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Since Thoebe utilizes only two stages of amplification between the phono inputs and the main outputs, with each stage individually servo-controlled, performance is raised by a whole order of magnitude. The success of this design is indicated by the extremely low distortion components above the 2nd and 3rd harmonic-below 0.005%.

Thoebe has features which make it one of the most versatile preamplifiers available. DC coupling after the input isolation capacitors, fully-complementary symmetry, and servo-loop phono amplifier and line amplifier reduce distortion and balance the preamp's output.

Thoebe is a highly powerful preamplifier, capable of delivering 1 1/2 Watts, which can drive low (or high) impedance headphones, and passive crossovers (see page 3 for complete passive crossover design instructions).

Included on Thoebe's rear panel is a jack for powering Goliath, GAS Company's moving-coil phono preamp, for use with moving-coil phono cartridges.

Other features include two pairs of tape inputs with full monitoring, copying, and tape-to-tape dubbing facilities, a four-position low-frequency filter (10 Hz, 20 Hz, 30 Hz, and off) for preventing turntable rumble from reaching the speakers and wasting amplifier power, a 15-Ampere power switch, and a 15dB muting control. Extremely flexible stereo-mode switching is also provided.

Thoebe is rack-mountable, with an attractive yet functional front panel array, and is an ideal companion unit for Son of Ampzilla power amplifier.
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• • Fully-complementary symmetry
• • Four servo-amplifiers operating completely outside audio path to maintain DC interstage Voltages at zero in phono section and line amplifier
• • DC coupling after input isolation capacitors
• • Single-stage servo-loop line amplifier
• • High output of 11/2 Watts with 60 Ohm source impedance
• • Four-position low frequency filter (10 Hz, 20 Hz, 30 Hz, off)
• • Tone controls located in feedback loop
• • Two fully-regulated power supplies
• • Provisions for powering Goliath II
• • Negligible Transient Intermodulation (TIM) distortion
• • Four AC outlets on rear panel (3 switched, 1 unswitched)
• • Gold-plated audio cables supplied
• • 16 AWG nickel-plated steel chassis

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Great American Sound Company has solved these problems with Goliath II. Goliath II is an RIAA-equalized phono preamplifier with up to 70dB of gain. It is the same revolutionary moving-coil phono preamplifier found in Thaedra II that provides the extra gain required for moving coils with none of the added noise and distortion of step-up transformers or pre-preamps.

Goliath II plugs into a high-level input-not the phono input. This not only reduces noise and distortion, it frees the phono inputs to accept standard magnetic cartridges.

• Anmerkung : Das ist natürlich überflüsiger Unsinn. Wer ein MC-System hat , benutzt keine schwächeren Abtast-Systeme mehr.

Goliath's circuitry is fully-complementary and DC servo controlled. The gain is user-adjustable on the front panel in 3dB increments, from 58dB to 70dB, accommodating from the lowest to highest sensitivity phono cartridges. A power jack on Thoebe's rear panel supplies Goliath's power requirements. Panel height is matched to Thoebe.
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for Goliath II and Self-Powered Goliath II
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• Total Harmonic and IM Distortion at any level to rated power|0.01%
• Signal-to-Noise-Phono, ret. 10mV-20Hz-20kHz|83dB
• Gain-Adjustable from 58dB to 70dB|
• Frequency Response-Phono departure from RIAA curve|±0.2dB
• Frequency Response|20Hz-20kHz±0.1dB
• Head Amp (MC) Signal-to-Noise|83dB
• Head Amp (MC) Sensitivity|0.2mV
• Dimensions: W x H xD/Weight:|2V4"x 51/4"x 8'75 lbs.
• Metric Dimensions: W x H x D/Weight:|6cm x 13cm x 20cm/2.3Kg.
• Self-Powered Gqliath II: Dimensions: W x H x D/Weight:|19"x3.5"x8'711 lbs.
• Metric Dimensions: W x H x D/Weight:|48 cm x 9 cm x 20 cm/5 Kg.

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• Anmerkung : Wie aufwendig ein Netzteil sein mußte, um einen Vor-Vorverstärker zu speisen, der über 80dB Rauschabastand haben mußte, zeigt die DENON HA-500 Entwicklung.

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Recently there has been much interest in biamplification and triamplification of multiple speakers or speaker systems to achieve lower distortion and more balanced sound. This usually entails inserting an active electronic crossover between the preamplifier and the power amplifiers to channel the frequency bands to their respective amplifiers.

