122 Absolute Modeling Amplifier

OVERVIEW - What is an AMA?

What makes a vintage Hammond Organ and Leslie so special? A question no less polarizing then the topics of politics and religion, there will be as many answers as there are readers of this article.

In the past few years, we have seen that the latest technologies are bringing us ever closer to a faithful reproduction of the sound source, but as has been the case for decades, the audio systems that accompany them have been lacking.

The question is, lacking what? What was it about the old design that gave it that elusive tone? Manufacturers have tried to answer these questions. They add a tube here, a distortion knob there, but still we are left wanting. Players abandon rotary simulators and get a modern rotary cabinet, it sounds closer, but it's still not quite right…

The fact on the matter is that there is no one element that makes “the sound”. Our research has shown that it is the whole system that makes the unique sound of the vintage tonewheel organ.

When originally conceived, the CityplaceHammond organ was intended as a replacement, or at least a low cost alternative, for the church pipe organ. The tone cabinet that Don Leslie created was inspired by the church organ's cousin, the theater pipe organ. As a result the amplification systems employed in both were of a conservative design. Unlike tube guitar amps, where most designs are meant to wring as much power as possible from tubes at the expense of fidelity, whereas the Leslie power amplifier is designed as a compromise between maximum fidelity and maximum power. As a result, it has a unique tone when pushed into distortion.

These factors, combined with the transformers in both the preamp and the power amplifier all combine to create the unique overall tone of the Hammond Organ's audio system.

Fig. 1 - A Pure Sine Wave

Fig. 2 - Typical Tube Distortion

Fig. 3 - Typical Solid State Distortion

Now you may be thinking to yourself, “I don't play with distortion” and you might even loath that sound, but even when an organ is played with a “clean” tone, you are experiencing a degree of distortion.

Vacuum tubes are flawed devices, and long before you hear what we musically call distortion, there is another more subtle distortion taking place. This distortion, which is often regarded by engineers and audiophiles as undesirable is very much a part of the sound that we have all come to know and love.

Consider these diagrams. In Figure 1 we see a sine wave, which is what you get playing one key with one drawbar pulled out on a tonewheel organ.

In Figure 2 you can see that the top and bottom are squashed a little, but it still has a more or less “sine wave” shape. Technically this is distortion, but you may be surprised to know that it's not the kind of distortion that you think of when you hear that word. It is however part of what makes tubes sound different from solid state devices.

This brings us to Figure 3, here we see a representation of how transistors distort. Unlike tubes, they will maintain a more or less perfect sine wave until this suddenly happens. Very un-musical.

After a considerable amount of research, we had the idea that since both power amplifier and the preamplifier are where the “magic” happens, why not recreate the system in miniature so that it could then be added to the more modern solid state system and give them that classic vintage tone.

At it's core the concept is actually nothing new, guitarists have used low power but good sounding amps as a source of good tone, and even our own preamp is based on the same idea of taking the important parts of the audio chain and reproducing them to infuse the “tube sound” into an otherwise sterile sounding solid state audio chain.

One example of the concept in action: In this diagram, the audio system on the right will sound the same as the one on the left, but it will have the potential for a much stronger volume level for stage performance

With these components in place the solid state amplifier is transformed from being a detriment to the sound quality to being an asset in bringing the previously developed tube tone to what ever volume level it can handle. It's really no different then taking a well recorded performance and listening to it at home on what is undoubtedly a solid state stereo system with good speakers. The stereo doesn't need to add that tube sound because it's already there.

CUSTOMER REVIEWS

Dave Bradley, an enthusiastic owner of a few of our products, reviewed and demonstrated the AMA as it was used for his Roadbox Rotary Speaker rig. CLICK HERE to go to his website and see what he has to say about our Absolute Modeling Amp.

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Walter J writes:

"I let some of Speakeasy's creations pass me by the last few years and went with what I was playing "from the factory." But Steve Hayes really hit a home run with the new AMA Absolute Amp Modeler! I got the complete unit, a 122/AMA, both SE preamp and modeling power amp stage in a 2U shallow rackspace size. I'm amazed at the sound with my Electro, both 'dry' with no rotary effect for jazz, and with the NE2's Rotary effect on. The AMA's not like an effect at all, much more than that. It adds its sound after the Speakeasy tube preamp, with a 10 watt tube power amplifier having similar characteristics to a full-size Leslie power amp - thus the "modeling" term - like a mini-Leslie amp to my ears.

The AMA does get hot in "cranked up" use - I have been known to play loud at times - so I put mine in a 3 space rackmount with a little breathing room for the top and bottom.

There's a line level connector output on the back along with a speaker output for an 8 ohm cabinet. The speaker output is enough for a small cabinet and sounds fine, loud enough for playing at home and low-volume practice. This has me thinking of miking a small hi-fi cab onstage or in my home studio. And I think the line out could go into a DI box. Speakeasy's AMA does seem to come with some great and extra-useful potential applications.

All the controls are on the front: Input Volume, Treble, Bass for the preamp side, and Power Amplifier with Line Out Volume for the AMA amplifier side. The apparently simple EQ controls really work well in this configuration. Turn up the Treble and it morphs right into the mix. Adding Treble almost seems to make the top octave "fatter" rather than "shrieky." Turn up the Bass and the bottom comes right up, smooth and fat instead of uncomfortably loud. Neither EQ control seems to emphasize certain frequencies at a loss to others.

For organists playing through solid state amplifiers, powered cabinets, rotary solid state cabinets: One of these 122/AMA modelers with your clonewheel organ will be IMO as close as you can get to investing in a real tube vintage Leslie - weighs a lot less too! I can't say enough good things about this piece of gear. BTW, you might want to get two. I haven't opened the second box yet!

Walter J"

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