solid state amplifier obsolete ??

[ontoaba]

Here it is , my voltage amplifier. It separated with the Voltage Follower as second stage. This VA is old and almost also obsolete (I have newer one) , I am using new VF here and it sounds amazing!!!. may be because of the new buffer, using KSP2222A/2go7A in classA 30mA bias before the hexfets driver (Voltage Follower with negative feedback output bumping facing KSP's at driver, it using +/-9.2V floating voltage). The VF I am not draw it yet.

PCB using A872E as original, hard to find it and I am out of stock, BC557B replace it. Also good with other transistors. Different footing need small changes. C3355 could be replaced with S9018I, different footing too.

 

[unclejed613]

AVE...

Darlingtons are slow because current on the base of second transistor doesn't change fast enough, but this can be overcame by adding a resistor of few hundred ohms between base and emitter of second transistor...

and that's because the miller capacitance of the transistor pair is the total B-E capacitance multiplied by the beta of the darlington (beta of the first transistor multiplied by the beta of the second). the "internal" resistor shunts some of that capacitance to the emitter, and so reduces it's effect. it also reduces the beta of the pair to some extent.

 

[ontoaba]

Darlington, is not just slow, but also with thermal drift problem if not good configured.

Hi, unclejed nice idea, "spammer trap" if every sites has million fakes email address on their pages, those spammer machine will death instantly when start to operating.

 

[ontoaba]

Redrawn version here (with better drawing and corrected components values). Sorry for my previous drawing, thats just fast drawing, you know, I am in happy listening test that time, and not really concern in drawing.
http://www.diyaudio.com/forums/soli...erformance-never-let-me-down.html#post2488064

 

[SMourareau]

A very answer

AVE...

May it seem a stupid question, but why these transistors are better than over 10k other low power transistors that are available?
Why these two transistors are considered superior to other ones?
Why not use for example pair of BC549C or BF245C?

BC549 & BF245 are 30V transistors which roughly limits rail voltage to +/_ 15V and so output power to 12W/8Ohms.

What is difficult to find is voltage transistors (120V) with good HFE at current values around 1mA.
But I finally whent for KSA992/KSC1845 available at Fairchild.

Stéphane

 

[SMourareau]

A very answer

AVE...

May it seem a stupid question, but why these transistors are better than over 10k other low power transistors that are available?
Why these two transistors are considered superior to other ones?
Why not use for example pair of BC549C or BF245C?

BC549 & BF245 are 30V transistors which roughly limits rail voltage to +/_ 15V and so output power to 12W/8Ohms.

What is difficult to find is transistors with VCE around 120V with good HFE at current values around 1mA.
But I finally whent for KSA992/KSC1845 available at Fairchild.

Stéphane