Super Triode Connected Aleph CCS Zen Amp

[FYC]

Hi All

I am thinking about building an experimental amplifier employing a Super Triode Connection (STC) with a Zen amp + Aleph CCS. The STC was discussed rather in detailed in some Japanese audio website and also in TubeCAD. Employing the concept laid out in TubeCAD around mid 2015, I combined a Zen Amp (with Aleph CCS) and draw up the schematics. The working point that I selected was based on the components available in my parts inventory. I would like to ask the help from the forum to see if there are obvious miss in the thought before attempting to build one. Thanks.

 

[Zen Mod]

maybe because still didn't get my morning coffee , but I can't see how's that going to work

 

[FYC]

Zen Mod, you hit the right spot. I do not understand this also, hence I call it an experimental build. Nevertheless the claims made by the concept are so attractive that I am willing to spend the effort to experiment.

According to the claims, the triode is NOT part of the gain stage, but an active feedback element. With this Super Triode Connection (STC), you get the sound characteristics of the triode but the power of the main amplifier. So in my case, I can get a E88CC (or 6DJ8) sound-like power amplifier. This is very interesting.

I basically share the concepts shown in TubeCAD
Single-Ended Amplifiers & Super-Triodes and so on in building the schematics. Also, there is even a commercial offering using a gainclone with a tube:
Nixiekits.eu • Finest quality Nixie clock and tube kits made in Germany

 

[Michael Rothacher]

Upon cursory inspection, this looks more like a hybrid than a super-triode.

 

[FYC]

Hi Mike

I would argue that since the plate of the E88CC is also connected to the drain (output) of the lower MOSFET, hence this is not a typical hybrid type gain stage connection. In AC terms, the plate of the triode get signals from the amp's output as feedback.

 

[Michael Rothacher]

Whatever you say, FYC. Seems like you've got it all figured out.

Append:
On second look, I'll buy it. Build away

 

[Zen Mod]

it could be supertriode amp , if you didn't omit entire biasing circuit for lower mosfet

this way , all you could get is poof! in speaker

 

[indra1]

it could be supertriode amp , if you didn't omit entire biasing circuit for lower mosfet
this way , all you could get is poof! in speaker

Why? I believe FYC took the schematic from art_zv2.pdf. I think some of us would need a bit more explanation. Is it because he used 47k instead of 4k7? But I just can't figure that as valid cause for a poof!

 

[Zen Mod]

as Mr. Broski said cleverly:

Wait a minute, John; what happens if the triode's cathode voltage isn't high enough to turn on the MOSFET; or too high, so the MOSFET over conducts and melts?

The answer is we need an auto-bias circuit to set the MOSFET's idle current flow, such as the one shown below.

and then he put this picture :

so , find that part on page , read and think

 

[Nelson Pass]

maybe because still didn't get my morning coffee , but I can't see how's that going to work

I see the logic of it - the Mosfet is driven by a Triode Cathode follower, and
negative feedback is provided by connecting the output (Mosfet Drain) to
the Plate and working the Triode characteristic of the tube.

 

[indra1]

I see the logic of it - ...

Mr. Pass, does this means the biasing change is still usable?

 

[Michael Rothacher]

ZM,

In this case, the cathode of the tube in the posted schematic is AC coupled to the gate of the MOSFET, so no poof

 

[Michael Rothacher]

@indra1

The schematic is hard to read, but it looks like Vcc is 20V. If the Drain of the lower FET is at 10V or so, he'll need to tweak those values, but that's an exercise for the designer.

 

[Zen Mod]

I see the logic of it - the Mosfet is driven by a Triode Cathode follower, and
negative feedback is provided by connecting the output (Mosfet Drain) to
the Plate and working the Triode characteristic of the tube.

I know these schmtcs from Broskie (entire page ) , what struck me in the early morning is fact that tiny details about biasing elements can't be omitted without bigbadaboom consequences , except if just basic schm. is in case

which isn't declared in post #1



now , I can draw working schematic , needing some optimizing of triode loading , but why should I ...... when almost everything is already shown in TubeCAD blog

 

[Nelson Pass]

as Mr. Broski said cleverly:



and then he put this picture :

so , find that part on page , read and think

Yes, you want the picture below it, and even then it would not be my choice...

 

[indra1]

..., but that's an exercise for the designer.

Agreed.

 

[Michael Rothacher]

ZM,

I generally refrain from answering the "What do you think of my schematic?" posts.

I get to spend spend about 30 seconds analyzing the circuit, and the rest of the day being judged

And some of them are Hucklberry Finn (design my amp for me) bait

 

[2 picoDumbs]

I was under the impression that the most desirable tubes for audio require fairly high voltages in comparison with mosfets.
Should the circuit be modified to allow for this or are you intending on using low operating voltage tubes.

 

[Michael Rothacher]

There are two supplies.

 

[2 picoDumbs]

Ok.
Too lazy to follow the links. I'm looking at schematic in post 15.