Making Valid Comparisons

When it comes time to make a change or addition to an audio system, we usually undertake listening evaluations to determine the best product for the application. This process can be fun and enlightening, or it can leave us fraught with dismay and no closer to making an informed choice than when we began. Our methods of evaluation are often the cause of this despair. If we understand a few of the basic rules, we can avoid most of the pitfalls associated with the process.

First, it is important to give each piece of equipment we audition an even break. We can help insure a fair comparison by following a few simple guidelines.

Be certain that the equipment is fully broken in. Or at the very least, compare two units with similar amounts of time on them. Comparing a preamp that you have had for several years with a new one straight out of the box may not give the new unit a fair chance. Of course if the new unit sounds better even before break-in, you can bet that it will only improve with use.

When we borrow a component from a Dealer, it is likely to be a new unit or one that has seen little use. It is unlikely to be fully broken in. As you are no doubt aware, significant changes (improvements) take place during the first few hundred hours of operation. The full sonic potential of any piece of electronic equipment may only be realized after full break-in has occurred. Electronics (amplifiers, preamplifiers etc.) usually require several days or weeks of actual playing time before they reach full potential. Please note that just being plugged-in and turned-on does not constitute break-in time, as the unit must actually be passing signal for the break-in process to take place.

Proper warm-up is a crucial prerequisite for evaluation. Warm-up is different from break-in, however. Even a unit that is broken-in must still be warmed up. Solid state amplifiers, and especially preamplifiers, require adequate warm-up time for them to strut their stuff. Tube equipment may sound fine after a much shorter time, but solid-state electronics should be warmed-up for at least several hours (and preferably overnight) before serious evaluation.

When comparing two items, be certain that their phase relationships are the same. Pay particular attention to this detail when comparing tube and solid state. Many, if not most, tube preamplifiers (and some tube amplifiers) invert absolute phase, while most transistor units do not. It would be folly to compare a tube preamp that inverts absolute phase with a solid state unit that does not. Additionally, it is not uncommon to find a tube preamp that inverts phase through the phono circuit and not through the line stage. Here the turntable would be out of phase with any line sources. Consult the manufacturer's specifications to determine phase compatibility. Better yet, try it for yourself by listening to both alternatives.

We must also consider important the aspect of proper A/C polarity with respect to the mains supply voltage. Obviously, with a standard two prong plug, there are two ways it may be inserted into the wall receptacle. Each and every piece of electronic equipment throughout your system will prefer one position or the other. The proper connection may be realized either by listening trials or with the use of a multimeter. Note: See our article on "AC Polarity" for details of how to determine correct AC polarity.

The final consideration may be the most important: component interaction. How well will the new component you are considering blend-in with your other equipment? This is an important question, and one that is not easily answered. Stereo systems are complex conglomerations of sophisticated electronic equipment. The sound of a given system is determined not only by the sonic character of each component, but also by how these characters mix or interact. A sort of "sonic synergy," if you will, is necessary if maximum potential is to be realized.

It is precisely this interaction that often accounts for differences of opinion between reviewers and audiophiles concerning a particular product. For example, a warm-balanced preamplifier used in a system that tends toward brightness might be just the ticket. That same preamp used in system which is already too "laid-back," would be the wrong choice. Even though the preamp may be superb in all other respects, its tonal characteristics would obviously favor only one of the systems.

It is impossible to predict all problems regarding component interactions, however many can be foreseen and should be avoided. For example, in a system configuration that requires an abnormally long run of interconnect cable between amp and preamp, we should be extra careful when using some tube preamps with some tube amplifiers and certain high capacitance cables.

We can avoid most problems regarding interactions by carefully examining the products we are considering, and by enlisting the help of a knowledgeable dealer to point you in the right direction. Unfortunately, there is no way to avoid the personal biases that creep into any comparison. It is quite common for two individuals exposed to the same system to have widely differing opinions as to the sound quality. Other differences of opinion between listeners can be accounted for by physiological differences in hearing acuity and personal preference.

In the end, we look to please our own tastes when selecting a new component. Trust your ears and follow the guidelines set forth here, and you will have no problem in choosing the right component to complement your audio system.