PRICE (exc. vat + carriage): available in 10K, 25K, 50K, 100K and 250K
all prices shown below exclude VAT
Mono stepped attenuator built on the 2 pole 23 way (one layer used) - kit £24.00, built - £39.00
Stereo stepped attenuator built on the 2 pole 23 way switch - kit £32.00, built - £52.00
Balanced Stereo stepped attenuator built on the 4 pole 23 way switch - kit £56.00, built - £96.00
Mono stepped attenuator built on an Elma 1 pole 24 way - kit £43.00, built - £58.00
Stereo stepped attenuator built on an Elma 2 pole 23 way switch - kit £75.00, built - £95.00

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 23 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 as in the Dale-Vishay design, 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, 25K, 50K, 100K or 250K attenuators to be constructed. The switch itself is a 2 pole, 23 way selector switch as used in the mono Dale-Vishay stepped attenuator and uses high quality silver plated contacts and tags. The resistors are from the famous Holco range. Holco metal film precision resistors have been used in hundreds of classic high end audio components over the past twenty years. They give a crisp, full sound; about as good as it gets in a metal film type.

When building the attenuator, it should be born in mind that the integrity of Holco resistors can be disturbed with the bending of their leads close to the body so it is essential that the leads should be bent by clamping the wire near the resistor body with pliers and bending the wire on the outside see FIGURE 4 and FIGURE 5.

To build the attenuator, start by constructing the channel at the bottom of the switch as shown in FIGURE 6,FIGURE 7., FIGURE 8 and FIGURE 9. Then complete the other channel nearest the spindle FIGURE 10 and FIGURE 11.. This allows the terminals to be accessed easily and the resistors arranged neatly around the body of the switch. In each case, start with position 2 and continue around until the last resistor at position 22 is reached. Position 23 is left open circuit corresponding to zero attenuation.

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

For the listening tests, a variety of known recordings were played through the Glasshouse passive pre fitted with the Dale-Vishay attenuator. It performed well and gave a good performance across the range and a smooth transition between steps.
It was an easy matter to replace the Dale-Vishay unit with the new Holco attenuator and, although the Holco resistors had not been run in, I couldn't resist connecting the unit back in my system for a quick listen!
There was indeed a very marked difference. The Holcos was significantly brighter and clearer than the Dale-Vishays and it would be fair to say that, with some recordings, they did sound a touch harsh. It was time to turn off the power amplifier and leave the unit with some FM radio interstation hiss (a good source of pink noise) playing through it overnight to run in the all-important series resistors and a few of the steps but turning the volume control during the evening.

Repeating the tests the following day gave a much more polished performance. The Holco unit had retained its bright characteristic but the harshness had been tamed some what. The result was a beautiful clean and open sound, which did rather leave the Dale-Vishay sounding rather flat and ordinary.

1. 2 pole 23 way switch
2. 21 off Holco resistors
3. 0.25m off 1mm diameter HGC 99.99% silver wire
4. 1m off Mundorf 3.8% silver solder

1. 2 pole 23 way switch
2. 42 off Holco resistors
3. 0.5m off 1mm diameter HGC 99.99% silver wire
4. 1m off Mundorf 3.8% silver solder

1. 4 pole 23 way switch
2. 84 off Holco resistors
3. 1m off 1mm diameter HGC 99.99% silver wire
4. 2m off Mundorf 3.8% silver solder

1. Elma 1 pole 24 way switch
2. 22 off Holco resistors
3. 0.25m off 1mm diameter HGC 99.99% silver wire
4. 1m off Mundorf 3.8% silver solder

1. Elma 2 pole 24 way switch
2. 44 off Holco resistors
3. 0.5m off 1mm diameter HGC 99.99% silver wire
4. 1m off Mundorf 3.8% silver solder

1. Soldering iron
2. Trimming knife
3. Snipe nose pliars
4. Cutters