DIY Sony VFET pt 1

If I remember correctly, the 16R - preferred load was for the "small" Sony VFETs (2SJ18 / 2SK60) - that's why they will get a Mu Follower in an upcoming variant of the DIY VFET amp.

I think the VFETs in part 1 (2SJ28) and part 2 (2SK82) like 8R loads - that's why the got a CCS.


Sorry, don't remember the post from the top of my head, will search for it ...


Edit:

Here: https://www.diyaudio.com/forums/pass-labs/370282-diy-sony-vfet-pt-1-a-37.html#post6602753
and here: https://www.diyaudio.com/forums/pass-labs/370282-diy-sony-vfet-pt-1-a-111.html#post6696445


Regards, Claas
 
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Agreed, But it is nice to know why.

The spectral content of the thd is dependent on the impedance of the
load, since it affects the load-line of the Vfet/SIT.

Works just like a Triode in this regard.

As a general approach we optimize it against an 8 ohm resistive load.

If you have a different load, it can be biased more toward that, or
you can give it some help, like with a mu-follower, or you can adjust
the load itself...

:snail:
 
I put these little filter critters in my vfet, one per channel. Seems a bit more 3D and deep in the soundstage. I’m doing a victory lap by cranking a favorite record at proper volume for the style: Tanith - In Another Time LP. Love it. On an SP10 - thanks Jim!

Next up will be some front end boards.
 

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Glad you enjoyed the additional filters in your VFET!

On top of the better soundstage, with time you may appreciate quite a step re tonalities, resolution (better highs and lower bass, helping in fact the better soundstage) and especialy music flow

And yes, perfect match for horns, I agree!

Enjoy music

Claude
 
Hi Randy and everybody,

we seem to be on a parallel path here ... I also added the PO89ZB filters to my DIY VFET (N, so 2SK82), one before each output stage.

Music-wise, the main difference I noticed was a bit more transparency in the bass (more info - you can better hear what's going on with all the instruments), and a bit less sibilance in some recordings. Otherwise, I don't have a lot of difference to report. I feel that the little hum that the amp has, has gotten a bit quieter. You have to be very close to my 100 dB/W widebanders to hear it. I took some distortion measurements before and after adding the PO89ZBs, and you can see a slight reduction in the 100 Hz peak. (second picture with later date is with the filter)
I now measure 480 uV AC at the outputs (both channels the same) - unfortunately, haven't measured that before adding the filters.
I guess the about 900 uF of filter capacity the PO89ZB adds helps a bit.

Next step will be some different front-end boards as well. I have a pair of completed and dialed-in Marauder boards sitting on my bench, but want to memorize the sound with the original front-end a bit more before I swap.

I'm really curious if an Edcor-less front-end will change the measured hum (since it's 100 Hz in the first place, and then also the Meanwell PSU is far away, I guess not), but expect much better square-wave response and frequency responce. Let's see ... 🙂


Best regards, Claas
 

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It may be interesting to try adding a modest amount of extra capacitance to the power rail on each output stage. The filter board may work to prevent the SMPS from going into a hiccup current limiting mode. Try values from 1000 uF to 10,000 uF.
Judging by the differences you have already mentioned, you can expect better bass instrument articulation, and improved separation.