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GFP-750

 

The GFP-750 is part of a series of ultra-high performance separate components from Adcom. It shares this position with our exciting GFA-5802 power amp and GCD-750 CD player. All three of these components were conceived under Adcom's long standing philosophy of providing exceptional performance for the money. But our goal was to go beyond delivering exceptional performance and value, to the "next level"; by delivering the sonics and effortless power, along with the finesse and sophistication of units costing two to three times as much. The fact that we exceeded our own expectations is a testament to our engineers' diligence and their unswerving dedication to these goals.

 

The preamplifier's role

From a design standpoint the proverbial audio component "acting like a piece of wire, but with gain" is always (or should always be) the goal. But approaching that goal is, in reality, an incredibly difficult task. With the GFP-750 we believe we've come significantly closer to this ideal than anyone near this price category has ever come before.

 

The preamplifier is "control central" for any system. It provides source selection, adds gain when necessary, lets you adjusts levels, balance, and other parameters, and sends the signal off to the system's "engine room", the power amp. As the switching and control center, the preamp must be extremely quiet and distortion free. Because the signals it receives and then sends out to the power amp will be multiplied hundreds of times before you hear them. So if the preamp changes the signal in any way, it'll be magnified big time when you finally hear it! Fundamentally then, a great preamp must allow control flexibility and source selection, while adding or taking away nothing from the original source.

Choose active or passive control

The GFP-750 can be operated either as a completely "passive" (no gain) unit, with absolutely minimal sonic impact, or as a sophisticated active (utilizing active components and providing gain) preamplifier. In passive mode the GFP-750 is strictly a "line level input switcher", with its high quality four gang volume attenuator that lets you adjust the volume. While its active circuitry is both unique and superb (details later), you always have the option of using the GFP-750 in this ultimate passive mode, for control with maximum fidelity.

Adcom's passive approach

Any "line level" source that you have (CD player, tuner, DVD player {audio output}, tape deck, etc.) can be directed through the GFP-750 in the passive mode. The only effect the GFP-750 will have on the sound is volume adjustment, using the built-in precision four gang volume attenuator. In this mode the GFP-750 adds no noise, no distortion, in fact, it changes nothing. So, as far as your ears are concerned, it's sonically invisible. And that's our goal, isn't it?

But what if you need the active capabilities of the 750? Do you sacrifice fidelity for convenience and added control? Read on and see why you don't.

 

Adcom's active approach

The engineering design specifications for the GFP-750 were simple:

• Minimize circuitry (the fewer parts and gain stages, the less chance there is for sonic degradation).
• Reduce or eliminate negative feedback.
• Incorporate true differential balanced audio signal paths for the best sound quality.
• Use high quality MosFet transistors throughout.
• Power the internal circuits of the GFP-750 with a power supply that can keep up with any conceivable signal demand.
• Incorporate an easy way to add home theater processing while maintaining the best performance.

Adcom's creative engineering solutions

• The GFP-750 has only one active gain stage. It's a pure Class A design, long regarded as the best sounding type of amplifier circuit. The active devices in this gain stage are exclusively reference grade HexFet transistors (an advanced hybrid MosFet device) that offer superb, dynamic sound with a smoothness and openness heretofore considered unobtainable in solid state devices. Countless hours of intense listening have proven to us that well designed amplifier stages using MosFet devices are the smoothest and most natural sounding. So you'll find these more expensive MosFets and HexFets throughout Adcom's line, because we won't compromise performance to save money on parts.
• The GFP-750's active circuits have extremely wide frequency bandwidth for uncolored sound, yet they've been designed to be impervious to RF (Radio Frequency) interference, as an added assurance that noise won't be an issue.
• The GFP-750 features both balanced XLR (for the CD) and unbalanced gold plated RCA input circuits. Using the balanced XLRs assures the quietest signal transfer between components. Balanced XLR circuits are also included for output connection to an appropriately equipped power amplifier, like the GFA-5802.
• The GFP-750's output stage acts as pure current source (as opposed to a voltage source). That means it's effectively isolated from the power amplifiers input impedance and the impedance of the cables used between them. (High quality cables are important, but should have less of a sonic impact on the GFP-750 than some other preamp designs.)
• The GFP-750 incorporates a power supply that would more typically suit a receiver or integrated amplifier! It includes a large toroidal (donut shaped) transformer which offers less internal resistance to current flow and lower induced hum than traditional transformer designs. This transformer has multiple output taps, one for each channel. Individual voltage regulators are mounted to special aluminum heat sinks for maximum stability and to allow high current draw during dynamic passages. Selected high capacity storage capacitors are mounted close to the individual circuit they service to supply clean, filtered power to the active components.
• The GFP-750's component parts are carefully selected reference grade devices, for maximum sound quality and minimum noise.
• The GFP-750 is direct coupled, eliminating capacitors entirely, where possible, to reduce their sonic impact.
• Input switching is accomplished with hermetically sealed high quality relays. This eliminates the noise and other problems associated with alternate switching methods.

