Sony vFET Illustrated build guide

[Rodeodave]

This one?

 

[wdecho]

Many thanks, I sold some V-fets to someone that I bought years ago from circuitdiy, acronman, along with boards and brackets I had been hoarding and the buyer wants to test the V-fets. I decided to pass them on for what I paid for everything so someone else can enjoy this amplifier.

 

[juanitox]

is there any source to find PCB for this Sony VFET1 ? i wonder if i can build one with my old Sony4650 2SK60 2SJ18vfet pairs .

 

[Dennis Hui]

is there any source to find PCB for this Sony VFET1 ? i wonder if i can build one with my old Sony4650 2SK60 2SJ18vfet pairs .

Maybe try here:

PCBPCBs for Nelson Pass‘ CSX1 SONY VFET amplifier

Good luck.

 

[juanitox]

thanks , what will be the safe Biasing of the 2SK60 vs 2SK82 ?

 

[Rodeodave]

Given the persistent rumors that the 82/28 parts are dual-die versions of the 60/18 parts, I'd say half the bias of the bigger parts.

 

[protos]

I am getting some hum or buzz on the output around 2uv, using the diyaudio PS. Is it a grounding issue you think?

 

[Rodeodave]

2uV (=2*10E-6 Volt) must be a typo.

And answering your question is impossible without any further info or pictures.

 

[protos]

2mV. My bad. Just a quick feedback if builders have experienced these levels of hum. If not will try different grounding. At the moment the speaker ground wire is connected to the pcb ground or 0- point, not to the ground on the PS. Cannot think of any other obvious change.

 

[Ben Mah]

Try rotating the power transformer. I found that there is a position where noise is at a minimum.

A picture is also helpful for long distance trouble shooting.

 

[Ben Mah]

Some good information on minimizing noise:

http://hifisonix.com/wordpress/wp-content/uploads/2018/07/How-to-wire-up-an-amplifier_3.pdf

There is some practical advice near the end of the article.

 

[dcbingaman]

If you have hum, try connecting the signal grounds (ALL of them) to the chassis ground via a CL60 thermistor. Usually eliminates hum or buzz problems.

 

[protos]

Thanks for the suggestions. I will post a pic soon but to my eyes the build does not seem to have any differences to what I have seen posted here or even classic Firstwatt pictures and connections which are very similar.
Though to be sincere the only difference is that I did not connect PS Ground to chassis with any method (ie diodes or thermistors). Only AC ground is connected to chassis for security. So this connection should not be an issue in a ground loop. I see First watt amps are quoted with noise usually around 50 to 100uV.

 

[Botte]

I chased this for a bit and the solution i found was to go old school. Look back to the A75 where Nelson used two diodes with a resistor across them to chassis ground. This made my units silent where with the CL60 i still had a buzz.

My two cents.

 

[carsten.witt]

This worked like charm. ;-)

Thanks to Dragan.

 

[Zen Mod]

to be nitpicky , diodes must be stronger than mains fuse

 

[carsten.witt]

@ZM,
yes your right ... that should be only a possibility (in my case was ist 300mA main fuse).

 

[protos]

 

[Rodeodave]

This is why we asked for pictures. The transformer is right inside the loop formed by the inputs' ground wires and the ground wires of the PSU (the loop is closed when you connect a source). The mains going to the primary of the transformer are way too close to the audio circuitry, it looks like they're running directly underneath the frontend portion of the pcb. I'm surprised you're not picking up more hum.

I would redo the AC wiring. Turning the bottom plate 180° should give you the correct arrangement of the transformer and the PSU pcb. That way the transformer will be outside of any ground loop. See pictures of First Watt amps for reference.

 

[protos]

So you are saying this is an EMF issue acting on the input wires and PSU wires. The funny thing is that I removed the input wires completely and there was no discernible difference in the hum. I also disconnected one channel to check if there was some kind of two channel loop area, as you say, and again no real gains. However your suggestion is easy to implement. In fact I can just distance the whole PSU with some cables and see if EMF is the issue.