The Viola Symphony is a 200W per channel stereo power amplifier with an integral choke input filter type power supply.  It incorporates many of the technological advances that were made during the development of the Viola Bravo power amplifier.  Like the Bravo, the Symphony is a virtuoso performer.  The bottom end is extended and well controlled.  A generously rated power supply ensures that dynamics are reproduced without compression, even when driving difficult speakers.  Careful attention has been paid to other aspects of the design ensure that the stereo imaging and reproduction of low level detail are equally impressive.

Audio Design

The signal path in the Symphony is fully balanced throughout the voltage gain stages. This is essential to achieve the maximum immunity from external sources of noise. Painstaking attention has been paid to the physical layout of the amplifier in order to optimize noise rejection. 

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. Bandwidth control results in nearly identical small signal and large signal frequency responses. This approach avoids slew rate limiting.

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 minimize distortion at lower frequencies, because the majority of energy is encountered at these frequencies in most music.

The Symphony'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 variations that would be introduced by the use of the wiring harnesses commonly used in high performance amplifiers.

Film capacitors are used on the individual circuit boards in 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 Symphony's ability to deliver large 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. Like the Bravo, the Symphony uses a choke input filter type power supply.  This produces far less Electro-Magnetic Interference than the capacitor input designs most commonly used in power amplifiers.

It also avoids the high peak current demands that would be placed on the mains supply by a conventional power supply and therefore minimises inter-modulation distortion on the power supply “rails” and ground returns.  This is an especially important consideration when operating from lower mains supply voltages such as 100V or 120V, where the supply voltage droop caused by the heavier peak current demands of a conventional supply, can significantly affect an amplifier's ability to accurately reproduce large transients. 

In addition, the Symphony'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.

 Expandable Power Output

Sophisticated Protection Circuitry

The Symphony employs sophisticated protection circuitry 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 Symphony 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.

High Quality Chassis

Great care has been given to the design of the Symphony chassis.   The front panel is machined from a solid aluminum slab and the side panels are custom aluminum extrusions. These are brushed to a super-fine finish and then anodized.  They are mated with heavy gauge top and bottom panels to produce a structure that is extremely strong and rigid.

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.