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Phono End preamplifier
Feb 7 st , 2009 

 
INTRODUCTION

This project born to be a no compromise phono preamplifier without budget limit.

These are the main characteristics:

Only 2 stages Only 2 vacuum tubes on the signal path No capacitor on the signal path (escluding RIAA network) No resistor on the signal path (escluding RIAA network) Less components of any other design Output impedance and level to drive any final amplifier without a pre-ampl. MC input option using a step-up transformer Amorphous core interstage transformers Passive power supply

COMPONENTS

In this projects has been used the top of the components like only tantalum resistors and Silver Mica Radial Capacitor in the RIAA network.
These kind of components are used by AudioNote in the top series production (price about 20000 - 30000$).
The two interstage transformers are amorphous C-core by Lundahl to get the best sonic performances.
On cathode the by-pass are good Sanyo OS-CON capacitors considered better than old ELNA Cerafine and Black Gate.
The power supply use a pair of 100H Lundahl choke and Jensen AudioGrade electrolytc capacitors.
This project can be fit in a normal chassie with height of 80mm like the GX 388 by Hi-Fi2000.
It is possible separate the power supply of each channel using one more 100H choke.
I have used a single solid copper wire for the ground from the input to the output llike Mr. Sakuma.

DESIGN

To calculate the RIAA network I have used the spreadsheet of Fabrizio Marignoni

The design of this phono preampl. is very simple, only 13 components per each channel.

The C3g is a very low noise pentode, made in Germary by Siemens.

This is a very long life tube, minimum of 10.000 hours.

This is a a perfect tube, if it is connected as triode (g2 -> a, g3 -> k) Ua = 200V, RK = 180 Ohm, Ia = 17 mA, S = 17mA/V, µ = 40, Ri = 2,3 KOhm.

In the measurement test I have seen 38Vrms with a distortion of only 1.5%.

I have buy the C3g from Classic Components eBay shop.

The operation point of the C3g has been the result of many measurement with the Clio system by Audiomatica.

 

I have choiced a passive power supply

For this power supply I have used the R-CORE model R26-90 by DiyClub.Biz with primaries 2 x 115v and seconaries 0-165v(0.2A) + 2 x 0-9v (1.1A).

For configuring the Lundahl transformers, Jac Music have designed a matrix programmable PCB, which makes it easier to switch between configurations to try things out. 

EE27 board

The same Jac Music shop have still a stock of NOS C3g tubes.

 

MEASUREMENTS

With an input level of 13mV rms we have about 2.1Vrms on output so the voltage gain is 161x = 44dB.

SONIC PERFORMANCES

The result is incredible. I suggest this project only if you have a very good amplifier.

TEST SYSTEM

To use the cartridge SUMIKO BLUE POINT EVO III is not necessary the step-up LL1931 because it is a high output level MC.

    

LISTENING TEST by Ronan Daly

From: Ronan Daly 
Sent: Thursday, August 19, 2010 5:36 PM
Subject: RE:

 
Hi Andrea,
                I compared it with the my Audio Innovation  copy using Teflon V-caps and Vishay TX2575 resistors built using the schematic on the Audio Note website using 1 tube  (two stages) per channel and no cathode follower so there was a  chance to compare V cap capacitor  vs transformer interstage coupling. The Audio Note was the best I ever heard up to now beating all the cathode follower units I  compared it with. The phono end was however better. The units sounded similar  but the phono end had slightly more definition, drums sounded more focused and cleaner sounding. Another listener in his seventies thought your unit was slightly  smoother  and easier to listen to.

Ronan Daly
 

 

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