Article - Sony VFETs part 1

[Zen Mod]

dady - start new thread for your amp

this way we are just going to get lost in these 1300 posts

then I'll be able both to follow and comment

 

[dady]

dady - start new thread for your amp

this way we are just going to get lost in these 1300 posts

then I'll be able both to follow and comment

Thanks dude-

 

[Soundhappy]

Thanks dude-

Congratulations Dady interesting vfet amp topology 😀
I need finish my diy first so i can go to new project
this evening Sony CSX1 on bench table , work in progress...
and lot's of joy

 

[dady]

Oh you are making your CSX1, when you goin to listen ?
Master French

 

[Soundhappy]

Oh you are making your CSX1, when you goin to listen ?
Master French

Listen master french 😀


https://www.youtube.com/watch?v=stjTVGy8uNU

and must choice few 1K resistances from candidates for buffer and CSX1 power stage
Greetings

 

[WalterW]

I'm nearby in Collioure, enjoying the sun with family, so if you need help soundhappy.....

 

[Soundhappy]

I'm nearby in Collioure, enjoying the sun with family, so if you need help soundhappy.....

Collioure is fabulous hope Walter you with all family have great time 😀

Yes i need help i dream you open new thread about vfet mini Sony Commomorative
so i can build one and hope some Diyers join us 🙂

My kindest regards

 

[WalterW]

yes, I will build one small Sony Commomorative 40 years VFET amplifier. Is my next project.
First have to finish my M2 headphones amp....

 

[WalterW]

On that photo, we had dinner in a very good, fish restaurant....eating "fruits de mer"

 

[Soundhappy]

yes, I will build one small Sony Commomorative 40 years VFET amplifier. Is my next project.
First have to finish my M2 headphones amp....

Mini 40 years Commemorative are advanced amp build with luck Mr Pass send us councils and guide.
Thank you Walter for YES 🙂

ps: hmmm i see Paëlla fruits de mer woow delicious food mniammniam perfect with cup of white wine

 

[dady]

Show pictures together there.
Saint-Saëns

 

[BDP]

First channel tested and biased. It's a beast for heat dissipation. It's very stable for bias adjusting. At 1.3 amp bias my test jig was getting hot. I just had the t-bar secured with C- clamps.
I previously set the bias voltage references at 12 volts without the main power supply. With the main supply connected I then brought the variac up slowly watching the current draw from each polarity of the supply and the voltage on the reference bias supplies. Once the supply was up to voltage I started alternating the bias supplies while watching the output offset and voltage across the .47 ohm sense resistors. Very little drift in the output offset, once set, it stayed in place even as things warmed up.
On to the next channel.

 

[ianc13]

Martin Logan XStat & CSX1

Help please,

I am thinking of mating my VFET CSX1 amp with a pair of Martin Logan Vistas for the upper registers in a bi-amp config.

The XStat panels drop from 4 Ohms at 400Hz to ~1.2 Ohms at 20KHz. I have heard that this can pose some problems for some transistor amps.

Can anyone help me understand whether this might be a problem for the VFET CSX1?

Thanks!

 

[Nelson Pass]

Only one way to find out.

I would try it, but I would also take it easy.

😎

 

[hifibluedevil]

Help please,

I am thinking of mating my VFET CSX1 amp with a pair of Martin Logan Vistas for the upper registers in a bi-amp config.

The XStat panels drop from 4 Ohms at 400Hz to ~1.2 Ohms at 20KHz. I have heard that this can pose some problems for some transistor amps.

Can anyone help me understand whether this might be a problem for the VFET CSX1?

Thanks!

You can use an Autoformer so Vfet amp will see a nominal 8 ohm load-or higher-all the time (e.g., check out zeroimpedance.com). I have a pair and they work very well with both tube and SS amps. Just a thought.

 

[ianc13]

Thanks Nelson, hifibluedevil.

I'll give it a shot and see how it goes, the really low impedance is right up at the top of frequency range which shouldn't require a lot of actual power, so it could well be AOK.

If it doesn't work out then I'm sure that I can figure something out, like an autoformer.

Thx

 

[dady]

I listened one of my favorite symphonies, Number 3 with organ.
Not genital of course.
Camile Saïnt Saens

 

[Soundhappy]

I listened one of my favorite symphonies, Number 3 with organ.
Not genital of course.
Camile Saïnt Saens

Hi Dady

Great !
Do you satisfy with your CSX1 build and his power supply ?
Yma Sumac

 

[ianc13]

Small Bias problem - just want to check

I have a small bias issue with my 2nd CSX1 AMP build.

I am hoping to bias it at ~0.8A, so pretty low. This amp will just feed a tweeter in a 3-way setup so it doesn't need much grunt and I'd rather run it at a lower bias for longevity.

I can't get 1 of the channels down to 0.8A, lowest I can get with 0V offset is 1.1A. The problem is that one of the VFETs is wanting more bias than I can provide at the moment. I am using 12V RMS supplies and can adjust the bias from ~6.2V through ~12.5V. I think I need more than 12.5V of bias.

In the schematic of the CSX1 power supply there is a 3.3Kohm shunt resistor in the TL341 bias circuit. If I want an extra volt or so of bias I need to reduce the voltage drop across this resistor - right?

So, if I dropped this to 2K or 2.5K or similar I would get a different bias range, one that would allow a higher bias.

Is my analysis right before I go fiddling with the circuit?

Thanks

 

[Zen Mod]

why not checking in TL431 datasheet , and having some faith in own conclusions .......