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Old 5th November 2013, 10:29 AM   #1
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Default The Hybrid SIT Parafeed

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.

Click the image to open in full size.

HyridSITParafeed.jpg

Last edited by DIYspaceW; 5th November 2013 at 11:04 AM.
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Old 5th November 2013, 12:12 PM   #2
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Hi DIYspaceW !
Sony sit's transistors be very popular at the end of this year
Your schematics its fuzzy , can You please made proper ones with PSU on
separate biger page ? Thanks for inspiration i like sit's 2

Best regards
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Old 5th November 2013, 02:13 PM   #3
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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...
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Old 5th November 2013, 02:42 PM   #4
Zen Mod is offline Zen Mod  Serbia
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......
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File Type: jpg HyridSITParafeed.jpg (69.1 KB, 1116 views)
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Old 5th November 2013, 03:30 PM   #5
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Nice. Plenty of iron!
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Old 5th November 2013, 03:59 PM   #6
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Here a better photo.

HybridSITParafeed2.jpg

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.

Last edited by DIYspaceW; 5th November 2013 at 04:29 PM.
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Old 5th November 2013, 04:40 PM   #7
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Very nice.

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Old 5th November 2013, 05:51 PM   #8
Zen Mod is offline Zen Mod  Serbia
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ignore 3V voltage
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File Type: jpg battery bias.JPG (7.6 KB, 1032 views)
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Old 5th November 2013, 07:02 PM   #9
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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.
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Old 6th November 2013, 11:55 PM   #10
Junm is offline Junm  Philippines
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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?

Last edited by Junm; 6th November 2013 at 11:58 PM.
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