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DIYspaceW 5th November 2013 10:29 AM

The Hybrid SIT Parafeed
1 Attachment(s)
My journey to build this amp started at you tube.
I watched the Nelson Pass presentation about SITs at Burning Amplifier Festival and so I got inspired.
First I began to search the net for SITs and quickly found the Little SIT amp,
designed by Michael Rothacher. By then it was clear to me that I would get me some of the 2sk82 transistors to play whit it.

I wanted to do a different approach, to higher voltage region,
where the lines look good. The only way I could do it was whit an
output transformer. The output impedance of 2SK82 in higher region is 10-12R. But this was a problem since there is very difficult to
make a good low impedance, high current and sufficient inductance transformer. This way it was done by Lennart Jarlevang, he used the PASS SIT-1 whit output transformer and it worked very nice, only the low end was limited. So after this review the best option was a parafeed topology.
I was familiar whit the high level matching UTC LS-33 and LS-34 transformers. So there was only one thing to solve,
the plate reactor for 2SK82. I talked to megaherz audio in Italy and they made it very well.
So the hybrid SIT parafeed was born.

After first listening sessions I concluded it had extreme potential.
The sound was very relaxed, full bodied and the bass region was extremely good articulated.
So my amp went to at least two revisions. The parafeed capacitors are PIO type. This schematic is the result.
I still want to do some distortion analysis, but will need to wait when my friend is not busy anymore.

Attachment 380794

Soundhappy 5th November 2013 12:12 PM

Hi DIYspaceW !
Sony sit's transistors be very popular at the end of this year:D
Your schematics its fuzzy , can You please made proper ones with PSU on
separate biger page ? Thanks for inspiration i like sit's 2:hbeat:

Best regards

DIYspaceW 5th November 2013 02:13 PM

Sorry about the schematic picture, this is the best I could do at the
moment. But if you minimize it a little bit it will look better.
If something is not readable I can help...

Zen Mod 5th November 2013 02:42 PM

1 Attachment(s)

Michael Rothacher 5th November 2013 03:30 PM

Nice. Plenty of iron! :)

DIYspaceW 5th November 2013 03:59 PM

1 Attachment(s)
Here a better photo.

Attachment 380849

And some more data.

The A+ power supply has a 500VA toroid transformer whit 60V secondary.
The SIT is biased at aprox. 62V at 750mA. On grid we have -12,5V.
I am using two 33R mundorf suprime resistors in parallel and bypassed whit 4x1000uF 50V Elna silmic 2 and 680uF carafine.
The parafeed caps are obbligato PIO 5x70uF bypassed whit russian teflon FT-3.

6E5P tube is biased at -1,5V, so I could also use a alkaline battery instead of auto bias.
The anode voltage is 132V and current 33-35mA. The output impedance is around 900R.

Its a lot of iron. But iron is good for sound to my ears.

Nelson Pass 5th November 2013 04:40 PM

Very nice.


Zen Mod 5th November 2013 05:51 PM

1 Attachment(s)

ignore 3V voltage

DIYspaceW 5th November 2013 07:02 PM

I also tried the battery bias and liked the cathode bias more,
it was more relaxed.
But the interesting part is experimentation. If you change only one
part, it has some impact on whole sound. I tested a lot and found to my ears,
this to be the best sounding.

Junm 6th November 2013 11:55 PM

Nice Hybrid... is the Impedance ratio of your OPT is it 53//8r ,and how many watts you squeeze from it?

Did you try using SE OPT only without the parafeed with higher A+(150v or higher) and lower idle current?

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