An alternative to this method is to utilize a passive crossover network, devoid of any electronics, which is driven directly by the preamplifier. Unfortunately, most preamplifiers have insufficient power output to drive passive crossovers directly.

But, since Thaedra and Thoebe have been provided with unusually high power output (1 1/2 Watts), they are able to drive passive crossovers easily.

The passive crossover network discussed here is high-impedance, and therefore should not be confused with the low-Impedance crossover network integrated into multi-driver speaker systems.

Because these speaker crossovers are low-impedance, they cannot be driven by a preamplifier. If such a speaker system is to be used in a biamplifier or triamplifier operation, its crossover network must be disconnected.

Passive crossovers have many advantages over active crossover designs. They are quite simple to construct and very inexpensive (the crossover circuits shown here will cost a total of only a few dollars for all of the necessary parts).

More importantly, the passive crossover cannot add I.M. distortion to the signal. In addition, the passive design results in no insertion loss, and allows the use of smaller, more-accurate components than speaker crossovers generally used.


In designing the passive network, the following diagrams apply:
LO-PASS NETWORK and HI-PASS NETWORK

The recommended impedance between the Thaedra or Thoebe preamplifier and the power amplifier is 2.2K Ohms. The corresponding values of capacitances at different frequencies to obtain a 6dB-per-octave attenuation are derived from the formula:

F = Crossover Frequency
Z = Crossover Impedance (2.2K Ohms)
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Der Rest dieser passiven Weiche ist leider Unsinn.
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But not just another super-amplifier. Godzilla is actually two powerful amplifiers on one chassis. It features a dual power supply, true peak-reading logarithmic meters, two low-noise computer grade fans, and power output that places Godzilla squarely in a class all by itself.

Godzilla will put out a minimum of 350 Watts per channel into 8 Ohms, 600 Watts per channel into 4 Ohms, and 1000 Watts per channel into 2 Ohms, all at less than 0.1% THD!

Godzilla is a professional component. The inputs are switchable in four different ways: balanced, unbalanced, high impedance (50K Ohms), and low impedance (600 Ohms), in any combination. Slew rate is an incredible 1000 V /u-sec!


There is a lot more about Godzilla that you will want to know. Look for it later this year at your authorized GAS dealer. In the meantime keep watching the Gasette for details.

Want to know more about GAS products? An 8-page, full-line brochure is available now from any authorized GAS dealer. The brochure lists all of our current products with complete specifications and descriptions. Also therein is a description of our design philosophy and some beautiful photographs of Thaedra II, Thoebe, Thalia, Ampzilla lla, Son of Ampzilla, Grandson, The Bridge, Goliath II, Self-Powered Goliath II, and the Sleeping Beauty series of moving-coil cartridges. It's at your GAS dealer now, and it's free.

Spread the word! GAS is now offering fine quality T-shirts, previously available only to employees and dealers, to the general public. The shirts come in blue or beige, in men's sizes of Small, Medium, Large and Extra-Large, and in women's sizes of Small, Medium, and Large.

The shirts cost $5.00 (a mere pittance) and can be obtained only from GAS. Get one-at least!

Reprinted from UK magazine Hi-fi Answers, Oct. 1977.

You'd expect an American amp and speakers to be pretty big, not to mention expensive. Adding a Thorens TD160 Mk II and the new Ortofon M20FL brought the total cost of the system to over £2000. Jonathan Mills thought it was all worth it, though. Some of it, anyway...

It was with considerable excitement that I trundled the various packages that contained this month's super system through my front door. The Dahlquist speakers I have heard several times before and always with enjoyable results.

GAS (Great American Sound Corp. Inc.) are, as their name suggests, a 'fun' company who name all their products rather than give them model numbers.

I received 'Thoebe' and 'Son of Ampzilla', but Hayden Labs, the importers, are also introducing the 'Sleeping Beauty' moving coil cartridge and its booster amplifier 'Goliath'.

Despite their light hearted attitude from the name aspect, GAS take a professional attitude to construction and enthusiastic approach to circuit design, listening tests taking prominence.

Thoebe has a veritable plethora of phono sockets on her back, all of which face upwards and are therefore very easy to get at. Half the switches you can see on the front panel control these inputs which include two phono, tuner, auxiliary and various methods of copying from one tape deck to another.

The other buttons switch in 30Hz, 20Hz and 10Hz filters and control mute and mono/stereo functions.

There is one large volume control with a slider balance control above it, and either side of it are bass and treble controls for each channel.

