If the intent was to have something more neutral so that what you put in front of the F4 amp dictates the sound, then matching mosfets would probably be best.
If what you have to put in front of the amp is also neutral then maybe mismatching mosfets on the F4 amp will be best.
There is no right or wrong answer.
It will depend on the equipment you have and your own taste.
If what you have to put in front of the amp is also neutral then maybe mismatching mosfets on the F4 amp will be best.
There is no right or wrong answer.
It will depend on the equipment you have and your own taste.
F4 is so incredibly neutral that changing anything isn’t going to make much difference. I’d just build it as designed.
The “sound” of an F4 is the sound of the preamp driving it.
The “sound” of an F4 is the sound of the preamp driving it.
You really have to have a clear purpose in mind (or curious to compare), if you decide tweaking it,
If you're unsure just build it stock.
If you're unsure just build it stock.
Yea, measuring distortion would have to be a part of that. Which I doubt you could here in this particular design.
OTOH, this is probably not the design to try different operating points. It’s just too neutral. The whole point here is transparency.
Built it as designed then drive it with some distortion and here just how transparent it is. My tube dac through the F4 sounds like the loudspeaker is being driven by the dac.
Thanks folks, that's all very helpful. Despite the obvious attraction to the Harris devices, I'll probably just go with a store kit so that I don't have to worry about matching myself.
These days I would select the same parts, but use the Harris P channel version.
Interesting, would you choose multiple output devices over a pair of 40N20P/40P50P?
These days I would select the same parts, but use the Harris P channel version.
Would it be due to transconductance shelving in mid audio frequencies in the original IRF P channel mosfets? I guess Harris devices do not have this phenomenon?
If you mean direct, the Korg doesn't swing enough voltage to be useful for F4.
If you have an additional gain stage between those 2 it would work.
If you have an additional gain stage between those 2 it would work.
It's one of my favorite combos, though with 105dB speakers. Loud enough for me.
Yeah with speakers like that no problem what so ever.
I run my F4 with a B1 buffer, or direct from a dac.
My speakers are around 98dB to 99dB
I run my F4 with a B1 buffer, or direct from a dac.
My speakers are around 98dB to 99dB
These days I would select the same parts, but use the Harris P channel version.
Hi Nelson
Have you had a chance to test Infineon IRFP9140
They are claiming 5th Gen Hexfet manufacturing (whatever that means) and specs look different to Vishay parts.
http://www.infineon.com/dgdl/irfp9140npbf.pdf?fileId=5546d462533600a40153562cd43e2031
Infineon Technologies
This has been bugging me for a while.
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Yes mine are in the Fostex 206 so in the range of 96dB and loaded in a back horn. Room is circa 35 m2. I understand that might "a little short"
It's going to depend on how loud you listen.
You could get lucky.
If you threw a Jensen or Cinemag transformer after the korg for another 6dB to 12dB gain it would work.
I would like to try that actually.
You could get lucky.
If you threw a Jensen or Cinemag transformer after the korg for another 6dB to 12dB gain it would work.
I would like to try that actually.
So, I know this isn't ideal (because the mosfets won't be matched at actual operating temperature), but would you all support matching with this device?
Nelson Pass' Easy Peasy MOSFET Vgs Measurement
Assuming that's sufficient, I'll buy a sleeve of the Harris parts and match away. If anyone wants a set, I'll be happy to share at cost.
Nelson Pass' Easy Peasy MOSFET Vgs Measurement
Assuming that's sufficient, I'll buy a sleeve of the Harris parts and match away. If anyone wants a set, I'll be happy to share at cost.