The Home Theater connection

A specially located and buffered (isolated) external processor loop has been included in the GFP-750. It allows easy connection of an external surround sound processor with no sonic impact. When this loop is employed, the GFP-750's volume control is bypassed allowing the processor to adjust all channel output levels. In this way, you can create a Home Theater while maintaining the GFP-750's (and the processor's) sound quality. It's quite an elegant solution to the problem of expanding an ultra-high performance system without affecting the sound.

Other important touches

• The GFP-750 comes with a slim, elegant remote control that lets you select inputs, adjust volume and balance, mute the output, and select the external processor loop.
• The front panel includes red LEDs which indicate Passive mode, Power on, and Processor loop engaged. There's also a convenient front panel control for Stereo, Stereo Reverse, and Mono.
• On the rear panel all input/output jacks are gold plated for maximum conductivity and to eliminate corrosion. There's an ON/Off "vacation" switch to completely shut down the GFP-750 when it won't be used for a long time.
• Infra-Red "repeater" jacks are included to allow sending IR signals along to other remote controlled units, using IR flashers available from your Adcom dealer. You can also connect a remote room sensor to the back of the GFP-750.
• The GFP-750's physical construction has been chosen to eliminate any concerns about external vibration coloring the sound. This design also helps shield the internal circuits from outside electrical noise. The GFP-750 is built using an extruded aluminum front panel with a heavy gauge steel chassis and top. The entire unit is finished in an attractive and durable powder coated black finish.

The GFP-750, like its Adcom stable mates, offers true audiophile high end sonic performance at a surprisingly affordable price. Its simple, clean control layout, combined with full remote capability, Home Theater expandability, and State-of the Art sound will certainly satisfy the most critical and quality conscious listener.

 

 

 

ADCOM's high-end audio heritage is apparent in our revolutionary GTP-740 Digital Processor/Tuner/Preamplifier.  Built with a unique combination of advanced circuitry and user friendly design, the GTP-740 forms the ideal control center for any home theater system and brings new precision to 5.1 channel information processing and playback.

Utilizing the very best of ADCOM's considerable experience on the analog side, combined with the very latest advances in digital processing, the GTP-740 represents our first true digital preamplifier.  As such, the GTP-740 offers many technical and sonic advantages over most traditional controllers and preamps.  All analog input signals are converted to 20-bit digital signals.  This allows the 740 to process the signal digitally, and if necessary, convert it to a surround format, or simply pass it through to the final output stage without any degradation of sensitive signal information.  Our experience in developing the renowned GDA model Digital-to-Analog converters (GDA-700 and GDA-600), the HDCD GCD-750 CD player, and our highly regarded CD changers all benefit the GTP-740.  These products were all acknowledged for their outstanding D to A sections and taught ADCOM about the importance of linearity in the digital domain.  The GTP-740 uses the same 20-bit technology for exceptional performance.  You can even use your 740 as an outboard D-to-A converter if your CD player has a digital output!

Digital processing speed and capability that would be the envy of computers from only a few years ago form the heart of the GTP-740.  To master the "digital domain" ADCOM uses two highly regarded and state-of-the-art Motorola DSP devices in combination, a 56007 and 56009, which provide the 740 with true 24-bit digital signal processing to ensure the most accurate retrieval and reproduction of all information contained in the original recording.  All processing of the 20-bit signal is actually done as 24-bit, eliminating rounding errors to preserve absolute signal integrity in the digital manipulation.  This level of digital sophistication is normally found only in products at several times the 740's price and ensures that all the information is accurately reproduced as an analog output for your listening enjoyment.

