Cary Audio SLI-100 Valve Integrated Amplifier

The Cary Audio SLI-100 Valve Integrated Amplifier is a high-end amplifier with advanced features. The components are specially selected to give the best possible sound and reliability. This is a powerful 100 watts per channel amplifier and operates in Class AB1. Also, the output transformers have been specially designed for this unit.

The sound has amazing transparency and resolution due to having very low crossover distortion. Four line-level inputs are provided as well as two subwoofer outputs. Lastly, there is a grille top that can be used to cover the valves.

The amplifier circuit

Two KT 150 output valves are used in a push-pull configuration for the Cary Audio SLI-100 Valve Integrated Amplifier. These operate in Class AB mode. This is a combination of Class A and Class B. Class A, also known as single-ended operation, uses one output valve.

There can be no crossover distortion however it is very inefficient, as a current is always flowing in the output. On the other hand, Class B has two output devices operating in push-pull mode. Each output valve conducts for half of the audio signal.

This is more efficient but can lead to crossover distortion as the valves switch over. Hence the Cary Audio SLI-100 Valve Integrated Amplifier uses Class AB. With Class AB the amplifier operates in Class A at lower listening levels, switching to Class B when needed.

Output transformers

Output transformers are needed with valve equipment, to match the output impedance to the speaker voice coil. The Cary Audio SLI-100 Valve Integrated Amplifier uses a bespoke design of transformer. Negative feedback is used from an 8 Ohm tap on the transformer to reduce distortion.

Only a small amount of feedback is used. Next, a phase inverter is needed between the preamp and power amp sections. This uses a self-balancing split load configuration utilizing the 6SN7 octal base dual triode.

Great Connectivity

The Cary Audio SLI-100 Valve Integrated Amplifier has four line-level inputs selected by a switch on the front. Standard gold-plated binding post outputs are used for the speaker terminals. These are situated at either end of the back plate for the best channel separation.

There are also two line-level subwoofer outputs. Additionally, there is a 4-ohm or 8-ohm selector switch. The front features the volume control, input switching, headphone output, and a power switch.

Why valves?

Valves are loved by audiophiles for their warm sound and musicality. They run at high voltage and hence use less current than transistors. As a result less loading is placed on the power supply, giving a very quiet output with no hum. Valves are known as thermionic devices. Triode valves have three terminals a cathode, anode, and grid.

The cathode has a special coating that emits electrons when heated. The anode is placed at a high voltage and attracts the electrons from the Cathode. In between these two electrodes sits the grid. This is used to control the flow of electrons. The grid is normally kept slightly negative of the cathode. An audio signal is applied via a capacitor to the grid and an amplified version appears at the anode.

A word about capacitors

Capacitors are used in valve equipment to couple stages. As a result, they can have several hundred volts placed on them. Their purpose is to block DC while allowing the AC audio signal through. However they can go leaky and allow a high positive voltage onto the grid.

This can damage the valve, known as red-plating. Modern audio-grade capacitors, as used by the Cary Audio SLI-100 Valve Integrated Amplifier, are designed to last much longer than the old paper types. They are usually made of modern plastics such as Polystyrene or polypropylene.