Ambrosia Preamplifier And The
Son Of Ampzilla 2000 Power Amplifier
Ampzilla lives again!
Review By Dick Olsher
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Ampzilla and its progenitor, James Bongiorno are no strangers
to a baby boomer audiophile such as myself. Originally conceived
as a construction project for Popular Electronics Magazine,
the Ampzilla's reception was so overwhelmingly enthusiastic, that
Bongiorno left his engineering position at SAE to found the Great
American Sound Company (GAS) in 1974. A colorful character, and
a musician at heart (be sure to check out his solo jazz piano
baby - an exceptional recording in my opinion), Bongiorno
was influenced by Marantz's Sid Smith, and had already put in
a stint at Dynaco (the Dynaco 400 is his creation) before landing
a job at SAE. It was here that he developed the dual differential
fully complementary amplifier topology, which has proven to be
a significant high-end design influence for over 30 years.
first exposure to the Son of Ampzilla, the Ampzilla's robust progeny,
was in the mid 70s. Auditioned at a MyerEmco store, where it was
partnered by Dahlquist DQ10 loudspeakers, the Son left a lasting
impression. Here was a solid-state amplifier that was neither
texturally grainy nor dynamically comatose, as was the case with
my Citation 12, and could dish out far more detail and bass punch
that I was accustomed to with the Dynaco ST-70. Not surprisingly,
the Son went on to become a commercial success; apparently, tens
of thousands of units were produced and sold. Proving how well
built these units were, I'm told that most of these units are
still in service today.
down by a life-threatening illness, Bongiorno overcame the odds
about five years ago and re-entered the high-end audio arena via
Spread Spectrum Technologies. His first products to market were
the Ampzilla and Son, 2000 series. The new Son is said to represent
a third generation evolution of the original SAE-GAS designs,
and incorporates several major improvements. First, it is completely
balanced from input to output with full four-quadrant differential
push-pull feedback from both sides of the speaker. Second, each
channel features twice as many (and beefier) power transistors
as the original. Unlike the original, the new Son is servo controlled.
The power supply filter capacity has been increased three-fold
to over 100,000 µF. In fact, the series name refers to the 2000
VA rating of the new power transformer. Finally, balanced/unbalanced
input section is automatic. Adaptors are included that allow the
XLR connectors to accept RCA plugs. Output devices are still bipolar
whose fashion sense is, let's say, a bit unconventional, chose
a blue finish for the fascia of the new Ampzillas. Since several
pundits declared this a fashion faux pas, the Son is now available
in an optional and more conventional black finish. However, for
the record, I love the blue and my sample of the Ambrosia is finished
in matching blue. On the other hand, the Bonge, as his friends
call him, has always had a knack for picking catchy product names.
My favorite example is the GAS "Charlie the Tuner" — a takeoff
on Charlie the Tuna, the cartoon mascot for StarKist Tuna.
cornerstone of this review article is the Ambrosia preamplifier,
Bongiorno's latest product offering, and one that he believes
breaks new ground. The Son is in the review loop because Bongiorno
had asked that the Ambrosia be reviewed in combination with the
Son. However, I felt that it was also important to listen in the
context of several other amplifiers to establish a more complete
total of about 10 man-years of development effort has gone into
the Ambrosia, and as you will shortly find out, it indeed represents
a complicated and ambitious undertaking. The Ambrosia is intended
as a full function preamplifier, and to paraphrase Vinny Gambini
(My Cousin Vinny the movie), I'm sure you'll be ‘mooore'
than satisfied with its functionality. For starters, separate
MM and MC phono stages are included. Each phono circuit has its
own switchable and dedicated low cut 20Hz filter featuring a quasi
fourth order phase-equalized network.
line amplifier is fully balanced and uses JFETs and Analog Devices
AD797 opamps in a topology that is said to generate essentially
zero distortion. The line amplifier incorporates sophisticated
bass and treble tone controls with four selectable inflection
points. Tone controls?! Now that's something you almost never
find in a high-end preamplifier, and I totally agree with Bongiorno
that it's an indispensable feature in tuning one's system, since
as he points out, "there is no such thing as a flat room." In
addition, I might add that fine-tuning a speaker's tonal balance
is also a possibility, especially critical in the frequency range
below 300 Hz where so many modern designs are anemic sounding.