Although I do not like the inclusion of tone controls or filters on amplifiers, finding they add a grittiness to the sound when switched in, the bass and treble on the GAS amp turned out to be reasonably innocuous.

They are obviously tailored for high quality speakers as they operate at the extremes of the audio range, the bass control affecting only the deep notes and the treble affecting cymbals rather than the midrange. Both tone controls and volume control have click stops allowing the listener to repeat certain settings at will.

The three high-pass filters are presumably there to avoid distress of bass units by record-warp modulations.

Use of the 10Hz filter avoided blowing the 2A fuse in the Dahlquists on transients, but this fuse can be uprated to 3A with safety. I mention this because the high pass filter causes a phase shift at low frequencies, which has effects higher up the range.

This is particularly noticeable on piano, which becomes 'clearer' when the filter is switched out.

This is a subtle effect and is not meant as criticism of the amplifier - in fact I am glad the designer had the foresight to make the filters switchable. The amp has no high frequency filters, for which I am thankful, as in my experience these degrade the sound even further!

Also on the rear are relay controlled outputs for two power amplifiers and, horror of horrors, three American type two pin power sockets of the unshrouded variety.

These, combined with the lack of mains earth would probably make the British Standards people come out in a rash, and one wonders whether Thoebe would pass the British Safety requirements.

Power is fed to the circuitry by push buttons on the front panel - one for on and one for off. Son of Ampzilla is powered from the switched socket on the rear, but the audio signal is not routed through until voltage levels have stabilised 35 seconds later.

There are no controls on the power amp at all, the matt black metal case is only embellished by two power level meters. These are claibrated for 8 ohm speakers and, unfortunately, do not respond very well to peaks and only show average power levels.

High frequency transient clipping occurred whilst the meters, which have a OdB level of 80 watts, were still showing under 50 watts output. Speakers are connected via screw terminals on the rear of the amplifier allowing a good connection. There is no method of connecting or switching two pairs of speakers, GAS having fallen in with the theory that any switch or relay contacts interfere with the sound quality. What is the point of having speaker cable of ultra-low resistance if switch contacts introduce more?

I am glad to say that 'Son of Ampzilla' was really happy playing with the Dahlquists. Output power was high enough to generate a really deep bass and clean, high transients in anything but the largest mansions. Clipping occasionally occurred while reproducing drums at high levels with brass overlay, though this was relatively unobjectionable and was heard as grittiness rather than the painful distortion that some amplifiers generate.

The real test for transistor amplifiers, as far as I am concerned is the sound they give when reproducing classical string sections.

Valve amps have the capability of keeping violins sweet at the top end whilst still reproducing the rasp of resin against gut.

Transistor amps usually reproduce all of the rasp and none of the sweetness. Aided by the Ortofon, the amplifier can, in my estimation, join the select few that are capable of sounding both smooth and detailed, perhaps not as rounded as the Quad but then it packs more punch!

The bass end was really tight and one wonders why Dahlquist bothered to bring out his sub-bass woofer (available as an extra) as organ pedal notes from the DQ10s shook the floor with ease.

Ampzilla itself has the reputation in some quarters as having the most gutsy and tight bass end around. Son of Ampzilla follows in his father's footsteps
from what the soles of my feet and my stomach were telling me.

As for the DQ10s I find it really difficult to put into words how pleasant they were to listen to.

Super smooth is probably the description that applies best, but there is also a touch of magic about them which makes them nice to come home to. In fact walking in the door after a hard day's work it is nice to think of Thoebe and her partner sitting there just waiting to give me all that listening pleasure.

It is a pity the Thorens lets the system down but if you want an alternative in the same price range try the Rega Planar 3 whose arm is perfectly happy with the Ortofon cartridge range.

Whether you think the sound this system offers is worth the money it costs should be decided by a demonstration, preferably in your own home.

Personally if I had £700 to spend on speakers Dahlquists would head my shortlist and Thoebe and Son of Ampzilla would certainly draw a lot of my attention.

Reprinted courtesy of :
SOUND ADVICE Volume 1 Number 4

SOUND ADVICE is published by Friday Publishing
Inc., © Copyright 1977 by Friday Publishing Inc,
all rights reserved. 68 Post Street, Suite 226, San Francisco, California 94104. (415) 362-4300.
Subscriptions: 4 Issues $12.00, $15.00 First Class, $18.00 Overseas.

