Official M2 schematic

Jump to Latest
#2,363
I have used an LED and a 1k resistor for R15 on the PCB thinking that it was just a power indicator. Looks like it is in the bias circuit. Looks like I need to eliminate them out of the circuit.

I believe the LED was provisioned by Grimberg for additional bias requirements.

Regards
 
#2,367
The pins/footprint for Q6/Q7 (LM385-1) regulators and JFETS are close/tight to each other. Make sure that there are no shorted solder connections. Also, there are only few resistors/components so double check values absolute correct (SOP to measure before inserting component).
 
#2,368
Help on M2 build

Zen Mod said:
please post actual schematic and pictures of build

write down what is voltage across source resistors , what is exact (minimal) DC offset you can get with trimpot on end , taking care of proper polarity (probes)

then we can help with more specific steps
Click to expand...

Hi,

Here are the readings:

Left Channel:

Minimal offset with trimpot adjusted +2.78V

P channel Source resistor voltage .. 0.667V
N Channel Source resistor voltage .. 0.673V

Right Channel:

Minimal offset with trimpot adjusted +4.09V

P channel Source resistor voltage .. 0.688V
N Channel Source resistor voltage .. 0.690V

As mentioned earlier I have used random set of Toshiba 2Sj201/2SK1530 pair (vgs of which I have never measured) and these were removed from my working F5 amp. May be there is a huge variance on the output transistors.

I do have very well matched IRF pairs and also a Fairchild Pair with a 1 volt VGS difference between N and P parts. I can replace the outputs if that is the reason for this huge offset voltage.

Thanks in advance.

Anil
 
#2,369
anilva said:
Hi,

Here are the readings:

Left Channel:

Minimal offset with trimpot adjusted +2.78V

P channel Source resistor voltage .. 0.667V
N Channel Source resistor voltage .. 0.673V

Right Channel:

Minimal offset with trimpot adjusted +4.09V

P channel Source resistor voltage .. 0.688V
N Channel Source resistor voltage .. 0.690V

As mentioned earlier I have used random set of Toshiba 2Sj201/2SK1530 pair (vgs of which I have never measured) and these were removed from my working F5 amp. May be there is a huge variance on the output transistors.

I do have very well matched IRF pairs and also a Fairchild Pair with a 1 volt VGS difference between N and P parts. I can replace the outputs if that is the reason for this huge offset voltage.

Thanks in advance.

Anil
Click to expand...

Replaced the Toshibas with Fairchild output devices withknown vgs. Also recleaned the close spaces on the jfets and lm385s transistors. Some or all of it worked. Nicely adjusts now to under 10mv. Thanks for the advice. Now to test the amp with my Altec horns!

Cheers
Anil
 
#2,373
Finally played my M2. Zero startup thump or switch off thump. Cannot make out that amp is on with ears close to speakers. When fed with music, the amp comes alive with full dynamics. Terrific dynamic range and clarity. Cannot make out which of Pa’s amps are great, because all of them are. My ears have got numbed listening to some great amps from Papa. Cannot out make out which is better.

Great addition to my Pa’s amp collection. Next is VFET 2.

Thanks to Pa and this forum for giving me years of Joy. May the tribe grow!

Merry Christmas and a great new year!

Cheers
Anil
 
You must log in or register to reply here.
Top Bottom