THE SOUND OF VALVES
Many factors went into the creation of the Clapton Marshall sound. The most significant and ignored is the technique of the man himself combined with the humbucking sound of the pickups. The SG provided greater microphonic feedback then the Les Paul and the Firebird a much thinner sound compared to both of them. The ES335 provided its own unique tone closer to the Les Paul.
Valves have a different distortion spectra (emphasis on
even order which is less harsh on the ears) compared to transistors and they
also have three other characteristics that creates their sound.
- Distortion in valves largely increases in a linear fashion ie as the power
output increases over the optimum output level (typically say .3% at half power,
1% at rated), distortion steadily increases until the valve cannot put out any
more power and begins to "clip". The clip point is when the valve cannot reproduce the wave
Transistors have low distortion and show only modest
increases as maximum power is reached (ie .08% to .12%).
At maximum rated output, distortion grows exponentially and very quickly
- Valves clip (run out of power) in a much less harsh way then transistors.
They reduce the wave form by rounding it down where transistors cut of
the top of the wave. Transistor clipping is very harsh on the ears - the diagrams
below literally represent the effect.
Effect - because valves are not solid state but made up of metal components
sealed in a glass vacuum tube, they are physically effected by vibrations.
The high volume environment of rock music most definitely would have
produced significant microphonic effects. Also
different valves had different characteristics with the KT66 having a great
propensity then the EL34.
- Valves are high impedance output devices and require a transformer between
them and the low impedance speaker. Transistors
virtually direct connect with only a resistor/capacitor network between them and
Transformers are long lengths of insulated copper wire
wound around a metal block, with current being transferred between coils by
induction. Transformers are complex
to build and always represent design compromises. High powered guitar amplifiers require large transformers and
that means large lumps of metal in the cores and heavy wire to handle the power.
That size effects their frequency responses with most amps having
frequency roll-offs starting at 50 and 15,000 Hz (hi-fi amps are flat
Transformers have two further effects - they add their
own distortion and saturate at high powers.
Saturation is when the electric current flowing through the copper wire
creates a powerful magnetic field that saturates the metal core ie it becomes
magnetised. When this occurs the
frequency response is altered (loss of bottom and top end) and distortion
1959 Chassis and transformer layouts - left is a very early aluminium chassis, far right is the 1968 config.
Note the changes in power transformer (bottom position) and the change of orientation of the output transformer
(middle of chassis) on 2nd from right.
Pickups and the amps
Clapton always used the flat input on the Marshall Amps
unlike Hendrix and Townshend (and most guitarists at the time) who used the
treble input which boosted higher frequencies. I believe he did this cause he didn't like a prominent high
frequency and because it gave him greater control from his guitar.
The use of a splitter would have effected the frequency
response as the pickup would have been seeing a halved impedance (what the
actual effect was I am unsure but I believe a high end roll-off).
The higher capacitance of the very long leads he used would have also
impacted on high end response (additional roll-off).
The effect on sound can be heard on the early bootlegs where the
guitar/amp sound is hard with a prominent treble and that of late '67 which is
much sweeter and rounded.
Speakers can also be overloaded which can result in
physical failure (a common occurrence in Cream's time).
However if it is done carefully they become overdriven ie cannot
physically move any further and begin to compress.
I believe this was also a component of the woman tone.
Unfortunately, as they evolved to the higher rated CG1230M speakers, that
effect was diminished.
How did Clapton Achieve his sound.
Eric Clapton took advantage of these effects in
Turning all amp controls to
ten which gave maximum gain and had all the valves at maximum load or near
overload. He then controlled the
sound from his guitar where small changes in control settings, picking pressure
or fret work would have a significant sonic effect.
Ran the amp at a sweet
overload level (KT66 valves) where the distortion enhanced rather then impeded the sound.
The distortion became part of the sound.
Selectively overloaded the
output stages and saturated the output transformers. This can be heard on the live woman tone with the guitar's
treble rolled off and bass up, producing a heavy thick singing sustain.
The distortion is massive but sweet on the ears.
Clapton's sound was a product of these factors in
combination plus the sonic interaction with the guitar.
The pickup - amp interaction even further complicates the picture.
The 1964 SG humbuckings must have had a nice sound - Clapton selected his
guitars on sound and feel.
The 1964 SG humbuckings must have had a nice sound - Clapton selected his guitars on sound and feel.
The sound evolved based on Clapton's technique and use of the available technology. It began to change as the technology rapidly developed and Clapton wanted to try a different sound.
the Clapton Cream sound be reproduced?.
No, for the following reasons:
Today's amps are much more refined and subject to tight quality control
Today's valves are much more refined and subject to tight quality control
Today's guitar pickups are much more refined and subject to tight quality control
Today's speakers are much more refined and subject to tight quality control
Even the "accurate reproductions" use much higher tolerance components than those of the sixties
Yes, by experimenting with effects rigs and using dual stacks on full!
Loud & Louder