorrectly and
not doing anything useful, but this oversight is very easily fixed...

The fix to bring collector resistors into the quasi equation does
not change bill of materials, nor alter any pinouts. But it does
cut and jump traces, so is a destructive modification to the PCB.
I would understand if you chose not to endorse doing so.

I am aware that some of the included parts have non-standard
pinout to match with actual layout. And cannot be substituted
for the standard pinout, even of the same generic part number.