integrated amplifiers

The puresound A30 amplifier was developed to meet the demand for an affordable Class A amplifier that would be compatible with all types of loudspeakers. The A30 is a line level integrated design that allows for the selection of up to 3 different source components and control of the volume by a high quality ALPS Blue Velvet potentiometer. Class A operation was chosen because it gives lower distortion and a more relaxing, natural sound.

NB. The factory that makes the A30 also makes a 60 Watt Class B amplifier with different output transformers, a different mains transformer, reduced bias current, a different feedback circuit and several different types of component. All puresound products are specifically made to suit our particular requirements.

The amplifier uses the very robust Electro Harmonix 6550 output valves in an Ultra Linear Push Pull configuration. This arrangement gives a combination of power and clarity that is difficult to beat. The amplifier uses an Auto Bias system, which means that replacement output valves should be fitted as matched pairs. There will be no need to reset or monitor bias conditions.

Very high quality components are used throughout including selected carbon film resistors and SCR polypropylene capacitors. The power supply makes use of twin valve rectifiers and choke smoothing.

The output can be configured for use with 4 or 8 ohm loudspeakers. The output stage can also be switched to triode-coupled configuration. This further linearises the operation of the valves at the expense of some output power. It may be preferable with higher sensitivity loudspeakers.

The A30 may also be used as a very high quality stereo power amplifier if the volume control is turned up fully. When partnered with appropriate ancillary equipment the A30 is capable of very satisfying performance.

Why this amplifier? Why now?

With the recent interest in lower powered Single Ended triode amplifiers has come the realization that to get the best from these, the speakers used have to be both sensitive and quite large to give truly satisfying results. There are also not that many good, high sensitivity (>97 dB/W) designs available at any price never mind at price levels the majority of music lovers can afford. However, there are some very good loudspeakers currently being made with sensitivities between 88 and 94 dB/W. These are sufficiently revealing to make the virtues of simple, high quality amplification readily apparent, although in most cases the output of a typical single ended amplifier is insufficient to give the scale and drama many types of music demand. A good amplifier with 25 -30 watts of output power is more than enough to drive this type of loudspeaker to sensible levels even in quite a large room. For simplicity a valve amplifier is preferable.

Recently, there has been an increase in the number of relatively affordable valve amplifiers made in China. Many of these are compromised by the quality of their transformers, components, layout and because they operate in Class AB or B to give a higher power specification. They often also use a lot of negative feedback in an attempt to compensate for these shortcomings with a consequential impact on clarity and low frequency control. For some 10 years there has been a lack of affordable Class A valve amplifiers.

The puresound A30 operates fully in Class A up to its rated output so it does not change character at any signal level. There is none of the distortion caused by output devices switching on and off and therefore no requirement for excessive feedback to correct for it. The 6550 valves supplied are the extremely robust Russian Electro-Harmonix variety and are quite content with dissipating the power required to maintain Class A operation up to 30 Watts. The valve rectifiers used keep the high voltage power supply clear of the noise that can be introduced by silicon rectifiers. A substantial choke is also incorporated to keep the power supply impedance low. The output transformers also give extremely wide bandwidth allowing very solid low frequency performance as well as exceptional reproduction of timbre.

These design features combined with the use of high quality passive components, octal based input and driver triodes and an elegant but simple internal layout results in an amplifier which sets a new benchmark for performance, build quality and value.

Features

Class A operation
3 Line level inputs
30 Watts per Channel Output
4 and 8 ohm output taps
Twin valve rectifiers
Choke smoothing
ALPS potentiometer
SCR coupling capacitors
Carbon film resistors (for better sound quality)

ElectroHarmonix (Russia) 6550 output tubes

Very substantial construction including cast metal transformer shrouds.

The earliest audio amplifiers made use of small, 3 element valves known as directly heated triodes. For many, the simple circuits that can be built around such devices better preserve the structure, colour and feeling within the music than any other circuit topology. One of the best sounding triodes, the 2A3, is in production again and its characteristic linearity has been employed in a novel configuration to create a particularly charming amplifier. The puresound 2A3 is an 18 Watt per channel line level integrated design that allows for the selection of up to 3 different source components and control of the volume by a high quality ALPS Blue Velvet potentiometer.

There are many amplifiers now making use of directly heated triodes but few which adequately address the particularly awkward issues involved in driving these devices properly. The puresound 2A3 amplifier features an unusual choke loaded driver stage which allows the 6SN7 driver valves to deliver the full measure of signal to the push/pull output valves. This rather exotic configuration usually results in a tremendous depth to the tone of instruments and the puresound 2A3 is no exception in this regard.

Very high quality components are used throughout including selected carbon film resistors and SCR polypropylene capacitors. The power supply makes use of twin valve rectifiers and choke smoothing.

The output can be configured for use with 4 or 8 ohm loudspeakers.

The puresound 2A3 may also be used as a very high quality stereo power amplifier if the volume control is turned up fully.