Senin, 24 September 2012

Aikido in Jfet version

This is one of my dream, to have a full solid state setup. Before, all my pre amplifiers are tubes driven, and hybrid one.
Don't get me wrong, I love my Aikido tube amp, this John Broskie baby served me very well, beside this Aikido is my first ever tube pre amp, quite a memorable and unforgettable experience I have. For example I remember when I got the breadboard working I'm kind of hypnotized watching all 4 tubes glowing in the dark, also I hand built my self special chassis for it. Here are the pics and imho the measurement speaks for it self.

So why then a solid state pre amp? It's just a next stage for me, more and more I need transparency, transient , better rhythm and pace. It is the rhythm and pace in reproduced music that make your head nod (or banging listening to Metallica) or tap your feet, hell, even did an ugly dance with it he he..

Aikido and the rest of my system provide that let says 7 out of 10, but not every time and not with every music genre's. And this already with deliberately tweaked to  fast sounding Aikido. I have listened to friend's tube pre amps at home, man..most of them are soo slow. I know I'm into a tough challenge now with solid state and limited knowledge, but my experience with Jfet on DAC output stage is encouraging me :).

Since I loved my Aikido and the way it works I want to have the same, instead of 4 tubes/8 triodes now I will have 8 jfets. Searching the net I found schematic from Juma at diyAudio ah ha...So it goes, I made a neat PCB, populated it and tested it...and?

And yes!...NO sound comes out!  what a disappointment, not even a hum. So before long the PCB is in pieces, all the drain and source resistors were replaced by trim pot , ah something comes out, a loud hum and faint music, what happened with that supply noise cancelling that 'trade marks' Aikido?.

After a few weeks with no success taming this board, that includes using 24V car battery I gave up on Juma's schematic and begin to look at the original Aikido schematic and modified, meaning I made a mess off jumpers on existing pcb to suit John B's original. I run some simulation on Orcad to get all the resistor values, improving the supply ..yup, finally it sing! comes the lengthy 'get that sound' tweaks.

I found out, although an experienced friend already told me, that individual matched Jfet sounds different. Out if 20 jfets, I have 4 pairs of matched ones and tried each and every Jfet at every possible position to get 'that sound', not to mention testing various resistor values, then resistor type and in the 4th month and the sound is just ok, no more and no less. With tube, when you're off by a margin it still will sing, often quite beautiful. Not so with solid state. I think somebody highly experienced told me that back then. Here is the so-so sounding AikiFet.
With next tweak, a CLCLC psu, or what ever it may be, getting closer..(large inductors are on my Aleph J clone psu) I can dance now :)
Now, even closer with GAD Vifa, MBM pio make place for K42-pio, better transparency..Pink Floyd anyone?
 These blue Bourns trim pot on the 'front' Jfets are my ticket to dance floor..
Measurement of the final AikiFet, not quite like the tube version, this at above my normal listening sound level btw. AikiFet needs the second harmonic a bit to sweeten the sound.

Topping it off, this AikiFet finally came to fulfill my dream, so a nice box is appropriate. I'm tired watching naked AikiFet all these months.
 Sing, baby sing..

Is it worth it to have an AikiFet? I'm biased of course but it's worth my every penny and pain. Thanks to my friends who gives critical reviews and suggestion on this pre amplifier, and thanks for reading.