PLUS P55 FET Stereo Power Amplifier
100 watts RMS per channel into 4 or 8 ohms, 20-20,000 Hz, with no more than 0.009% total harmonic dist High speed DC circuitry, strappable for high power 200 watt mono operation. 12-section LED peak power indicators.
With a combination of attractive design, outstanding features, and specifications that surpass the wildest dreams of just a year or two ago, the new Sanyo PLUS P55 is assured a prominent place in the new generation of "ultra-fi" audio components. With sound quality to please the most discriminating ear and ample power to handle almost any speaker, this is one amplifier that can truly complement virtually any collection of audiophile components.
In the few cases where its 100 watt per channel output does not provide quite enough headroom, a pair of P55's can be operated in their strapped mono mode for an extremely flexible, yet reasonably priced high power amplification system. In either mode, the precision LED peak power indicators permit constant monitoring of the amplifier's performance, while the inherent self-limiting properties of the power MOSFE⊺ output devices and the sophisticated protection systems quard against unsafe operation, no matter how bizarre or difficult the load. And even under sustained high power operation, the P55 remains remarkably cool, thanks to its unique Fluid Convection Badiator heat dissipator, which also permits the P55 to be lighter and more compact than any other amplifier in its class - without requiring noisy cooling fans.
The P55 teams perfectly with any high quality stereo preamplifier, but makes an especially attractive combination with Sanyo's PLUS C55 DC preamplifier.
CIRCUIT OVERVIEW
The PLUS P55 is a totally direct-coupled (DC) design, with signal flow from the input jacks to the speaker terminals unobstructed by coupling capacitors. Thus, even at frequencies far below the audible range, there is no phase shift to distort important waveshapes and alter critical time relationships between different components of the music. And, should the amplifier be driven past its limits, the balanced DC design assures instant recovery without audible distress.
Thanks to the extremely low drive current requirements of the P55's MOSEET output transistors, the entire circuitry for each channel can consist of only three relativelv simple voltage amplifier stage plus the high power parallel MOSFET output stage. Particularly noteworthy is the fact that all three low-level stages are fully dif ferential at both outputs and inputs (except the final driver stage, which develops the sinale-ended drive required by the output stage). The benefits of this all-differential configuration are well known, and include higher gain with better linearity (due to inherent distortion-canceling properties), simplified biasing, higher slew rate, and freedom from interaction between feedback and feed-forward circuit paths
Audio signals entering the PLUS P55 pass through a first-order Butterworth lowpass filter with a rolloff frequency of approximately 600 kHz. This filter serves to eliminate RFI (radio frequency inter-
ference), as well as prevent possible transients from non-audio sources from causing transient intermodulation distortion.
The input stage uses an integrated pair of FETS in differential configuration to provide high input impedance and superior feedback isolation. A second pair of bipolar transistors is connected to the FETs in cascode configuration, to improve their operating speed and transient response. The use of integrated transistor pairs assures excellent device matching and superior thermal tracking, for better bias stability and response linearity. A temperature-compensated active current source with precise Zener regulation biases the input stage.
Two more differential stages follow, the second of which drives the output stage directly, and combines cascode and current mirror transistors for higher gainbandwidth performance.
The output stage consists of four high power MOSFET power transistors in parallel complementary configuration. Thanks to the negative temperature coefficient of MOSFETs, complicated output stage biasing and thermal compensation circuitry (the traditional nemesis of conventional Class AB amplifiers using bipolar transistors) is completely eliminated. The PLUS P55's output stage idling current actually tends to decrease as the amplifier warms up, ruling out the possibility of output stage destruction due to thermal runaway.
Other well-known advantages of the MOSFET transistor include higher speed and absence of "storage time" effects, yielding better waveform symmetry and transient response, and a more appealing harmonic spectrum for audio applications (FETs are "square law" devices, and tend to produce primarily even-order harmonics, which are far less irritating to the ear than the odd-order harmonics produced by bipolar transistors, which are "exponential law" devices).
The P55's combination of advanced circuit techniques yields an amplifier that not only delivers exceptional performance measurements, but is also extremely "musical," with none of the subtle flaws that often mar the sound quality of otherwise excellent amplifiers. The PLUS P55 may be confidently teamed up with the most critical, revealing speakers available with no worries about sonic irregularities showing up.
FEATURES Switchable bridged mono mode
For applications demanding more power than the P55's 100 watts per channel, the unit may be operated in the bridged (or "strapped") mode to deliver 200 watts RMS into an 8 ohm load — with no impairment in specifications. In fact, in the bridged mode, the amplifier's effective slew rate is doubled — to a staggering 300 volts per microsecond. Bridged mode is selected simply by flipping a rear-panel switch and connecting the load between the left and right channel positive output terminals.
12 section LED peak power display.
Although it is customary to equip amplifiers with some form of power output indication, many manufacturers have stayed with conventional average-reading mechanical meters. While these may be of some use to professional PA system operators, they are valueless to the home user,
who is concerned much more with possible peak clipping distortion than with average power levels.
The P55 uses a pair of high-resolution LED "staircase" displays, with twelve LEDs per channel for unusually precise indication. The LEDs respond instantly to peak
| PEAK POWER INDICATOR | ||
|---|---|---|
| 500 | ||
| 200 | ||
| 100 | ||
| 50 | ||
| 25 | ||
| 10 | ||
| 5 | -10 | |
| 2.5 | 3 | |
| 1.0 | ||
| 0.5 | -21 | 0 |
| 0.25 | -2 | |
outputs, and unlike many systems, read both positive and negative peaks. A display range selector increases the sensitivity of the system by a factor of ten, allowing power outputs as low as 25 milliwatts to be accurately read.
