Bypass caps

Hi folks, in many discussions I come across the use of bypass caps as a means to improve circuit performance. Can anyone explain the theory behind the application of bypass caps? Is it always better to use bypass caps or do we have a dichotomy here of proponents and opponents with regard to that? I can imagine that using bypass caps extensively makes the circuit board's appearance a bit "crowded". I'm a proponent of as simple as possible circuit design, because the more parts you have the higher is the failure rate of the unit and the more difficult to get all the parts "matched".


A "bypass " cap should never exceed 10% of the value of the original cap.Changing a bypass for a small cap from .01Uf to 750Pf can change the perceived "brightness>>too bright,then step down to the smaller.In a capacitor set-up(cap w/bypass) ,the larger the cap the lower in frequency the effect,smaller values will change the higher frequencies.And the perCeived tonal balance in some cases.Electrolytics are generally the first to be bypassed.
Unfortunately, this is one of those topics where you first have to define your terms. The term “bypass cap” is used quite differently by audiophiles and electrical engineers. Audiophiles typically use the term to refer to multiple capacitors wired in parallel in the same physical location, or nearly so. The purpose of this (at least within the realm of high-end audio) is to create a single, conjugate capacitor that outperforms ("sounds better than") any single cap in the same application. The mix of caps is usually arrived at through a series of listening evaluations, so the process is mainly subjective. For the purposes of high-end audio, bypass caps are almost exclusively film types (polyester, polypropylene, polystyrene, teflon, etc.) The ‘theory” is simple enough - smaller value caps may (for a variety of reasons) have better high-frequency performance than larger ones (especially when the larger caps are electrolytic), so combining large and small caps may (when everything works well) result in a single capacitance with outstanding full-range performance. As with many things in audio, this is easier said than done, but it remains a very popular practice among hobbyists.

Electrical engineers usually use the term to refer to multiple capacitors connected in parallel electrically, but distributed along the power supply path so that the smaller caps with superior high-frequency performance are located adjacent to critical circuit elements (particularly wide-bandwidth gain blocks). The intent is to improve the stability of these circuits by providing a superior low-impedance path to ground on the power supply lines. Many modern wide-bandwidth circuits will not operate properly (or at all) without these local bypass caps in place.

Best regards,

Steve McCormack