Crazy Gain - Down the Drain


The Cloverotron 4L V 2.0
MONO AND STEREO HIGH-END AUDIO MAGAZINE

It must be a Triode. Because Triode is Fad. Because Triode is Linear. Because all Audiophiles use them. But should I really? Why should I use a triode, be it even an "audiophile" one, if it only provides me with very "mediocre" amount gain ? But what if I were to tell you that I need a VAST amount of gain? That I **NEED** such a crazy amount of gain, so that, ... So that I can flush it down the drain ? A Crazy amount of gain that can only be achieved by a Pentode ( Yuk! sounds awful, does it not ? ).
In the "Part I" of this article, in my previous postings relating to the Cloverotron 4L, v. 1.0., I held stead fast to the assumption that the lower tube, the voltage amplifying stage … that it **MUST** be a Triode. I held to that presumption sort of ... automatically, based on the "easy-go-lucky" type of "go-with-the-flow" thinking.


But that was the Part I. That was the Cloverotron 4L, version V.1.0. But now it is time to stir up some dirt again. 

Yes, a Pentode, loaded with an Constant Current Soure, of the Alan Kimmel style. Considering that the Voltage gain of a Pentode is equal to the transconductance (= high !), multiplied by the load resistance ( ...and guess what: in the case of an Allan Kimmel Constant Current Source, this effectively means at least a few megaohms) …. I think that what I am talking about here is some really crazy amount of gain. Crazy to the borders of Oscillation.


At this point – you might as well ask: BUT WHY do I need a CRAZY amount of gain? Well, the reasoning may seem to be a bit from the borders of sanity, but let’s just say, that I need this Crazy amount of Gain, so that I can Flush it down the Drain. Throw it away. Junk it. I need it for my newer version (not necessarily better version) of the Cloverotron 4L, V.2.0.

Say what ?


Say again ? ... so as to flush it down the drain ? Throw it into the waste bin ? Is this guy NUTS ?

Well, you may have heard about, or may remember, that nice piece of an article, by Bruno Putzeys:
“The F-Word - or, why there is no such thing as too much feedback”

“(c) Linear Audio www.linearaudio.net”.

So, let's just assume that I am a ** Converted Believer **.
I Believe.
YES, indeed, I DO believe, that there is no such thing as too much feedback. ( Heresy number 1 ? )
YES, indeed, I DO believe that a LARGE amount of feedback is GOOD. Higher than 45dB Loop Gain. The more feedback - the better. ( Heresy number 2 ? )
YES, indeed, I DO believe that a small amount of feedback (~20dB) is the WORST possible thing, that can be implemented in an audio device. ( Heresy number 3 ? )

And YES, I do believe that there is such a thing as the Other Side of the Rainbow, ( Heresy number 4 ? )
or more precisely speaking, the Other Side of the Bandaxall’s Hump. ( ... a mathematically derived set of curves ! )

An area, that requires a loop gain of at least 45 dB, but at the same time, a loop gain that is sort of unconditionally "stable" and that does not oscillate.
Indeed, if we were to succeed in such a challenge, this whole thing just may make sense.

So the thinking is as follows: Instead of mentally triodizing myself to death, following the go-with-the-flow, the safe route, kind of like: ”the triode is an audiophile device that is best suited for linear voltage gain” …. Since we shall be on the other side of the rainbow (specifically, on the other side of the Baxandall hump), it is totally irrelevant, if we use a highly linear triode, or maybe just a not-so-linear, and frankly speaking, quite-a-lousy Pentode ? A pentode inserted into the eye of the cyclone: into the position of the lower, voltage gain tube of the Allan Kimmel Mu Follower Circuit ?

We hence achieve a crazy amount of gain, … and then – PURPOSEFULLY – we flush it down the drain, kill it almost to zero, but as a side effect thereof … we achieve a loop gain of a whopping 45dB of more.
So – now we are basically in Wonderland and we do not have any concerns any more relating to the Pentode being a 'less-than-ideal' audiophile device.
If you do not believe me – ask Alice.


The circuit as above,
{{ "Cloverotron 4L, V.2.0."; (C) zjj_wwa of hiend-audio.com }}
... the circuit is most probably just but another hallucination, and mind you, an even bigger hallucination than the on presented in the version V. 1.0., as described in "Part I" hereto.
But anyways, I like it.
I do hope, that you like it too.
I hope that we can discuss it.

Please feel free to criticize, suggest amendments, modifications, corrections, betterments - Whatever. I simply LOVE your feedbacks. 

I am sort of inclined to believe, that the thing as above - that it just might work.

The only thing that I am totally in the dark with … is what to do with the other end of the capacitors C13 and C16 …

Should, or should they not, be connected to the cathodes of their pentodes ? The way of thinking is as follows: Allan Kimmel uses the S2 grid of the upper triode as a means to boost the performance of the current source, by “modulating” the S2 voltage of the pentode with the Ouput voltage of the stage. What If we were to do something similar with the cathode of the lower pentode, the voltage amplifying pentode ? What if we take a small piece of that output voltage, from a resistor divider, and …. apply just a tiny little bit of … positive feedback, feeding this signal into the cathode ? Theoretically – we are heading for trouble (oscillations). But maybe, just maybe, we shall fall in the safety net of the GIGANTIC negative global feedback of that 45dB overall loop gain to keep us stable ? Such a tiny bit of this “local”, positive feedback, into the cathode of the Pentode – it just might further boost the amount of crazy gain, so that we have more of it to flush it down the crazy drain ….

Hmmm …. I think that I better first leave those caps .. unconnected, for the time being, or at least look around for some very cheap speakers (guinea pigs), prior to connecting those caps and doing some testing …. There is a small chance that the membranes will turn into a lethal weapon as soon as I switch this thing on. Or maybe not ? 

Please kindly comment.

Best Regards,

http://hiend-audio.com
zjj_wwa@hiend-audio.com

P.S. ... But where is the "Part I" of this article ??? Good question. Search, and you shall Find.

Matej Isak. Mono and Stereo ultra high end audio magazine. All rights reserved. 2006-2013. www.monoandstereo.com. ..:: None of the original text, pictures, that were taken by me, links or my original files can be re-printed or used in any way without prior permission! ::..