RMI-FC100, a single stage audio power amplifier

[roender]

roender
D1 is there because of tempco?

also 2SC3423 .......... there are here because of noise and temp. behavior ?

tnx.

D1 is there for tempco. It is thermally coupled with input stage cascode devices.
c3423/a1360 are used becose they have a very low Cob. IMHO those are the best VAS transistors, even if I don't have a truly VAS here

 

[roender]

Why do you call this a single stage amplifier?

"VAS" has a common base topology

 

[destroyer X]

Class A sounds beautifull..... but not possible to my environment

Under normal weather conditions is already hard to face the temperature here.

Without heaters, as Television, Owen and equipments in stand by is supportable....but with a class A powered on, here, is a suicide.

Nice design, pretty construction, congratulations.

Made from an European and to the Europe....and only during the winter.

Correct...no one use more than 2 watts.... so... the normal AB amplifiers will operate into class A till 2 watts and will be reasonable....but, for sure pure class A is another thing...better!

It is lovely and interesting how people is different....Nelson Pass and also me will feel very unconfortable using so many parts when 1 or 2 will produce the same power.

regards,

Carlos

 

[roender]

Re: Class A sounds beautifull..... but not possible to my environment

Correct...no one use more than 2 watts.... so... the normal AB amplifiers will operate into class A till 2 watts and will be reasonable....but, for sure pure class A is another thing...better!

It is lovely and interesting how people is different....Nelson Pass and also me will feel very unconfortable using so many parts when 1 or 2 will produce the same power.

regards,

Carlos

Thank you very much Carlos.
The question is, at the same output power an amp with few parts will sound better or worse than one with a lot more components?
I have made a lot of amplifiers and I've come to this conclusion:
One can use components "outside" signal path, to make an amplifier response more linear, without hurting how that amp will sound.
Regarding A classe, the power dissipated at idle is 35W per channel. With 0.37W/C heatsink, the radiated temperature will not be unsupported.

 

[destroyer X]

Yes...you are rigth....those surrounding sub circuits helps a lot

For sure you are rigth.... will sound better.

regards,

Carlos

 

[Duo]

Okay, so I suppose that the input pair is operating into the common base amp which is a sort of cascode driving the output stage. But would this still not be a two stage amplifier at the very least?

 

[roender]

Okay, so I suppose that the input pair is operating into the common base amp which is a sort of cascode driving the output stage. But would this still not be a two stage amplifier at the very least?

No
The LTP is not in common base topology , it is the only stage which amplifies signal.
The output stage is a unity gain stage. It's an impedance adapter, emiter follower ...

 

[Duo]

I see that the LTP is not in common base, it is common emitter with jfet drivers.

But it appears as if it drives a common base stage before the output stage.

EDIT: I meant common source jfet; no drivers. I'm pretty tired right now. I should sleep.

 

[roender]

But it appears as if it drives a common base stage before the output stage.

What gain is in that stage?
1!

 

[Duo]

I never said the gain wasn't 1. But it is still considered a stage.

 

[roender]

I never said the gain wasn't 1. But it is still considered a stage.

Well, you could call it so if you want, a pseudo VAS

 

[Duo]

I just think that it's not really truly a 'single stage' amplifier... I like the design though.

 

[roender]

Yes it is.
Only one stage amplifys signal and the name of the schematics is... amplifier.
Semantic ...

 

[Duo]

Ah... But do any of the other stages have anything to do with amplifying current?

 

[roender]

Yes, it is a multistage transconductance amplifier
You got me

 

[Duo]

Just what I was getting at. hehe

 

[kASD]

Immaculate use of folded cascode with current source loading and a current mirror to keep the drive symmetric.........

Very neat implementation!!!!!

 

[aparatusonitus]

Re: Re: Class A sounds beautifull..... but not possible to my environment

I have made a lot of amplifiers and I've come to this conclusion:
One can use components "outside" signal path, to make an amplifier response more linear, without hurting how that amp will sound.

That's exactly my view on amp design…and the reason why I’m in process of PCB torture for this monster FC preamp.

 

[Duo]

Yes, I definitely like how he gets the drive from the LTP out to the output stage.

 

[roender]

Thank you guys.
Who want to build one?