T E C H N I C A L R E F E R E N C E

FIELD SERVICE CONSIDERATIONS

A primary focus during the design and development of the P7000 was to ensure the dependability of the amplifiers. The use of lateral MOSFET output transistors and the low voltage trans•nova input stage combined with careful component selection for the circuit assembly made the reliability goals achievable. However, a parallel effort was also undertaken to make sure any down time caused by an amplifier fault was minimized by making the amplifier technician “friendly.” The modular construction allows exchanging the entire operational portion of either channel quickly and easily without the need for soldering or specialized equipment.

This section of the manual contains descriptions of circuit operation and block diagrams to assist technicians with component level repairs.

THEORY AND OPERATION OF trans•nova

The trans•nova (TRANSconductance NOdal Voltage Amplifier) principle is based on our 1984 U.S. Patent 4,467,288. This patent describes the advantages of audio power amplifiers in which a MOSFET output stage is connected in a grounded source configuration. In this connection the output stage has its full voltage gain of typically 20dB (ten times), instead of the usual 1dB loss of voltage follower designs. The output stage is further refined into a trans- impedance stage (current-to-voltage converter), to achieve extremely short loop (fast) negative feedback. The output stage is driven cooperatively by a transconductance stage (voltage-to-current converter).

Using the output stage to supply voltage gain inherently increases the power gain (for the same bandwidth) of the output stage by typically ten times over the conventional follower connection, using the same MOSFET devices. This increase in efficiency allows the use of a much simpler input section than in the more common high voltage designs. The number of serial stages, from input to output can be reduced from five or more to only three. This also allows the input section to be designed with the criteria of high quality Class A line amp with the characteristic high linearity and wide bandwidth.

The disadvantage of the Class A driver stage is the limited current headroom available. A conventional Class A transconductance stage has a 2:1 or 6dB limit on peak-to-quiescent current. The number of MOSFETs used in the P7000 imposes a significant capacitive load on the driver stage, enough of a load to strain the ability of the driver to deliver the required current at the high audio frequencies.

Since the operation of the transconductance driver stage is a major factor in the reproduction quality of the amplifier, we developed our proprietary DIABLO (Dynamically Invariant A-B Linear Operation, patent application in process) circuit to satisfy the current headroom requirements. DIABLO does this by smoothly and continuously varying the current transfer ratios of the two transconductance paths, under the control of the signal current itself. This implementation allows the current transfer ratio of one path to be smoothly and continuously reduced to zero while the other path is smoothly and continuously increased by a factor of two. This yields an additional 14dB of current headroom to drive the MOSFETs. The result is a dramatic reduction in high frequency distortion, combined with improved ultrasonic stability.

The P7000 has the highest power rating of any amplifier utilizing the basic trans•nova principle. Designers of systems with high power requirements can now take advantage of the natural and realistic reproduction characteristic of the trans•nova circuit topology.

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Hafler P7000 manual C H N I C a L R E F E R E N C E, Field Service Considerations
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P7000 specifications

The Hafler P7000 is a professional power amplifier renowned for its robust performance and reliability in live sound and studio applications. A cornerstone of the Hafler brand, the P7000 embodies advanced technology and engineering, making it a popular choice among audio professionals.

One of the standout features of the P7000 is its high power output. It delivers up to 700 watts per channel at 4 ohms, providing ample headroom for demanding audio environments. This powerful output makes it suitable for driving large loudspeakers or multiple speaker systems, ensuring clear and dynamic sound reproduction even at high volumes.

The P7000 utilizes a class AB amplifier design, combining the benefits of class A and class B architecture. This design choice ensures low distortion levels while maintaining efficient operation. As a result, users can expect a warm and natural sound with low signal degradation, making the amplifier ideal for critical listening environments.

In terms of build quality, the Hafler P7000 is constructed with durability in mind. The chassis is made from robust materials that can withstand the rigors of frequent transport and use in various settings, from professional studios to live concert venues. Additionally, the amplifier features a well-ventilated design, minimizing overheating and ensuring reliability during extended operation.

The P7000 also includes advanced protection circuitry to safeguard against overload and short circuits. This feature not only protects the amplifier itself but also the connected speakers, providing peace of mind during high-energy performances. Furthermore, the amplifier incorporates a soft start circuit, which gradually ramps up power to the speakers, preventing sudden jolts that could cause speaker damage.

Connectivity is another key aspect of the Hafler P7000. It offers a variety of input options, including XLR and 1/4" TRS connectors, making it compatible with numerous audio sources and easy to integrate into any existing setup. Balanced inputs help reduce noise and interference, ensuring clean signal transfer over long cable runs.

With its combination of powerful output, reliable performance, and versatile connectivity, the Hafler P7000 stands out as a professional-grade amplifier. Whether used in a studio setting or live sound application, it provides audio professionals with the tools they need to achieve exceptional sound quality and consistency.
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