The GTP-740 design incorporates three Dolby surround modes: Dolby Digital (AC-3), Digital Dolby Pro-Logic® and Cinema Pro-Logic.  Dolby Digital offers five full-bandwidth channels: front left, front right, center, rear left, and rear right; plus a dedicated Low Frequency Effects (LFE) channel specifically for subwoofer applications.  This configuration comprises essentially six channels of sonic information yielding the "5.1" designation since the LFE channel is limited bandwidth.  In the "Cinema" implementation of Dolby Pro-Logic the front channels are equalized and diminishing multiple delays are added to the rear channels.  This more closely approximates the sound of a large theater for older soundtracks and other sources not mastered to the latest 5.1 standard.

One key advantage to this high degree of sophistication is the implementation of digital bass management in Dolby Digital (AC-3) applications.  This adds substantial impact to the LFE information when using a subwoofer by improving phase coherence, frequency and transient response.  The more typical analog bass management others use results in compromises with the LFE information, by relying on bass "comb filtering" that can result in phase shifts and muddy bass response as opposed to the crisp, well-defined low bass effects ADCOM achieves through DBM (digital bass management).

The Dolby Digital mode in the GTP-740 presents a spatially correct soundstage with precise lateral imaging and front to back depth with full-range signal information for the five main channels.  This perfomance rivals, or even exceeds, the sonic experience of going to see a movie at the theater. Wide dynamic range creates greater emotional impact,  while accurate imaging (directional cues), special effects localization, clear dialogue and dedicated subwoofer effects assure the best in home theater presentation.  In this mode the GTP-740 decodes all the latest software sources from DSS, DVD, Laser Disc, as well as forthcoming digital TV broadcasts from both conventional means and satellites.

There is also a version of the GTP-740 with DTS capability as that 5.1 software format has gained acceptance and wider availability.  This model is designated the GTP-740/dts, or if you wish to purchase a conventional GTP-740 you can later opt to have ADCOM upgrade the unit for a modest cost, all with the assurance the modification and upgrade is being done directly by ADCOM.  As of this writing, DTS encoded software is primarily available in Laser Disc format, but DVD titles are increasingly appearing with DTS soundtracks.

The GTP-740 also includes three Digital Signal Processing modes.  These delay modes create psychoacoustically correct environments, from an intimate nightclub to an outdoor stadium, all at the touch of a button.  This choice of delay mode options gives you the freedom to create custom soundfields for your favorite videos or music events making listening and watching more of an experience.  A brief description of each DSP mode follows.

STADIUM mode is used for non-Dolby Surround encoded material to recreate a large and acoustically reverberant environment well suited for video sporting events and playback of music events performed in large outdoor arenas.  Vocal frequencies are slightly emphasized in the front channels to enhance intelligibility.  Stadium mode is also well suited for playback of older epic movies.  Chariot races, gladitorial combats and outdoor rock concerts all grow larger in Stadium mode.

SYMPHONY HALL mode replicates a relatively large indoor performance space.  Front channel frequency response is flat for maximum musical clarity while the diminishing multiple rear channel delays enhances the sense of spaciousness.  Operas and orchestral performances are recreated with surprising realism and spatial sense.

JAZZ CLUB mode synthesizes a smaller, closer and more intimate soundfield ideal for many types of jazz and popular music. This mode is also a good choice for playback of classic movies with mono soundtracks.  Create the ambience and warmth of a small club setting for a bit of romance at home.

In addition to the DSP modes, the GTP-740 offers a Five-Channel Stereo mode that makes full use of a home theater system's speaker complement, and is intended primarily to reproduce large scale musical events such as a full orchestra concert or an opera using conventional two-channel (stereo) recordings.  Naturally the GTP-740 also includes a premium quality two-channel stereo mode to enjoy the true stereo sound you expect from an ADCOM preamplifier.

