Balanced Phono-Amps: An Extension to the 'The Sound of Silence' Editions

871 Pages·2019·25.597 MB·English

by  Burkhard Vogel

Burkhard Vogel
Balanced
Phono-Amps
An Extension to the
‘The Sound of Silence’ Editions
Second Edition
Balanced Phono-Amps
Burkhard Vogel
Balanced Phono-Amps
‘ ’
An Extension to the The Sound of Silence
Editions
Second Edition
Primary Focus: Lowest Noise Solutions with
Triodes and Solid-State Devices
•
Calculated
•
Simulated
•
Measured
123
Burkhard Vogel
Lab6-11
Information andAudioTechnology
Stuttgart, Germany
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To Beate
Preface to the 2nd Edition
This 2nd edition marks a turning point in my life as analogue audio amplifier
enthusiast. In the past as General Manager and/or CEO of several software-
producing companies I had to learn to live with the sometimes rather strange
looking attitudes towards customers. What I mean is the way of developing and
selling software by use of astonishing approaches with eg taking customers by
surprise with huge announcement actions, offering of beta versions, steadily ship-
ping of releases to improve incomplete or defective versions, collecting of
improvements via ‘let the customers do the job demands’, continuous and
never-ending bug fixing, etc. These software related experiences triggered my
mistrust most when it comes to acceptance questions concerning simulation soft-
wareforaudioequipmentandtheirdevices.Nevertheless,Ihadtolearnthatduring
the past three decades things changed a lot on the field of software-based simula-
tions of electronic circuits. Very expensive softwares had to go, replaced by free
solutions à la LTSpice from Linear Technology.
That’swhyI’mconvincednowthat—concerningthelow-noiseaudioequipment
I present in the book on hand—this modern simulation software will be able to
yield results very close to the calculated and measured ones.
However,theapplicationofsuchsoftwarewillworkwellonlyifweunderstand
howthesimulatedDUTtreatsallkindsofamplifiertransferquestionsinallpartsof
its electronic circuit. In most chapters of this book the basic focus is on noise
generation of audio pre-amps. It is a very wide field that is eg poorly managed by
manySpicemodelsofbipolarjunctiontransistors(BJTs),valves,andtransformers.
Despite the easy time and cost-saving work with LTSpice I’m also convinced that
only a mathematical description of the DUT’s circuit will lead to a full under-
standing of its noise generation.
I think, after many tests, LTSpice offers the right power to produce reasonable
results. Therefore, concerning the goals of this 2nd edition the enlarged emphasis
lies on the simulation approaches of all presented amplifier and measurement
solutions,ofcourseincludingtheirtraps.Gainedresultswillalwaysbepresentedin
conjunction and comparison with the necessary calculation results. In most cases,
measurement results judge the software’s usability additionally.
vii
viii Prefacetothe2ndEdition
Thus,withregardtothe1stedition(TSOS-E-1)theherepresented2ndeditionof
“Balanced Phono-Amps” (TSOS-E-2) shows the following improvements and
add-ons:
1. A very new ‘Part I: Basics—Simulations and Calculations’ with nine chapters
covers the fundamentals about the noise calculation and simulation alternatives
of fully differential amplifiers, based on solid state (BJTs and op-amps) and
triode designs. It also includes excess noise calculations and simulations of
resistors.
A new and extensive chapter allows calculating the Spice flicker noise coeffi-
cientsAFandKFofBJTs.Exclusively,applicationofthesefactorswillleadto
useful and sense-making noise simulations of electronic circuits with BJTs.
In the professional as well as in the consumer world small-signal triodes still
play a major role in audio pre-amplifier circuits (triodes in power amplification
are not on the focus of this book). A new chapter about the triode’s noise
production allows simulating any kind of triode in any kind of small-signal
audio configuration.
2. In‘PartII:ExamplePhono-Amp—TheRIAAPhono-AmpEngineII’(formerly
Part I and now with 12 chapters) various simulation approaches complete the
measurement and calculation results of all shown amplifier stages of the
headline’s Engine II. Its main focus is on MC cartridge amplification.
3. ‘Part III: Knowledge Transfer’ (formerly Part II and now with 12 chapters) is
still a collection of amplifier designs (also with new and extremely low-noise
ones) and useful measurement devices. Additionally and under the light of the
balanced or un-balanced question, I add a further discussion on MM amplifi-
cation including or excluding very sophisticated load synthesis (also called
electronicresistorcooling)approaches.Thispartisrounded-upbyanextensive
chapter with—partly self-developed—Spice models of all devices used in this
book.
4. Verydetailedindexesofthisbook(black)andofthe2ndeditionof‘TheSound
of Silence’ (red) close the book’s ‘Part IV: Appendices and Indexes’.
5. Readers may be surprised that I do not tackle noise issues of Junction Field
EffectTransistors(JFETs)indepth.Infact,comparedwithBJTstheydonotfall
into the lowest-noise category of singletons in MC amplification circuits. Like
