Why is it that people always value something that is very difficult to obtain and not value the things that are right in front of their face.
Even though they are great parts there are many other suitable parts at a fraction of that cost that will get you a great amp.
Even Nelson is not ashamed of using the cheap non-assuming IRFP240 devices anyone can buy for around $2 each for this amp. IRFP240PBF Vishay Siliconix | Discrete Semiconductor Products | DigiKey
I personally feel at $122 each that is not good bang for the buck. For one Semisouth device you could buy 2 tubes of IRFP240 for that money.
If you have the money to spare go for it, but if you feel that the Semisouth's are your only choice to get a great sounding amp think again.
Just to put a little perspective on the matter back in 1980 the IRF devices were not considered "cheap".
"The power mosfets used in this project are International Rectifier IRF 130's, a 150-watt, 100 volt, 12-amp device in a TO-3 style case. They are part of a relatively new line of transistors using IR's proprietary hexfet process, which combines a particularly high voltage capability with very fast switching times and low saturation losses. Except for the steep price tags, this type of device has a number of advantages over regular bipolar transistors in audio power amplifier use."
Nelson Pass
Now they are cheap and everyone is shunning them.
Last edited:
Not everyone. I love them and have a couple hundred, matched in triplets and pairs, to prove it. They are at the perfect price point.
I see lots of F5, F4, Alephs, BA3s, M2, F6, ... built with IR devices, so I don't think people are
necessarily shunning them. I think it may be more of a case of folks trying
to stick closely to the original devices. In the case of the J2, this means trying
to find Semisouth jfets.
I have no doubt a similar topology rendered using IRFP240's will make a mighty
fine amplifier.
Personally if I have a couple of spare semisouth jfets I would try the mu-follower
with a couple of IR mosfets for the current source.
necessarily shunning them. I think it may be more of a case of folks trying
to stick closely to the original devices. In the case of the J2, this means trying
to find Semisouth jfets.
I have no doubt a similar topology rendered using IRFP240's will make a mighty
fine amplifier.
Personally if I have a couple of spare semisouth jfets I would try the mu-follower
with a couple of IR mosfets for the current source.
Turns out only 2, really:
You can build a perfectly fine version with something else, like the IRFP240, on the current source. I have done it for test, and there were no complaints.
The output stage sound is dominated by the gain device on the negative rail. The mu follower is quite neutral due to it's own local feedback.
I just used JFETs all around for consistency, and to avoid the internet troll accusation "It's not really a JFET amp", which I saw in a posting once regarding the F3. (Not on this site)
So if anyone else is interested in a pair (or four) at extortionate prices, drop me a PM.
Somebody may not agree with me, but my approach to Diy audio is to try to build the best sounding (it could be just 2w amp, no problem) with parts that I happen to find in my drawer or that I could easily find at the local market. In this case, I have IRFP250, and would happily use it with no regret
They weren't that expensive when new...
I just got a quote from them for $157.54 each for SJEP120R100 from Sierra IC. They must like you more than me. To add to the hilarity, they quoted me $9.85 each for the tiny little 2SK715 JFET by ON Semi, which recently went EOL and can still be bought from Rochester Electronics for pennies (albeit for a couple thousand of them).
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.