Sony vFET Illustrated build guide

[mr_whocares]

update

my quick update...

VFETs are now in place. after approx. 1h warm up , following values could be set:

R5: 1506 mV

R6: 1516 mV

R31: 0-30mV

R32: 100mV

output DC: 14mV

I am going to build the other channel during the next days and then check the sound

many thanks to you all, especially nelson, for this nice project and all the support.

cheeers

 

[Seegs108]

Awesome! Thanks for the feedback guys. Much appreciated.

 

[mr_whocares]

hi everybody,

today i finished the amp. i measure followings:

cold (after 1 minute):

..............left channel / right channel

output DC: 90 mV / 61 mV

R31(T18): 212 mV / 370mv

R32: 106 mV / 107 mV


warm after 45 minutes:

............left channel / right channel

output DC: 20 mV / 8 mV

R31(T18): 1 mV / 1 mv

R32: 100 mV / 102 mV

I think these values are ok. But for the PSU I measure with both channels connected just 26,7 V. (with one channel it was 29,5 V ). the voltage drop over the R19 and R20 is 2,7 V which should still be sufficient according to Nelson. However, before I go forward and connect the speakers , I want to make sure if there is any need for further actions? any suggestions?

thanks and regards

 

[Zen Mod]

I believe you're good to go

 

[Bare]

Wow lotsa meters.
erm... Whats' the Vaseline for ?

 

[Dennis Hui]

The only thing I would ask is if you did the final adjustment after warm up
with the lid on. (In case there is some difference because of temp)

Happy listening.

 

[mr_whocares]

hi zen mod, bare and dennis,

many thanks for the feedbacks. i will go and connect the amp to speakers today

indeed, the situation changed as i put the lid on i had to re_adjust the settings again. the amp gets almost stable after 60 minutes ;-)

i get following settings now with the lid on (please see the attached image).

@bare: the vaseline was used for a plaster cast . but maybe i could give it a try and oil the VFET engines too :-D
i was lucky to have/find some DMMs. they were very helpful for setting the amp. i was propably lost if i had to do it with just one DMM . as a matter of fact, i use 6x DMMs to set the amp with the lid on :-D

i will report when the amp is playing music ;-) . many thanks again!

best regards

 

[mr_whocares]

update

update:

the amp plays music very nicely, dynamic, transparent with a dark background.

let me give him around 100h of playing time before i compare it to my single-ended 300b ;-)

at this stage may i send again lot of thanks to everybody, especially to nelson and the diyaudio team for making this experience possible!

best regards

 

[mr_whocares]

two questions please:

- which input level (RMS) is needed in order to get the full output power out of this amp? (how is the calculation? ).

- is the input impedance of the amp about 50K ohm?

many thanks and regards

 

[Zen Mod]

Rin equals value of R2


gain of amp is pretty much ratio of R3/R4 , so 6.67V/V

15W/8R means ~31Vpp

divided with 6.67 , that's 4.65Vpp

divided further with 2 , then with 1.41 , it will be 1.64Vrms

so , any modern source will drive it to full throttle

 

[mr_whocares]

many thanks for the lecture, dear zen mod!
best regards

 

[Seegs108]

Quick question guys. I cheated and bought one of these amps pre-built from a DIYer who was looking to offload a few of their self made amps. I'm coming from a Parasound Halo A21 which only does about 8 watts of pure class A before going to A/B. So I was expecting this amp to run hotter. But how hot is too hot? I'm measuring ~115 degrees F (44C) at the edge of the heatsink fins and ~130 degrees F (54C) at the base of the fins where they attach to the side wall of the aluminum chassis. The faceplate and rest of the amps outside surface area are also around 115 degrees F. Is all of this within "normal" operating temperatures? It just barely passes the 5 second rule that I've read about.

 

[coolnose]

I would say that sounds OK for a Pass Amplifier. But can certainly be changed, also you might want to check some internal values as you did not build it yourself - whoever build it.

 

[Zen Mod]

if everything is ok electrically , just make Babysitter

 

[wdecho]

Quick question guys. I cheated and bought one of these amps pre-built from a DIYer who was looking to offload a few of their self made amps. I'm coming from a Parasound Halo A21 which only does about 8 watts of pure class A before going to A/B. So I was expecting this amp to run hotter. But how hot is too hot? I'm measuring ~115 degrees F (44C) at the edge of the heatsink fins and ~130 degrees F (54C) at the base of the fins where they attach to the side wall of the aluminum chassis. The faceplate and rest of the amps outside surface area are also around 115 degrees F. Is all of this within "normal" operating temperatures? It just barely passes the 5 second rule that I've read about.

55C degrees is considered normal for Firstwatt amplifier. Some including myself push 60C to 65C without any problem.

 

[Seegs108]

Thanks guys. I appreciate the information. The only thing I worry about when making some kind of cooling solution is that the fan may be audible during quiet musical passages. I've heard Noctua fans are extremely quite. I may look into building something using those.

 

[Zen Mod]

re-read Babysitter thread

only drek fan is audible at 5-7Vdc

 

[Seegs108]

Thanks. I'll look into that thread more for quiet fans.

 

[Seegs108]

I think the most practical way to go about it wouldn't be a fan underneath the amp. My VFet amp is housed in First Watt clone chassis. So I'm going to try and mount a fan on the back side of the chassis blowing air down each of the heatsink fins. I think this would work quite well and very efficiently cool it.

I'm going to buy two Noctua NF-S12A ULN fans. They're rated for only 8.6dB and still move a lot of air. I can find a cheap 2 amp 12volt DC power supply with a molex connector. Then I just need a molex to two port 3-pin fan adapter. I can do all of this for about $50. I'll probably end up spray painting the fans matte black. The only thing I haven't though of is how I'm going to affix the fans to the back of the amp. I want to avoid glue. I may just build a cheap stand for each fan and have them behind the amp instead essentially butted up against each heatsink.

Items Needed:

Amazon.com: Noctua 120mm, 2 speed setting Anti-Stall Knobs Design SSO2 Bearing Case Cooling Fan NF-S12A ULN: Computers & Accessories

Amazon.com: AC Adapter Hard-Disk Power Supply For Hard Disk Drive Black 12V+5V: Home Audio & Theater

EnLabs LP422TX425CM 10 inch Black Sleeved 4pin IDE Molex to 2 Ports 3Pin/4Pin PWM Fan Power Splitter Adapter Cable - 12V DC Only - Newegg.com

 

[Zen Mod]

do it in your own way ...... though , I made Babysitter as sort of universal solution

cheap too ....... generic 12cm fan , scavenged from dead PC PSU

mobile phone charger ....... pretty much anything can be used for fan power

Noctua is overkill ....... wise to use where you need more wind , but this is where you need 5-10C difference , and this setup is doing the work

if possible - try to make it in cheapskate way then , if not satisfied , invest in more efficient solution