Finally, since Bongiorno is big on headphone listening, expect
no less than a pair headphone jacks on the front panel which can
deliver several hundreds milliwatts into even very low impedance
cans. The headphone driver is very good; my Grado RS-1 cans were
driven cleanly and with plenty of headroom.
are plenty of unbalanced inputs, two balanced inputs, and two
tape loops. Both RCA and XLR output jacks are provided. This is
a heavy chassis; at 50 pounds, it outweighs many power amplifiers,
including the Son. Most of the weight is due to a huge low EMI
power transformer mounted in its own can. It features four secondary
windings that are used to power each circuitry section independently,
and in the process eliminate ground loops. In addition, 15 independent
power supply regulators are employed throughout for immunity against
AC mains fluctuations. The level of finish is superb: all metal
surfaces, including the front panel, are powder coated. All of
this is clearly fitting for a device that references Greek mythology.
Ambrosia, the food of the G-ds, was thought to confer immortality,
and in this context, presumably celestial sonic delight.
Ambrosia is fully menu driven. Its front panel is dominated by
a large, bright display that is visible from a distance. Functions
are accessed via the ‘select' buttons and individual options within
each menu grouping are accessible with the optical encoder knob.
For a selection to take effect it needs to be entered into memory,
the display then defaults back to Volume and the encoder knob
may be used to make level adjustments in 0.5 dB steps. It was
considered absolutely mandatory to design a remote controlled
unit and to do so in a manner that does not involve a "gazillion"
remote buttons, which naturally tend to be a major pain. Thus,
the remote is a carbon copy of the unit's front panel. The only
difference between the two is that that a mechanical (rather than
optical) encoder is used on the remote in order to save battery
power. The volume control consists of an integrated chip audio
attenuator whose output is digitally controlled. All switching
is performed via 11 programmable CMOS integrated chips, with each
chip providing 16 sets of analog switches. However, and this is
important, there are no digital circuits or digital processing
in the signal path, which is totally analog. The digital control
firmware only wakes up when a function is accessed. By firmware
I mean a software program that is resident in a read-only memory
(ROM) integrated chip It is possible to hear a faint "click" when
accessing a function or changing volume levels and. This is normal
and cannot be fully eliminated with this type of control firmware.
after the initial production run, and mainly to appease the Japanese
and other aficionados of high-efficiency speakers, an "attenuation"
function was added which is accessible from the filter options
section of the menu. This firmware change provides a -14dB level
cut and may be applied if desired to all inputs or to a particular
phono input. Of course, ‘attenuation' should not be invoked when
it is not needed, which would be the case for most users. It takes
about 30 minutes for the Ambrosia to reach optimum performance
and really start singing, but Bongiorno sees no reason (an neither
do I) to leave the unit on continuously.
speaking, a preamplifier is the spark plug of an audio system.
It has the potential to jump-start the audio signal and set the
stage for the power amp. But because it sits at the head of the
amplification chain it can also imprint its personality on each
and every input signal. Virtually every preamp I have reviewed
over the past 25 years has been vacuum tube based. At the risk
of sounding like a tube supremacist, I would like to point out
that there is a reason for why tubes have ruled preamp land. Tubes
have always had the gift of microdynamics, harmonic textures and
spatiality. They have been able - far more convincingly than transistors
— of dishing out the music's emotional content and drama as well
as fleshing out believable instrumental timbres and soundstage
dimensions. Transistors have had bass, detail resolution, and
low noise to brag about, but in my book ‘enjoying the music' counts
for far more than accurate sterility. The notion that tube magic
is partially due to euphonic colorations of the signal does not
bother me at all. Because above all else, I value the ability
to connect with the music's message. J. Gordon Holt's ‘Goose Bump'
test is still as valid today as it was 50 years ago. By the way,
his favorite preamp was the Marantz 7, which went on to become
a classic. It was only in the past couple of years that my respect
for solid-state preamplification took a leap forward. It started
with the GamuT D3, and now the Ambrosia.
