Sony vFET Amplifier Part 2

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#2,542
syklab said:
Hi,
Can I replace C1,2,7,8 with 330uF Silmic II instead of 220uf? What is the impact ? or may be go with Pana. Seems like the 220 Silmic II are out of stocks till May from Mouser.
Click to expand...

Mr. Pass commented on possible instability with higher values in these posts:

http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-133.html#post4761256

http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-174.html#post4807913

Cheers,
Dennis
 
#2,543
Nelson Pass said:
Interestingly, while I don't care how excessive you get above the 35V figure
for the regulators and supply filters, I recommend that you use the values
of 47uF and 220 uF where noted. Increasing the 47uF to much higher
values slows the turn-on time to the bias circuit, and for some strange
reason much higher values on the 220 uF for the voltage references seems
to generate some stability issue with the TL431's with a little bit of motor-
boating (I know, it shouldn't).

😎
Click to expand...

Yes, Sounds like there are stability issue when value is above 220. May be can try Nichicon Muse BP 220uf 50V if I can find them.
Thanks
 
#2,544
Gyuri said:
Hey, John,
I have an idea what do you check, assuming that your amp's DC voltages are O.K..
Put a about 2.2VAC 50Hz signal on input.
An audiocard output can be good, and there are online signal generators, like this:
Online Tone Generator - Free, Simple and Easy to Use.
Choosen 50Hz, because it can be measured most of the DMMs.
(In my case it is about 2.2VAC RMS, because this is the level, where my amp started to clipping.)
Measure AC signal at T18, there should be about 17.3VAC.
While output shows about 14VAC RMS.
It is almost exactly 16dB, as Papa stated in the article.
This is a triumph of science and engineering, as I used to say.
Kind regards,
Gyuri
Click to expand...

Gyuri,
Good idea to check AC throughput. I have used something called Sigjenny (I've used this before) with as you suggested a 50Hz output coupled from the PC to my BA3 , set the volume to give an output of 2.2V and took a reading at T18. Result was hardly any output, just 200mV. Even turning the vol on the BA3 to full, giving just over 8Vac in to the amp resulted in just 0.6V at T18.
As I have already suggested it looks like the problem is in the FE somewhere.
The voltage at the LS terminals with 0.6V at T18 was 0.49V which seems to correspond exactly with your relative voltages of 14/17.3 with a ratio of 0.81. So looks like the output stage is ok.
Thanks again for your suggestions. Need to look at it again later this afternoon as I am going out now for my Wednesday run.
Regards, John
 
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#2,545
Well it looks like I built an amp! For my first one it went surprisingly smoothly. Thank you to Nelson and the DiyAudio crew for making this possible!

I spent yesterday installing the VFETs and making adjustments. Left channel went fine but right channel was tough. As I was adjusting the output I would go back and check the front end. At times it felt like I was chasing my tail. I am wondering how critical the T18-G offset is? Right now I have it within about 150mV and the DC offset at the output at 2mV.

I'm going to recheck tonight and see if I can drum up a cheap speaker.
 
#2,547
Dear John,
It is a good feeling for me, that I was able to help a little to you, despite my well known limitations in the fields of EEE.
And perhaps the result is a good news to you.
Do you use Fairchild MOS-FETs or something other than Toshibas, as Dennis guessed?
Regards,
Gyuri
 
#2,548
Gyuri said:
Dear John,
It is a good feeling for me, that I was able to help a little to you, despite my well known limitations in the fields of EEE.
And perhaps the result is a good news to you.
Do you use Fairchild MOS-FETs or something other than Toshibas, as Dennis guessed?
Regards,
Gyuri
Click to expand...

Hi Gyuri,
Yes I used the Fairchild mosfets FQP3N30 and FQP3P20 but It surely can't be those as several others have used them with no problems. Currently thinking and indeed looking at what I can do/check next.
It is good news in that it looks like it is not the all important output stage!
Regards, John
 
#2,550
jaab6
folk have been asked not to clutter-up this thread with this type of post

If you search this forum (or read it thru!!) search for posts from jason (who is acting as Santa's Maker-Elf and all round hero of this project (amongst others)
In fact onlt 2 pages back you would find this post--

Everything is now in stock, and orders should ship in the next 1-2 days.

The VFET status page has been updated with current information:

Sony VFET Kit Status Page – diyAudio Store

We'll offer batch 3 around February 6th, as usual email notifications will be sent out, in order of when you signed up on the list, however based on previous sales I am quite sure there will be enough for everybody and the remainder will list in the store to the public. It won't be ready to ship for a few months.""
Everything is on the store link
 
#2,551
Hark. What is that I hear? Could it be? No, surely not......... yes, yes it is.......... 'tis the sound of a quartet of Sony Vfets singing their melodious song at last!
Those who have seen my recent posts will know that I have had a problem with my Vfet amp, well, I have now discovered what the problem was, fixed it, and now it sings.

Big thanks to Jason, Variac et al for their sterling work in managing this project and even bigger thanks to Nelson for creating this wonderful design and indeed for sharing his personal collection of these rare Vfets

I would also like to thank my friend Gyuri for his support in trying to resolve my amp problem.

Regards, John
 
#2,555
Yes it was something simple, I'm somewhat embarrassed to admit it but it was 2 resistors of an incorrect value (too high). I obviously was either distracted or lost my focus for a very short time when building the boards.
Anyway, it was an easy fix and I have to say that the amp sounds wonderful with holographic imaging and a real sense of presence.

Regards
 
#2,559
Thanks Dennis /Soundhappy.
The casework is not fully complete as yet, I still have some machining work to do on the front panel but I do have some pics taken as part of the build process so I will see what I can post over the weekend.

Regards , John.
 
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