X250 - My next project.

I like symmetrical topology, and today, i try to build this front-end, for my next project.

I's based symmetry topo, like Symasym, Mongrel CX, Gold Mouth :D...
LTP used BC550C matched pairs. It's very good small signal transistor. Of course, you can use JFET (as 2SK170, 2SK30 or dual matched in one package like LSK389B/C, 2N3958, 2N5564 to better). I suggested 2mA - 3mA for BJT and >4mA LTP Iq for JFET ver.

Vas is simply. First, the Vas's current mirror used 2-Q mirror, but i have some problems with unbalance Ic of Vas. I read Rod Elliott page Current Sources, Sinks and Mirrors in Audio and I try with the Wilson improved current mirror 4-Q. He wrote it's extremely balance currents, improve dynamics, banwidth, distortions...
Wow, two Ic of Vas very balance. I set 12mA for Vas (6mA each). If you want, you can change R17 (10K/3W) by one PNP Medium power trans (2SA1381E is a good choise) - Active load of Vas differential.

In prototype circuit, i used EF2 like PB120/PB250N of Mongel II with 2 pairs Sanken power trans 2SC2922/2SA1216, drivers are 2SC2344/2SA1011 (Toshiba 2SC5171/2SA1930 are better, but i can't buy).
For last, i'll build EF3 output stage, to improve dynamic. And use ON-Semi audio power trans, like MJL4281AG/MJL4302AG...

For power supply, this project named by ''X250'' - it's means 250W per 8 ohms, 500W per 4 ohms and maybe 1KW @ 2R if i become rich man, keke:p (OMG, i don't want my money go away by this project :(, in my country, ON-semi power trans arevery expensive, about 10$/each.) The rails about 75 - 80VDC to make it. In this prototype, i used +/-55DC.

Anyone can comments about this? Thanks!!!


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I'm attact schema of JFET version. It's improve high frequency, lighting sound, soundstage larger, little more bass... I used equivalent devices is 2SK170 matched.

But, i have two questions:
Is current mirror needs for load of LTP (like Honey Badger schema) and about the lateral MOSFET like ECX10N20/ECX10P20 replace BJT on output stage.
Which are better? For sounding and anothers ... NguyenLabs-X250-Front_end-pwr-sch__Wilson_improved_current_mirror.gif
Today, i plan to build triple emitter EF3 for output stage. I'll use 8 pairs per channel. Supply rails around +/-75V. Power transistors are MJL3281AG/MJL1302AG. Drivers are MJE15034/MJE15035, 2SC3503E/2SA1381E in pre-drivers.
Can anyone suggest me quiescent current of pre-drivers, drivers and power transistors output to get best result. Vas set at 6.5mA.

At 75VDC rail, the driver transistors (MJE15034/MJE15035 or MJE15032/MJE15033) can drive 8 pairs power transistors? On datasheet, it's ok. But i wonder which good. Used a power transistor, like MJL/MJW/NJW, a driver is ok. But Cob too high.
Mark Levinson No.33H, used 2 parallel transistors MJE15030/MJE15031 in driver, to drive 10 pairs 2SC3281/2SA1302. Why they do not use a power trans as driver?