I’m reluctant to use the word ‘sexy’ when it comes to hi-fi gear because, well – it just feels weird. If I were to use it though, it would be about this baby Sony TA-4650 VFET amplifier.
What can one say after working one of these stunning Sony TA-4650 VFET integrated amplifiers? I really fell for this little beauty and came to understand why so many people treasure these amps.
Having said that, there are a few critically important things to be aware of, if you own one of these or are planning on buying one. You definitely don’t want to take one of these to just anyone for service. I’ll explain why as we go.
Power output: 30 watts per channel into 8Ω (stereo) Frequency response: 10Hz to 100kHz Total harmonic distortion: 0.05% Damping factor: 45 Input sensitivity: 2.5mV (MM), 150mV (line) Signal to noise ratio: 70dB (MM), 90dB (line) Output: 150mV (line), 17mV (DIN), 1V (Pre out) Speaker load impedance: 4Ω (minimum) Semiconductors: 6 x VFET, 4 x FET, 36 x transistors, 26 x diodes Dimensions: 460 x 168 x 323mm Weight: 12.4kg
So, VFETs or vertical field-effect transistors are a long since obsolete output device that promised and delivered great sound. This is great of course if you own one of these little 30 watts per channel beauties, with original output devices. If you blow them, however, you are s$%t out of luck. There is NOTHING that can replace these very unusual output devices, though I can still obtain some of them.
Because they are FETs, these devices are sensitive to static discharge and mishandling. You can kill these just by handling them the wrong way. And because of how Sony implemented them in these amplifiers, they have little protection in the event of something going wrong. Because of all of this, many owners stockpile VFET amps and the VFETs themselves, whenever they find them.
The legendary amplifier designer Nelson Pass, famously pissed off the entire worldwide Sony VFET community when he purchased the very last stocks of VFETs, directly from Sony, for use in his modern VFET amplifier. Lots of unhappy Sony VFET owners…
Sony used a varactor dual-diode package in the bias circuitry of these amps. I’ve studied the schematic and can verify that, if/when these diode packages fail, they will take out the VFETs. This apparently happens quite often, too often to leave them in place.
If you follow what I do, you’ll know that I aim to improve the reliability of hi-fi gear wherever possible. This approach means we keep great equipment like this running well into the future, maybe longer than it’s even been running already. I suggest that, rather than scrounge around for VFETs, you should have your VFET amp properly serviced, to achieve the lowest probability that the VFETs will fail in the future.
As usual, we’ll start by looking at the amplifier layout and then break it down and look at the details of the reliability enhancement process I applied to this little beauty.
And that’s it, the work on this Sony TA-4650 is complete. Her owner reports that she sounds absolutely fantastic after the service she just received and he is very happy with added peace of mind he now has when running his TA-4650.