Sony vFET Illustrated build guide

many thanks, stijn. would you please share the dc-offset values at cold state and after 1.5h warming up?
do you hear a difference in sound quality when the offset changes duo to the airflow condition?

best regards



I measure:


L channel, cold: 152mV, warm -7mV
R channel, cold 225mV, warm 20mV


I don't know what I can attribute sound wise to the fluctuation in the offset. The amp does sound better warm.
 
Voltages are as follows
G-t6 +30.1; g-t4- .35; t6-t7 +1.35; t6-t11 10.54; g-t18 .93; g-t14 +14.66; g-t19+8.06; g-t17 -9.27;g-t8 -30.06;g-t2 +.56; t8-t9 1.37; t8-t13 -10.15;g-t15 -14.64;g-t20-11.43;g-t16 +6.63

I figured it out it was my tl431 they were both fried from putting my c5 and c6 in the wrong place. On my way to having my very first amp built
 
I have one of these amplifiers pre-built, but with two devices (VFET) per channel rather than the four of the circuit diagram. It has slots for the extra VFETs. I have read that the power goes up slightly and the distortion drops a bit if you use four per channel rather than two, but are there any other advantages i.e. longevity, less stress on the VFETs etc.to using the full complement of four VFETs per channel? It appears to be a drop in as long as the VFETs are matched and the board has the resistors for the extra pair. Any other precautions?
 
Letting the 'magic smoke' out of something is a typical right of passage on the journey to your first DIY amp... Congrats to you - now it's official :)
ive learned alot building it and i've enjoyed it every step of the way.

Eric I just realized that it was your website that inspired me to start doing my own builds and set me on my journey. it was your ib sub build on your website that i was going to actually build first but ended up being the vfet.
thanks for the inspiration and putting your builds out there for me to find .
Brandan
 
Ha- that's too funny, Brandan! A few years ago, I was describing my system to a co-worker only to learn that her father had been using my IB sub web page as a guide to what he was building. We were in a van on the way to the airport when she started texting her father: "You'll never believe who I am sitting next to..." What fun! I hear from people all around the world each week because of my web pages.
 
This is a very good amp don't give up on it just yet.
If you have 32V rails then increase R15 and R16 to 47.5k or 48.7k, this will give you more voltage swing before clipping.
Essentially it will convert it to around a 25W amp.

If you have 31.5V rails use 47.5k
If you have 32.5V rails use 48.7k

We can also increase the gain a little bit but I don't think we need to go there just yet.
Finally managed to change the resistors 15 and 16. After a more accurate reading the rail voltages were just above 32 so I used 48.7k resistors. there is audible improvement. I am beginning to think the amp needs a preamp with lot of gain. The volume on my pre is at about 1'oclock, with other sources never go past 11. I can live with that though. The initial burn in has been completed and everything is very stable now. Was able to get less than 10mV on DC balance. I been comparing the amp with few other vintage Vfets I have and is a worthy contender. Thank you Mr Pass! And thank you to all offering help to complete the project. :)
 
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The stock DIY Sony VFET amp does 15W rms into 8R and has a closed loop gain of 16dB. The input sensitivity is thus about 1.7V rms, which is well within line level, um, levels.

Are you sure your R1 at the input is 2.2k? Maybe you have unintentionally formed a potential divider by using a higher resistance.

Also, a logarithmic pot at 12 o'clock (50% rotation angle) will only pass around 10% of the signal, so you'd just be wasting even more signal and passing more noise with a higher gain preamp.
 
Got my boards stuffed and they have passed the resistance test. Applied voltage as required for part 2 and I'm not sure what to think of some of the readings. Everything looks good until I get to t-6 to t-11 where I have +16.15 volts. At t-8 to t-13 I have -16.15 volts and at G to t-18 I get -16.69 volts. Should I be concerned or is this normal before the pots have been adjusted?
 
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Are T14 and T15 to G close to zero? Sounds like Q3 and Q4 are not turned on properly. Check that Q3 and Q4 are the correct part and are correctly orientated in regard to their respective pinout. Also, check R7 to R10, they're supposed to be 2.21k each. That's where I'd start at least...

Also, pics, plz. Why doesn't anyone post pics, it makes troubleshooting so much easier.
 
Last edited:
G-T6=30.6v. G-T8= -30.6v
G-T4=-24.1v G-T2= 24v
T6-T7= 0.714v T8-T9=0.822v
T6-T11=16.15v T8-T13=-16.15v
G-T18=-16.69v
G-T14=14.36v G-T15=-14.34v
G-T19=12.43v G-T20=-12.68v
G-T17=-13.36v G-T16=7.38v

All of the resistors are in the correct position. The semiconductors seem to be installed correctly as well. Q3-Q4 seem good also. I have inspected the solder side and found nothing. I will post photos later when I have a chance
 
Here are the photos, hope someone can see something I would really like to hear this baby sing
 

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