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WEGA V4810 / SONY TA5650 V-FET Amplifiers   

The my friend Alessandro after reading positive comments on various forums about older amps that use Sony V-FET has purchased a pair of these.

The VFET were used from 1974 to 1981 mainly in equipment produced by Sony and Yamaha and these have a so good sound characteristics that they have become a myth among audiophiles.

After doing a first series of listening sessions with these amplifiers we are convinced of the quality of the sound reproduced by these devices.

Another special feature of these amplifiers is the mosfet drain output on the final stage instead of the most common source output.

This configuration, also used in some old Musical Fidelity amplifiers, prevents the alternating mosfet switch-off so the amplifier work with characteristics similar to class A but without high bias.

I am not a lover of the upgrade made ​​on vintage equipments, in fact I hate these for many reasons such as: difficulty to find materials after a fault, almost impossibility to replicate the project and the changes of materials after a long time.

I have already created a source for my friend with my last DAC so I decided to undertake this upgrade and I hope that everything goes without problems.

We started with a Wega Integrated Stereo Amplifier V4810, very similar to Sony TA5650, in which we had to remove all the unnecessary parts, leaving only the volume control and the final section.

The space obtained  by the elimination of the pre-ampl. section and tone controls will be used to create a CLC power supply in order to reduce the noise derived from the current peaks on the rectification diodes.

Follows a photo of the original version before the upgrade.

Step 1 -  remove all the unnecessary parts

I have removed all modules relative to the pre-ampl. section and input selection, only one wire must be cut for this operation.

Step 2 -  create new panels

To keep the same external look I have created two panels to fix 4 regulators without wire and this allow to keep the knobs.

Step 3 -  convert the power supply in CLC

The original power supply use a pair of 10000uF 50V Nichicon capacitors with about 300mVrms ripple.
The new power supply use a pair of Hammond 159ZJ chokes and a pair of 10000uF 50V Nichicon KG Super Through.
Each channel receive a separated power supply +VCC and -VCC at 44V and a regulated +VDD and -VDD at 80V for the mosfet drivers so keep attention.
All the parts has been found is these web shop.

The CLC power supply skip any noise problem and it is superior to any pure capacitor design also if large value are used.
In the following simulations with PSU Designer II you can see the big difference in residual noise, with CLC type we get a pure sine wave so it mean low harmonics.



The Hammond 159ZJ (L=10mH Rdc=0.16ohm Imax=5A) used in this amplifier are not difficult to integrate in any amplifier because these have a compact size and these are not expensive.

 

Step 4 -  insert ALPS volume control

I have decided with Alessandro to use a common ALPS 50K but if the budget is not a problem use a DACT stepper attenuator.

Step 5 - modify input cap

There is a single capacitor on the signal path so must be of extreme high quality, the original value is 10uF 100V but this work at about 0.7V-1.4V.
Probably Sony have used 100V to be sure to separate the source in case of transistor fault but it is practically impossible that the first transistor of a mosfet amplifier  go in fault and the base go to +VCC.
I have used a Sanyo OS-CON 10uF 6.3V to keep the low frequency band to 0.2Hz like original but you can use one 1uF or 2.2uF if you prefer.
I consider good MKP only the Auricap or Jantzen Z-CAP red so there is no space to mount these and please forget Solen, Mundorf, Audyn-Cap, Wima.

Step 6 - re cabling outputs

I have replaced the output cable with CS16 to eliminate the output selection on the signal path, the relay must be used to keep the protection.

Follows a photo of the new version after the upgrade, new wooden sides will be realized in the short solid wood.

Here the total cost of this operation, many parts got from Audiokit webshop

description number unit price tot price
Cable KS675 2 6 12
Cable CS16 black 2 4 8
Cable CS16 red 2 4 8
Hammond 159ZJ 2 22 44
Capacitors KG 10000uF 50V 2 15 30
Sanyo OS-CON 10uF 10V 2 3 6
L aluminum 40mm x 1.5mm 1 5 5
ALPS RK27 50K 1 11 11
total     125

Soon comments on listen test by Alessandro.