I talked to Nelson Pass about the transformers once. He said that First Watt assigned a summer intern to measure the frequency response of every incoming Edcor transformer, so they could eliminate the outliers and only ship the good ones.
Whether IPS_Zout interacts with the Zobel, producing a perceptible change in the sound of the amplifier, I have no idea. It certainly does vary by a factor of at least 500-to-1 across the five M2x daughter cards. Thanks to the presence or absence of integrated circuits and their enormous Avol at DC. It'd be fun to mock up a modified Tucson board which adds a 1 watt 100 ohm trimpot (and bypass jumper) in series with the output. What Zout sounds best to your ears, Mr. Wurcer?
I'll find out eventually, packing now for hopefully the last move. Any classic through hole parts you might need, rms converters, in-amps, multipliers, etc. No fakes, I guarantee (sorry I gave my last AD1862/65's away a couple of years ago).
Vishay | Mills source resistors is new product in stock at Mouser.
Not very cheap 4 pcs.= 10$
https://eu.mouser.com/ProductDetail...=sGAEpiMZZMtbXrIkmrvidNRNJp1YrdA3CgRAAiLyIXI=
another type is MPC74 made by Futaba Company in Japan cost 5 pcs.= 5 $
RS have this in stock from time to time.
MPC74 0R47 J | Fukushima Futaba MPC Series Solder Metal Plate Resistor 470mΩ +-5% 5W +-350ppm/degC | RS Components
https://docs-emea.rs-online.com/webdocs/156d/0900766b8156d150.pdf
Smooth music with superb clear and deep jumping bass.
Try by Yourself don't believe me
Attachments
It is interesting to note that the 3W resistor proposed in the BOM, while of higher tolerance (5%) has a flat derating curve up to 70ºC (which is the temperature mine are working at in the ACA amp).
The ones by Vishay, while narrower tolerance (1%), start loosing power at 25ºC, and by 75ºC have around 80% of the rated power. Would that affect some characteristics of the amp?
Best regards,
Rafa.
Say no more, we never put 797's in the white ceramic (those packages were very gold intensive) but I can find a few other candidates. I think I have some cerdip 797's though.
Member 6L6 measured the AC power consumption of his M2x. You could use his measurement to estimate the power dissipated in R13 and R14.
Assume DC power = AC power measured by 6L6; i.e. no power dissipated in the CL60 inrush current limiters and no losses in the toroidal power transformer. Assume the input stage and the optoisolator stage (bias stack) consume negligibly small amounts of power.
The 2 x 18VAC transformer + First Watt power supply design, produces plus and minus 23 volts DC.
Then DC power = 2 x (23 volts) x (DC current) = AC power measured by 6L6
Then DC current = (1/46) x (AC power measured by 6L6)
Half of the current flows in the Right Channel amplifier board, and the other half flows in the Left Channel amp board
Then current in Right Channel R13 = (1/2) * (1/46) * (AC power measured by 6L6)
Then power dissipated in Right Channel R13 = 0.47 ohms * DCcurrent * DCcurrent
and boom you're done. Compare calculated power in R13, versus its power rating and versus its datasheet.
Since M2x is a Class A amplifier, max power dissipation occurs at idle, with no input signal. It's a DC calculation.
Just find out what AC power consumption member 6L6 measured on his M2x, and tap a few keys on a calculator. It's not rocket surgery.
You could also look it up in the First Watt M2 manual. It's right there on page 10 of the pdf file.
Assume DC power = AC power measured by 6L6; i.e. no power dissipated in the CL60 inrush current limiters and no losses in the toroidal power transformer. Assume the input stage and the optoisolator stage (bias stack) consume negligibly small amounts of power.
The 2 x 18VAC transformer + First Watt power supply design, produces plus and minus 23 volts DC.
Then DC power = 2 x (23 volts) x (DC current) = AC power measured by 6L6
Then DC current = (1/46) x (AC power measured by 6L6)
Half of the current flows in the Right Channel amplifier board, and the other half flows in the Left Channel amp board
Then current in Right Channel R13 = (1/2) * (1/46) * (AC power measured by 6L6)
Then power dissipated in Right Channel R13 = 0.47 ohms * DCcurrent * DCcurrent
and boom you're done. Compare calculated power in R13, versus its power rating and versus its datasheet.
Since M2x is a Class A amplifier, max power dissipation occurs at idle, with no input signal. It's a DC calculation.
Just find out what AC power consumption member 6L6 measured on his M2x, and tap a few keys on a calculator. It's not rocket surgery.
You could also look it up in the First Watt M2 manual. It's right there on page 10 of the pdf file.
Low temperature coefficient ppm is always better , all resistors types are different :
materials, mechanical construction for example metal film compare to metalband etc.
0R47 Panasonic 3watt's are very good too but for make low resistances values = less 1 Ohm match ,
we need multimeter with 4 wires Kelvin mesurements option.
Yes resistors affect little charecteristics of the amp ( let's try build one M2 with carbon composite haha ) , capacitors much more and input transformer and transistors influence ( sweet spot ) to the final sound are huge
Best regardsGood luck with the move, Scott. I wish I was close enough to pack up a box of your stuff and add it to my stuff in the basement. My daughters are going to be cursing when I make the real big last move.
Depending upon how much empty space you have inside your chassis, one or the other of these two Antek transformers would be an excellent choice:
Click on the three little thumbnail images at the left side of the web page, to see photos and datasheets.
Click on the three little thumbnail images at the left side of the web page, to see photos and datasheets.
Thanks for the answers!! So, if I were to plan in advance to buy parts to build an M2x when the PCBs are available and have the case also compatible with, say, a future F6... is there any chance to make the PSU more or less 'universal'? One requires +-25V while the other is listed for +-23V ... (although the schematic for the F6 PSU is identical to the one posted by Soundhappy, so not sure what makes those +-2V difference?).
Maybe I'm just over complicating things and there is no need for both and their similarities would make building both a bit redundant... I just wanted to know if there is a way to make it a truly 'universal' PSU for the different FirstWatt amps or if there are enough differences that require each to have a different PSU.
Thanks.
Rafa.
ps. Perhaps this was better asked in the PSU thread? Still, since the M2x is the on I will most likely build first, I jumped here first.
Maybe I'm just over complicating things and there is no need for both and their similarities would make building both a bit redundant... I just wanted to know if there is a way to make it a truly 'universal' PSU for the different FirstWatt amps or if there are enough differences that require each to have a different PSU.
Thanks.
Rafa.
ps. Perhaps this was better asked in the PSU thread? Still, since the M2x is the on I will most likely build first, I jumped here first.
