What's it worth???

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I'm about to purchase the fets for my Aleph-X's. Due to using parts from an existing chassis, I'd like to stay with TO3 style outputs. So, here's my question:

What is the subjective difference in sound quality between the IRF140's and 240's really worth? My inclination is to go with the 140's because they were designed for higher current... But, how noticeable is the difference?

Also from a matching perspective, I need a total of 96 matched fets. I can buy either part number all from the same lot so that will help, but how many should I buy to get 96 matched devices? I was planning on buying 150. Is that too many?

Lastly, on one hand it's only a couple of hundred bucks difference between the two... On the other hand that couple of hundred bucks directly translates to a bill going from $525 to $750 just for output devices - hence why I'm taking the time to ask... :bigeyes:

Are the 140's really worth the extra couple of hundred bucks???? I'm figuring on using these in a biamp configuration and am planning on keeping them for a long time...


Hi Peter,

Thanks for the link... Yes, I'd already seen and have been following it...

I asked because I really hadn't seen any comparison between the two besides what was presented in the Zen articles... The problem is that the articles didn't really clearly state what the subjective differences between the devices was... At this scale, I figured it was worth asking...

I'm planning on 16 devices per channel... I figure I can dissipate ~ 700 watts per chassis and am planning on ~100 - 125 watts per channel per stereo chassis (times 3)...
I'm using the same numbers. You need devices matched in banks of 4. My guess is that 120 woiuld be enough to get the match.

To tell you the truth on my current AX amp I'm using TO-3 IRF 230, but if I had to start from scratch I wouldn't bother with TO-3 package. Dealing with plastic TO247 is a lot easier and more convenient for short connections and signal path. I'll be using IRFP 140 on my future projects. Check this link to see what I mean http://www.diyaudio.com/forums/showthread.php?s=&threadid=3840
Thanks Peter for the matching info and the link... I do remember that thread...

Did you ever finish the X that is P2P wired? I'm still curious how this design actually sounds and if the Grey's design is stable when scaled???

As far as using the IRFP packages, yes I agree they'd be far easier and considerably cheaper... Unfortunately, I have my reasons for wanting to stay with the TO3's on this project... I could make new rails for the chassis but I figure by the time I purchase the metal (the sides are 1/2" thick), cut and machine it I'd have spent the money in material, time and hassle... I'm making a concerted effort to not change the boxes too much... You'll see why when they are finished... ;)

The one and only
Joined 2001
Paid Member
I didn't find that the difference between the 140 and
240 to be enough to get excited about. If you are
running less than +/-25 volt rails, it is worth a little
extra to get the 040's or 044's.

The difference is greater in the Zen amps becuase they
need every ounce of gain they can get. The X and Aleph
circuits have intrinsically more gain, and are not as
dependent on the transconductance of the devices.
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