VANDERVEEN TRANS VALVE AMPLIFIERS

Transcription

1 VANDERVEEN TRANS VALVE AMPLIFIERS Ir. Menno van der Veen Web proof reading 2014 Copyright : Menno van der Veen All rights reserved. No part of this book may be reproduced in any material form, including photocopying, or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication, without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act Applications for the copyright holders written permission to reproduce any part of the publication should be addresses to the author. The author has used his best efforts in ensuring the correctness of the information contained in this book. He does not assume, and hereby disclaim, any liability to any party for any loss or damage caused by errors or omissions in this book, whether such errors or omissions result from negligence, accident or any other cause.

2 CONTENT (Not completed yet, I am improving chapters 8 12) 0 Introduction; about the Author 1 Historic foundation of Transconductance 2 Basic principle of Transconductance 3 Why DC coupling? 3-1: The first try-out amplifier 3-2: General qualities of this first amp 3-3: Local feedback around filters 3-4: Why DC-coupling is mandatory? 4 SE-Vanderveen-Little-Trans-1 and : ETF2012-One-Valve-Amp converted into Vanderveen-Little-Trans-1 4-2: Measurement results 4-3: Subjective results 4-4: More output power with Vanderveen-Little-Trans-2 5 Trans has to meet high demands 5-1: Demands on the output transformer 5-2: Demands on the voltage controlled current source 5-3: DC-coupling and Auto-Bias 5-4: Pentode or Ultra-Linear or Triode power valves? 5-5: Pairing/matching of the components 6 Trans try-out with an opamp current source 6-1: Basic concept with an opamp current source 6-2: How the current sources A and B are realized 6-3: The active auto-bias circuit 6-4: The Trans circuit per power valve 6-5: The complete PP-Trans amplifier 6-7: Conclusion and how to proceed 7 The Vanderveen-Trans-30-A valve amplifier 7-1: Concept of the Vanderveen-Trans : The Trans circuit per power valve 7-3: The auto-bias circuit of the Trans : The complete Vanderveen-Trans-30 circuit 7-5: Objective results 7-6: Subjective results 7-7: The next step to audio heaven? 8 Trans-30-B without coupling capacitors

3 0 Introduction It was 1985 when my first valve amplifier design became published. Proud that I was! Many designs followed in my books and AES-papers. In all my work I used the immense experience and knowledge of my predecessors. Fortunately I discovered some new findings, like my toroidal output transformers. It was 1995 when I read a special article about transconductance in valve amplifiers. I sensed that it was very valuable, maybe containing some flaws. I had to wait till 2013 to find the time to really study it. I found the small flaws and decided to follow this approach. After one year of trial and error my first Trans-amp was ready. I was deeply impressed, like having delved gold. To make sure not to be too subjective and pleased by myself, I used my TubeSociety students, golden ears at Rhapsody and the guys at the European Triode Festival to give me feedback. They told me all was nice and wonderful and fantastic. So, maybe my Trans-amp was not that bad. This gave me hope for the future. After that, reality made me ask some questions. I had a new amp: so what? Bring it to the market and start a new Vanderveen production company, or some other smart idea? Taking my age into account (whoa, this is hard to say), I decided for two future routes. I wish to share my knowledge with my TubeSociety students and I will write a new book. In there you will find my research on high quality transconductance valve audio amplifiers. I call them TRANS and when it is a small amp, the name shall be LITTLE TRANS. In my research I have been largely supported by my friend Pierre Touzelet. He applied his fast knowledge to control my findings. He is often mentioned with gratitude and some of his reports are in the attachment for further research and clarification. I hope you will enjoy reading about TRANS, and I encourage you to follow this trail to make your own wonderful designs. The Netherlands Hichtum

