Oestex ©
GUITAR
AMPS PAGE
SECTION 2: INTRODUCTION:
2.1. INTRODUCTION
2.2 IMPORTANT
REMINDER
2.3 A
NOTE FOR THE UN-INITIATED
INTRODUCTION:
Throughout the history of live performance or
recorded music the guitar has been a featured instrument for many genres,
ranging from classical through to modern styles.
The guitar part may be performed by natural
acoustic instrument or electronically amplified and modified.
In popular music, be it blues, jazz or rock,
the guitar has always been a lead or featured instrument in recorded music and
live performances.
The primary function of the guitar is to
provide a melody line, background chords or “fill” to add body to the sound.
Musicians know that a three piece band
comprising guitar, bass and drums, can sound “empty” or “lacking” in some kinds
of music.
Add a second guitar, usually called a
“rhythm” guitar, and the sound lifts to become full bodied.
In a trio, the guitar has to perform the
functions of both lead and rhythm as the music unfolds, so requires a high
grade of skill and experience to deliver a pleasing performance – but it is
often done very successfully.
As the name suggests, the “lead” guitarist
performs the function of leading the band’s musical performance through the
melody line and solos, setting tempos and loudness, leading starts and stops,
and performing as the lead instrument.
In many bands the sound produced by the lead
guitarist becomes the sound of the band – because all the other instruments are
backing instruments.
Those bands are immediately recognised by the
sound of their lead guitarist. Consequently the lead guitar style and sound
become a band’s trademark.
The actual guitar instrument comes in many,
many forms and variants.
The two primary forms are hollow body and solid
body. Necks vary in width and thickness but are usually, but not always, built
with the same standard length and fret spacings.
The traditional hollow body has variants
ranging from the classical Spanish through to the full bodied contoured
soundboard hollow body modern country designs to semi-hollow, classical
acoustic, folk, thinline and mid-sized “travel” styles.
Solid body guitars are many and varied.
Bodies may be solid timber or laminated plywood or composite wood. Body timbers
may be hardwood or softwood. Necks may be straight grained or random grained.
The weight of guitars varies also, depending
upon construction.
From time to time double-neck versions are
released – usually one six string and one 12 string neck – but they are heavy,
difficult to tune and awkward to handle on stage so are relatively rare.
The electric pedal steel guitar, popular in
country music, has been around for a very long time. It sits horizontally on
legs with the player seated.
Another aspect is the choice of strings.
Change the strings - change the sound.
Steel, stainless steel, nylon bound, nylon
dipped, round, flatwound, light and heavy gauge etc strings all exhibit
different playing and sound characteristics.
The standard historic and most popular string
setup is six strings, but from time to time specialty music genres prefer a 12
stringed instrument.
Electric Guitars are fitted with
electro-magnetic pickups to convert the vibrating string energy into electrical
energy that can be amplified electronically.
Pickups also come in a wide range of designs
and fixing positions internally or externally on the guitar.
Acoustic guitars are limited to gut or steel
strings but can be amplified with an internal or external microphone.
At this point it is pertinent to
differentiate between recorded and live performances.
RECORDED PERFORMANCES
In the case of recorded performances, since
the 1920's when electric recording was introduced the guitar has been
successfully recorded in classical, orchestral and popular music.
This is simply because the guitar is a
popular instrument and an easy instrument to record. With gut strings it does
not exhibit strong harmonics so presents a simple waveshape in a frequency
range easily recordable and replayable with low quality equipment. Even when
harmonics are absent due to limitations in recording or playback, the guitar
still sounds like a guitar – sweet and melodic.
An important difference between recording and
playback is that recording and sound processing is performed electronically within
electronic devices or equipment. Once the performance is captured on a
recording, it is not usually subjected to external forces or influences, such
as venue acoustics, microphony or extraneous magnetic fields.
In the case of electric guitars, unshielded
amplifier components can readily pick up induced magnetic fields when the
instrument is physically located near the amplifier or a loudspeaker -
resulting in hum or microphony or instability.
Finally, digital recordings may be manipulated
manually or with software, to produce a myriad of variations upon the original
recording.
Recorded
performances and playback are not covered in this paper – for designing and
constructing DIY playback amplifiers see the home page at https://www.oestex.com/tubes/
RADIO AND STREAMING FREQUENCY RESPONSE
AND DYNAMIC RANGE
Recording a performance allows us to
keep it forever if we want and to play it back as often as we want.
We might even want to record for
commercial sale.
However if you are recording your
playing for broadcast or streaming then much of the effort that goes into
producing your work and attaining the “sound” you want is lost in the system.
