2005 V-FET PAGES

Sony TA-N7 "King V-FET"

updated Feb 2008 (Important preventative service advice added plus listening impressions)

(vertical field effect transistor)

Junichi Nishizawa

TAF7 PAGE TA-N7 PAGE

Here are some pictures of my silver TA-N7 serial number 6000008. This is a two owner amplifier and was once owned by a former Head of Sony (UK) Mr Morecombe.

Its in almost mint condition. There are some minor marks on the left grab handle.

This is a supremely capable performer. Having just built some very nice single ended valve amps I can confirm very confidently that a V-FET has many valve like qualities. However, it runs much more coolly and is much more powerful.

This amplifier is completely silent and generates no background hiss at all.

How does it sound?

The VFET internal structure is supposed to mimic that of a triode valve. I haven't found any reference that helps to confirm or explain this.

However, the TA-N7 certainly sounds like a valve amp. It is wonderfully relaxed presenting all types of music. Acting as two completely separate mono amps built in one chassis it is able to spray sounds around the room. Even in my small listening area it generates an incredibly life like image. It is free of distortion and able to extract surprising detail. Listening in the evening I find myself relaxing getting sucked into that hologram only to be suddenly brought back by all that sparkling insight and detail.

It is completely unforced unprocessed + natural.

You simply do not hear the amp even with highly efficient full range drivers. Its stony black silence just lets the music flow.

This is a wonderful sounding piece of equipment. Easily the best sounding solid state amp I have heard.

IMPORTANT SERVICING INFORMATION

Dec 2007-Jan 2007

This amp has always run very cool. You should be able to feel some warmth coming from the slotted top grille. I didn't think much of the fact that this summer it seemed to be running cooler than ever.

The sound during Dec 2007 became increasingly thin and bass light. Suddenly without any incident the left channel started to get a bit quieter and developed quite a distinct distortion. I check a range of preamps CD players etc.The TA-N7 had a problem On its first inspection it became clear that all the fusible resistors on the main power amp boards and wandered well out of specified value. In the worst case a 220ohm was now reading well into the meg range.

All fusible resistors (both channels) have been replaced. 4 small capacitors had also moved out of value and were replaced.

Rubber? pads mounted between the protection relays and PCBs have been removed. They had deterioated into a corrosive goo that was actually starting to attack the PCB underneath. As it turned out the relay's clicking has not altered since.

The distortion problem was only evident at low volume.

Distortion patterns have not been seen on any CRO

All key voltages around the VFETs were perfectly normal.

The large filtering caps 22,000uF were all checked and all worked perfectly. These are very high quality caps and well worth keeping as is.

The actual problem was found to be caused by very low bias voltages around driver transistors in the left channel. Some of these transistors appeared to be getting less that 0.2V bias. One non fusible resistor was actually causing the problem.

Conclusion.

Your fusible resistors may need checking. Some caps may change value. Remove the mounting pads under the switching protection relays.

this shot was taken with a 30s exposure. COOL METAL EH?

The green neon is very difficult to capture

here sitting on top of a Coral BL-25D

the internal arrangement showing 6 V-FETs per side. They are mounted vertically behind cast metal panels (Allen heads). The whole lot weighs about 22kg. One toroidal transformer per mono amp and access to approx 90,000uF charge storage

grab handles are a very good idea in this case

press power on and there is slight delay and twin protection relays click in. Neon glows green

grand scale

Following recent issues

Mr wonderful, Feb 2008 (30 years young)

Currently ticking over with my Lowther PM7s

some of those wonderful VFETS