One feature the GTP-740 adds that improves usability is a Dynamic Range Control.  Adjustable to 100%, 75%, 50% and 25%, this control allows dynamic range compensation to suit various listening conditions and sources by reducing the ratio between the loudest and softest passages.  This allows for lower, yet still enjoyable listening levels.  Soft dialogue and background information are preserved, while really loud special effects are "tamed."  Now you can watch that DVD rental late at night without disturbing the family or raising the ire of the neighbors.  How thoughtful.

When it comes to FM broadcasts the GTP-740's highly sensitive tuner section delivers the clearest sound the transmitted signal allows.  All tuner circuitry is isolated on its own low-loss, epoxy board and constructed with specially crafted RF, IF and multiplex decoding circuits for minimal interference and optimal clarity of FM broadcast reception.

The lessons learned in the design of ADCOM separates directly benefit the GTP-740 as do high-precision electronic parts: 1% metal film resistors, the same class of biased linear gain amplifiers developed for ADCOM's reference class components, an oversized transformer that projects superior soundstaging and imaging and NINE separately regulated power supplies!  Separate power supplies eliminate stray signals, false signals and potential cross-talk.  ADCOM also ensures complete separation of digital and analog sections, including dedicated power supplies, for optimal performance.  All 740 circuit boards are exclusively single-sided glass fiber FR4 grade, the same MIL-Spec. specification required by the most demanding aerospace applications -- such as radars, avionics and weapons systems.  FR4 boards offer superior mechanical and electrical performance (including die-electric properties) to preserve the signal integrity so absolutely essential in these applications.

The GTP-740 combines extensive switching and signal processing capabilities with a rare degree of operational simplicity. Straight-forward design and logical control groupings replace the typically intimidating front panels with often inaccessible and confusing multi-function controls.  All these features are easily operated by the ADCOM infrared remote for total control from anywhere in the room.

To further enhance the capability and usefulness of the GTP-740 we have included a Room 2 feature that allows you to send any of six analog audio/video sources to a completely separate location in your home.  And with the use of an infrared repeater you can control your GTP-740 from this location as well.  Want to adjourn to another room, but continue listening to the program you were playing-- just send it to Room 2.

And the GTP-740 is fitted with high quality input and output connections for eight audio (five analog and three digital) and six video sources with a full complement of S-Video connectors in addition to the standard composite video jacks.   These multi-conductor connections provide high resolution signal transfer for advanced televisions, DVD players, DSS receivers, LD players, VCRs and more.  Naturally all the audio and video RCA jacks are heavily gold-plated to maximize signal transfer and to minimize oxidation.  These multiple configuration options ensure complete compatibility and flexibility for all your home entertainment needs for years to come.

ADCOM's GTP-740 is the clear choice for a unique combination of high-end sound and full featured ease.  We pay attention to details so you can enjoy the sound!

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Adcom GTP-740  Technical Specifications

Preamplifier Section Output Impedance  Main Outputs.....600 ohms  Tape Outputs.....500ohms  Output level (Rated) .....2.0V  Input impedance.....20k ohm  Frequency Response  20Hz to 20kHz........ +0,  -0.5dB  THD+N at Rated Output  20Hz to 20kHz.......<0.02%  IM Distortion (CCIF at 15kHz and 16kHz).....<0.009%  Signal to Noise Ratio (Ref. to 2 volt)  "A" Weighted.........>95dB  Surround Modes Left, Right, and Center Channel Line Outputs  20Hz to 20kHz.....+0, -0.5dB  THD+N at Rated Output (5 Channel Mode)  20Hz to 20kHz.....>0.005%   THD+N at Rated Output (Dolby Pro Logic Mode)  100Hz to 20kHz.....>0.05%   Signal to Noise Ratio  (All Surround Modes, Ref. to 2 volt)   "A" Weighted.....>95dB  Rear Channel Line Outputs  Frequency Response (5 Channel Mode, No Delay)  20Hz to 20kHz.....+0. -0.5dB  Frequency Response (All Modes With Delay)  20Hz to 7kHz.....+0, -3dB  THD+N at Rated Output (5 Channel Mode, No Delay)  20Hz to 20kHz.....<0.008%  THD+N at Rated Output (All Modes With Delay)  1kHz.....<0.4%   Signal to Noise Ratio (5 Channel Mode, No Delay, Ref. to 2 volt)  "A" Weighted.....>95dB  Signal to Noise Ratio (Ref. to 2 volt)  "A" Weighted.....>70dB

