September 2018

Townshend Allegri+ Preamplifier
Martin Colloms undertakes a renewed (albeit brief) re-acquaintance with the 2017-2018 edition of a respected auto transformer volume control.
Review By Martin Colloms

  I had so used (and abused!) my first edition Allegri passive volume control that the volume wafer ganging had gone out of alignment and the input and output sockets were well worn. In the post came a refreshed example, which was first shown at the September London Indulgence show 2017 and reported by me. It would be fair to say that this compact auto-transformer line controller has been completely re-engineered, as it also now has a front panel 3.5mm input socket for portable audio sources.

PVC ribbon cable, with matching plugs and sockets, is still used to join everything up inside, but certain lengths and connections have now been abbreviated through intelligent design. One consequence is that it is certainly easier to build in its new form. There are no changes of significance to the technical design, and the specifications are also unchanged, apart from minor shuffling of volume settings. As a result the Allegri+ remains somewhat frustrating, as it only has 24 volume steps, mainly using 1dB or 2dB extra attenuation settings.

As a review tool it needs to be used with great care when comparing line sources. Generally I would like to match levels to better than 0.5dB, and will therefore use a precision volume control to do so. But when I wish to hear what an audio component can really do, the Allegri+ demands that I install it for my pre-to-power interface.

From new the unit had already sounded really good, but then it managed to slowly climb the sound quality ladder over the first few weeks. (This could only be detected by swapping back to the older example.)

Audio Excellence
For those new to the concept, the design comprises a single winding multi-tapped inductor (a.k.a. an auto-transformer) which accepts the input signal at a very high impedance (and therefore minimal loading), while a rotary switch selects from taps stepped down the winding, representing stages of attenuation or reducing volume.

Different source and load sensitivities (such as a CD player or streamer) and those of a following power amplifier would suggest provision of a wide range of settings. However, the range is limited by the volume switch, which here is typically 24 steps. The most used central volume range (from 11 to 18) has 1dB steps. With position 23 representing 0dB, it then has 2dB steps from 19 to 24, and again from 4 to 11. The lowest settings begin at 1 (-52dB) then 2 with -46dB, 3 for -33dB, and 4 for -30dB.

A lever switch enables convenient muting and switches over to the 3.5mm input. Single-ended throughout, it has six RCA/phono inputs (selectable from the left hand front panel knob) and two paralleled outputs. There are no power supplies or electronic amplification, hence the term 'passive control'. Technically the unit is also direct coupled, as there is no break in the connection between input and output, and no coupling capacitor. (Even the inclusion of a solitary very high quality capacitor is audible.) This means that there is a finite limit (here 5mV) to the level of stray DC offset which can be tolerated at the input, e.g. from an errant source component.

There is some natural variation of output impedance with source and setting, but the values are generally so low as not to be a factor. Distortion is typically less than an utterly negligible 0.008%, and the unit cannot generate hum or noise. The frequency response is quoted at 8Hz to 100kHz ±0.1dB, and our sample actually did even better on the test bench.

Now well run in, I can say that the exceptionally high accuracy and sound quality has been maintained. Indeed, on critical A/B comparison and now well run in, the new is improved by about 5%. The Allegri+ must therefore continue to be highly recommended for those who value focus, transparency and dynamics, and not least pace, rhythm and timing, and who do not mind getting up to change the volume!

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Specifications
Type: Autoformer passive stereo preamplifier
Frequency response: 8Hz to 100kHz (+/- 0.1dB)
Maximum signal level: 4V RMS 8Hz; 10V RMS 20Hz
Maximum DC offset : 5mV. (For undistorted 8Hz)
Distortion: Less than 0.01% at 400Hz, 10V (2nd and 3rd harmonic only)
Input impedance is dependent upon the load impedance and gain setting. So, with a power amplifier having 20kohm input impedance (typical)
Impedance: At 0dB, input impedance is 20kohm 
At -10dB (normal listening) input impedance is 200k
Inputs: Six pairs RCA phono sockets (gold plated) 
One 3.5mm stereo socket on front panel.
Outputs: Two pairs RCA phono sockets (gold plated)
Width: 135mm (5.3in)
Height: 53mm (2.1in)
Depth: 326mm (12.8in)
Weight: 2kg (4.4 lbs)
Price: £2400 (approximately $3125)

Manufacturer
Townshend Audio
7 Bridge Road, East Molesey
Surrey, UK
KT8 9EU

Voice: 44 (0) 208 979 2155
E-mail: mail@townshendaudio.com 
Website: www.TownshendAudio.com