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X250 - My next project.
X250 - My next project.
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Old 13th February 2013, 08:47 AM   #1
Walkalone is offline Walkalone  Viet Nam
diyAudio Member
Join Date: May 2011
Location: Ho Chi Minh city
Default 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 ...
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 (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!!!
Attached Images
File Type: gif NguyenLabs-X250-Front_end-pwr-sch__Wilson_improved_current_mirror__BJT_ver..gif (45.3 KB, 392 views)
File Type: jpg DSC00718__Edited.jpg (137.5 KB, 388 views)
File Type: jpg DSC00721__Edited.jpg (120.6 KB, 351 views)

Last edited by Walkalone; 13th February 2013 at 08:52 AM.
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Old 13th February 2013, 09:31 AM   #2
Walkalone is offline Walkalone  Viet Nam
diyAudio Member
Join Date: May 2011
Location: Ho Chi Minh city
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
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Old 5th March 2013, 02:03 PM   #3
Walkalone is offline Walkalone  Viet Nam
diyAudio Member
Join Date: May 2011
Location: Ho Chi Minh city
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?
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