Thoebe's internal organs. Standard of construction is superb. Rear views show input/output connections and Son of Ampzilla's massive heatsinks. No speaker switching is provided

GREAT AMERICAN SOUND Thoebe Servo Loop Preamplifier. Serial no. A511174. Source: loan from private owner. Retail price is U.S. $495. Manufactured by Great American Sound, 20940 Lassen St., Chatsworth, CA 91311.

This attractively styled preamp offers exceptionally accurate sound with more features than we would expect for its modest $495 retail price. From a sonic standpoint, the Thoebe outperformed every other preamp except the Paragon 12.

Features the Thoebe has in abundance since one comes to expect minimum flexibility from a top-quality preamp as with the DB or Paragon E, both of which are priced at $500 and do not offer tone controls, etc.

We found the Thoebe's volume control to be poorly positioned and the horizontal slider for balance less convenient than a rotary switch.

The two spiffy relay switches for power had a nice feel to them. On the left of the front panel is a brace of 15 push button switches-5 for inputs including 2 phono, a handy stereo reverse, an interesting three-position low-frequency Filter and a variety of tape and mode switches. Front panel jacks are provided for tape and headphones, which is handy.

We would characterize the sound of the Thoebe as extremely clean and open but tending toward the bright side, particularly in the upper mid-range.

Bass was impressive-deep and well controlled with good definition. It was a close second to the Paragon 12 in this respect, and a shade better than the Rappaport. The Paragon had a little less punch in the mid-bass but was slightly better in definition.

Thoebe's imaging was excellent and equal to the Paragon and Rappaport. Transient response was exceptionally good, again, the equal of the best we have heard.

In the mid-range, the Thoebe had that richness in the lower mid-range area that gave body to the sound of a cello, a quality which we found missing in the SP-4. We were bothered by some smearing in the mid-range of the Thoebe as well as a bit of raspiness in the upper mid-range area. Neither quality was noticed on the Paragon 12.

Considered on balance, the Thoebe represents an excellent value. It offers close to the best performance we have heard from a preamp in this price level.

Another New Product from the G.A.S. Co.

In keeping with its desire to market affordable and needed products for audio aficionados, Great American Sound Company introduces the Bridge. The Bridge offers a simple way to electrically couple two amplifiers into one in order to increase power output.

The Bridge contains a pair of 180° passive phase inverters which will combine two stereo power amplifiers into one amplifier with approximately quadrupled power output and a slew rate double that of the original individual amplifier. For example, two 40-Watt* Grandsons bridged result in an amplifier with 160 Watts per channel at 8 Ohms and a slew rate of 40 Volts per microsecond. Two 80-Watt* Son of Ampzillas bridged become one amplifier with more than 300 Watts per channel at 8 Ohms and a slew rate better than 70 Volts per microsecond.

* per channel at 8 Ohms.

Bridging two 200-Watt Ampzilla II's results in a staggering 720 Watts per channel at 8 Ohms, with a slew rate of 100 Volts per microsecond.

Why is so much amplifier power necessary? The accurate reproduction of musical transients (the instantaneous "attack" or onset of a particular musical sound, such as a trumpet blast or cymbal crash) can require up to twenty times more power than the average musical signal.

If an amplifier has inadequate power (headroom), these transients will introduce distortion because the amplifier is clipping. If inefficient speakers are being used, the problem of inadequate headroom is further aggravated. Using the Bridge with an additional amplifier is an economical method of increasing this headroom.

The Bridge offers great flexibility to those who wish to upgrade their stereo systems without investing in a higher-powered amplifier. The Bridge comes assembled on a 19-inch rack-mount panel.

NOTE: It is imperative that the two amplifiers being bridged are electrically identical, preferably the same make and model. Otherwise, bridging will not function correctly, and damage to speakers and one or both amplifiers might result. It is equally important that the user of the Bridge strictly adhere to the hook-up instructions provided with the unit.
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Reprint courtesy of Hi-Fi Buyers Review 1978,\ Published monthly by FM Music Program Guide, Inc., 20 Hampton Road, Southhampton, New York 11968 (516) 283-2360 Subscriptions $15 per year. Printed in U.S.A

The oddly-named Thoebe preamplifier is made by the "Great American Sound" Company which is responsible for the Ampzilla series of power amplifiers. It measures 16 inches long by 6 1/2 inches deep and 5 inches high. Projecting from the rear, at the bottom, is a 1-inch extension on which are mounted the various input and output sockets. These are placed so the plugs are inserted vertically, which many people find more convenient than most conventional arrangements.

