The importance of power supplies in audio amplification is becoming increasingly appreciated. We believe that the quality of the power supply is as important as the audio circuitry itself. Good circuit design requires careful specification of valve operating voltages and these voltages should not vary significantly under dynamic conditions. Should the voltages fluctuate, the careful circuit design work is undone as the valves then operate under completely random conditions. Similarly, if the components used in the power supply emit noise, this noise will be imprinted on the audio signal being clearly audible as distortion and obscuring vital low- level information.
In order to discuss power supplies it is useful to split the subject into two although as we will see the sonic implications are often interdependent.
1. REGULATION. In valve amplifiers we are primarily concerned with voltage regulation, and, avoiding a rigorous technical definition, it can be described as the ability to maintain a fixed voltage despite a varying current draw. In a poorly regulated supply the voltage will vary as the current draw changes, rising as the draw decreases and falling as the draw increases. Amplifiers present a rapidly varying current demand in response to the signal they are amplifying and the power supply should be able to meet this demand without the operating voltages changing significantly.
2. NOISE. Noise takes on two main forms. Suppression of the ripple on the supply to create a quiet amplifier is often discussed and is important but most PSUs easily fulfill this requirement. Hum should be a thing of the past;- even on valve amplifiers. The second form of noise comes from the components used in the supply and has a much more profound and undesirable effect on sound quality. Solid-state rectifiers generate unwanted reverse pulses which the smoothing capacitors in the power supply are unable to remove and which also feed back into the mains transformer affecting other parts of the circuit and dropper resistors will emit noise, pick up RF and offer little rejection of high frequency spuriae. All of these effects are clearly audible.
SONIC IMPLICATIONS. Poor regulation manifests itself in a number of ways. Poor bass control and extension, so often a criticism of valve amplifiers, is a direct result of poor regulation. Deep bass notes require lots of power and a rapid succession of bass notes will get the supply completely out of shape. With little recovery time a ponderous, overhung mess will result. This is the classic 'Valve amps can't play rock' phenomenon.
As the amplifier approaches maximum power; a condition regularly approached with low power amplifiers handling demanding program material, (deep bass, orchestral crescendos, transients) the current draw will rise. At this point the effect of poor regulation becomes readily apparent. Just as the music needs all the power the amplifier can supply, the amplifier is dying because its high voltage supply is collapsing under the strain. This is the familiar dynamic compression or flattening, accompanied by lack of focus and control. The effect of the power supply falling apart manifests itself as the sound falling apart! All too often this condition sets in before maximum power is achieved and the only option is to turn it down or choose another record.
A general softening on peaks and inability to resolve complex passages are other undesirable effects resulting in an overall lack of clarity and composure.
The effect of the power supply noise artifacts are widespread and undesirable. Solid-state rectifiers impart a hard, metallic and mechanical colouration which becomes fatiguing when listening for long periods and obscures fine timbre details. The background seems polluted with a random electrical hash impairing low level resolution and generating a busy, fussiness which reduces the sense of calm and relaxation.
The BorderPatrol PSU uses a Mullard GZ37 valve rectifier with a choke (inductor) input filter. This arrangement gives an ideal combination of regulation and freedom from noise. The choke input filter configuration gives the best possible regulation from a passive supply and 'chokes' high frequency spuriae completely out of existence. Reduced core distortion and saturation effects in the mains transformer are other benefits. Valve rectifiers emit none of the damaging reverse pulses that afflict solid-state devices and sound refreshingly clean and relaxed as a result. The sound is more fluid and calm with a more natural timbre. Background hash is significantly reduced as is graininess. Another beneficial advantage of the GZ37 valve rectifier is the slow turn-on characteristic which gives the audio valves plenty of time to heat up before the high anode voltages are applied thereby significantly increasing valve life.
With the BorderPatrol PSU the bass stays strong and deep, even on the most demanding of material. The amplifier will appear to play louder and at the same time remain clearer and more firmly in control with finer resolution and improved dynamics. Bandwidth will appear to be extended, and a general air of greater calm and less fuss will be apparent. The amplifier will be both more assured and more relaxed in its delivery.
INSTALLATION. The installation is straight-forward but some experience with electronics/electrics is essential. Potentially lethal voltages are present inside the amplifier and the power supply so if in doubt please refer to us or a qualified technician. We cannot be held responsible for any accidents that may occur as a result of this component. Once installed the power supply is activated from the on/off switch on your existing amplifier. A protective relay will shut down the supply in the event of the umbilical cord being removed whilst the unit is on preventing risk of electrocution.