Official M2 schematic

[Zen Mod]

as I see it - voltages you measured around JFets are ok

one thing - if you don't have chassis yet - did you heatsinked output mosfets for these first tests?????

[darrr]

I used a replacement heatsink. Too small to work but sufficient to run for measurement. When I turned off the mosfet temperature it was around 100 ° CIMG_20190902_172323.jpg

[Zen Mod]

good

and I thought that I'm sole dumb kwayzee lucky bstrd around

leave it in cardbox , please , while waiting for proper chassis

[darrr]

Good advice . Chassis and pair of jfets....

[metallicus69]

I have built only the final stages, 2 stages per channel, to be driven by a differential Aikido tube stage. I was always looking for a Vertical stage in place of the Laterals used at Moskido. And this seems to be a great solution.
My problem is that the static current through each MOSfet is around 1,15A at 24V supplies and 1,3A at 30V supplies. The offset is quite stable after warming up to 55-58C and easily set after changing the P1 to 10kohms and R7 to 51kOhms.
Decreasing R13 and R14 to 0,33 would bring the current over 2,2 A, so probably I should rather increase R11.
The question is: should I aim to increase it more? Is it 1,2A enough considering a dual stage (so 2,4A in total per channel) driving 8Ohm speakers? Or will it leave the A class too early?
Thanks for your time to read my post and applologies if this is not a good thread for my questions!

[Zen Mod]

if you're content with sound , leave it

for gradual increase of Iq , try increasing resistor in series with opto-led

sensibly,please

[aljordan]

Is there an ideal voltage for the power supply to be delivering to the M2 boards under load? My power supply is delivering ~ 21.2 volts under load, and my heat syncs are not very warm, so I am wondering if I should do a little work on the power supply.

Thanks

[Extreme_Boky]

The transformer specifications should say 2 X 20V AC at the secondaries... to begin with.

Some transformer manufacturers will let you specify the secondary voltage in 1V increments, so 2 x 21V AC might be perfect.

The voltage sag will also depend on the transformer VA rating; the higher the VA, the lesser of a sag.

I use 230V-specified transformers, at 2 X 20V AC, connected to 240V mains.... so that gives me around 2 X 21 V AC or so.

Of course, the quiescent current per each output transistor will also influence the whole thing.

It is also important to remember that mains voltage could vary substantially, depending on your electricity provider/distribution network. Just another factor to take into consideration.

There's a bit of a voltage drop across the thermistor as well.

Also, the power dissipation is directly proportional to (an increase) of supply voltage... so with 5U / cooler climates, it ain't gonna be a problem.

[metallicus69]

Originally Posted by Zen Mod

if you're content with sound , leave it

for gradual increase of Iq , try increasing resistor in series with opto-led

sensibly,please

Thanks!

No extensive sound auditions yet, I have to build the solid state protection relay first and connect everything in the boxes; at the moment I am just testing the static and thermal parameters, to be sure they will survive.
I did some audition with them though directly from a headphone output to the power buffer and the sound seemed ok in my modest test speakers.

As all is done p2p It would be easier to replace the 0R47 resistors with 0R33 but I don't feel like it will be a good idea, so I will probably leave it as it is.

[aljordan]

Originally Posted by Extreme_Boky

The transformer specifications should say 2 X 20V AC at the secondaries... to begin with.

Some transformer manufacturers will let you specify the secondary voltage in 1V increments, so 2 x 21V AC might be perfect.

The voltage sag will also depend on the transformer VA rating; the higher the VA, the lesser of a sag.

I use 230V-specified transformers, at 2 X 20V AC, connected to 240V mains.... so that gives me around 2 X 21 V AC or so.

Of course, the quiescent current per each output transistor will also influence the whole thing.

It is also important to remember that mains voltage could vary substantially, depending on your electricity provider/distribution network. Just another factor to take into consideration.

There's a bit of a voltage drop across the thermistor as well.

Also, the power dissipation is directly proportional to (an increase) of supply voltage... so with 5U / cooler climates, it ain't gonna be a problem.

I used a 2 x 18 volt 300 VA transformer. I thought the first watt power supply specified 18 volt. Does the M2 specify 20 volt?