Official M2 schematic

[xrk971]

Wdecho,
Thanks! 🙂

This amp is for testing only and probably won't get a box (like 99% of my amps). However, good point about being careful with covering it in case one drops a screw driver or other piece of metal - be prepared for arc welding.

I learned accidentally the power of a 400va toroidal trafo. I was testing something and did not have a fuse yet. Accidental short instantly smoked the piece of 16ga copper wire in 2 seconds. Vaporized the insulation and left a mess. Nonetheless - learned my lesson to always have a fuse in place when testing.

 

[Bangla H]

I believe you'll find that answer few pages back

Thank you ZM.
will go read back and learn.

 

[xrk971]

Now that I have run the M2 for a while and measured the max current draw at 1.3amps. With class A the current doesn't seem to change with music playing. So I am thinking to myself: do I really need a big 400va trafo to make 25v rails? I have a 24v 3amp SMPS that I could easily put two in series with a center tap for a 24v dual rail supply that should handle the 1.3A no problem. I could technically power a stereo pair of M2's from a pair of the SMPS as the rating is 3amps. I may just try it and see. I think ripple of the SMPS going through the CRC PSU's should make ripple even less than 19mV. Maybe 1mV even?

 

[chrismercurio]

Hi,

Is there a relatively easy way to scale up the M2 for higher power that retains the overall character? Alternatively, since I have a stock unit, how can they be converted to mono?

Thanks,

 

[xrk971]

With other MOSFET output amps I have successfully scaled up by doubling the outputs and splitting the gate drive into two paths. As MOSFET gates are high impedance, so you can drive more than one with a single driver. I always model it first to make sure it works in the sim. I wonder if another set of outputs can be added here.

 

[syklab]

Did anyone try to run the M2 above 24VDC ? Any change required on the circuit ? I have a transformer with 20AC output and want to see if I can use it for the M2.

Thanks

 

[generg]

Did anyone try to run the M2 above 24VDC ? Any change required on the circuit ? I have a transformer with 20AC output and want to see if I can use it for the M2.

Thanks

Poor J-Fets at the input......need of cascoding.

 

[Zen Mod]

build bigger FW amp = BA3

Greedy Boyz are sometimes too greedy

lets see few moments , needed for more watts :

-greater swing ....... means more Vpp through autoformer ; test behavior by your self

-higher PSU rails , input Jfet needs cascoding ; no problem , shown and done myriad times ..... but you need to choose cascoding way which will not impede swing envelope


-need for increased gain through autoformer ....... demanding different one ; issue of output impedance of buffer/autoformer combo ; test behavior by your self

-more output pairs ; not overly critical , but still of importance , in combination with previous issue ; test behavior by your self

 

[generg]

I tried one output pair more some time ago and the sound was worse than with one pair for my ears.

 

[xrk971]

Just built this simple Apex Audio preamp (10.3dB gain):

http://www.diyaudio.com/forums/soli...imate-fidelity-amplifier-861.html#post4822088

Clean and transparent with just enough gain to make the M2 loud enough with my usual inputs. Conveniently, it uses same 25v rails as M2, so it's easy to add on without any extra PSU considerations.

 

[Zen Mod]

try something in line with M2 spirit , not stage with ton of NFB

that preamp is decent , but not sharing most of M2 virtues

 

[xrk971]

You mean like BA-3?

 

[massimo]

That schem is named for "Fet Stereo Pre-Amp", but where are the fets?

 

[2 picoDumbs]

You mean like BA-3?

Or simple buffer or simple buffer with gain, aka The KISS

 

[gadut]

Just built this simple Apex Audio preamp (10.3dB gain):

X, thats not simple, very complicated design just for preamp, look at so many transistor simbol

for me who enjoy soldering rather than understanding basic EE, what I call simple is like BA3 pre, ZM iron pre, or Luminaria

ahh, maybe thats why i love this subforum rather than solidstate 😀

 

[ElFishi]

You mean like BA-3?

too much gain.

I did this.

 

[xrk971]

It's all symmetric and that's two channels - just look at veroboard implementation. I agree 6 transistors is a lot more than the 4 on the M2 but there's very low distortion as a result. Yes, this is usual stuff from SS forum but it drives me nuts that a power amp doesn't come standard with 24dB to 30dB gain like the usual designs on SS forum. We don't need no stinkin' preamps for those cases. Also, let me ask you all this question: is an amp with 4 transistors really a simple 4 transistor amp when it requires a preamp to be useful?

 

[ElFishi]

I only use the pre-amp when I need the volume, i.e. almost never.
Normally it is bypassed.

 

[xrk971]

That schem is named for "Fet Stereo Pre-Amp", but where are the fets?

Typo because there is a FET variant with sk170/sj74's and Apex forgot to rename drawing:

Maybe I should have made this one - perhaps more acceptable to this forum?

 

[xrk971]

too much gain.

I did this.

That is indeed clever and simple. How much gain do you get and what is added distortion like?