PRICE (exc. vat + carriage): available in 10K, 50K and 100K
Stereo stepped attenuator - kit £170.00, built - £200.00
Mono stepped attenuator - kit £90.00, built - £105.00

The Hi- Fi Collective stepped attenuator is based on a shunt design where the signal is fed through a fixed series resistor, Rx and the shunt resistor, Ry, is selected from 24 values ranging from zero to infinity by means of a selector switch. See FIGURE 1.

A simple ladder design has the disadvantage of having a number of resistors in the signal path. A switched ladder switches pairs of resistors, but this required two sets of switch contacts in the signal path, which is undesirable and a more complicated switch is required. Although a shunt design presents a variable input impedance to the signal source, this does not matter in practice and the benefits of a single resistor and switch in the signal path far outweighs this issue.

Resistor packs are supplied to enable 10K, 50K or 100K attenuators to be constructed. The switch itself is a 24-way unit made by the Swiss company, Elma. It is a high quality, non-magnetic bodied switch with gold over silver-plated copper contacts. The wafers are ceramic with gold plated solder tags.

This allows the terminals to be accessed easily and the resistors arranged neatly around the body of the switch. Start with position 2 and continue until position 11.
Next fit the resistor at position 13, then position 12 as this allows the step 12 resistor to be fitted neatly between the pillar and the step 13 resistor. Continue around until the last resistor at position 23 is reached. Position 24 is left open circuit corresponding to zero attenuation.

The other ends of all the resistors are joined together with a circle of wire, which will be connected to earth and also position 1 of the attenuator, which corresponds to infinite attenuation, i.e. zero volume, as the first step. The wire supplied is the HGC 99.99% silver solid core wire and all joints are soldered using Mundorf 9.5% silver solder. Personally, I am not a great fan of unleaded solder as I find it's flowing properties inferior to good old 60-40 multicore leaded solder. However, the Mundorf silver solder is every bit as good as leaded as far as solderability is concerned, but with far superior conductivity and sound qualities.

Finally, connect the input series resistor to the wiper of the switch. The input of the attenuator is input lead of the resistor and the output of the attenuator is the wiper or other end of that resistor. That completes the construction of one channel.

Now carefully dismantle the switch as shown in FIGURE 4 and swap over the two wafers. Re-assemble the switch. You are now ready to repeat the process for the other channel. When that is completed, the attenuator is complete and ready for installation in your pre-amp see FIGURE 6.

For this review, the attenuator was installed in the Glasshouse Passive Pre-Amplifier No.1. The original pre-amp was fitted with the Dale-Vishay stepped attenuator and as the new unit is a smaller and more compact design, no difficulties were encountered. Indeed, the size of the finished unit compares favourably with many high quality potentiometers and can therefore be used as a replacement for these.

However, for the purpose of the listening tests, the new attenuator was installed alongside the Dale-Vishay and the output was taken to a separate pair of phono connectors to enable easy switching between the two attenuators.
So how did the new attenuator stand up against the Dale-Vishay unit?

Over the years, I have found that many upgrades make subtle changes to the sound and require repeated comparisons to enable the changes to be quantified. Not so with this unit. Although the Dale-Vishay is a significant improvement over conventional potentiometers, it was completely out-classed by the new unit.

One of my many standard 'test' recordings is a superb recording of Tchaikovsky Suites from Swan Lake and the Nutcracker by the Israel Philharmonic Orchestra conducted by Zubin Mehta on Decca 410 551-2. This CD has very quite tracks with solo instruments balanced by the full orchestra, complete with an almost sub-sonic bass drum. Both these extremes showed the limitations of the Dale-Vishay attenuator.

In comparison, the new unit has a far cleaner and more open sound. The high end was brighter but less harsh sounding. The bass was tighter and more controlled and the midrange was more balanced with the top and bottom ends of the spectrum. Without wishing to run down the excellent value Dale-Vishay attenuator, it is really a case of getting what you pay for. Overall, the Dale-Vishay sounded slightly tinny, harsher and had a woolly bass in comparison, as though there was a slight peak in the mid range and bass response.

As far as the sound image was concerned, some instruments in the orchestra, such as the string sections, were slightly more forward with the new unit, while others like the kettle drum were further back. This gives a much fuller and more realistic sound stage that is less constrained by the two loudspeakers in the listening room.

Further comparisons were made with other recordings from early baroque to jazz and light music recorded in the '60s, '70s and '80s which reinforced the above comments.
When the listening tests were completed, the new attenuator was fitted in place of the existing Dale-Vishay in the Glasshouse Passive Pre-Amp - see FIGURE 8

. All-in-all, this attenuator is a superb unit which oozes quality and will be at home installed in the finest audio equipment. designed and written by Neville Roberts

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1. Elma 2 pole 24 way switch
2. 46 off Shinkoh resistors
3. 1m off 1mm diameter HGC 99.99% silver wire
4. 2m off Mundorf 9.8% silver, supreme solder

1. Elma 1 pole 24 way switch
2. 23 off Shinkoh resistors
3. 50cm off 1mm diameter HGC 99.99% silver wire
4. 1m off Mundorf 9.8% silver, supreme solder

1. Soldering iron (25 watt Antex)
2. Trimming knife
3. Snipe nose pliars
4. Cutters