Kennedy 500 Pure Class 'A' amplifier

Mono Channel Amp For Bass Guitar

The Kennedy Audio mono channel amplifier is intended for bass guitar
or night club applications. It is a 500 watt RMS intended to self match
the typical high quality subwoofer or set of 8 10 inch speaker cabinets.
In American stereo listening amp designs, the thinking has been that a
seperate sub-woofer should not be necessary if setups are controlled.
With our transformer capacities such speaker overdamping and impedance
reductions are not needed to vastly improve power hungry bass response.
This optimal match-up of speaker power tolerance and possible power
gives a wide possible range of operation capacity and sound pressure.

At low frequencies (10-40 cycles/sec) our transformers do not have

the universal problem of becoming saturated and producing distortion.
The higher tolerances to power are typical of edge wound voice coils,
such as JBL or any speaker supplied with a Kennedy Audio power amp.

Two areas that this amplifier exceeds most consumer level products are
cone excursion dynamics and all tonal fidelity, even exceptional loading.
This means this amplifier can drive much larger numbers of speakers.
It also provides higher cone excursions by delivering all the current to
these speakers at a fast enough rate, satisfying the power hungry coils.

The amplifier main circuitry was 5 years in development. All available
designs were examined as well as the technology used in machine tool
industry amplifiers and high energy power supplies for servo controls.

This prototype phase was then followed by 4 years of proving and
testing, on a variety of speaker sizes and configurations, from dual
spider cone bases and high temperature voice coil varnish coatings
to outer edge suspension and break-in and clearance experiments to
punch and power burn out and harmonic distortion quality concerns.
The result is an amplifier with .05 percent total harmonic distortion
that is not vulnerable to 'snowball effect' caused by ring modulation
feedback from any speaker or set of speakers in series or parallel.

A third area this power amplifier brings to the market is a very similar
sound and general feel of a vintage vacuum tube amp, like a Marshall.
Because of the importance of this third facet, we will explain in some
detail how various vintage 'classes' of amplifiers compare or contrast.

AMP CLASSES compared and contrasted

Tube amps use an output transformer to gear the high voltage down to a
lower voltage while matching output impedance. They modulate an output
transformer. A vintage name in tube bass tube amps was Sunn amplifiers.
Many other low low cost solid state (not vacuum tube) amps used class D
design and these had capacitors feeding the speakers instead of an output
transformer. If you have a class A/B amp like most consumer amp's today
you don't get silky smooth midrange sounds of tubes but you get all the
noise and distortion and heat loss inefficiency you were missing in class A.
Yet, Tube power amplifiers send weak signals below 20-100 Hz, so they are
generally a poor choise if only powering subwoofers and larger bass speakers.

Tube amplifiers are also generally known for:

Output tube drift, soft top octave, mushy not punchy bass, high clipping
noise levels, slow overload recovery, distortional tone coloration at high
gain and erratic frequency response into difficult multiple speaker loads.
The overdrive at high gain is really a form of soft clipping in these amps.
As design criteria, these relate to the power amplifier for live performances.
Tube power amps exhibit a peak in their frequency response by as much as
10 dB or more at the resonance frequency of the speaker they are driving.
Thus the use of several speaker cabinets makes the Kennedy design preferred.

Sometimes distortion is desired, but sometimes it is not. But class A cannot
turn on the distortion without any distorted source signal while tubes cannot
turn it off. The tubes themselves allow signals to be 'overdriven' as a result of
their structure. The high voltage of the tube amplifier however allows higher
velocity and longer speaker cone excursions with equivalent fidelity however.
Thus a class A transistor amp with more wattage power used to be required at
similar volume compared to similar tube amps. Such amp’s are often class A/B.
Class A amplifier designs in the past were also characterized by low efficiency.

NO MORE. With as much power as the classic Threshold S/500 stasis or other brand name
circuits we will restrain ourselves here from enumerating, the Kennedy 500 attains
a slew rate of greater than 87 volts per microsecond and 20+ amperes to back it up.

