The RESISTOR is one of the most discussed components in audio amplifiers. Most people are using metalfilm resistors and we have been delivering our KITs with 0.5W/1% Roederstein MK-2 metalfilms. These are very good quality resistors, however, they have their own sonic signature. Customer feedback indicates that, like most metalfilms, they sound a bit dry, and they emphasize the high-end of the frequency range. Unfortunately, we are not able to “measure” these sound qualities; consequently, selecting the “right” resistor is mostly a cut-and-try process.

We have been experimenting with a number of different type resistors and found the non-magnetic Shinkoh Tantalum resistors to solve some of the problems mentioned. They sound less dry than the metalfilms and they do not emphasize any particular frequency range. They sound more natural, more musical. They work equally well in semiconductor and tube amplifiers. Most of the customers, who tried the tantalums, say that they would never go back to the common metalfilm type resistors.
Having said that, some also said that the tantalums sound too “nice”, with less control in bass and a touch less “presence” in the midrange. Further experiments with resistors led us to the Caddock MK-132, which are also non-magnetic. These are also metalfilm resistors, but they do not exhibit the typical “metallic” character of the metalfilms. They sound very clean with good dynamics, focus and a very good control of bass. Unfortunately, they are very expensive. Although you can build a whole amplifier with only Caddocks (which we do in our top-of-the line custom made amps!), it is not necessary. To take advantage of their unique sonic qualities it is usually enough to put Caddocks in the input stage and the feedback network. A combination of Tantalums and Caddocks gives the best result in most amplifiers.
Unfortunately, the Shinkoh tantalum resistors are no longer manufactured, and although we still have a sizable stock, they will disappear when this stock is exhausted. We are looking for resistors that can replace the tantalums.

In the meantime our search has led us to the VISHAY-DALE RN60D. These are non-magnetic, and sound-wise have proven to be almost as good as the Caddocks. Although rated conservatively at 0.25W, note that these are larger in size than the normal 0.5W metalfilms!

POTENTIOMETERS have received lots of attention in audio magazines, and there are good quality ones on the market. The ALPS 27mm blue and the 40mm black (“Black Beauty”) potentiometers are probably the most used ones in DIY projects. They have exceptionally good tracking and are very reliable.

In audio chains with extremely high resolution we recommend to use stepped attenuators. They offer very good tracking and, with good resistors, a very neutral sound. There are two versions of stepped attenuators used: the series connected and the ladder-type. In a series connected attenuator, there are as many resistors in series as the number of steps, essentially replacing a potentiometer. At very low volume you have practically all the resistors in the signal path, and as you increase the volume, the number of resistors are reduced. Using a good quality switch and good resistors, this type of attenuator is still significantly better than most potentiometers. A typical example of the series stepped attenuator is the one offered by DACT. These are very high quality attenuators, using specially made ELMA switches and SMD resistors. We are using these in our balanced lineamps.

In a ladder-type attenuator there are only two resistors and a couple of switch contacts in the signal path at any volume setting. This is the best solution to a volume control. Of course good resistors are very expensive, but you don’t have to use Caddocks and/or tantalums for all positions. Use them only in the positions where most of the listening is done.