4 1 Historic foundation of Transconductance It was around 1950 when valve amplifiers were in full development. Peter Walker introduced cathode feedback. Lackey and Chilton (1933) and Blumlein (1937) and Keroes and Hafler (1951) (1, 2) gave birth to Ultra Linear amplifiers. McIntosh (1949) (3) realized the ultimo, combining cathode and screen grid feedback. Many years later I described their inventions in one standard model (4; chapter 3). The years following, special ways of local feedback were introduced, like from the anode of the power valve to the cathode of the driving triode. PPP and Circlotron were invented and Futterman (5) made his famous transformer less OTL amps. Years later Baby Huy inspired the world by his synergy jump of local feedback between the anodes of the driving triode and the power valve. I built and researched most of these famous circuits (6). They all lead to two objectives. Make the power valve linear and drive the output transformer with a low impedance voltage source. As a result the distortions in the power valve and in the output transformer will become negligible. That really will create true analytic hi-fidelity audio enjoyment. Almost contrary were the early approaches of Electro Voice and Eastern Electric (strongly adapted by Japanese audiophiles, see (7)). None overall feedback and Single Ended were applied there. This old approach resulted in very pleasant and musical reproduction, although harmonic distortions were terrible. Certainly not around a millionth (PPM) as available nowadays. I will not discuss these important and valuable designs in this book. When you apply local negative feedback at the cathode and the screen grid of the power valve, you realize small distortions inside the power valves. However, to drive such compensated valves you need huge drive voltages at the control grid. Because you have to make them huge, they will get distorted which has to be cured by applying overall negative feedback. This was true until Hot Audio Power was published (9, 10 and 11). There a minuscule small linear voltage driven current source was introduced to drive the power valves. This new transconductance method included 100 % local feedback around the power valves, recreating them into low impedance and low distortion voltage sources. Through this the output transformer is driven in the best way imaginable. In this new circuit the output transformer was not included in the feedback path! I will explain why this is important. Transconductance is a new route to high quality sound reproduction. It is based on the high quality inventions of the oldies. It gives a modern answer to the old goal of true audio reproduction: highly linear undistorted sound reproduction with valve amplifiers. This small booklet is devoted to this subject.

5 In the introduction I started to mention the most important sources. To enable you to follow what I say, I now already give the (yet incomplete) literature list. 11 Literature (1) F. Langford Smith and Chesterman: Ultra Linear Amplifiers ; Radiotronics, May (2) D. Hafler and H.I. Keroes: An Ultra-Linear Amplifier ; Audio Eng ; (Nov., 1951), 15. (3) Frank H. McINTOSH and Gordon J. Gow: Description and analyses of a New 50-Watt Amplifier Circuit ; Audio Engineering, December (4) Menno van der Veen: High-end Valve Amplifiers 2, Elektor; ISBN (5) Julius Futterman: An output transformerless power amplifier ; JAES, Vol.2, Oct., (6) Menno van der Veen:"Universal system and output transformer for valve amplifiers"; 118th AES Convention 2005, Barcelona; paper (7) Jean Hiraga: Initiation aux amplis a tubes ; Eyerolles. (8) Jens Hjortkjaer and Mads Walther-Hansen: Perceptual effects of dynamic range compression in popular music recordings ; JAES, no.62, 1-2; pp (9) Jeff Macaulay: Hot audio power ; EW + WW 1995 Oct., pp (10) Letters: Hot audio power ; EW + WW 1995 Dec., pp (11) D. C. Haigh: Letters: Improved Hot audio power ; EW + WW 1996, Jan., pp.36. (12) Dutch section TubeSociety project 2012 (13) Menno van der Veen: "Low level audio signal transfer through transformers conflicts with permeability behavior inside their cores"; 122nd AES Convention 2007, Austria, paper (14) Menno van der Veen: "Signal level and frequency dependent losses inside audio signal transformers and how to prevent those"; paper 8360, 130th AES Convention 2011 in London. (15) Menno van der Veen: Ontwerp van een unieke 1-buis-versterker ; Masterclass DVD; Elektor; ISBN (16) (17) Dutch section TubeSociety project 2011 (18) P.touzelet@orange.fr (19) Menno van der Veen: Dieper kijken in de uitgangstransformator ; Elektor Audio Special-5; pp (20) en (21) W. Marshall Leach Jr.: Current Mirrors ; Georgia Institute of Technology, School of Electrical and Computer Engineering; Copyright (22) Menno van der Veen: Designing Tube Amplifiers ; Elektor; ISBN: (23) Hessel@haagsma.nl (24) Dutch section TubeSociety project 2013 (25) Frank Blöhbaum: Multiplied Transconductance Amplifiers Part 1 ; Linear Audio Vol. 6; pp ; ISBN: (26) Dr. Tom Hodgson: To Be, or Not To Be, Linear!, The Single-Ended Transformer ; Sound Practices Issue 10, pp