Total Domination VFET (TDV) Amp (using 2SK2087C)

[swak]

To have a sit amp that is h2 dominant on the entire power bandwidth you need to increase vds and bias proportionally else it will become h3 dominant from a certain point if you increase only vds. If you increase only the vds without the bias you will get better performance(lower thd) but the amp won’t be h2 dominant on the entire power bandwidth.

This was my impression looking at measurements posted here, thank you for confirming that.

This makes me think I will keep the voltage at or even a bit below 37V.

 

[von Ah]

I’ve been cycling through a handful of my power amps in the recent weeks. My TDV stepped up to the plate today. I heard something new in a familiar song this evening. THAT is the sign of a good amp.

 

[toto34]

Hello, can we use a 36 volt voltage instead of 37.5 volts for your circuit?
Should the intensity be reduced or increased?
Thank you in advance.

 

[ra7]

Yes, 36V is fine. Anywhere up from 20V should be fine. Playing around with the operating point will result in different sound because the VFET device curves are not flat with respect to the drain voltage. This triode behavior is similar to a 300B for example. This is the fun part where you can get different sound by changing either the drain voltage or the drain current. It is a fun experiment. Just be sure to not exceed the dissipation limit of the device.

 

[toto34]

Hello ra7 thank you for your reply.

 

[toto34]

Good morning to all of you.
I realized TDV with THF-51S and power supply with two power supplies (Mean well UHP-350-36) do you have to connect the Gnd of 36volts to the chassis with a CL-60?
Thank you in advance.

 

[ra7]

Yes, that’s how it is typically done with a linear supply. I am less certain about the Meanwell though it looks like it should work. You could try it and report back. I don’t have experience with the Meanwell supply. But others here do. @Ben Mah , have you tried this? I am wondering how the chassis can be connected to earth ground as well.

Congrats on your build! How does it sound?

 

[Ben Mah]

I have never used a SMPS to power an amplifier.

Here is the specification sheet for the Meanwell:https://www.meanwell.com/webapp/product/search.aspx?prod=UHP-350(R)#1

Looking at it, it looks doable as long as V- is ground.

From a practical point of view, power supply output ground and audio ground are the same thing. An amplifier has a source such as preamp connected to it. Usually the preamp power supply/signal ground is connected to safety ground. The preamp's safety ground is therefore connected to the preamp out ground and then through the interconnect to the amplifier signal ground, which is connected to the power supply. So the amplifier ground is safety grounded through the preamp, and since the amplifier ground is also the power supply V-/ground, the power supply is also safety grounded. I hope my logic is correct. So a direct connection of the SMPS V- should work and from a safety point of view should be done rather than rely on a connection through interconnect to the preamp.

However I have not used a SMPS to power an amplifier and I am not an expert on this subject. The above are only my amateur diyer thoughts. So seek confirmation before proceeding.

 

[toto34]

Hello Mr ra7
I recommend the realization of this montage which is really excellent.
A great sound with very few components, but thank you very much to you, and thanks to the whole community that helps realize the dreams of many enthusiasts.

 

[toto34]

Thank you, Ben Mah, for your explanations.

 

[ra7]

When in doubt, look to Papa for answers. From the Sony VFET Pt. 1 article:
https://www.firstwatt.com/wp-content/uploads/2023/12/art_diy_sony_vfet_pt1.pdf

This Sony VFET amp also uses a Meanwell supply. It may not be the same one you are using, but the below circuit should work the same. It looks like V- is connected to power ground and then to chassis ground through a thermistor.