The graph of impedance below shows that while speakers are rated at direct current impedances, the actual impedance is different because of skin effect in engineering or crest factor in musical waveforms.
Skin effect gets worse for thicker wire. The alternating current frequency also makes it worse as it gets higher as well as having a negative impact on the coil's ability to retain voltage, a kind of resistance called inductive reactance - summed with impedance and capacitive reactance for a coil to get total resistance.

For simplicity we want to know the approximate curve of what would be impedance if the alternating current audio signal was possible to measure without skin effect. For the best stereo wires, good is considered 16 guage and best is 14 guage. For 14 guage copper the AC impedance is equal to 17.6 times the Dc impedance times the square root of frequency. For 15 feet that is .6 ohms times the sq. root of frequency. This happens both in the line run and the speaker coil. Coil lengths are usually more like 30 feet. Resonances and standing waves (both unwanted) account for dips in the graph down to 8 ohms.

Watts vs, Total Number of Speakers & tweeters & midranges the watts drive

#spk  1       2        3        4        6      9       16

100	7.1	10	12.3	14.2	17.4	21.3	28.4
200	10	14.2	17.4	20	24.6	30	40
300	12.3	17.4	21.3	24.6	30	36.9	49.2
400	14.2	20	24.6	28.4	34.8	42.6	56.8
500	15.8	22.4	27.5	31.7	38.9	47.7	63.5

SWR (SleW Rate) formula:   2 Π ƒ

Table of required slew rates in Volts per Microsecond = V/uS for each channel

For stereo specs not bridged you need to multiple the overall required slew rate given by 2.

One new Crown amp claims 4000 watts @ 200 Volts peak bridged into 8 ohms for instance.
Each speaker 8 ohms or 16 total impedance with wire. Frequency= is 20,000 hertz.
Thus the higher the power rating of an amplifier, the higher slew rate is required to avoid
distortion in transfer. Many common op-amps have extremely slow slew
rates (1/2 volt per microsec) and very limited bandwidth (they cannot handle large
magnitude changes in input voltages ) because they respond only to changing of current in their inputs.

This results in a very smooth tube-like sound, but without very high temperatures
of operation and without the buzz and static background hum of a tube amplifier.
As we all know, the amp is only as good as its power supply. The Kennedy amp
utilizes a double-the-wattage formula and spares no expense on filter capacitors.

It takes a 500-watt sine wave rated amplifier to continuously deliver 100 watts to a

loudspeaker if the program material has a 10 dB crest factor. Most music has a 6-10

crest factor in midranges and highs. Percussion and similarly sharp sounds have high

crest factors which require less power per time but more speaker sensitivity and high

enough slew rates for the amplifier to respond fast enough that the quick peaks aren't

flattened out. In a nutshell, there is no such thing as too high a slew rate for the same

power delivered by sine wave. Remember that sine wave continuous or RMS is a worst

case rating like a bass guitar where the most power is being delivered in the signal per

unit of time. This absorbs power rather than rejecting it or skipping it at the speakers.

Not all amplifiers are rated using real speakers or continuous all channels active output.

The bottom line:

· Twice the voltage and still as stable or more stable as lower power designs.

This is 500 watts at 8 ohms.

· Rugged all silver solder custom work.

Much greater volume of lower frequency harmonic tones.

· Better low end bandwidth^*, signal to noise, slew rate and

filter power reserves makes live performances unforgettable.

*When comparing to sound reinforcement amplifiers, remember that in general it takes

four times as much power on average to amplify bass guitar and drum signals

versus power needed for vocals and all other instruments based on averages of frequencies.

Remember that any amp will always draw at least 25% more than it puts out; even the
most efficient ones. When rated power adds up to more than 110vac @ 20 amps or more
than 2200-600 =1600 watts, the system output is overrated if it plugs into an ordinary wall outlet. That's 800 watts/ channel maximum for class D. Class A is usually not even that power efficient.

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