NAD 304. Single folded VAS?

[GEirin]

Hi all.
I´m very interested to know this topology of the VAS. What is yours opinions? Pro and cons.
Thanks.

[Lumba Ogir]

GEirin,
it´s a good topology, no cons.

[GEirin]

Hi Lumba,
Thanks for your reply. This is a grounded base VAS circuit?

[Lumba Ogir]

GEirin,
purely applied grounded base, just as it should be.

[tiefbassuebertr]

Originally Posted by GEirin

Hi all.
I´m very interested to know this topology of the VAS. What is yours opinions? Pro and cons.
Thanks.

For me it is a normal folded cascode, like pass "X-series" input stage
Q318 (perhaps Q316 - I cannot read exactly) is the cascode transistor, because it's base is connected to Uref. point from cathode zener diode D307 (at the same time the ref voltage for current source Q311)
I guess, the upper half of this circuit is the same, but mirror symmetric. This means, that the collector of the complementary part of Q318 must be connected with the collector of idle current voltage source transistor Q317

Einstein, Cyrus-IIIi and AVM uses also such topologies. The great advantage of this topology is, that I have one voltage gain stages in the global feedback loop, and not two, that means, not too high values of high order THD, even by Class-AB mode with only 20-50mA idle current for the output devices.

[GEirin]

Hi tiefbassuebertr
Yes, your explanations is correct.
Thanks for you recommendation.
My idea is to improve the VAS tipology in a lin amplifier.
Now I think to use this tipology in my amplifier.

[GEirin]

Tiefbassuebertr

A question: Which is the best VAS tipology, Lender VAS (Stevens amplifier) or single folded VAS (NAD304)

[Lumba Ogir]

GEirin,
as pointed out, grounded base is the way to go. Besides, too many stages, I would omit two-three of them.

[tiefbassuebertr]

Originally Posted by GEirin

Tiefbassuebertr

A question: Which is the best VAS tipology, Lender VAS (Stevens amplifier) or single folded VAS (NAD304)

some years ago I have try to find out this through compare of this both topologies (together with some other) at the same power supply. At pure class a in the output the LENDER topology delivers the better sonic performance (less harsh). The different was low. But after reduce the idle current to the most used values of 30mA nobody hears a different between this two topologies.
But it must be mentioned, both versions wasn't mirror symmetric by first and second stage.
Additional I am not shure, whether the audible differences (observed by class A mode) are comes through the topology of circuit or not ideal layout and wiring, i. e. parasitic effects. So I would say the same as Lumba Ogir - through the folded cascode topology you have only one voltage gain stage in the feedback loop and effects though layout and wiring are lower

If you me tell about more of your loudspeakers, what you want to use, so as about your prefer music stil, I will give you more exactly recommendations.

Please note still, one amplifier for the whole audible frequency range is still a compromize and not the royal way, independend of the output power and the price class