FM Tuner Section Usable Sensitivity (Mono)........3.0 uV / 15 dBf  Quieting Sensitivity (5O dB)  Mono.....3.4 uV / 22 dBf  Stereo.....31 uV / 41 dBf  Signal To Noise (65dBf, "A" weighted)  Mono.....78dB  Stereo.....70dB  THD+N (1kHz, 65dBf)  Mono.....0.05%  Stereo.....0.09%  Capture Ratio........2.0 dB  Alternate Channel Selectivity (±400kHz).....>55 dB  Separation (at 1kHz).....>50 dB  Frequency Response (±0.5 dB).....30Hz to 15kHz  AM Tuner Section Sensitivity.....300uV/m  Selectivity (±10kHz).....> 40dB  Signal To Noise (5mV/m "A" Weighted).....>45dB  General Power (available in 230V on special order)  120 VAC/50-60Hz   Chassis Dimensions  4"(102mm) x 17"(432mm) x 11 1/2"(292mm)   Maximum Dimensions  4 1/4"(108mm) x 17"(432mm) x 12 3/4"(324mm)   Weight.....16 lbs. (7.3kg)  Weight, Packed.....19 lbs. (8.7kg)

Adcom's high-end audio heritage is evident in the revolutionary GTP-550 Surround Sound Tuner/Preamplifier. Built with a unique combination of advanced circuitry and ergonomic design, the GTP-550 is the ideal command center for any home theater system.

The GTP-550 is designed with two Dolby Pro Logic® modes: Dolby Pro Logic and Cinema. In the "Cinema" implementation of Dolby Pro Logic the front channels are equalized and diminishing multiple delays are added to the rear channels. This more closely approximates the sound of a large theater.

In the Dolby Pro Logic mode the GTP-550 presents a spatially correct soundstage with precise lateral imaging and front to back depth. This is the second of two preferred modes to properly process Dolby Surround® encoded video soundtracks, a growing number of CDs and even the audio portion of some computer games.

The GTP-550 also includes three Digital Signal Processing modes. These delay modes create psychoacoustically correct environments, from an intimate nightclub to an outdoor stadium, all at the touch of a button. This wide array of delay mode options gives you the power to create custom soundfields for your favorite videos or music events.

The GTP-550's Stadium mode is used for non-Dolby Surround encoded material to recreate a large and acoustically reverberant environment well suited for video sporting events and play back of music events performed in large outdoor arenas. A slight upper midrange frequency emphasis is added to the front channels to enhance intelligibility. Stadium mode is also well suited for playback of older epic movies.

The GTP-550's Concert Hall mode replicates a relatively large indoor performance space. Front channel frequency response is flat for maximum musical clarity while the diminishing multiple rear channel delays first seen in Cinema mode enhance the sense of spaciousness.

In Nightclub mode the GTP-550 synthesizes a smaller and more intimate soundfield ideal for many types of jazz and popular music. Nightclub mode is also a good choice for playback of classic movies with mono soundtracks.

The Five Channel Stereo mode makes full use of a home theater system's speaker complement and is intended primarily to reproduce large scale musical events such as a full orchestra concert or an opera. In addition, the GTP-550 also includes a two-channel stereo mode for true stereo sound.

The lessons learned in the design of Adcom separates directly benefit the GTP-550 as do high-precision electronic parts: Roederstein 1% metal film resistors, the same class "A" biased linear gain amplifiers developed for Adcom's reference class components and an oversized transformer that projects superior soundstaging and imaging

When it comes to FM broadcasts the GTP-550's highly sensitive tuner section delivers the clearest sound the transmitted signal allows. All tuner circuitry is isolated on its own low-loss, epoxy board and constructed with specially crafted RF, IF and multiplex decoding circuits for minimal interference and optimal clarity.

