.... and discover that it's
playing flat, compared to the Kurzweil. 20 seconds later, it's in pitch
again. Before the end of sound check, it's gone in and out of tune a dozen
times. The guitar and bass players are looking at you and the Hammond as
if you're both on drugs. Everybody's looking around at everybody
else. It gets real quiet all of a sudden. This can't be
happening.
But it is.
WE'RE
IN TROUBLE
The only instrument on
that stage that uses a motor to create its sound is the Hammond. If the
motor is spinning either slow or fast, the organ is out of tune. Period.
Many large, outdoor concerts
must use a generator, because adequate power isn't available any other
way. The generator is a large trailer, or sometimes it's a self contained
truck. It generally has a diesel motor, plus all the connections to hook
up power feeds, and send them to the stage area. It's usually parked
pretty close to the stage, and some huge, monster sized cables run from the
trailer to the power distribution boxes on the stage, which are actually breaker
panels, very similar to the ones in a house. Somewhere on the trailer,
there are typically meters and dials to indicate voltage, current, motor RPM,
fuel, temperature, and other details relative to the generator.
As far as our Hammonds are
concerned, only one detail has any real importance:
LINE
FREQUENCY
Unless the Hammond is getting a true
60 Hz power feed, it's going to play out of tune. The Hammond run
motor maintains its precise speed by synchronizing with the line
frequency. Unfortunately, this situation is virtually unknown to many of
the generator operators. A large percentage of their generator rentals are
for construction sites, where the focus is on voltage and current supplied,
rather than on precise frequency of the voltage. Very few guys on the
stage crews know about this, either.
This situation has no noticeable
effect on anyone except the Hammond player. That may be why so few
people know about it. The generator companies supply power to anybody that
needs it, not just musicians or Hammond players. The amplifiers, sound
system, instruments, lighting, and all the other devices that use electricity on
or around the stage can operate at 59 Hz or 63 Hz, and nobody ever knows the
difference.
WHAT
CAN BE DONE ABOUT THIS?
The first option is to find the
generator man, and see if he's able to get the power stabilized to 60 Hz.
If his equipment is capable of fine frequency adjustment, you can probably work
with him to lock it in. I would strongly suggest you do this with your
ears, comparing the Hammond to a known pitch (for example, another
keyboard), and not with the dial or gauge on the truck. Those dials live
through a life of endless vibration on that truck, and may or may not be 100%
accurate. I would also strongly suggest you read the line frequency with
one of the better digital voltmeters, such as a Fluke 85 or 87. Just
insert the probes into an outlet, set the meter for VOLTS AC, and read Hz on the
meter by pressing the Hz button. My own house reads 59.99 Hz as I'm
writing this.
Many generator rental companies
leave the generator on site, and don't return until after the concert is over to
pick it up. If the generator man is gone, or the control panel on the
trailer is locked, you're in deep, deep trouble today.
A
POSSIBLE SOLUTION
One possible preventative
solution is to build your own stable power supply system. This is quite
simple to build, and doesn't cost very much, plus it's fairly lightweight and
easy to transport. And it can be easily built to work in foreign
countries, using several different supply voltages.
The basis of a stable power
supply is an amplifier. I've used a Crown DC300 amp in the past, and these
amps are commonly available and fairly inexpensive. They're also built
like a tank, and can take a lot of punishment.
You'll need a stable signal
generator, called a sine wave generator. Many of these are crystal locked,
so the output frequency doesn't shift, although the line power might
fluctuate. The sine wave output, at exactly 60 Hz, is fed into the
amplifier's input, and the speaker output of the amplifier is now the power
supply for the Hammond. Using an AC voltmeter, raise the gain on the
amplifier until the output reads around 110-120 volts. If you have a scope
available, view the signal generator output, and adjust it to just below
clipping. Some amplifiers may need to be bridged (ie; mono operation) to
produce that much voltage to the speaker output terminals. The speaker
output voltage is connected to a standard type of wall outlet box, and the
Hammond plugs right in. The entire power supply should be enclosed in a
small rack, protecting the components and making transport simple. All the
internal wiring can be permanent. Once it's built, you just plug it in,
and plug the Hammond into it, as if it were a regular wall outlet. Changes
in line frequency will no longer affect the Hammond, because it is now regulated
to 60 Hz.
I'd recommend using a large
enough rack to accommodate at least one cooling fan. You can fine tune the
power at every gig, and make sure it's right on 60 Hz. A small, panel
mount frequency counter and AC voltmeter should be easy enough to find, and
could be permanently mounted in the rack with the wave generator and
amplifier. This would make setup almost instantaneous. Various power
converters - such as a 220v to 110v - could also be mounted in this rack, which
would enable it to be used in foreign countries as well. The final design
is determined by how elaborate and elegant you care to get with this
project. The possibilities are nearly endless.
At this point, I'm not certain
exactly how much current a Crown DC300 will provide. I recall using this
system with two Leslies in England, but this was about 30 years ago. I'm
not sure if it could be used successfully with three, four, five, or more
Leslies. Obviously, if more power (meaning amperes) were needed, a more
powerful amplifier could be substituted for the DC300.
I've heard suggestions that only
the Hammond's run motor needs a stable power supply, and the Leslies, Hammond
preamp, reverb, etc., could be operated on whatever power was available.
This is correct. However, for the sake of simplicity, my preference would
be to use a single power cable from the AC supply to the Hammond, and a single
cable to each Leslie, rather than having any exotic connections, or special
power cables for the run motor. I'd rather keep this as simple as
possible, making setup and teardown that much easier on everyone.
Other possibilities include
various UPS systems and commercial power supplies. Most of these will cost
quite a bit, and some of them are large, heavy, and difficult to
transport. Some use internal backup batteries which will need replacement
after some period of time, and are extremely expensive.
