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WolfX700 Measurements of My DIY Replica FirstWatt F4

WolfX-700

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#1
Nelson Pass's FirstWatt series amplifiers have many interesting designs. I built several of the most interesting devices for myself. Here is one of them: FirstWatt F4. This is a Class A design with no negative feedback, no gain, and pure current amplification.

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After the completion, this unit brought me endless troubles: because of its gainless characteristics, I had to find a front-end device with a large voltage swing. (So you know why I paid attention to the preamp)

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:facepalm:
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In fact, the Spec of this design is [email protected] THD :p
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Dynamic-Range---No.jpg

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NTomokawa

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#2
Yikes that distortion. At least the innards should look good, with a huge toroidal transformer and an array of caps.
 

daftcombo

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#3
How much for this garbage?

Edit: just realized it was yours, sorry. Couldn't do it myself.
 

daftcombo

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#7
Nelson Pass once sold original units for $ 2,500. I spent about 300 dollars to complete this one.:)
I admire the work. But if the original measures the same, some 80$ full digital amplifiers run circles around it.
 

solderdude

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#8
But it sounds so nice and musical, 2nd harmonic is highest and the harmonic profile is to die for.
I hope 2020 is the year when we finally find the missing metric and learn how to measure musicality.
 

NTomokawa

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#13
From various pages of the Audio-GD site:
We known that the proper 2nd THD makes the sound become smooth and rich, the proper 3rd THD makes the sound become transparency and lively,
Who's "we"!? What the Hell is an Aluminum Falcon!?
we increase the even harmonic and odd harmonic, spend a lot time to adjust and test the harmonic and frequency band
"Engrish" aside, I'd rather be spending a lot of time suppressing harmonics instead.

Then again, this is the only place where I can laugh at Audio-GD without being hounded.
 

LTig

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#15
Nice review. At least it's in specs. I'm glad I resisted my urge to build such an amp some 20+ years ago.:cool:

To all on this side of the datum border: I wish you all a happy new year - may all your dreams come true (except the nightmares of course;)). To all others I just wish the same.:)
 

levimax

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#16
I don't think comparing measurements of a DAC to a class A power amp makes sense. For a class A amp these measurements are reasonable and my guess is it sounds very good. No cross over distortion, no ultra sonic content, no heavy handed ultra sonic filters, and a distortion profile with lots of second order masking harmonics. As solder dude said I hope we can come up with measurements for power amps that correlate to real life listening ... Class A amps, while expensive to build and hopelessly inefficient will reliably sound good.
 

levimax

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#17
The caps are probably too small, just look at the PS noise!
PS noise/ cost is one of the biggest disadvantages of class A. Since the power supply has to supply full power at all times regardless of output the ripple from the PS is constant and does not get covered up at lower power like other amps. Caps can only get you so far.... Often times large and expensive chokes are used. While the amps tend to be noisy at idle once the music starts playing it is usually not noticable.
 

Doodski

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#18
@ WolfX-700
How is the linearity at 1KHz from 8 Ohms, 4 Ohms and 2 Ohms @ clipping? It's a risky test. How about some pictures of your amp inside ;)
 

pozz

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