ProKeys - Power Supply

Until you turn on the Hammond

.... 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 very strangely. 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 rotating either slow or fast, the organ is out of tune.

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. This situation is unknown to most 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 56 Hz or 65 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 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 (also read this page - there may be more than one reason the Hammond plays out of tune!)

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 different supply voltages.

The basis of a stable power supply is an amplifier.

I 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.

You want one that is crystal locked, so the output frequency doesn't shift, although the line power might fluctuate.

This means the signal generator won't change frequency, even if it's powered at 86 volts, 100 volts, or 129 volts. It's locked.

Our sine wave generator was a $29.00 Heathkit (build it yourself) model. It took about an hour to build it.

The sine wave output, at exactly 60 Hz, is fed into the amplifier's input. 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 amplifier output reads around 100-110 volts.

That should work fine for one Hammond and two Leslies.

If you have a scope available, test the signal generator output, and adjust it to just below clipping.

Some amplifiers may need to be bridged (ie; mono operation) to produce sufficient voltage to the speaker output terminals.

I don't recall if my Crown DC300 was bridged or not. (Decades of time do unusual things to your memory.)

The speaker output voltage is wired to a standard wall outlet, and the Hammond plugs right in. (polarity is not important)

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 plug it in to the available power, test the output voltage, and plug the Hammond into it - just like 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, possibly two.

If I recall correctly, the Crown amp got pretty warm when using it for several hours.

You can fine tune the power at every gig, and make sure it's right on 60 Hz. Keep reading ....

A small, panel mount frequency counter and panel mount AC voltmeter should be easy enough to find.

They could (and should) be permanently mounted in the rack with the wave generator, amplifier, and wall outlet.

This would make setup instantaneous. "Instantaneous" means less than one minute.

Various power converters - such as a 220v to 110v - could also be mounted in the rack.

This would enable it to be used in foreign countries, as well as any shows in the U.S. where stable power frequency is questionable.

The final design is determined by how elaborate and elegant you care to get with this project. The possibilities are nearly endless.

I'm not certain exactly how much current a Crown DC300 will provide.

I recall using my system with a Hammond B3 and two Leslies, but that was a long time ago.

I'm not sure if it could be used with three or more Leslies.

Obviously, if more power (meaning current) was 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. Theoretically, this is probably 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.

I'd rather not have 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.

This unusual project - after it's built and adjusted properly - results in a reliable solution to a very serious problem: instead of plugging the Hammond into a generator power outlet, just plug it into the rack. AND - the rack is yours! So if you play jobs with different (backline) Hammonds and/or different generator suppliers - you can always have a stable power supply!

Other possibilities include various UPS systems and commercial power supplies. I've never tried any of them.

The research I've done has shown they aren't designed to stabilize frequency.

This "amplifier power supply" definitely works.