AM (Amplitude Modulation) Radio was the primary broadcasting technology in most of the
world until about 1940 when FM radio became a commercial success. AM radio
continues to this day throughout the world and in many countries remains the
primary public broadcast system. AM coverage is broad and reaches further than
FM. The useable commercial audio frequency response is from 50 Hz to 5000 Hz
including harmonics. The HF quickly rolls off.
Nowadays in-studio processing is mostly digital via computer storage
with live record/CD playing diminishing. AM broadcasting suffers from static
and interference.
To
save on power, AM broadcasting has reduced dynamic range to only a few db.
FM Radio was commercially introduced in the USA in about 1940
and offers reception advantages over AM.
Coverage is dependent upon straight line reception. Audio frequency
response is nominally 40 to 15 kHz including harmonics. The HF quickly rolls
off. FM gradually spread throughout the
world and is displacing AM as the preferred medium for “hi-fi” broadcasting.
Nowadays in-studio processing is mostly digital via computer storage with live
record/CD playing diminishing. FM broadcasting is usually free from static and
interference. To save on bandwidth, FM broadcasting of music has reduced
dynamic range via compression to only a few db.
DAB and DAB + Radio – compression and dynamic range. See https://www.orban.com/dab-audio-processing
and https://legacy.presonus.com/learn/technical-articles/sample-rate-and-bit-depth
Regardless
of the technical specs and claims, in my own wide-range hi-fi system due to
compression in transmission the DAB radio sounds awful compared to FM. To save
on storage and processing requirements, DAB broadcasting of music has reduced
dynamic range via compression to only a few db. DAB appears to be aimed at a
mass young audience who do not know what quality wide-range sound actually
sounds like.
Radio In
all cases radio stations decide their own tonal and EQ settings so a track
played on one station will often sound different on another. In particular,
digital audio compression is now common because few broadcasters use analogue
media and most listeners will not detect the difference between compressed and
full dynamic range.
You Tube MP3 - 128 or 256 kBPS
Spotify Streaming see https://support.spotify.com/us/article/audio-quality/
Recording technical specs see
https://www.youtube.com/watch?v=DGwm6llYv5g Note:
Standard CD players are 44.1 kHz 16 bit capable. DVD and Blue Ray players are 192 kHz 24 bit
capable.
Video footage of
recording studios typically show monitor speaker systems as being compact style
with small diameter woofers and midrange. This is to better match recording EQ
and tonal balance to real world home listening systems. As playback systems
change recording techniques change to suit.
Analogue recording sounds
far more natural than digital but is difficult to mix and edit. Most recording
nowadays is digital.
Headphones are
used to monitor recordings and for private playback. Specifications vary
dramatically. Typical frequency response is often very uneven and nowhere near
flat.
For
headphone frequency response tests see https://www.rtings.com/headphones/tests/sound-quality/raw-frequency-response
The Consumer factories,
offices, supermarkets and motor vehicles are noisy places, busy people do not
have time to sit and listen to hours’ of music
and people like variety in their listening pleasure, so do not expect
the world to stop for you and only listen to your contribution. A few succeed – otherwise enjoy the
music.
LIVE
PERFORMANCES
The second consideration is for LIVE performances. Here the situation
is very different and we can create the sound as we want it to be heard.
A live performance is presented as-is,
whatever the musicians create in real time.
People can come and hear us play for them.
Therefore loudness, tone and dynamic range
are presented in real time without compression or equalisation (unless there is
a PA console operator active).
Notwithstanding its "warmth" of
tone and commanding presence, the guitar has a limited audible sound level.
Acoustic guitars are suitable for small room performances but the typical
electric guitar is nearly inaudible without amplification. The guitar is
therefore limited as to the size of venue it can service without amplification.
This magnificient performance of Soler’s “Fandango” shows
just how live acoustic guitar can enthrall an audience. Studio echo has been
added. In comparison this is a studio version of the
same piece. Notice how echo can diminish the definition of the sound.
Once the point is reached where amplification
is required for live performance, the electric guitar becomes the favoured
instrument. With suitable amplification, it can produce a wide range of musical
and sound effects.
Given that a typical guitar amplifier will
deliver around 40 to 120 watts rms and that for effective tonal balance the
audible bass amplifier power output level
needs to be about four times that, we have a need for a bass amplifier and
loudspeaker system capable of producing at least 150 to 500 watts rms of power
at 40 Hz. That is something for the guitarist or sound engineer to bear in mind
when planning performances.
