Installation manual

MYTHS, MAGIC AND FACTS
Let us use a 50w amplifier as our example. We shall assume a lossless output stage and
a perfectly regulated power supply capable of tons of current and enough rail voltage to
supply 8 ohm loads..
The constant voltage amplifier will deliver 14.14 volts across whatever load we present to
it. So at 8 ohms power is 25w, at 4 ohms it is 50w, at 2 ohms 100w...you get the idea so
far?
The constant current amplifier will deliver 14.14 volts across a 4 ohm load (The design
centre point) and this means we are running 3.5 amps through this load and thus the
amplifier delivers 50 watts. OK now let us increase the load to 8 ohms. Cool things
happen. The amplifier will deliver the same 3.5 amps into the 8 ohm load. The power
formula is I x I x R (Current x current x load impedance). A “funny” thing has happened.
The power is now 98 watts, so it has INCREASED from the 4 ohm load (opposite to what
we are accustomed to with constant voltage amplifiers). Well now it is kind of downhill
when we throw on a 2 ohm load. The output is 3.5 x 3.5 x 2 = 24.5 watts!
So what can we conclude from all of this? Well constant current type amplifiers are sort of
distant cousins of tube amplifiers which traditionally have high output impedances. (Think
of taking your amplifier and putting great big 2 to 4 ohm resistor in series with the output).
A constant current amplifier behaves the same.
An interesting idea comes to mind to have a mixture of both constant voltage and
constant current in the same amplifier. Keep your ears and eyes open for some future
product from Zed with this feature.
Amplifiers, be they class A, B or D behave and sound better into higher load impedances
like 6 or 8 ohms. Class A amplifiers buy virtue of their design do behave better at lower
load impedances than the B and D versions but they are not immune to these ills..
This is the first time I bring up low impedance loads and it will not be the last.
The idea of trying to maximize the output power simply because the manufacturer states
that his amplifier can deliver 8.24 Zillion watts into 1 ohm means nothing to us at Zed.
Every one of these monster class D (They generally are not made as class B any longer)
amplifiers has proved to be unreliable and sound just as bad. More about this on the
following pages.
We rate our amplifiers at 2 ohms ONLY because we recognize that firstly 4 ohm speakers
have impedance dips at various frequencies and that as much as we try to steer our
customer to higher impedance loads, there will be a contingent that will insist on the 2
ohm route. We have done design to keep our amplifiers more linear into these 2 ohm
loads however.
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