WHAT IS THE ULTIMATE VOLUME CONTROL?

The weakest link in the electronic audio chain is the volume control. It lies at the very heart of every Hi-Fi system, all you hear must pass through it, so it is crucial to have the best control possible.

After much research, analysis and audio trials, the Townshend audio team have condensed the available volume control options, into the following categories:

Passive potentiometer 

The regular potentiometer has well-known shortcomings; distortion at the wiper/resistive-film interface and the film/contact interface.

Also, there are serious capacitive loading problems with the tone of the music changing as the volume changes.

 

Active potentiometer 

The active potentiometer solution is the most popular, as it eliminates the capacitive loading, but not the contact distortion.

Unfortunately, the active circuitry adds distortion and noise.

 

Passive switched resistor array 

The switched resistor array eliminates the contact distortion problem, but not the capacitance problem.

Also, there are not enough steps and remote control is difficult. Further, the switch contacts wear out after only a few thousand operations.

 

Active switched resistor array 

The active switched resistor solution solves the capacitance problem but adds noise and distortion.

As well there are not enough steps and the switches wear out prematurely.

 

Opto

Opto volume controls seem a good solution, but there are distortion issues with the non-linearity of the light-sensitive phototransistor and there are the usually associated amplifier problems of hum, noise and distortion.

 

Digital

At first sight, the digital volume control appears to be the ideal solution, but even the best digital volume control must have an amplifier to drive subsequent equipment and the output noise does not reduce as the volume is reduced. 

Also, as the volume is reduced, the bit-depth of the music is reduced and this is audible. It may be equal to, but cannot outperform the best transformer volume control.

The best solution for fidelity is to set the digital volume at maximum and then attenuate with the best analogue volume control possible.  

 

Transformer

Transformer volume controls are best, as they have near-zero noise, have virtually no distortion and the impedance issue with capacitance loading is eliminated.

There are two transformer designs. The regular two winding transformer volume control (TVC) and the single winding autotransformer volume control (ATV). The advantage of the TVC is true balanced operation and galvanic isolation (no direct connection between input and output). This is important in the recording studio environment but is irrelevant in the domestic Hi-Fi situation.

The AVC has the advantage of a smaller core size compared with an equivalent TVC, which means it has lower leakage inductance. This gives it a flatter frequency response and a far better transient performance.

 

Switched TVC or AVC

Most units do not have enough volume steps, they are rarely remote-controlled and the switches have limited life. The regular copper wired designs are a bit dull sounding and the silver wired ones are typically bright and edgy.

 

Reed Relay switched AVC

Reed relays are by far the best switches for low level audio signals. They have very low resistance, the contacts wipe when making and there is no contact corrosion as the contacts are in a vacuum. Further, they have a far longer life, at 30,000,000+ operations, compared with a rotary switch, at 3000 operations.

 

THE TOWNSHEND APPROACH:

Historically, preamplifiers had to amplify the weak source signal to drive the power amplifier. Modern source components typically have 2V output (Red Book CD standard) and power amplifiers have 1V sensitivity for 100W output (29dB gain into 8 ohms). Why amplify 15dB (typical active preamplifier) and then attenuate 30dB, for normal listening? Logically, for the purist, the pre-amplifier/volume control should only attenuate.

The best solution is a passive, multi-tapped, Fractal™ wired AVC. The advantageous impedance ratio between the inputs and outputs present the perfect interface between source and power amplifier.

For example, if the source impedance is 100 ohms, at 0dB, the output impedance is 100 ohms. At -6db, where the output voltage is half the input voltage, the output impedance is ½ the input squared, which is 25 ohms. At minus 12dB, the output impedance is 6.25 ohms. This is the ideal, as it presents the perfect drive to the power amplifier, it is cable independent and has zero added noise or distortion. 

THE END OF THE SEARCH FOR THE ULTIMATE VOLUME CONTROL

The new Townshend Allegri Reference preamplifier has a reed relay switched AVC, with 129 0,5dB steps as the ultimate attenuator. It is remote-controlled, wired with point-to-point Fractal-Wire™ throughout and suspended on the latest inbuilt Seismic Isolation

The Allegri Reference is the new audio standard in volume control. Uniquely it manages to transform the entire sound-stage into a holographic like experience. Instruments, singers and the original acoustics from the venue, morph from between the speakers into a ‘real’ performance.  

It sounds magical! 

 
 

For more info please send an email to: mail@townshendaudio.com


Trials are available to evaluate any of the Townshend products.

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