Guitarists should not feel upstaged or
disadvantaged when their bass player has relatively huge equipment compared to
theirs. It’s all about the sound baby !!
In modern terms, with transistor amplifiers
available that can easily deliver several thousand watts of power it would not
seem to be a problem to achieve this.
However, life is not that simple.
Since the invention of the vacuum tube, LIVE
electronic reproduction of a musical instrument has always been a challenge for
musicians, audio designers and constructors - and remains so to this day.
Over the years, various approaches have been
made to adapt hi-fi technologies to electronic instrument amplification, but it
is clear from practical experience and theoretical analysis, that requirements
for musical instrument amplification are very different to those required for
hi-fi reproduction of recorded music.
"HIGH-FIDELITY" is a term that literally means "TRUE
FAITHFULNESS" - to the original. Obviously that is not necessarily an
objective for musical instrument amplification and reproduction, because what
we are after is that elusive "sound" that creates the particular
AUDIBLE musical effect we want.
What happens to the sound quality and
characteristics within the reproductive system is not of concern to the player,
because it is what we actually hear that matters.
This principle is most aptly demonstrated by
the "electronic keyboard" - formerly known as the "electronic
organ" - where the sound reproduced is created completely artificially.
The only human involvement is to depress a key or press a button !!!!
Conversely, if we know the cause and effect
relationships that create and manipulate the sound within the system, we can
design a system that will do what we want. That is of course the methodology
used by electronic organ designers, sound processors, effects pedals and
suchlike
For nearly a century since the advent of
electric recording, countless researchers and engineers have endeavoured to
attain that elusive standard of performance described as
"High-Fidelity".
If we review audio amplifier circuit designs
from an audio engineering perspective we can see much commonality between them,
but most might be described as "variations on a theme". This is because
designers have been constrained by a small choice of vacuum tubes – i.e.
triodes, tetrodes, pentodes and beam power tubes. From this base we have only a
small number of practical output stage configuration options.
In fact, many tube amplifiers have attained
their superior performance simply by taking a proven design, tweaking it
(optimising circuit values) and using the very best components available at the
time of manufacture. That approach is still pursued today by both commercial
designers and enthusiasts alike.
If we then look at the evolution of musical
instrument amplifiers, we see the same "follow-the-leader" approach
at work - in this case "the leader" being the big names in commercial
musical instrument amplification.
This paper takes a fresh look at some of the
important elements essential to designing and constructing a vacuum tube based
audio amplifier intended to reproduce GUITAR.
Some of the concepts can be easily adapted to
existing designs, often with very minor component or voltage changes to those
chosen for an existing circuit.
Some suggestions are set out in the following
pages.
IMPORTANT REMINDER
The
professional Audio Engineer designing for a commercial application must
consider design elements and factors such as performance, construction and
safety specifications and standards; tube types, characteristics and
availability; tube and component availability; continuity of supply; component
cost; component quality; corporate vendor/supplier policies and preferences;
corporate design policies; fashion ideologies that control appearance, shapes
and finishes; component and complete device colour, machine tooling
constraints; sheetmetal suppliers and materials; labour costs and assembly
times; packaging and delivery requirements and costs; market/buyer preferences
or trends; warranties and guarantees; after-sales service; and brand-reputation
etc.
In
recent years, many countries have introduced consumer protection laws that
require a product to be what it is claimed to be – i.e. must meet its
performance specifications. Consequently, all of the designer, manufacturer and
retailer must consider the validity of performance claims when viewed from a
statutory compliance perspective.
Manufacturers are also
required to provide a statutory repair or replace warranty, guaranteeing
performance and reliability over a specified time period.
All
of these considerations and more impose constraints upon the professional
designer when approaching the design of high-fidelity and professional audio
amplification equipment for commercial sale.
However
the home constructor has no such constraints !!
In
our quest to attain our required "sound", as a DIY constructor :-
We are blessed with more or less total freedom from
all or any of the above.
We can take an existing commercial amplifier and
modify it, optimise it, tweak it, or do anything else we want.
We can use new, used, second-hand, salvaged,
hand-me-down, or recycled components.
We are not usually constrained by original component
price or cost.
We can use non-ideal, oversized or approximated
components, or components that would not normally be used in such a device.
We can compromise.
We are not locked into printed-circuits and can use
point-to-point wiring with confidence.
We are free to use any design we want.
We are free to have any layout we choose.
We are free to instal extra shielding wherever we
want.
We are free to modify the design without having to
be concerned about guarantees, warranties or product specifications.
We can use recycled industrial, military or
broadcast quality components.