Amplifier and load protection.
The PLUS P55 contains sophisticated circuitry to protect both itself and the speakers connected to it from unusual operating conditions. The protection sensing and logic circuitry drives a pair of relays, which disconnect the load from the amplifier under any of the following conditions:
At turnon, when the circuit provides a delay of approximately 5 seconds before reconnecting the speakers. This provides adequate settling time for the circuitry in the P55 and any other components preceding it, to prevent high current transients
("thumps") in the speakers when power is applied.
- Whenever a pair of thermosensors detects a potentially unsafe temperature increase due to inadequate ventilation or sustained overload.
- 3. When special DC detection circuitry senses the presence of a DC offset at the amplifier output terminals (a condition which can result from a malfunction in the amplifier or in a component farther up the signal chain, and which can quickly overheat and destroy the woofers in the speaker system).
Whenever the protection relay operates, a front panel LED lights to inform the user. In addition to these systems, sensors continuously monitor current through the MOS output transistors, and instantly remove the drive signal when unsafe levels are reached.
High efficiency heat dissipation.
Rather than adopt the usual approach to heat sinking and use several pounds of black aluminum, Sanyo fitted the P55 with a totally new heat dissipator — the exclusive Fluid Convection Radiator. In this system, a sealed metal loop partially filled with liquid Freon connects the output transistor mounting blocks to an array of thin, closely spaced fins. When heat builds up in
the output devices, it quickly causes the Freon to boil. The gaseous Freon travels to the upper end of the loop, where it gives up its heat to the metal fins and changes back into its liquid state. Gravity then causes the liquid to run back to the lower half of the loop, where the process is continuously repeated.
The result is extremely efficient heat removal — with approximately 80% less weight than conventional heat sinks, and without the annoyance of noisy cooling fans. And since both channels are thermally coupled via the Freon loop, the full heat dissipation capacity of the radiator is always available to both channels — an advantage if one channel is required to work harder than the other.
Speaker switching.
A front panel selector allows energizing two pair of stereo speakers separately or simultaneously. Speakers may also be switched off for listening through the builtin headphone jack — a convenience missing from many power amplifiers.
Gold plated input connectors.
Once reserved only for exotic, ultra-high priced components, the improved signal transfer and freedom from oxidation of gold-plated input jacks have been included in the P55.
Sanyo's new PLUS SERIES includes a variety of components in professional black finish, with rackmount capability. Handles (supplied with each unit) attach to the chassis sides, and permit secure mounting in EIA-standard 19-inch equipment racks.
1200 West Artesia Blvd. Compton, California 90220
PLUS SERIES philosophy
Sanyo PLUS SERIES — a new collection of ultra-high performance audio components designed, literally from the ground up, to excel in every way: outstanding specifications, useful "human-engineered" controls, features combining the best of traditional functions with unique new solutions, and styling of enduring beauty — plus , most importantly, audio reproduction quality that transcends simple formulas and numerical specifications.
This distinguished new series is the result of a unique design and production concept. Within one of the world's largest and most diversified electronics companies. we set up an independent team of audiophile-engineers and gave them full freedom to draw on Sanyo's massive technological capability. A major part of their assignment was to devote special attention to eliminating those small but audible departures from sonic reality - problems that seldom show up on spec sheets or test benches, yet can make the difference between sound that is merely good, and sound that communicates a spine-tingling sense of life, openness, and "air."
To support the PLUS SERIES group, Sanyo produces virtually every part required by their designs: transistors, capacitors, integrated circuits (both analog and digital), circuit boards, motors, meters, frames, knobs, cabinets to name only a few. We control our quality to tolerances far stricter than outside suppliers can match. We back up our production systems with 30 years of know-how from our
consumer and industrial electronics divisions.
Computerized component evaluation with automatic printout
The development of the Sanyo PLUS SERIES was one of the most difficult goals we have ever set for ourselves: to produce true "state of the art" audio components embodying the enlightened aesthetic and technological perspectives of the 1980's, and to make them available at a cost only slightly greater than the best of today's mass-produced audio equipment.
Our success — or failure — in achieving this almost superhuman goal can be evaluated now by arranging an audition with a PLUS SERIES dealer.
Specifications
|
Continuous Sine Wave Power
per channel, both channels driven from 20 Hz to 20,000 Hz at no more than stated Total Harmonic Distortion into 8 ohms |
100W at 0.009% THD |
|---|---|
| into 4 ohms | 100W at 0.009% THD |
|
Power into 8 ohms,
bridged mono mode |
200W at 0.009% THD |
|
Maximum Total Harmonic
Distortion (from 250mW to rated power, 4 or 8 ohms, 20 Hz to 20,000 Hz) |
0.009% |
| Intermodulation Distortion (rated power, 60 Hz & 7 kHz 4:1) | 0.009% |
|
Frequency Response
(1W cutput, 8 ohms) |
7Hz-100kHz;
+0,-1dB |
|
Signal-to-Noise Ratio
(IHF-A Network) |
110dB |
|
Damping Factor
(1kHz, 8 ohms) |
60 |
|
Residual Hum and Noise
at Speaker Outputs |
0.2mV
(83dB below 1 watt) |
| Input Sensitivity/Impedance | 1V/47k-ohms |
|
Transient Response (Slew rate)
bridged mono mode |
150V/μ sec
300V/μ sec |
| Dimensions (HxWxD) | 3½" x 17¾" x 10%" |
Loading...