Rocktron Velocity 250 - Manual (Page 5)

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Velocity 250 Design
Velocity 250 Design
Designers have been working at creating solid state amplifiers which sound like
tube amplifiers ever since the transistor hit the scene. We at Rocktron first produced
the Velocity 150 & 300 amplifiers with that goal in mind. The Velocity 250 takes what
those first models provided to a whole new level.
Every tube amplifier has some amount of output impedance due to the output
stepdown transformer. Conversely, solid state amplifiers have little or no output
impedance, because the speaker terminals are connected directly to the output
devices. This difference in impedance is the primary reason why the two types of
amplifiers sound differently. The reason the output impedance makes such a differ-
ence is because these amplifiers get connected to
speakers (which also have their
own impedance curves), not 4 or 8 ohm resistors. When a tube amplifier drives a
speaker—each with its own characteristic impedance—they react to each other (i.e.
one will effect what the other is doing). This is not the case with solid state amps—at
least, not until now!
The engineers at Rocktron have developed a circuit which actually measures a
speaker’s impedance and changes the output response of an amp to match what you
would hear from a tube amplifier—automatically! After developing this circuit, the only
question that remained was "Which tube amp do we design to match to, since each
one is different?". We came back and said "ALL of them!". By giving you a variable
REACTANCE control, you control the amount of
effective* output impedance of the
Velocity 250 to match any number of tube amplifiers. With the REACTANCE control
at the minimum setting, a very low output impedance is simulated—similar to a good
solid state amplifier. As the control is turned clockwise, the effective impedance
increases and sounds more like a tube amplifier’s output stage.
*Note: The word "effective" is used because if we actually increased the output
impedance to, say 2 ohms for example, and had a 2 ohm speaker cabinet
(for a total of 4 ohms), we would lose one half of the power before it even
got to the speaker! That means our 125 watts/channel would only be
good for 62 watts/channel. But with the Velocity 250, you still get the full
rated output delivered to the speaker.
What this means for you is that you get an amplifier that will react differently with
each speaker cabinet you use with it, just like a tube amp would do. Plus, you get to
control how much reactance you want to tailor fit the sound to your needs. The
REACTANCE control in conjunction with the DEFINITION control gives you an
incredible amount of flexibility that few amps on the market can touch. And, if you are
really power hungry and want to mono bridge your amp, you won’t sacrifice any of
these features. Plus, with the massive heatsinking available on this amplifier, you
won’t have to worry about heat issues.
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