But if you value sound quality, it’s well worth it.īut wait, there’s more: There’s one other critical place for this bypass treatment that is almost always overlooked – the output stage cathode bypass capacitors.Įlectrolytics used for cathode bypass must be replaced or bypassed with good quality polyethylene types for the best sound-even though they can be rather expensive. The answer is simple: It adds more than ten times the cost of power supply capacitors. One might ask why this is not done by most other system designers. We also add one or more high quality, high capacitance polypropylene types in parallel, allowing higher frequencies in the return signal path to bypass the electrolytics, thus avoiding the problem. For this reason when we use electrolytics, we always select premium types specially chosen for low ESR and high ripple current capability. The power supply is actually part of the signal path, even though we tend to consider it as a “separate circuit,” and the caps used there can cause the same types of distortion. In Solid State amps, electrolytic types are commonly used everywhere, making this one more reason great sounding tube amps are easier to design.īack to those evil electrolytic capacitors:Įlectrolytics in the power supply need the same attention as signal path capacitors. In tube amps electrolytic capacitors are mostly found in the power supply, but are also widely used in the cathode bypass of the power output stage. Above that value, polypropylene is the type of choice, with nearly the same qualities of dissipation factor (DF) and dielectric absorption (DA) as polystyrene (these are the two capacitor “qualities” that most affect audio applications).Ībove 50 uF aluminum electrolytic capacitors are a necessary evil. Polystyrene is the first choice, but are only available in values up to. The best capacitor types for audio circuits are polystyrene and polypropylene. Any amp using them in the signal path will benefit by from the substitution of premium polystyrene or polypropylene types. In our opinion, polyester capacitors should never be used in an audiophile system. Unfortunately, our tests revealed that this type of capacitor produces distortion and “coloration” that can be easily heard in any high-quality sound system.
Polyester capacitors were the most widely used types in vintage amps, due to their low cost and high availability. These types of tests have also been conducted by others, with consistently similar results. Our tests revealed that a single coupling capacitor of the wrong type can noticeably degrade sound quality. We have conducted both computerized signal analysis and blind listening tests using various capacitor dielectric types including aluminum, tantalum, silver-mica, ceramic, polyester, polystyrene and polypropylene. It’s not surprising that an enormous improvement occurs, since the effects of changing even a single capacitor from one type to another can be heard- And a typical AEA restoration replaces up to a dozen or more! Replacing aging, underperforming capacitors with modern high-performance audio grade types specially selected for each amp’s type of circuitry, can easily take any vintage amp far beyond it’s original sound quality. Today we even have capacitors that have been specifically designed for high quality audio use (the so called “Audiophile ” caps).
#Audio signal path plus
Just as in other electronic components, there has been huge improvements in the design and manufacturing of capacitors over the past 50 plus years. Carefully choosing the right type of replacement capacitors results in a remarkable improvement in sound quality, even when the original caps were in perfect condition.
It’s not that old capacitors “go bad.” They do- But it’s that the original capacitors were not “audiophile grade” types to begin with. Not just the power supply electrolytics, or caps that test bad, but ALL caps. The single biggest improvement you can make to any vintage amp is replacing its capacitors with the correct “Audiophile Quality” types. When cooking up good sound, audiophile grade caps should be on the list of ingredients…