The front panel extends 1 1/2 inches each side of the front so the unit can be mounted on a standard 19 inch rack. Styling is cuall-black" with white lettering and the only touch of color comes from a tiny green indicator light.

Layout is unusual too, with the whole appearance dominated by a group of 15 push-buttons on the left-hand side arranged in three vertical rows.

The first group selects the five inputs: phono 1, phono 2, tuner, aux 1 and aux 2. The next row has four b ttons for two tape recorders, with dubbing, while the fifth is a mute switch to reduce the preamp's output by 15dB. Row number three contains two low-frequency filters, stereo reverse, stereo and mono switches. The five rotary controls at the bottom are bass and treble controls for each channel plus a large one in the center for volume.

All these controls use multi-contact switches with accurate resistor elements: there are 21 steps in 2 dB increments for the volume control and 10 detents each for lift and cut on the four tone controls.

Above the volume control is a horizontal slider for balance, and just to the left of it is a pair of tape recorder jacks. On the other side are two more for headphones. On the extreme right, is the power on-off switch plus the indicator light mentioned earlier. Purists (for whom this preamp is designed) will query the absence of a tone control defeat switch but it is claimed that one is not needed as the controls are effectively out of circuit when the knobs are turned to the center positions.

At the rear are no less than 22 RCA type sockets plus 4 ac outlets-three switched and one unswitched for use with a turntable.

Under the heavy metal cover, the components - or most of them - are dispersed on seven printed circuit boards and it was noticed that the power transformer was totally enclosed in a mu-metal can.

Apart from a block diagram in the instruction book, no circuit details were available, other than the statement that a DC coupled complementery
arrangement is used throughout, and some kind of servo circuit is used to prevent drift.

This can be a big problem with DC circuits as slight changes in the characteristics of one stage due to thermal effects and so on can upset the operating parameters of tht whole amplifier.

The Thoebe is no lightweight as it turns the scales at 28 pounds, hence the two handles are functional as well as decorative!

The first test was for voltage output and distortion with the results show in figure 1. THD was virtually immeasurable below 4 volts output and was only 0.3% at 13 volts.! As most amplifiers need only one or two volts at most, there is a more than adequate margin.

IM distortion was 0.005% at 3 volts output, falling to an infinitesimal 0.003%> at 2 volts. Harmonic distortion did not increase significantly throughout the audio band so no graph is shown. Figure 2 shows the overall frequency response and the effect of the low frequency filters. One cuts at 20 Hz while the other cuts at 30 Hz, but depressing both buttons brings the turnover frequency down to 10 Hz which is rather surprising, but well, that's how they are labelled and it is absolutely correct.

The tone control characteristics can be seen in figure 2: note that the treble lift is deliberately curtailed at the highest frequencies. The volume control matching was exceptionally accurate and the deviations were less than 0.2 dB.

Crosstalk measured 52dB at 1 kHz, and 48dB at 10 kHz, channel A to B with 44 dB and 48 dB, channel B to A (phono inputs, 600 ohm termination).

Input required for 2 volts output, 600 ohm load was 200 mV for the high levels and 1.4 mV for phono.

Signal-to-noise (ref. 2 volts output, "A" weighting) was better than 100 dB and 80 dB respectively.

Overload point for phono was 110 mV with symmetrical clipping.

In a word: neutral. For the initial listening tests it was connected to a G.A.S. Son of Ampzilla power amplifier and comparisons made with other super combinations. Among the phono cartridges were a G.A.S. "Sleeping Beauty" (Naturally!) ADC XLM, Empire 2000Z and a Stanton 88IS. In addition to several top-rated speaker systems, a pair of Audio Technica electrostatic headphones was also used to check whether the Thoebe was introducing any audible coloration.

There were indeed slight differences between the various cartridges (also apparent with other preamps), but I believe any other discrepancies were due to barely measurable matching differences.

As mentioned earlier, the Thoebe is designed for the purists who would never dream of using a high-frequency filter or loudness control so they won't miss these items.

On the other hand, most of them will appreciate the flexibility of separate tone controls and the choice of subsonic filters. Furthermore, they will appreciate the ability to use up to three tape recorders and especially those recording jacks right on the front panel.

Another refinement is the use of a relay with time delay to avoid speaker-damaging switch-on surges.

This preamp is not particularly cheap but then the precision controls and the small tolerance components necessary to provide really accurate RIAA equalizing are quite expensive and you can pay much more and get a lot less for your money!

One other point: allow plenty of ventilation as the unit runs pretty hot - at least for a preamp. -

George Tillett