playback through the internal Moving Magnet (MM) stage provided
superlative sound quality. No, I didn't experiment with the Moving
Coil (MC) stage since for the past six months I've been living
quite happily with my Grado Reference MM cartridge and hence I've
had little incentive to tinker with a winning setup. The rest
of the phono system components have been fixtures in my system
for several years, namely the Graham 2.5 arm and the Kuzma Reference
table. Most of the analog listening sessions were conducted with
the Venture Audio Excellence III loudspeakers. For starters, I
used the LAMM Industries M1.2 Reference monoblock power amplifiers,
a hybrid design, and a synergistic match for the Venture Audio
speakers. At least in my listening room, these speakers sound
a bit too lean to suit my taste in the lower midrange/upper bass
range. The Ambrosia's tone controls gave me the opportunity to
tweak the speaker's tonal balance to my liking. A +2dB lift below
a hinge frequency of 270Hz did the trick. I also experimented
with the 20Hz bass-cut filter but did not like its impact on mid
bass timbre, which lost body weight. Generally, in the case of
bass-reflex loaded speakers, an infrasonic filter is a good idea
as woofer loading is lost below the bass box tuning frequency.
Any problem with arm resonances or turntable rumble will cause
severe cone pumping and produce associated Doppler distortion
of higher frequencies. Perhaps the cut frequency needs to be lowered
a bit, but in any event, I decided to bypass the low cut filter.
music's harmonic tapestry was remarkably silky and yet exquisitely
detailed. The soundstage was solidly fleshed out with an excellent
depth perspective and extremely stable image placement. Most telling
was the manner in which vinyl surface noise, clicks and pops,
were dispensed with. They disappeared so quickly, and with such
a fast time signature, that their annoyance level was greatly
reduced. This speaks volumes for the Ambrosia's transient response.
Both the leading edge and decay portion of each transient were
clearly enunciated, allowing low-level detail to naturally bubble
to the surface. But just like the real thing, textures were not
outrageously detailed. Some preamps flaunt it in your face with
enough brightness and dissonant sizzle to fry eggs. The Ambrosia
follows a different sonic path. Its low distortion signature and
superlative transient response were responsible for a fluid delivery
and enhanced clarity. Although microdynamics were reproduced very
well indeed, I did notice a slight contraction of emotional intensity
relative to my current reference, the Concert Fidelity CF-080
line preamplifier and the Air Tight ATE-2 phono stage. Just as
a reminder, these findings were generated with the M1.2 Reference
amplifier in the chain. In this context, the Ambrosia did nothing
to detract from the overall perception of first-rate bass extension
and pitch definition.
Son of Ampzilla had already spent some time in my system prior
to the arrival of the Ambrosia driving both the Final Sound 1000i
ESLs and the Esoteric MG-20 with its cast of all-magnesium alloy
drivers. It became clear that it was totally unphased by difficult
loads. And because of its low source impedance it did not roll
off the Final Sound ESL's treble, even though the latter approaches
an impedance of 1 Ohm at 20kHz. Its sonic character was always
smooth and never offensive at any drive level. Bongiorno coined
the term ‘Tubistor' to characterize its sound, since the Son's
smooth distortion characteristics, according to James, recall
the sound of vintage tube amplifiers. However, on the debit side
of its report card were the observations that the Son was tonally
a bit laid back through the midrange and that it lacked in soundstage
transparency (read: slightly veiled) relative to the two, albeit
much more expensive, amplifiers in the house — the LAMM Industries
M1.2 Reference and Silicon Arts Design ZL-120. Enter the Ambrosia.
Partnering the Son and driving the Venture Audio speakers, transparency,
that is illumination of the inner recesses of the soundstage,
was judged to be very good during vinyl playback. In addition,
bass control was exceptional, and harmonic textures were consistently
smooth and liquid in character — most unusual for a solid-state
amp. Yes, the Son could be bested in terms of immediacy, emotional
intensity, and soundstaging, but at a much higher price point.
I was less enamored with this partnership during CD playback,
at least when feeding the Esoteric SA-60 analog output through
the Ambrosia's line stage. However, late in the ball game, the
PrimaLuna ProLogue Eight CD player (with the Super I/V Board Plus
upgrade) joined the fun. Revisiting the Ambrosia plus Son of Ampzilla
combination, I was shocked by what now could best be described
as superlative soundstage transparency. Image outlines were tightly
focused within an expansive soundstage. Detail resolution and
clarity now rivaled far more expensive amplification chains. This
in essence is the definition of synergy; the sum being greater
than the individual parts.
lives again! It would appear that James Bongiorno is still riding
tall in the saddle. Part musician and part audio magician, and
a national treasure in my humble opinion, Bongiorno delivers the
goodies yet again. While the Son of Ampzilla represents a safe
recommendation at its price point (and for the record, I'm a proud
owner of a Son), the Ambrosia is a sensation at any price point.
