Stock First Watt F4: Complete Distortion Measurements?

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oltos

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Joined 2012
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#1
I count myself very lucky to have this amp. But AFAIK, the stock First Watt F4 never got put through the wringer the way the J2 did.
https://www.stereophile.com/content/first-watt-j2-power-amplifier-measurements

And unlike the J2, no distortion measurements were included in the F4’s manual.

Here's some ("quick and dirty?") distortion measurements from 6L6's first build of the F4 build, post #2.
https://www.diyaudio.com/community/threads/a-guide-to-building-the-pass-f4-amplifier.234355/

Okay, so even a stock F4 is not a low distortion amp. But my speakers are ~ 94db/w, they don't fall much if at all below 7 ohms and only play down to 70Hz, below which my Rythmik F12 subs takeover.

So, with a line stage like the Aikido Rev. F providing plenty of gain https://glass-ware.stores.turbify.net/ainost.html
https://tubecad.com/2018/03/blog0415.htm, how much 3rd or 2nd harmonic distortion would the F4 produce which would likely be audibly offensive?
 
#2
At the output levels you’ll need for speakers, the Aikido will be higher distortion than the F4.

And ignore those old measurements in that guide, they are referenced to nothing and are useful only in showing that distortion does decrease with an increase in bias current, where the sweet spot will be found at the recommended bias. (Funny how Nelson recommends that… )

😎
 
#3
6L6 said:
At the output levels you’ll need for speakers, the Aikido will be higher distortion than the F4.
Click to expand...
Given the stated efficiency and average impedance of my speakers, my ~ 2880 cu ft room, that my subs takeover below 70Hz https://en.wikipedia.org/wiki/Equal-loudness_contour and that the Aikido is a low distortion line stage then I suppose audible amplifier distortion's not going to be an issue for me., yes?
 
#5
Speaking of which, have you ever driven it with the 6SN7 tube? Dick Olsher, who favorably reviewed the XA30.5 and several First Watt amps, seems to count it among the best driver tubes, like the 85. See https://www.enjoythemusic.com/superioraudio/equipment/0905/dehavillandmercury2.htm

And unlike many great sounding tubes, the 6SN7 actually seems to be currently in production. Nor does it have an especially crazy price.
https://sophiaelectric.com/collecti...roducts/sophia-electric-blue-glass-6sn7-tubes
 
#7
6L6 said:
And ignore those old measurements in that guide, they are referenced to nothing and are useful only in showing that distortion does decrease with an increase in bias current, where the sweet spot will be found at the recommended bias. (Funny how Nelson recommends that… )

😎
Click to expand...
But assuming WolfX700 built it properly, wouldn't you say those IM distortion vs. power output measurements look pretty horrible?
https://www.audiosciencereview.com/...rements-of-my-diy-replica-firstwatt-f4.10647/
 
#9
I've been too busy listening to contemplate modding the circuit. I did build a pair of them and running them in balanced which reduces some distortions.

I am looking at popping the power supplies into separate chassis. Might lower the noise floor, keeping the AC out of the signal chassis. However, the main goal of such an exercise is to have a universal 1st Watt power supply to try all the various builds with minimal surgery.

As far as ASR, unless I've done the measurement myself and have a vast library of other amps to compare it to, they are meaningless. Too much armchair engineering goes on these days. I know too many engineers that throw up measurement results that don't comprehend what they really mean because they haven't built tonnes and tonnes of different designs to be able to translate to human speak.

btw, Jim heard the balanced F6s I built and was astounded. I wish he could have heard these "monsterblock" F4s because they are even more "not there" but I got them done after I moved out of Colorado.
 
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#10
oltos said:
But assuming WolfX700 built it properly, wouldn't you say those IM distortion vs. power output measurements look pretty horrible?
https://www.audiosciencereview.com/...rements-of-my-diy-replica-firstwatt-f4.10647/
Click to expand...

I'm rather reading what's written on Tom Sawyer's fence than (majority) of internet forums
Heck, hordes of arm-chair racers are exactly knowing who's greater - Rossi or Stoner.....

:rofl:

tomsawyerfence.jpg
 
#17
#18
The manuals were written many, many years apart. I’m not surprised they are different.

And, the F4 is such a different amplifier from every single power amp you’ve ever had (and in truth, from any that had ever been sold before…) that I suspect that the attention paid in the manual to how it could be used was significantly more important in Nelson’s mind than including whatever measurements.
 
#19
oltos said:
Well, DIYers may feel differently, but as a customer who purchased a stock J2 and F4 (originally from Reno Hi-Fi), I feel that if the J2's measurements were not only presented here https://www.stereophile.com/content/first-watt-j2-power-amplifier-measurements but also in the manual, then the F4's measurements should have at least all been included in the F4 manual.
Click to expand...

I believe nobody forced you to buy them

so, all thinking about credibility and available information, logically goes before actual purchase

now, if you're happy using them, leave it be

if not, sell them
 
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