anyone know where i can get a 5k P/P DPDT?

[jrfrond]

Just FYI: every nitpickin' audiophile rag I've ever read slags on tantalums for poor audio quality like there is no tomorrow.

It would be GREAT if we could use all non-polarized poly caps instead of electrolytics, but their size (and price) is astronomical once you start getting into more than a few uF.

[Chuck H]

Just FYI: every nitpickin' audiophile rag I've ever read slags on tantalums for poor audio quality like there is no tomorrow.

Yea, but I usually see that applied to caps used in the signal path. As cathode bypass caps the only distortion they could add would be what they're NOT adding, so to speak. But I have also seen them get beat up for adding audible distortion when used in power supplies... This from the same group that cryo freezes their tubes and hears a difference between power cords

I personally use different hi fi equipement depending on the borometer reading in my listening room

Chuck

[pvsage]

I've heard of people using small poly caps in parallel with electrolytics for cathode bypass. Any merit to this?

[Chuck H]

Thats a trick thats been used for decades to improve the comparitively poor performance of aluminum caps. You typically see alot of MFD in a filter system. If I understand it correctly (open to corrections as always) you don't actually need that many MFD for filtering. The rest of those MFDs are for storing a charge and smoothing out the ripple. So a biggish film cap bridged over a filter can improve it's performance in most areas other than storage charge like removing AC more completely from the +V rail. It reduces the ESR of the circuit at the audio level.

I'd like to throw another log on the fire. Whats up with "low impedance" caps? Once upon a time you got ESR figures in the specs. Now it's rare to see ESR data, but you do see impedance data more and more. And many companies are offering low impedance caps. For the intended purposes of these componants, wouldn't the impedance and ESR (equivalent series resistance?) be very closely related anyway?

[Enzo]

Um, he did ask about cathode bypass caps, not filters.

[pvsage]

If I understand it correctly, ESR and impedance are pretty much the same thing for caps. Because the foils are rolled in an electrolytic, the impedance may vary with frequency...

I've seen the film cap across power supply decoupling caps thing as well...also seen a similar configuration recommended in voltage regulator data sheets.

What I've heard about using film caps across electrolytics for cathode bypass is that the film cap compensates for the electrolytic's rather sluggish response at higher frequencies - something about time constants?

[Chuck H]

Thanks Enzo. Your vigilance doesn't go unnoticed

I was giving what I know about it. I figured that if the typical implementation was understood then any practical merit for a different part of a circuit would be easier to theorize.

But he did ask about cathode bypass caps. And I don't have any personal experience with that. I'm sure some of the same principals apply. But at typical preamp cathode impedance the effective frequency of even a biggish film cap should only serve to improve the top end. And at maybe 10s of ohms difference in ESR, with a cathode R of say, 1K, would it even be audible?

It would be an easy enough place to experiment in an amp though. And I will next time I have one opened up.

[jrfrond]

Technically, cathode bypass caps ARE in the signal path. True, they are used to stabilize cathode voltage at audio frequencies, but above the corner frequency, AC signal is superimposed on them, making them part of the signal path.