I'm building my second M2x, this one is for me to play with (first M2x build resides at my folks place).
I'm curious if anyone has tried the Fairchild FETS FQA12P20 / FQA19N20. If so any comparison to the IRFP240 / IRFP9240. I was gifted a set of the Fairchilds from a very generous fellow DIYer for just such a build.
I see @Bones13 mentioned using "Fairchild" FETS, but wasn't sure which type and my thread search so far hasn't turned up anything.
I'm curious if anyone has tried the Fairchild FETS FQA12P20 / FQA19N20. If so any comparison to the IRFP240 / IRFP9240. I was gifted a set of the Fairchilds from a very generous fellow DIYer for just such a build.
I see @Bones13 mentioned using "Fairchild" FETS, but wasn't sure which type and my thread search so far hasn't turned up anything.
Haven’t used the Fairchilds in M2x, (but have in F5T, BA-3, and Aleph J) generally speaking, they are fantastic sounding devices and I’d look forward to hearing them in M2x.
🙂
🙂
Thanks Jim, I think I'll give them a try!
Anyone have thoughts on if I should be changing any resistor values to accommodate the Fairchilds (FQA12P20/FQA19N20)?
I'm still too much of a noob to feel confident I won't make a dumb mistake that other more experieneced builders might consider an obvious oversight.
Anyone have thoughts on if I should be changing any resistor values to accommodate the Fairchilds (FQA12P20/FQA19N20)?
I'm still too much of a noob to feel confident I won't make a dumb mistake that other more experieneced builders might consider an obvious oversight.
Nah.
The optocoupler bias won’t care one bit who made the output devices.
The optocoupler bias won’t care one bit who made the output devices.
There really any difference between the farichilds and the IRFs? I almost used FQA12P20/FQA16N25C for the M2X but keep saving them for some future use I have yet to identify 🤔
I bought the Fairchilds many years ago for an F5 turbo I eventually realized made way more power than I needed 🙂
What makes the Fairchilds sound more neutral?
What makes the Fairchilds sound more neutral?
Don't have any equipment to measure, but I will do a wild guess based on how I picked the jfets and mosfets. Keep in mind, my boards were for the original F5 without P3. I did:
- Matched 2SK170 and 2SJ74 with Patrick's degeneration trick.
- Matched the mosfets at the intended biased point, in other words, tried to get matched NNPP as close as I could.
- Do the above for each channel and tried matched the 2 channels as close as I could.
Their designs are similar. Each is a composite amplifier, employing a pair of ICs within a single NFB loop. JFET inputs are used in both designs. Both have high output current (200mA and 100mA) and both feature a high slew rate output. (4200V/usec and 1700V/usec) .
I built both, but I don't remember liking one more than the other. The are a great design, I think you, may worry more about quality of all parts working together than just the one part. The only way you will really know is to build them both. Everyone's perceptions are different.
Anyone used semi south SJEP120R100 in m2 output stage?
I read that the 500 microvolts noise floor as stated on the first watt website can be attributable to the IFRP output devices, so trying to overcome this.
I read that the 500 microvolts noise floor as stated on the first watt website can be attributable to the IFRP output devices, so trying to overcome this.
Thanks Zenmod.
Rationale is trying to get an amplifier with tube qualities but doesn't need significant interventions, like a DIY Strom or balanced isolation transformer to get there.
Out of all of the FW designs M2 has good PSRR/CMRR noise removal, but by what I read once you've shielded the auto-former, it's the IFRP's that contribute to the 500uv noise floor (its intrinsic to this design, Nelson states here). Other FW offerings are typically 50-100uV, but a SE amp like Aleph J would still need a pretty good power supply (e.g. CLC to get to this) compared to an M2. So the theory is that switching out the IFRP's would remove this intrinsic noise in the design, which power supply upgrades could not overcome.
The effect is quite obvious in practice, my backup amp (MyRef) works great straight of dirty mains power, but my SE tube amp needs mains treatment because it has negligible PSRR/CMRR compared to the MyRef.
Rationale is trying to get an amplifier with tube qualities but doesn't need significant interventions, like a DIY Strom or balanced isolation transformer to get there.
Out of all of the FW designs M2 has good PSRR/CMRR noise removal, but by what I read once you've shielded the auto-former, it's the IFRP's that contribute to the 500uv noise floor (its intrinsic to this design, Nelson states here). Other FW offerings are typically 50-100uV, but a SE amp like Aleph J would still need a pretty good power supply (e.g. CLC to get to this) compared to an M2. So the theory is that switching out the IFRP's would remove this intrinsic noise in the design, which power supply upgrades could not overcome.
The effect is quite obvious in practice, my backup amp (MyRef) works great straight of dirty mains power, but my SE tube amp needs mains treatment because it has negligible PSRR/CMRR compared to the MyRef.
Oh I fully agree - you won’t hear hum/hiss or anything like that on a 94dB speaker. But the intrinsic noise masks detail and dynamic range - if you’ve ever experienced this?