Here is a full function preamplifier complete with MM and MC phono
capability that for me bridges the sonic gap between solid-state
and tube designs. If you already own a tube or hybrid amp, the
Ambrosia should prove most complementary. With a tubed CD player,
such as the PrimaLuna ProLogue Eight at the head of the chain,
the Ambrosia-Son partnership partnered makes for a synergistic
amplification chain competitive with the best money can buy.
happened in Las Vegas, but it certainly did not stay there. I
was seated late one evening in the VMPS Audio room at the St.
Tropez during the January 2008 CES, simply enjoying the music,
when Brian Cheney turns to me and says something to the effect
that I should give a pair of Son of Ampzilla (SofA) a listen in
monoblock configuration. He already knew that I was in the process
of evaluating the SofA as a stereo amplifier and indicated that
as monoblocks they sound much different.
took some time for James Bongiorno to send me another SofA, and
eventually I spent most of April evaluating a pair as monoblocks.
It is important to note that SofA is a bridged amp so it cannot
be bridged again, but simply using a single channel in each of
two amps gives not only a power increase but also improved sound
quality. In fact, when I asked Brian why he tried this configuration
in the first place he said that he wanted more power and estimated
the power increase as about 40% in monoblock configuration.
have to confess that I was totally unprepared for a dramatic leap
in sonic refinement. A clear demonstration of the power of two:
a pair of SofA sounded at least factor of four better. What was
truly amazing was the change in sonic personality. The presentation
gained considerable immediacy with more treble air. Dynamics,
and especially macrodynamics, as in the surge from loud to very
loud, were more convincing. In addition, rhythmic drive, aka the
boogie factor, was more pronounced, all in all making for a persuasive
emotional connection with the music. Soundstage depth perspective
was deeper and better layered. Image focus also improved noticeably.
Brain Cheney believes that channel crosstalk is always a problem
in stereo amps, especially at high frequencies, and impairs imaging.
The monoblock configuration, he says, takes care of that.
a period of several weeks I auditioned the SofA monoblocks with
some of my favorite loudspeakers, including the TEAC Esoteric
MG-20, the Venture Audio Excellence III Signature, and the Final
Sound 1000i electrostatics. In every case, the SofA performed
flawlessly. It became apparent as I changed preamps and front
ends that this was essentially a neutral sounding amp that strictly
mirrored the sonic flavor of what came before. The SofA could
be made to sound tube-like, at least through the midrange, by
a good tube preamp, while the increase in speed with a solid-state
preamp in the chain was clearly noticeable.
the end of this period I realized that I could no longer live
without the reliability, purity of tone, and bass horsepower offered
by the SofA monoblocks. In my opinion the SofA twins are more
than competitive with any power amp on this planet. Considering
their asking price, they truly are a bargain in high-end terms.
Type: Stereo power amplifier
Power Output: 100 wpc into 8 Ohm
THD: < 0.05% 20 Hz - 20 kHz
Noise: - 110 dB
Input Impedance: 33 kOhm
Sensitivity: Balanced inputs: 0.707V for 100 watts; Unbalanced
inputs: 1.414V for 100 watts
Dimensions: 9 x 12 x 15 (HxWxD in inches)
Weight: 52 lbs.
Type: Stereo preamplifier
Gain: MC: 64dB max; MM: 42dB; Line: 21dB
THD (MC & MM): <0.05%, 20 Hz to 20 kHz at 2 V at tape out
THD (Line): <0.05%, 20 Hz to 20 kHz at 2 V at main out
Input impedance: MC nominally 1 kOhm; MM nominally 47 kOhm; line
inputs nominally 40 kOhm
(Balanced: +/- 50 kOhm balanced; Unbalanced: 50 kOhm)
Weight: 50 lbs.
Spectrum Technologies Inc.
716 North G Street #2
Lompoc, Ca. 93436
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