Multi-Layer Ceramic Capacitors

[jazjamr]

I recently did a service and recap on a friend's Mesa Boogie Mk.1 Reissue. There had been some questionable work done, prior to his purchase of the amp. The tone stack and phase inverter capacitors had been replaced with Old Black Cat caps, having improper values and voltage ratings. I replaced those with 630-volt Panasonic ECQ caps. I wanted to reduce the Bass response slightly, so I replaced the 15 uf tantalums with 4.7 uf @ 100-volt TDK Multi-Layer Ceramics. I searched The Amp Garage and Hoffman's Forums but was unable to find any reference to MLCCs being used as cathode bypass caps. The substitution worked well, with a slight reduction in Bass response and the size of the MLCCs fitting on the board. Thanks to all The Amp Garage crew.

[maxkracht]

I use them on occasion. Guessing some will argue that they sound bad or harsh or something, but I don't think you would have any issues with a bypass cap. There's some potential for added microphonics, but I think that would be more likely if you are using them for coupling instead of bypass. C0G dielectric are less microphonic, so probably best to stick with those if you have the option, but plenty of amps have used other kinds of ceramic without too many issues.

Other problem is potential to fail short if they are flexed at all, so careful handling and make sure they aren't in a spot that might bend, especially if using surface mount parts.

[pdf64]

When I've perused the manufacturer's info of modern MLCC, the class 2 status seems inappropriate, their temperature etc coefficients seems barely any worse than class 1 ceramics.

[jazjamr]

I initially tried to find film caps for this installation due to the fact that the tantalum bypass caps in Mesas are known to be failure prone. The small footprint of the tantalums made this unwieldy. The MLCCs fit, have a better voltage rating, sound good and the bass reduction was effective, with a small reduction in bass response. As I could find no posting of other techs using this substitution, I considered this an experiment, which to this point seems effective.

[maxkracht]

Can't think of a production amp that uses mlcc for cathode bypass off the top of my head, but I know i've seen it before. I think electrolytics are still cheaper mosta the time. Marshall uses 630v mlcc for plate bypass in some newer amps, I believe they are a TDK C0G part.