Over my career, I must have
been asked 10,000 times what makes my designs better than everyone
else’s. That of course is a really loaded question. It is
extremely difficult to convert engineering jargon into layman’s
language. There are however a few up front things that can be
rebuked here & now.
INPUT ADAPTERS
I have of late received some criticism of my input jack scheme
on my Son of Ampzilla2000 amplifier. Let me make things absolutely
clear. These criticisms are totally and completely unfounded.
They are voiced from utter ignorance. A true completely balanced
amplifier with integrated quad differential feedback has one drawback.
The input must be driven by a perfectly balanced signal in order
to prevent common mode gain errors in the output signals. In other
words, if the input signal is not perfectly balanced, then the
gains of the two outputs of the balanced bridge will be significantly
different. From day one (at Sumo), I determined this to be an
unacceptable situation, although I have seen other designs that
have completely ignored this problem. (mainly because the engineers
were ignorant and incompetent)
My first Sumo amps as well as my current original Ampzilla2000
monoblocs used a single ended to balanced converter stage ahead
of the main amplifier inputs and were switch selected. Obviously
there are two drawbacks to this approach. The first drawback is
having to run the signal through an additional amplifying stage.
The second is the need for a switch to select between the phono
input jack or the balanced XLR.
I have always hated this setup and for 25 years I have vowed to
find a way to alleviate it. I DID!!! This solution would not have
been possible without the invention of the “Combo Jack”.
The way this works is as follows. The combo jack is an XLR jack
(gold plated of course) with a center hole that also accommodates
a standard ¼” phone jack. In order to use a standard
phono plug, one must use a phono to phone adaptor (which we supply
with the amplifier. The adaptor is all metal and all gold plated.
Therefore, there are NO losses of any kind through the connector.
Using a mono ¼” phone plug, the sleeve automatically
grounds the negative input to the main amplifier. This then requires
some clever circuitry to bring the main amp back into AC balance.
To accomplish this, I use an auxiliary circuit that receives the
balanced signal from both the +/- inputs wherein under balanced
conditions, there is no output. However, when using an unbalancede
input, this circuit outpuyt approximately 4% of the signal and
sends it to the feedback inputs of the main amplifier therefore
bringing the outputs back to a completely balanced state. This
sure beats running 100% of the signal through a buffer stage (with
its noise and distortion), and then a switch. The use of this
concept uses NO switching or extra stages in the signal path and
is completely automatic. This is the concept that was incorporated
in my Son of Ampzilla2000 stereo amp and will be used on all future
SST amplifiers. No other amplifier in the world can claim anything
like this. Enough said. Finally, if you are still unhappy with
this arrangement, you can always buy cables with a phono at one
end and a phone plug at the other end. To me however, that’s
just a waste of money.
THE TRANSFORMER
The power transformer in an amplifier is one of the most critically
important devices. Too many engineers either overlook this, or
they are just plain incompetent because they are incapable of
doing magnetic design themselves. Many audio engineers that I’ve
talked with over the years seem to view magnetics as witchcraft
or a black art. This of course is ridiculous as it isn’t
rocket science at all. Early in my career while at Dynaco, I sort
of felt intimidated by magnetic design. But my lifelong friend
and mentor, Sidney Smith, practically beat me over the head declaring
that the only way to get a perfect transformer was to design it
yourself. How right he was. If one were to merely give a transformer
company the desired D.C. specs regarding voltage and currents,
I can assure you that you would NOT get an optimum design. Left
to their own devices, a transformer company will design a unit
that optimizes their costs and production efficiencies. Unfortunately,
they are just not audio savvy. A perfect power transformer (or
as close a one could get) will have an AC regulation of about
1%. Equally important is to construct the windings and layers
to minimize flux radiation. This is NOT easy. It has taken me
many years to develop the unique philosophy in designing my transformers.
My power transformers are the most perfect that can be had on
this planet and I challenge anyone to prove otherwise. The other
aspect of the design is the total and complete elimination of
ground flux which of course maximizes the elimination of ground
loops and noise.
Starting with SAE, where I was Director of Engineering, with only
one exception in my career, I have designed every power transformer
in every one of my product designs. The only exception is my current
Ambrosia, which is so complicated that I worked jointly with a
PHD magnetics engineer to achieve the results that I wanted. And
indeed, the results are spectacular. My goal was to improve on
what I’d previously done in the original GAS Thaedra. Don’t
get me wrong as the original Thaedra power transformer and power
supply design was truly a work of art. Even up to the present
time, NO ONE has attempted to design a complete preamp with a
high gain MC circuit AND a totally integrated power supply all
in one chassis. The entire secret to this philosophy is the power
transformer and power supplies. My current Ambrosia espouses this
same thinking with better specs.
And finally, why a full wave balanced bridge amplifier. To me,
the single most important reason is to have complete PUSH-PULL
negative feedback from EACH side of the loudspeaker. No other
concept can achieve such tight control over the speaker –
not possible.
Lastly, a word about noise. My current SST amplifiers are without
a doubt and NO exception, the absolute quietest amplifiers ever
made in history. Nothing else on the planet even comes close.
How Quiet? The wideband (only an 80kHz filter) input noise on
my amps is lower than virtually every PHONO input known to man.
Yes, less than .3uV (300 nanovolts). This allows us to verify
accurately the distortion character even into the sub-milliwatt
level without noise contamination. Of course this would not be
possible without the special transformer design and unique grounding
layout.
All for now. More later.
James Bongiorno
