The Viola Bravo stereo power amplifier has been designed to be  the last word in fidelity, musicality and dynamics. It will effortlessly deliver large amounts of power whilst preserving the delicate nuances in the music signal.  In its standard mode of operation it will provide 350W of continuous music power per channel into 8 ohms. Where greater levels of power are required, the unit may be used in one of two bridged modes and operate as a mono block amplifier to deliver either 1200W continuous music power into 8 ohms, or 1600W into 1 ohm. This provides the versatility to cope with a wide range of systems and speaker types and also a high degree of system upgradability.

To ensure the greatest isolation from mains borne noise,  the Bravo employs a choke input filter type power supply, which is housed in a separate chassis.

No-Compromise Audio Design

The signal path in the Bravo is fully balanced throughout the voltage gain stages. This is essential to achieve the maximum immunity from external sources of noise. To minimize the effects of the strong magnetic fields that are a consequence of the Bravo's high output current capability, painstaking attention has been paid to the physical layout of the amplifier,  including careful mirror-imaging of circuits to cancel magnetic fields.

Particular care has been given to the overload conditions that are often encountered under normal use. Soft clipping circuitry is used to limit sonic degradation if the amplifier is overdriven (voltage overload). Bandwidth control results in nearly identical small signal and large signal frequency responses. This approach avoids slew rate limiting (frequency overload). In order to ensure accuracy in the time domain, the bandwidth control has a flat group delay characteristic. This implies a linear phase verses frequency relationship and means that all signals pass through the amplifier with the same amount of delay. In plain English the output signal looks exactly like the input signal, only bigger. 

Great efforts have been made to minimise distortion at lower frequencies, because the majority of energy is encountered at these frequencies in most music. Obtaining low distortion without the use of large amounts of corrective feedback requires the use of more output devices and more refined lower level stages. Consequently each channel of the Bravo uses 20 matched pairs of power transistors.

The Bravo's output stage has been designed to operate with a relatively high quiescent current in order to improve transparency and the resolution of low level signals.

Heavy oxygen-free copper bus bars enhance the efficiency of power distribution within the amplifier and eliminate the variations that would be introduced by the wiring harnesses commonly used in high performance amplifiers.

Film capacitors are used on the individual circuit boards within the unit to provide the high frequency bypass for the power supply and ensure that all sections of the amplifier see a uniformly low power supply impedance.  This is key to the Bravo's ability to deliver massive amounts of power whilst preserving all the subtle aspects of the music signal.

Low Noise Power Supply

The heart of a power amplifier is its power supply.  The Bravo uses a choke input filter type power supply with a generously rated 2kVA mains transformer. Four 80,000μF filter capacitors are located in the power amplifier chassis to provide optimum power supply decoupling.  The Bravo's choke input filter design power supply produces far less Electro-Magnetic Interference than the capacitor input designs most commonly used in power amplifiers. The power supply is housed in its own separate chassis to prevent stray magnetic fields from the mains transformer or other inductive components from having any effect on the audio circuitry.

The Bravo's power supply design completely avoids the generation of the high frequency noise that often occurs when switch mode power supplies are used.  It also places less stress on the power supply components, leading to higher reliability and longer life.

An additional advantage of the choke input type of power supply is that it enables the virtual elimination of high peak ripple currents, thereby minimizing inter-modulation distortion on the power supply “rails” and ground returns.  This further enhances the sound quality by reducing both the noise and distortion levels.

Effortless Power Delivery

The Bravo operates as a virtually perfect example of a "voltage source".   This means that the unit's output power doubles for every 50% drop in load impedance.  Thus the Bravo's 350W continuous rated power per channel into 8 ohms, becomes 700W per channel into 4 ohms and 1400W per channel into 2 ohms.  This is an essential attribute if speakers with low impedances are to be driven without the dynamics of the music becoming compressed. This level of power delivery is unusual. The output of most power amplifiers starts to sag once the load impedance falls below 4 ohms.

No known high quality loudspeaker can absorb the continuous full power capability of the Bravo (nor would you want to be present in the room were you to find one that could do so). However, many high quality loudspeakers may require extreme power levels for short periods when reproducing music at realistic levels.  The Bravo will supply such needs effortlessly, without any power supply "sag" and without altering its sonic performance in any way. The resultant imperturbable nature of this amplifier is reflected in the authority and control with which it reproduces music. Your selection of any particular mode of operation depends only on the maximum power you need, based on your loudspeakers, listening room, and listening habits.

Expandable Power Output

A major increase in the output power of the Bravo may be obtained by connecting the two channels of the unit together form a single mono power amplifier. This is called bridging.  A second Bravo is then required for a stereo system. There are two modes of Bridge connection possible with a single Bravo power amplifier, either of which may be quickly selected by switches on the unit's rear panel.

Half-Bridge Parallel Mode.  Here the output stages of the two channels in the Bravo are connected in parallel. This is ideal for speakers with a very low input impedance, typically 4 ohms down to 1 ohm.  In this mode a single Bravo will deliver:

Full Bridge Mode.  Here one channel in the Bravo is fed with a signal that is the exact inverse of that fed to the other channel and the speaker is connect between the H terminals of the two output stages.   In this mode a single Bravo will deliver:    

1,200W into 8 ohms
1,600W into 4 ohms

Sophisticated Protection Circuitry

The Bravo employs sophisticated protection circuitry to to shut itself down should it detect any one of a range of fault conditions that might damage either the amplifier, or the speakers it is driving.  These conditions include:

In the case of either a significant DC offset or an over-current condition, the amplifier will shut down to protect itself and the speakers. Normal operation may be quickly restored by removing the cause of the fault and switching the unit off then on again.

If the AC mains voltage is either too high or too low for safe operation, the amplifier will automatically shut down. The amplifier will not turn back on until the AC mains voltage is within the acceptable range for normal operation.  A 120V unit will operate between approximately 90-140V; a 240V unit will operate between approximately 180-280V. Outside these generous limits, the amplifier will shut off.

Should any one of the amplifier's internal sensors detect an excessive temperature, the amplifier will automatically shut down. Once the fault condition has been removed and the unit has cooled down sufficiently, the amplifier can  be turned on again.

In addition, the AC input to each transformer is fused to protect against excessive current conditions such as may occur when driving shorted outputs. In-rush limiting circuitry prevents premature aging of power supply components during power-up, and is automatically switched out of circuit once the power supply has been charged.

Finally, the Bravo incorporates a controlled clipping circuit that prevents the output devices from saturating.  This prevents the damage to the speaker's high frequency drivers caused by the high-energy high frequency harmonics that would otherwise occur under heavy clipping.

Cooling System

The Bravo uses both passive cooling via large heatsinks and active cooling using 2 fans. These were selected for their ultra-low noise and long service life.  Under normal conditions they run at reduced speed and produce negligible mechanical noise.  Should the amplifier's internal temperature rise above a pre-set level, such as may occur when operating in a high ambient temperature, or with inadequate ventilation, the fans run at full speed until the temperature is reduced to within normal limits.  This approach ensures a longer service life for the unitt.

Elegant Chassis Design

The Bravo chassis uses a precision die-cast front panel and heavy custom aluminum extrusions for the top and side panels in a design that gives a very clean appearance, with no fixing screws readily visible.

Warranty

Products of Viola Audio Laboratories are warranted to be free of defects if used under normal conditions for a period of five years from the date of manufacture.