Sony vFET Amplifier Part 2

[Eric]

Yep, as Radiodave indicated, by shorting that resistor leg to ground, it was trying to draw somewhere near 28v/0.1R or 280A of current out of your power supply! Instant toast. That little guy didn't stand a chance, it's only rated for 3w...

Good to hear that it seems the rest of your circuit survived! Does it still make nice music?

 

[akapezi]

Good to hear that it seems the rest of your circuit survived! Does it still make nice music?

It's making very nice music. Prior to the R32 smoke-up incident, the amp was only hooked up to very inexpensive non-powered desktop speakers that I purchase at thrift store specifically for amp testing. I have since moved on to better speakers - small bookshelf speakers with a single wide-band driver that I can actually place on my workbench.

I'll be moving the amp to my listening room this weekend for a good long listening session.

 

[BDP]

Has anyone experimented with changing the distortion character. Nelson states in the Sony vfet part 2 article about adjusting the Cascode feedback resistors.

"There are numerous variations and lots of little tricks, and besides lowering the output impedance of the front end, it is convenient and effective for reducing and tweaking the specific distortion character of the circuit, as the positive and negative halves of the circuit can be adjusted independently."

My Dual Vfet version matches were not the best, so there is more 2nd harmonic. Maybe not a bad thing? Each channel is a little different when measuring the distortion so I was thinking about playing with the Cascode feedback values.

BDP

 

[Zen Mod]

nothing wrong with dominant 2nd

I believe thingy is made for that

of course , you can play a little with values of resistors fo cascode feedback , to even THD spectra between channels

what is situation when overall NFB is applied ?

 

[BDP]

The overall feedback is with the mods Nelson had posted, I think they called it R2. Its 4.75K and 332 ohms.
The Cascode feedback resistors are 22K.

I was thinking I would put a 10 times larger pot. in parallel and see what changes I might get.

 

[Zen Mod]

try it .........

 

[Botte]

Since the mis match is in the output, you could also tweak the power supply voltages for the output section a bit.

 

[BDP]

That would be easy enough to change the voltage regulator output.

Thanks for the idea

 

[nashbap]

That would be easy enough to change the voltage regulator output.

Thanks for the idea

Do let us know if you try it. Do you mean changing the voltage to Q1 and Q2?


If you are using the Teabag board there is a provision for adding source resistance to the input Jfets thereby changing the H2/H3. Will this work?

nash

 

[BDP]

Do let us know if you try it. Do you mean changing the voltage to Q1 and Q2?


If you are using the Teabag board there is a provision for adding source resistance to the input Jfets thereby changing the H2/H3. Will this work?

nash

Yes, by changing the TL431 shunt regulator. Change R15 or R16 about 250 ohms per one volt change.

I have Teabags boards and that would be another option.

Making the adjustment at the outputs, where the mismatch occurs makes sense, but the Cascode feedback resistance would be easy to implement.

BDP

 

[nashbap]

Yes, by changing the TL431 shunt regulator. Change R15 or R16 about 250 ohms per one volt change.

I have Teabags boards and that would be another option.

Making the adjustment at the outputs, where the mismatch occurs makes sense, but the Cascode feedback resistance would be easy to implement.

BDP

Thanks.

 

[Mescalero]

I’ve been listening to my amp, off and on, for about one half of a year. It’s now hooked up to a good pair of Klipsch Cornwalls (the very earliest “Cornwall II”) and it sounds clean and clear. I’m a very happy builder.
In my past, I have done a little professional audio work for a tiny $5B/yr company. I have also got an innate passion for good, clean audio. I’m of the opinion that the scarcity of the V-FET is most unfortunate, yet, that makes this project that much more special.
Mr Pass, thank you for sharing. Job well done, sir.

 

[Quantensprung]

Hello
This might be a dumb question. But where do I find the BOM for the VFET Amp 2 (the one diyaudiostore is still selling pcbs for)?

Kind Regards and thanks in advance

Phil

 

[Dennis Hui]

Hi Phil,

Try post #2766:

https://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-2-a-277.html#post4991406

Cheers,
Dennis

 

[WBS]

Here is a link to the Supplemental kit that was offered by diyaudio way back when. It doesn't give all the part numbers, but it's a start:

Pass VFET Power Amp Supplemental Kit – diyAudio Store

 

[Quantensprung]

Hi Dennis and WBS

Thanks a lot. That helps me. Now I only need to find someone who wants to sell his essential kit with the matched VFETs. I know that it is relatively hopeless, that this will happen.

Kind Regards
Phil

 

[fabrice63]

Matched Vfets , let's call them Graal ..........

there's a Papa up there , so how knows

.

 

[Dennis Hui]

Hi Phil,

For the Diyaudio version (2 vfets for each channel), no matching is needed.

I've seen the essential kit pop up on the swap meet from time to time so
hopefully you will find something.

Cheers,
Dennis

 

[Russellc]

I bought the Vfet kit, wish I had latched onto the essentials kit and the heat sink bracket for the Vfets!

Russellc

 

[juanitox]

any update on the Sony VFET part3 ? 🙂