The Art of Bypassing
Bypassing capacitors is a little like blending watercolors. With watercolors, the dominant pigment can be brightened, softened, darkened or lightened with small additions of other hues, and it takes a delicate touch to make the perfect shade.
With capacitors, the signature of the base cap can be brightened, softened, darkened or lightened with the addition of the appropriate choice of bypass capacitor. The "perfect" tonal balance can only be determined by ear.
And, like watercolors, the whole is often greater than the sum of its parts.
The bypass capacitors we have developed have very specific subjective characteristics that can be applied to improve the performance of most loudspeaker crossover capacitors significantly:
Classically, bypassing a capacitor means paralleling a very small cap (0.5% to 1% of the base cap) to improve the effective high frequency performance of the base cap. While this works to a point, the problem with simple bypassing it that it tends to sound a little discontinuous, with the large cap dominating the signature at the low end while the bypass cap dominates the upper extreme.
Cascade Bypassing (or simply "Cascading") is a bypassing method that yields the best and most homogeneous sounding combination of capacitance. Cascading is essentially paralleling smaller and smaller capacitors of increasing voltage to reach the target value. We usually suggest a cascade of 5% to 25% steps, with each smaller cap having a higher voltage rating.
Examples of Cascade Bypassing are:
100.0µF = 100µF 100V + 4.7µF 225V +1.0µF 625V (=106µF, within 10% of 100µF)
6.8µF = 4.7µF 200V + 1.0µF 600V + 0.10µF 800V
4.0µF = 4.0µF 200V + 1.00µF 600V + 0.10µF 800V
Cascading sounds better than simple bypassing because it yields an overall homogeneity to the sound of the equivalent capacitor.
Bypassing with North Creek Capacitors
Harmony Capacitors were designed specifically to bypass other metallized capacitors. Their signature is lightweight with a wealth of detail, and the top end has a nice sparkle without being bright or forward. They are also much quieter than most capacitors, particularly those that wound with very high tension. We best describe the Harmony caps as "cleaning up the sound" of other capacitors.
Crescendo Bypass Capacitors were designed to correct the harmonic imbalance we found in most of the film capacitors coming out of California; that is, a weak lower midrange, forward upper midrange and over-emphasized treble.. Many listeners equate this tonal imbalance with a "wealth of detail", although we find it unnatural and unsatisfying for long term listening. The Crescendo bypass cap, with the thick 600 Volt and 800 Volt film and heavy conductor, is very rich through the midrange and much softer in the top end than most of the premium capacitors coming from California. In designs where both the tweeter and the electronics tend to be bright, but a "wealth of detail" is a primary design goal, the combination of a "West Coast" capacitor with a Crescendo bypass capacitor usually yields the best of both worlds.
Unusual Qualities of the Crescendo Capacitor
We have noticed some of the strangest things can occur when one bypasses with a 1.0µF crescendo capacitor.
Perhaps the most unusual is the way this cap can "quiet down" a woofer when used in the capacitor stack going from the output of the low pass input coil, to ground. This is true of both Zobel circuits and shunt legs of second or higher order low pass filters. Frankly, we can not pin down why this effect is so dramatic in a parallel application, but it is. Try it - you'll like it. It may even blow you away.
We have heard of several customers using five 1.0µF 600V Crescendo caps bypassed with a single 0.10µF 800V crescendo to drive a Focal T120 tweeter. This is a driver with excellent information retrieval but when used with the wrong caps tends to get a little brittle. The stack of Crescendo caps is said to yield the ultimate combination .
For those using the Scan Speak Revelator tweeter, one should cascade Crescendo caps throughout. The Revelator has a broad peak in the 8kHz to 20 kHz region that will be emphasized considerably by any of the brighter film and foil caps available. Make no mistake - this may be the best tweeter in history, but it needs proper care and feeding to sound its best. See our Rhythm-Revelator project for more information.