The GTP-550 combines the extensive switching and signal processing capabilities with a rare degree of operational simplicity. Straight-forward design and logical control groupings replace the usual intimidating front panels with often inaccessible and confusing multi-function controls.

All these features are easily operated by the GTP-550's infrared remote for total control from anywhere in the room. And the GTP-550 is fitted with high quality input and output connections for four audio and four video sources. This configuration ensures complete compatibility and flexibility for all your home entertainment needs for years to come.

Adcoms GTP-550 is the clear choice for a unique combination of high-end sound and full featured ease.

GTP-600

The GTP-600 and the GTP-550 share the same operating circuitry and delay mode features. In fact, the internal components (resistors, capacitors, etc.) are almost identical. However the GTP-600 was designed with several upgraded features that create a discernible difference when compared to the GTP-550.

The GTP-600 includes the RC-65 "learning remote" that can be programmed to control up to eight additional audio or video components. The benefit is obvious. Rather than depending on a collection of remote controls, the GTP-600's simplified remote can easily operate an entire audio/video home theater system.

Aiding in this complete control of the components, the GTP-600 includes an on screen display for quick system set up and customized operation. The display shows the selected input, operating mode and delay choices and provides visual feedback to facilitate proper level adjustments.

The GTP-600 also accommodates a wider selection of input and output types by providing a full complement of S-video connectors to supplement the standard composite video jacks. These multi-conductor connections provide high resolution signal transfer for advanced televisions, laserdiscs and VCRs.

In addition, the GTP-600's rear panel RCA audio and video jacks are heavily gold plated to ensure maximum signal transfer and to minimize oxidation. Adcom's GTP-600 offers the highest levels of home theater performance at an equally amazing price

The GTP-450 is sonically superior to many separate preamplifier and tuner combinations that cost 2, 3, even 5 times more. A value that is typical of Adcom components.

To meet the exceedingly high standards and design objectives, the GTP-450 displays that same state-of-the-art component parts that Adcom engineers have implemented in their award-winning separates, including proprietary linear gain amplifiers, polypropylene capacitors, low-loss printed circuit boards, and 1% metal film resistors.

The same Class "A" high level output circuitry specified by audio perfectionists in the 'price is no object' stratosphere benefits the GTP-450 as well. It responds more accurately to the musical input and is largely responsible for the clarity, superior resolution and soundstage accuracy for which Adcom performance is known.

FM reproduction is station-monitor quality, the highest standard the broadcast signal allows, thanks to an all-new, specifically built multiplex decoder that minimizes noise and hum without sacrificing stereo separation or compressing the dynamic range of the music.

Sonic excellence doesn't come at the expense of control flexibility, however. A full-function wireless remote control is standard and extends input selection, tuning and volume adjustments to the comfort of your listening position. You can even turn the entire system's power on and off.

Don't hesitate to compare the Adcom GTP-450 to the most expensive separate preamps and tuners available. Then evaluate its flexibility next to the most fully-featured control centers you can find. You'll see and hear the Adcom difference. It's in the details.

The true triumph of Adcom's design and production techniques lies in the radical improvement that has been brought to sensibly-priced components. Although the GTP-350 Stereo Tuner/Preamplifier is Adcom's most affordable, it has much in common with its more costly counterparts.

Both engineers and audiophiles acknowledge the superiority of Class "A" biased linear amplifiers. But it took Adcom to bring this enhancement to an affordable price range. Proprietary Adcom circuit topology affords the listener the stability, headroom, tonal balance, superior resolution and accurate spatiality once reserved for the world's very best (and most expensive) components. At other critical circuit points, discrete components are used in place of generic, off-the-shelf ICs.

The tuner section strikes the perfect balance between sonic performance and ease of use. The quartz-referenced, digitally synthesized tuning system achieves tuning accuracy of 99.99975% locking the station instantaneously without drift or signal error. Sound quality has been optimized by preventing digital control pulses from bleeding into the very sensitive sections of the tuner's front end. This virtually eliminates the synthesizer noise, distortion and phase shift all too common in other designs.

The GTP-350 interfaces perfectly with all of Adcom's legendary power amplifiers, so you need only invest in the amount of power your loudspeakers and environment dictate. Seldom have both sonic performance and value been so well served by audio technology.

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