Post by Robert ManktelowPost by Robert ManktelowPost by Robert ManktelowThanks Steve
It was the amp on its own I was asking about. Will get the scope &
soldering
Who cares?
Post by Robert ManktelowI was most surprised what a dramatic effect the speaker has on the sound
when I changed mine from an Eminience to a Celestion Vintage 30
recently.
Post by Robert ManktelowWhich explains why amps are designed to work with particular speakers. The
frequency response of the combination (amp and speaker) is far more
important.
Phil
I was unaware that guitar amps are designed to work with particular
speakers. Presumably the amplifier design also takes account of the speakers
enclosure type (vented/open backed/tuned/..) as well?
Well the amp part of things is pretty straightforward. It's designed for
cost (you need smaller output transformers for 50Hz-20kHz than you do for
20Hz-20kHz but the rest of the power section is plain vanilla. Then you've
got speaker/amp interactions that should be designed into a system. A good
example is the use of 4x celestion Blues (25W) for use in an overdriven
marshall (120-140W) The saturation is a big part of the sound as is cone
break-up and how harmonics are produced/handled. Here you've got a big
difference between different amplifier types in terms of negative feedback
(often called presence) which basically controls how the amplifier tries to
compensate for differences between its input and output signals. Different
valves also behave differently a difference that you can hear pretty well by
comparing overdriven el34's and 6550's in the same circuit. The key question
is how the amp is designed to operate. Take a classic Marshall - It's not
designed to produce a Fender "clean" sound but can be modified to do so.
Output transformers play a huge role here as well where you have frequency
response as well as saturation properties and resonances. Complex.
The type of tone stack (talking preamps here) - every head has one - is a
lot more complex in its relationship to the choice of speakers. In a tone
stack, you've got a few things happening. The presence control (isn't really
part of the tone stack but is thought of as such) is already covered. Then
based on the different designs, you can have a frequency cut or boost (or
both) at the predefined frequencies. Also there's the general predisposition
of the circuitry to colour the sound e.g. bass and treble rolloff, where
humps are in the frequency response (setting the amp as flat as possible for
instance) and how the controls interact (e.g. a fender mid control does a
lot more than just control the mids and Marshall tone stacks are almost
always V shaped regardless of the knob settings).
Then go into how hot the amp is biased, cabinet design and construction,
cabinet materials (Solid pine is great for baffles for instance), speaker
breakup character, power handling, efficiency... and you've got such a huge
number of variables that you're going to need a huge budget to get your head
around all of it and understand it in practice that it's worth paying for
the experience of someone else to be applied.
Interestingly enough it's the "fudges" that amp makers integrate (try a
sound city 120 or similar) that make the tone have more character
I bet you never knew that "basic good tone" can mean so much being a
statement so small.
cb
Post by Robert ManktelowIs the aim of the amplifier design to compensate for the non - linearity of
the speaker in question or what?
How would I obtain this information - from the speaker manufacturers?
By reading about all of the above in a lot of detail, looking at the
circuits of a lot of classic amps, understanding them, understanding how
speakers work, understanding materials, tone stacks and of course components
and fudges.
cb