Class A amp based on STK 3102-III

[muddasirwaheedmalik]

Hi i have a pair of Sony Amps whose output stage is driven by STK 3102-III.
Its simple Emitter follower output stage with simple (not darlington ) driver driving cmplimentry pull-push via VBE multiplier.

Project. Design a separate pull-push Ampliffier output stage , 50W rms class A.
Simple eemitter follower driven by Darlingtons, with multiple x10 output devices at 200mA quiscent current ???

Any design ideas.

BTW i intend to implement fully regulated output stage at +/- 50volts via power mosfet modules/power BJT modules for linear regulation ???

Any ideas? Is the sound Quality of SKT good enough for a real highend style output stage, fully regulated , high bias, fully balance( BTL) ?

 

[jaycee]

There's no real reason to use the STK module. They're obsolete, so if they ever need replacement, they're difficult to get. There's nothing special inside them now that you cannot do with a discrete circuit.

 

[5th element]

I don't know what the Sony amplifier's heatsinks are like, but a standard EF output, biased high enough to give you 50w/8ohm class A, is going to produce a huge amount of heat if run on 50 volt rails.

 

[muddasirwaheedmalik]

Agreed with both Jaycee and 5th Element.
Reason. i want to keep the enclosure , power supply etc from sony. I will take dual twisted pair from SKT outpu to speaker terminal from which i will connect to separate current gain stage externally.
Benefit 1. I have this thing in pair and is bridgeable via a inverter section and selector so i can monoblocks, fully balanced.🙂 and all i have to do is to design and make separate output stage. The existing transformer, 300VA is shielded toriod and will provide excellent regulation for small load of SKT, plus i will use the existing heat sinks in SONY for series voltage regulation at around +/-50V, existing rail voltage is around +/- 60V using IRFP450 200W, 400V, 15A mosfet (which i have in sufficient quantity)

I am going to use a separate enclosure and separate heatsink , separate power supply and separate output stage for final current gain stage.

Here is the schematic of existing output stage.
So is there Any approved/suggested design for class A 50W output stage (pull push/single ended ????)

 

[franzm]

You really want to attach some long wires (=antennas) to a VAS? These wires will have some unpredictible capacitance and will collect a lot of parasitics. What about stability?

 

[muddasirwaheedmalik]

well we can use RC cables ????? just like we use between pre-amplifier and amplifier ?????

 

[muddasirwaheedmalik]

what about coaxial wire ???it will carry sufficient voltage swing , and some current as well ???

 

[franzm]

Leave that Sony amp as it is and use it as the modulator amp in a Technics class A+ topology (see Power amplifier ). Doing so you'll get what you want: re-use the Sony, a (external) class A amplifier (to be build) and the wires to interconnect them.

 

[muddasirwaheedmalik]

can u explain a bit ???

 

[muddasirwaheedmalik]

I mean if i refer to page 5, for two stage , how i get floating refernece for load on first power supply and how i get fixed reference for second. seems intriguing but a bit of more literature could do the trick ???