We can use any tube type or mix of tube types we
want.
WE CAN EXPERIMENT
ACCORDING TO OUR OWN IDEAS AND PREFERENCES!!!!
WE DO NOT HAVE TO COMPLY
WITH THE CONSTRAINTS OF THE ESTABLISHED CONSERVATIVE PARADIGMS IN DESIGN
OR CONSTRUCTION.
WE CAN REACH BEYOND THE
COPY-CAT SCHOOL OF DESIGN.
WE CAN INNOVATE!!!!
But please, before you
abandon all of the hard-won knowledge developed over a century of tube audio
design and application, do follow the essential core design rules set out
in the "CHASSIS AND COMPONENT LAYOUT AND WIRING" page - ignore them
at your own peril.
A NOTE FOR THE
UN-INITIATED
Here are some basic
ground rules:
Electricity is a
force. Hence it can have all manner of
forms - not just regular AC (Alternating Current) or DC (Direct Current).
Electricity
normally behaves like a fluid. Hence when
we observe the behavioural characteristics of water, we can see much relevance
with electric current flow.
Electricity will
flow when there is a pressure difference between the two ends of a conductor or
a circuit.
Electricity will
not flow unless there is a "circuit". A circuit can be created by hard-wiring - or by electro-static,
inductive or electro-magnetic coupling through the air.
Electricity
flow can be controlled electrically, electronically, electro-magnetically,
electro-statically or mechanically.
A
"circuit" can be created by
adjoining components, wires or even through the air. Never assume that because
a hard-wired circuit is not evident, high-frequency AC current or
electromagnetic forces cannot be present to influence circuit behaviour.
Generally speaking, the greater the current
through a conductor the greater the extent of the electro-magnetic field around
it.
Generally speaking, the longer a wire the
greater the risk of electro-magnetic interference or coupling.
Generally speaking, the longer a wire the
greater the electrical energy losses within the wire.
Doubling the cross sectional area of a
conductor will increase its current carrying capacity four times for the same
temperature rise. 80% of the electrical energy is carried in the outer 20% of
the conductor.
Electricity is
"lazy" – it
will ALWAYS try to find the shortest path – i.e. path of least resistance. This attribute creates problems with devices and
wiring in high-voltage and/or high-current circuits. In the context of vacuum tube
amplifiers, "high-voltage" means anything above about 450 VDC. Above
that, life becomes more and more difficult as all manner of unexpected
phenomena occur in the amplifier.
Power Out = Power
In minus Losses. This works like a garden
hose. What comes out = what goes in less friction in the pipe.
.
In an amplifier, AC power out = AC power in minus conversions losses from AC to
DC then DC back to AC, multiplied by tube and Operating Class efficiency and
losses in transformers and filters.
In a sound system, that output is further
reduced by speaker efficiency when converting the electrical energy into
acoustic energy we can hear.
A NOTE OF INSPIRATION:
For those who want to be different and own
and use tube amplifiers for your guitar amplifier - notwithstanding tube
amp shortcomings and limitations - good luck to you and enjoy what you have.
If you feel inspired to improve what you
already have then hopefully these pages will have helped in your quest.
There is no restriction or cost imposition
upon the home hobbyist constructor to using these concepts - the only
restriction is on commercial exploitation where copyright is applicable - so if
you do not like it do not do it.
If you want your guitar amp to improve its
performance at minimal cost to you then experiment. The concepts presented here
do work and cost very little to implement.
However to those who say that a product is
only as good as what you pay for it, then these concepts are of no value to
you because they are free. You would be wiser to spend a hundred grand on a
commercial system and feel better. While you are so doing, ask the manufacturer
to justify the circuit design parameters and component choices to you.
Thank you for reading and considering my tube
amplifier ideas and technologies as expressed in these pages.
Please let me know if you can add to this
body of tube guitar amp knowledge and I will add it to this commentary, which
is intended to communicate the results of my personal research and
experimentation over more than 60 years of my life.
HAPPY CONSTRUCTING!!
MAY YOUR PROJECT BE A
SUCCESS!!
LISTEN TO THAT SWEET,
CLEAR TUBE SOUND!!
These articles, courtesy of Electronics
Australia, June 1983 edition, may cause you to reconsider what you are actually
hearing!!
REMEMBER - ALWAYS TAKE CARE WHEN WORKING WITH
HIGH-VOLTAGE - DEATH IS PERMANENT!!
Contact:
"electron"
Email: contact
This page is located at http://www.oestex.com/tubes/guitaramps/2_intro.html
This page last modified 08 July 2023