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the my new STAX Amplifier with 6BX7
zero noise and lower cost with the same sonic performance of the previous project with 4300B

started 1 jan. 2002 update 2 september 2012

UPDATE:

In 2002 I had not yet measuring instruments so my projects were still only based on calculations and simulations.
This project presents a serious problem on first stage, the parasitic capacitance of the inductance creates a limitation in the frequency response.
I suggest to modify the stage by inserting a resistance on anode and completely eliminate the inductance LL1667.
If you have not implemented the project suggest using a D3a triode instead of the 6SL7, see my last 300B SE.
You can change the big 8uF and the 100uF 400VAC with the new Jensen electrol. 100uF+100uF 500V and the 220uF ELNA Cerafine with Nichikon MUSE 220uF 50V.

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Photos of the first release

INTRODUCTION

After many attempts to get the maximum performances from high quality dynamic headphones, the SESS Single Ended Single Stage amp is the my lastest creature, I have started to think about electrostatic headphones.
The electrostatic headphones are on paper, and in the opinion of many people the best for resolution and detail.
I have seen many schematics about amps to drive these headphones from the solid state solution to vacuum tube project and slso the original Stax products.
The first two steps have been search for the best supplier and to find the best product on the market.
I have compared specifications of many different models..
STAX is a leader in this field, because it is specialized in this kind of product and the models SR-303 or SR-404 seem to be the best choices.
I bought the SR-303 headset from Audio FX (see http://www.audiofx.com/) using the secure ordering system at a very good price, and the waiting time for delivery was very short.
The datasheet of this product can be seen at the official Stax website (see http://www.stax.co.jp - english version is available).
The SR-404 has a higher price but seem to be very similar to SR-303 in specifications.
After acquiring the headset I started to think about my design for a no compromise amp.
 I made a list of target requirements:

- all tubes on the signal path
- no feedback
- min signal output voltage 250Vrms push-pull
- min signal output current 7mA
- max 2 stages
- only hi-end audio components on the signal path
- passive power supply
- vacuum diode on power supply
- no custom power supply transformer
- no regulator tubes or pentode with low linearity
- inductive power supply to prevent the generation of current peak on diodes
- no dc coupled of stage
- no dual power supply
- indirect heating tubes for zero noise

The requirements are not few items but the design is very easy.


COMPONENTS

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

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.

The input stage is the very good Golden Dragon 6SL7.

The input stage is the incredible  RCA 6BX7.


The vacuum diodes used are the 5Y3 Mullard.

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 best of the ELNA Cerafine or other 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
 

 

CHASSIE