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the my new reference 2A3 Amplifiers - 2W

ATTENTION: two versions available!

zero noise and max performance to drive full range high efficiency loudspeakers

by Andrea Ciuffoli - 1 jan. 2002

The photos are only of the version 1.0

photo 1
photo 2

Introduction

This new reference amp. born to create a no-compromise project to use with hi-end full range high efficiency (min 98db) loudspeakers like Lowther or AER.
I have design two versions with a differente use: the first is the max expression of a tube amp. because there are no passive components on the signal path, the second give very high performances only when the output tubes work in class A1 but is more easy to drive.
The first version must be driven only from preampl. with low output resistance about 300ohm and the input transformer could be replaced by a normal resistor (about 220Kohm) when the gain is enougth.
The second one could be driven directly (as I do) from the DAC so reducing the signal path. I actually use this second version.

Components

All the audio transformers used in this project are Lundahl products and the distributor list is available here

Only for the version 1.0

2 x LL7903/10mA Lundahl anode interstage transformer
2 x LL1660/10mA Lundahl anode interstage transformer

Only for the version 2.0

2 x LL1667/5mA Lundahl anode choke transformer

For both the versions

2 x LL1623/60mA Lundahl output transformer
2 x LL1648 Lundahl power supply
2 x LL1638/10H 140mA Lundahl power supply choke
MQA-3G3 Jensen 100uF double metallized paper and polypropylene

dielectric impregnated with mineral oil.

MQA-3G2-4045D805KA Jensen 8uF double metallized paper and polypropylene

dielectric impregnated with mineral oil.

Lundahl is one of the world´s leading manufacturer of audio transformers used in many professional studio recording and radio stations so He have a very big experince and all these products use a custom audio C-core.

I am using a DACT stepper attenuator instead of the normal ALPS or NOBLE solution, because the the sound is clearer. A good review of these components can be found on the article published in Hi-Fi World.

For the version 1.0 the input stage tube is the Golden Dragon 6SN7.

For the version 2.0 the input stage tube is the Golden Dragon 6SL7.

The output stage tube is the Golden Dragon 2A3.

The vacuum diodes used are the GZ34 Mullard.

datasheet of the GZ34 (pdf format)

About passive components types, I don't leave many choices: Caddock resistances on cathode, ELNA Cerafine capacitors on cathode.
In all my previous projects I have used in the power supply the ELNA Cerafine capacitors with a very high sonic performances and compact size.
If we skip any economic aspect and no size problem the first components is a paper in oil capacitor.
In comparation test the paper in oil are better than ELNA Cerafine or any electrolityc type.
Searching a paper in oil capacitor is very important buy new product as the Jensen and not an old stock.

About wire forget the teflon ! use only stranded tinned copper wire with pvc isulator and for loudspeakers the same.

A very good quality stranded tinned copper wire could be buy directly from E-Z-HOOK that carries an extensive line of fine stranded and extra flexible wire.

Design of the version 1.0

ATTENTION: This version could be driven only with preampl. with low output resistance about 300ohm

Design of the version 2.0

NOTE: This version could be driven directly by any DAC

Chassie

Sonic results

top performance !