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carpenter 15th August 2009 10:38 PM

Solid state tube?
 
2 Attachment(s)
Hi all,

I've been fretting over the obsolescence of the LU1014D power jfet. In my search for a suitable replacement, I stumbled across Gabe Velez's web site. He suggests a mosfet/bipolar configuration to duplicate the "tube" sound. I'm submitting a differential simulation I ran and would appreciate some feedback. You can see the mosfet/bipolar combination in the middle horizon of the drawing.

Best,

John

Wavebourn 15th August 2009 10:46 PM

Sure, it will sound clean, but power dissipation will be the price for sound quality. Here is what I use for output stages, drivers, and line outputs:

http://wavebourn.com/images/audio/Tower-concept.gif

carpenter 15th August 2009 10:54 PM

Quote:

Originally posted by Wavebourn
Sure, it will sound clean, but power dissipation will be the price for sound quality. Here is what I use for output stages, drivers, and line outputs:

http://wavebourn.com/images/audio/Tower-concept.gif


Thanks for the drawing. I need a bit more detail with regards to the power/signal sources.

Regarding my circuit: yes, the sim depicts rather poor efficiency.

I'm going to build it for kicks, just to see how it sounds. The LU1014D has such a beautiful sound. I'm hoping the mosfet/bipolar combo will sound as sweet.

Wavebourn 16th August 2009 01:48 AM

Quote:

Originally posted by carpenter



Thanks for the drawing. I need a bit more detail with regards to the power/signal sources.

Regarding my circuit: yes, the sim depicts rather poor efficiency.

I'm going to build it for kicks, just to see how it sounds. The LU1014D has such a beautiful sound. I'm hoping the mosfet/bipolar combo will sound as sweet.

For better efficiency I use modulated in counter-phase current sources.
It was used long time ago in White cathode follower, but current source was modulated by feedback by current that depends on load impedance. In my version it is modulated feed-forward.
Bootstrapping follower on top of cathode follower was used long time ago, in Tekronix oscilloscopes, it was called Augmented Cathode Follower.
I was looking for ways to minimize modulations of parameters of a source follower and come to this combination. It can't be patented, I believe, because both of approaches were used before, in test equipment, long time ago. And second, it can't be patented because it is already in public domain, I drew schematics that use such approach on many online forums.

carpenter 16th August 2009 02:25 AM

Fascinating! I'll have to explore your concepts further.

Wavebourn 16th August 2009 03:02 AM

Quote:

Originally posted by carpenter
Fascinating! I'll have to explore your concepts further.
Here is one practical schematic (though not breadboarded yet), I've made it from my previous version of the amp eliminating one power source and one bootstrapping source follower on top, it works also very nice such a way. Just set standing current equal to half of peak current needed to drive the lowest impedance your speaker has, and you get a single ended amp with maximum of effeciency available. If you set a standing current equal to peak of current through the load, the source follower will see almost stable load current (however, not so stable since real speaker is a complex load).

http://wavebourn.com/images/audio/Tower-III.gif


Currently, I build a full version again, with some sneaky tricks, it is not in public domain yet since I plan to get some money for my future projects.

You can see the thread in Tube forum, about my Pyramid design. I describe the process of building of a Designer's prototype, step by step.

carpenter 16th August 2009 03:21 AM

I appreciate your gift of knowledge. :)

Lumba Ogir 16th August 2009 03:34 AM

carpenter,
in the absence of something better, the LU1014D is not obsolete (maybe unobtainable). Generally, JFETs are preferable to MOSFETs. I cannot see why that circuit, particularly the lousy (and much more obsolete) N3055, could produce a "tube sound".

Wavebourn 16th August 2009 03:55 AM

Quote:

Originally posted by carpenter
I appreciate your gift of knowledge. :)
Thank you!
Actually, it is typo: I meant Tower thread, not Pyramid. Pyramid is a pure tube amp on MOSFET voltage regulators.

Quote:

Originally posted by Lumba Ogir
carpenter,
in the absence of something better, the LU1014D is not obsolete (maybe unobtainable). Generally, JFETs are preferable to MOSFETs. I cannot see why that circuit, particularly the lousy (and much more obsolete) N3055, could produce a "tube sound".

Why not? 2N3055 are used as single ended emitter follower, so no "transistor sound" can be made such a way.

carpenter 16th August 2009 04:12 AM

Quote:

Originally posted by Lumba Ogir
carpenter,
in the absence of something better, the LU1014D is not obsolete (maybe unobtainable). Generally, JFETs are preferable to MOSFETs. I cannot see why that circuit, particularly the lousy (and much more obsolete) N3055, could produce a "tube sound".


The 3055 is easy to locate, the LU1014D is a bear to find at a reasonable price. The 3055 can be replaced with another bipolar, the power jfet can't.

The output sine in the sims on the 3055 (in my circuit) have a strong resemblance to the power jfet output sine.

Makes for an entertaining evening, yes? :)

Thanks for the corroboration, Wavebourn


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