triodes,theirsingletonplacecouldbefoundinotherthanMCinputstages;egin
inputstagesofMMphono-ampsorinintermediateampstages.Iguess,thetwo
editions of‘TheSoundofSilence’andtheherepresentedChaps.22and23do
offerenoughinsightintothematter.Nevertheless,inChap.22Ipresentpre-amp
solutionswithseveralparalleledinputJFETsand/orextensiveparalleledJFETs
in long-tailed pair (LTP) configurations, however, not designed by myself.
6. Ofcourse,ItriedtofindandItookcareofalltypos,bugsandcalculationerrors.
Additionally, I’ve changed the temperature and tolerance settings on all
Mathcadworksheets:fromT:=315Kor300KtoT:=300.15K,fromdefault
TOL := 10−3 to TOL := 10−12 or 10−14. Thus, direct comparisons with simu-
lation results are based now on common treatments.
Prefacetothe2ndEdition ix
7. On Springer’s website of ‘Extra Materials’ readers will find all Mathcad
worksheets presented in this book. They can be downloaded free of charge.
8. Many thanks to:
8:1 The authors of ‘The Art of Electronics’, Mr. Hill and Mr. Horowitz, who
provided me with important spectra about the noise voltage density of
extremely low-noise BJTs.
8:2 Douglas Self, who convinced me to produce a clearer statement about the
advantages and disadvantages of balanced and/or un-balanced input stages
of MM phono-amps, of course in conjunction with his special approach of
load synthesis.
8:3 Jan Didden, who did not hesitate to publish short versions of some of the
book’s chapters in his Linear Audio bookzines, completed by a number of
letters to the editor, still available on LA’s website free of charge.
Stuttgart, Germany Burkhard Vogel
October 2018
Preface to the 1st Edition
In2011,the2ndeditionofmy“TheSoundofSilence”(TSOS-2)bookappearedon
the markets. The integration of a broad range of valve solutions became the main
difference to the 1st edition (TSOS-1). In the July/August 2014 volume of their
JAES publication the Audio Engineering Society published an article about “The
Vinyl Frontier” showing remarkable sales quantities of vinyl LPs in the UK: from
200,000 in 2009 to 780,000 in 2013. At the same time, I have read in US, French
and German newspapers about an equally massive sales increase. Parallel to those
increasing LP sales very interesting newly developed turntables and phono-
amplifiers of all kinds of technology entered (and still do) the markets. The price
rangeishugetooandapriceof (cid:1)15,000.00EUR/(cid:1)18,000.00$foraphono-amp
or turntable is no longer impossible. Hence, despite the still rather small overall
quantities, vinyl is back again-and it produces reasonable revenues and profit.
Having studied theabove-mentioned editions of my books the observantreader
mightstumbleoverthefactthatthedesignofafullybalancedRIAAphono-ampis
missing.Finally,inthesebooks,allmathematicalanddesignorientedeffortsledto
thesemi-balanced“RIAAPhono-AmpEngineI”thatincludesdifferentmodulesof
solid-state and triode driven phono-amps. The latter module in the second edition
first. Semi-balanced, because Engine I offers balanced and/or un-balanced inputs,
followed by an un-balanced treatment of the RIAA transfer function creation via a
feedbackpathinthesolid-stateenvironment,andviaonepassivenetworkbetween
two triode gain stages. The outputs are balanced and un-balanced too.
The content of the herewith-presented TSOS-Extension shall fill the obvious
gap. No matter if actively or passively configured, in the book on hand fully
balanced means that each phono-amp stage ends up in a balanced or, in other
words, symmetrical solution, differentially amplified. Un-balanced/single-ended
intermediate solutions are not in the scope.
xi
xii Prefacetothe1stEdition
There are only two exceptions with un-balanced inputs:
1. In cases of input amplifiers for MM cartridges and the MM cartridge has a
connection from one of its output leads to the case (eg many Shure cartridges),
2. In cases of turntables that offer un-balanced connectors and the user does not
want to install balanced cables.
In these cases, it makes sense to integrate un-balanced-in/balanced-out gain
stages via an external input.
Consequently, I call the presented rather complex phono-amp solution “RIAA
Phono-Amp Engine II”. It is thus a kind of platform fulfilling a high number of
designgoals,focusedmainlyonMCcartridgeusage.Amongthesegoals,EngineII
offers
(cid:129) Many testing possibilities of very different active and/or passive amplifier
technologies and cartridge/turntable combinations.
(cid:129) The selection of a simple-mode Engine II for private use or of a complete
test-purpose lab instrument.
(cid:129) A deep insight into all design matters concerning electronic noise and stage
circuitry through extensive example calculations with Mathcad worksheets.
Theseworksheetsincludesignal-to-noiseratio(SN)calculationapproaches,and
allnecessarycalculationaspectsconcerninggain,inputandoutputresistances,and
frequency and phase response-settings.
The inclusion of the TSOS-1/-2 indexes should ease follow-ups across the dif-
ferent books. Like in TSOS-1/-2, lowest noise results and an excellent sound
production are still on top of my efforts.
Stuttgart, Germany Burkhard Vogel
March 2015