Commercial solid state amplifiers with no loop feedback around the output stage

[hbc]

Interested to know of commercial solid state amplifiers, i.e. not kits or home brews, with no loop NFB around the output stage. I was researching the Dartzeel (again) and found mention that this has been done else were, NAD and Tandberg were mentioned but no model numbers. I would like to exclude Quad current dumping type amplifiers as well. Would be nice to fill this out a bit.

to start the list:

DartZeel NHB108
DartZeel NHB458

 

[LKA]

TANDBERG TPA 3016A, 3026A
ETALON INTEGRA

 

[analog_sa]

NAD S300 which is a copy of Gryphon Tabu Century

Krell KAV300i

Threshold and the offspins under Nac and Usher


obviously many Pass Labs and First Watt amps.

 

[bmtas]

Onkyo A9911,A9711,A927
All Gryphon amps

NAD S300 was made by Gryphon in Denmark after produktion end of Tabu.

 

[bmtas]

Nakamichi PA-7,PA-5(made by Nelson Pass)
Onkyo A9911,A9711,A927
All AYRE amps
D"Agostino amps
Progressive Audio
NAD S300 was manufactured by Gryphon after the production end of TABU

 

[analog_sa]

Ayre amps. Perhaps all of them.

 

[sgrossklass]

Onkyo A9911,A9711,A927

NACK. That's a current feedback unity gain buffer thingy. Not within the gain stage feedback loop, of course, but definitely not open loop.

That's a good thing, too, since AB amps with open loop output stages tend to measure like absolute garbage, as you might expect (given that the output stage tends to be the #1 contributor of distortion). Either that, or they have to run pretty hot while still giving mediocre performance. A design like that just makes no sense.

 

[hbc]

Jeff Rowland model 7

 

[analog_sa]

(given that the output stage tends to be the #1 contributor of distortion)

And i thought it was only #2 after the VAS 😉

 

[daec]

All recent production of Bartolomeo Aloia , ST series and GY50 / Antu 100 is zero feedback in output stage

 

[hbc]

So having looked at a lot of these I think only the dartzeel and the Ayre are running the diamond buffer output, with no feedback.

I don't know if it's my imagination (or selective reading) it it feels like the the cutting edge of audio veil removal etc seems to have moved to higher Res digital into NOS DAC and big low to no feedback solid state amps.

Whilst reading the speculation about the dagostino's latest Steam punk toaster inspired monsters circuit I found reference to the Thule amps.

A quick simulate of the output was quite thought provoking.

Quite fancy cobbling something together, for the ultimate ultimate ultimate prototype amplifier amplifier....

 

[Bigun]

Check out Steven Dunlaps KRILL amplifier. He came up with a nice sounding amplifier but was treated poorly on this forum. Unfortunately, due to ill health, he's no longer in business and not participating here but he sold many commercial units. I adopted his output stage into one of my projects, which I haven't had time to build but have some PCB's waiting for me. TGM11 - no GNFB - inspired by Steven Dunlap 'KRILL'


http://www.parttimeprojects.com/audio/diy/Krill.php

 

[as_audio]

Add to the topic various Audiolabor amps.

 

[adason]

Some top line Tandberg amplifiers.

 

[as_audio]

.. as seen in post 2.

 

[Mark Johnson]

First Watt M2. No loop feedback anywhere. Here is a review, written in July 2010

Nelson Pass published the schematic after First Watt ceased M2 production. Quickly thereafter, diyAudio Forum members built clones, published PCB Gerber files, etc. One of the clones is offered as a set of PCBs in the diyAudio Store, right now. Today.

 

[CFT]

Pioneer MZ-1, circa 1979, first in world commercial amp with no global feedback applied. 🙂

Pioneer M-Z1

 

[as_audio]

Surely not the first one !

 

[forr]

Some top line Tandberg amplifiers.

No global negative feedback but error correction in the output stage.

 

[adason]

good to know...thanks
is it a bad thing?