SUN AUDIO SV-2A3 amplifier

This Japanese single-ended, vacuum tube amplifier can be purchased in ‘kit’ form or fully assembled.

Power output is 3.5 watts/channel.   Supplied with Russian Sovtek tubes – 2A3 (2), 6SN7 (2), 5U4G (1).   Amplifier weight is 16 kgs.

Input Sensitivity is high (150mV), so with the in-built volume controls, this amplifier will accept Line level sources easily.

This is the amplifier in ‘kit’ form with chassis hardware factory pre-assembled:



Completed amplifier:





Mr Uchida of Sun Audio has a close association with Tamura:



1.6mm steel chassis:


This is one of the drawings supplied by Sun Audio:


Completed wiring:


One component was changed – Cardas twin 21awg shielded input cable was used:

(Supplied volume pots are TKD.)


Another view of the input/driver tube socket assembly:


The schematic with 3 triode stages, looks not unusual, except for direct-coupled input-driver tubes. Not inexpensive, however this amp sounds excellent.

sv 2a3

Japanese electrical devices typically have un-Earthed chassis.  However in this country, I connected chassis-to-Earth and also connected the Circuit Ground to the chassis Earth post (adjacent to the input sockets) via a 10 ohm resistor / 0.1uF cap bypass.

(The so-called a ‘Ground loop break’, minimises Ground loop currents, whilst maintaining RF shielding.)


(This amplifier kit was built many years ago and has not been in use for 5-10 years, so a Variac was used as a precaution to gently ‘re-form’ the 500v electrolytic filter capacitors, slowly lifting voltage over say 30-60 minutes.


The sound:

As said, this amplifier sounds very good, surprisingly good – lively and dynamic, open and ‘fresh’.  Plenty of ‘resonance’ and ambient ‘decay’.  Bass is strong, deep and rhythmic, but controlled.  Treble leaves no complaints – as any tube-rectified, single-ended triode amplifier should. Plenty of bandwidth and  attractive tone.

Of course, the Tamura transformer components (the Output Transformers in particular) will be of high quality, excellent possibly, sonically and mechanically.

Postscript 03 Jan:

I note that the Power Transformer runs VERY hot (summertime here, 20-24deg C), too hot to hold a hand on it  – I will monitor this & maybe employ a computer cooling fan for the summer months.

Power Transformer case temperature reaches 53deg C (at 27deg C ambient temp.) – reduced to 33-35deg C using a cooling fan.




5 thoughts on “SUN AUDIO SV-2A3 amplifier

  1. Hi Owen,

    I am very impressed with the beautiful work you did assembling your SunAudio. I would be ashamed to show you the inside of mine 🙂

    It is my first and only kit i ever assembled 5 years ago and i have been completely faithful to it ever since.

    I moved from a Pass Aleph 0s to the SunAudio 2A3 when i went back to analog and i am a big enthousiastic of Class A SE tubes amps with low power output on efficient speakers.

    My system is nice as it is, if i ever upgrade it, i would be looking for maybe 2 monoblocks similar SE class A 2A3. Any thoughts ?

    I am also wondering why you did not use your SunAudio for that long ?

    Cheers 🙂


    • Hi Maxime – thanks for your comments.
      The Sun SV-2A3 is still in use in a 2nd system in my office, playing mainly FM Radio.
      However, DIY building is my main interest & I use my DIY 2A3PP amplifier – which also provides a little more power & lower damping factor than SE output.

      If you build monoblocks, there may be no advantage unless you build a more powerful amp design. IMHO a single large PSU is better than 2 x smaller PSUs. Not sure what amp design you have in mind.
      Cheers, Owen

      • Hi Owen,

        Thank you so much for the tip on power supplyand mono blocks. So i chose to upgrade with active amplification, 2 more SE class A amps similar to the SunAudio. The small 6EM7 and from McChanson.

        I ll let you know how they all sound together once i set them up.



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