The Amazing Fet Circlotron by Mike Rothacher

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#13
Great article Mike, thanks for sharing (and Nelson for hosting) this piece. I'm also fond of the MOSFET circlotron approach and have built several examples, but I have to say, nothing as DIY-friendly as your design (at least as long the 2SJ74 supply lasts).

In my experience, these types of amps offer a "clean and clear" character and (given a low-noise power supply) preserve instrumental timbre and low-level detail very well. I speculate that this is due to their relatively clean harmonic residual, whose effects may be less audible than the (already respectable) THD numbers might suggest.

So, I encourage anyone considering this project to jump in. If you don't happen to have a balanced source to drive it, there are some simple solutions. For example, you could add a quality line transformer to the front end, or build a balanced-out version of Nelson's B1 JFET buffer that uses the JFET as a phase splitter to produce both inverting and non-inverting outputs.
 
#14
I am interested from now to this .
Just the usual question about V types of 2SJ74 , that I have around , if they will work fine . .I am sure, anyway , here the 2SJ109 will do a nice job given the balanced nature of the circuit .

Also I would be interested in a simple , but very well "harmonized", differential pair made with 2sk389 to use as a SE to Balanced converter , maybe we can made something out of the AlephOno circuit .

Thanks for the nice work .
 
#16
Circlotron.

Since I heard it Circlotron from topology, I believe it in that manner an one like this is needed. But which one?
I do not want electron tube one. The life is too complicated without it.
With a look my weak electronics knowledge, AFCMR would be a kind the optimal one.
Isn't it?

Gyuri
 
#17
Yes, the theory is the same :xeye: However, I see some difference in the aproach of Mr. Rothacher's adaption vs. what I've done. I had trouble getting my brian around that schematic at first. I thought there must be a mistake. But, it of coarse should work 😕 Except maybe for the P ch FET symbol on and N Ch FET. opps
In the circuits I did, the load was connected to the Source of the FETs along with the - of the supplies.
Very Nice 😀
 
#18
Thank you all for the kind words. You have my humblest appreciation.

When Nelson says I "generously agreed" He means I fell out of my chair, did a backflip, and ran around my house shouting "You'll never believe this!"

Seriously, I can't thank NP and the PassDIY crew enough for posting my debut article.

Now, I hope a few of these get built so Mrs. R will consider increasing my R&D budget for more articles.🙂
 
#20
lumanauw said:
Can a circlotron work in low bias classAB, or classA is a must?
Click to expand...

This particular one doesn't have a lot of open loop gain to work with, so its performance in AB will be limited. You can experiment with the bias a bit, but class A (or very near) is where you'll want to be. Class A and low NFB are where it's at.

Joe Berry said:
In my experience, these types of amps offer a "clean and clear" character and (given a low-noise power supply) preserve instrumental timbre and low-level detail very well. I speculate that this is due to their relatively clean harmonic residual, whose effects may be less audible than the (already respectable) THD numbers might suggest.
Click to expand...

Joe, that's much in agreement with what I'm hearing. They can be downright eerie.

Of course, that could be due to my choice of music.🙂
 
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