The subject of ceramic caps in audio must have been discussed more than once before, but I'd like to have your inputs on a specific aspect.
I'm aware of the shortcomings of ceramic capacitors of high dielectric constant like the X7R types and I wouldn't consider using them in signal paths in production designs. However, I'm wondering about their use in one-off constructions for personal use, in particular when the aim is not to achieve the highest hi-fi quality possible.
This is my thinking: First, for a 50V capacitor, the reduction in capacitance with DC bias shouldn't be significant where the bias is no more than a volt or less. Secondly, the distortion introduced by the nonlinearity with voltage swings <<5V would be apparent only at very low frequencies. Both of these effects could be largely swamped out by using large capacitances to get cut-off frequencies well below the audio range.
My concern is about the microphonic effect. I've come across it 2 or 3 times during the course of a long career in electronics, but I'm not an audio specialist. How commonly is it encountered in real life? That is, when the effect is severe enough to be a problem in low-level stages?
I'm aware of the shortcomings of ceramic capacitors of high dielectric constant like the X7R types and I wouldn't consider using them in signal paths in production designs. However, I'm wondering about their use in one-off constructions for personal use, in particular when the aim is not to achieve the highest hi-fi quality possible.
This is my thinking: First, for a 50V capacitor, the reduction in capacitance with DC bias shouldn't be significant where the bias is no more than a volt or less. Secondly, the distortion introduced by the nonlinearity with voltage swings <<5V would be apparent only at very low frequencies. Both of these effects could be largely swamped out by using large capacitances to get cut-off frequencies well below the audio range.
My concern is about the microphonic effect. I've come across it 2 or 3 times during the course of a long career in electronics, but I'm not an audio specialist. How commonly is it encountered in real life? That is, when the effect is severe enough to be a problem in low-level stages?
I often use X7Rs in line level (around 1VRMS) stages for signal coupling. Most probably I wouldn't consider them in lower level (say phono) stages. I agree about the over-sizing to counteract LF distortion.
It must be possible to mount X7Rs in such a way as to reduce their microphony but so far I've not explored alternative mounting methods as I've not been plagued by audible misbehaviour. The level of microphony of an X7R in practice is not so dissimilar to that in electrolytics.
It must be possible to mount X7Rs in such a way as to reduce their microphony but so far I've not explored alternative mounting methods as I've not been plagued by audible misbehaviour. The level of microphony of an X7R in practice is not so dissimilar to that in electrolytics.
The problem with C0G/NP0 types is that they don't come in high enough capacitances for some applications. Electrolytics are bulky, more so when two of them have to be combined for use in a circuit that doesn't have enough DC bias. Bi-polar types are not easy to get from where I live. Film caps of multiple uFs are even more bulky and expensive. All of this makes high K ceramics attractive if their shortcomings can be partly compensated for and tolerated.
I've used Aerovox gold 4.7 and 10 UF ceramic caps, as input caps to my 1966 design dynakit ST120 amp, and as coupler caps in organ envelope shaping circuits (Hammond H100). I've had no microphonic problems. The organs have considerable internal pressure from the built in speakers at 70 watts. The 10 uf were CPO, which was a one off find and no longer stocked anywhere, though still in the Aerovox catalog. The input caps were X7R and sounded much better than the tantalum caps I bought at the local store that had frying pan popping noise from day one. Both applications were 50 v rated caps on 2 v max signals, which IMHO reduces the non-linear effect of the dielectric on the signal. The ST120 with djoffe OT idle current mod sounds at 1.0 v pp base level just like my Peavey CS800s which is a straight through no caps in signal path amp. The organ circuits are much crisper than equivalent circuits using 10 uf polyester caps, which is cool on glockenspiel envelope for example.
While I can buy NP rated caps, they come with no life specification and are probably sealed with red gum rubber for at least 500 hours of trouble free service. I use my main entertainment amp 2000 hours a year, so I look down at my nose at NP. However, polyprophylene won't fit in the chassis in the 68 uf size in an Allen S100 amp I'm upgrading. That amp will only be used 20 minutes a week, so cheapo NP would not a problem I suppose.
So do the experiment. Not totally stupid. I think some of J Curl's prejudice against ceramic comes from the *****y quality of the average ceramic cap in his prime years. Manufacturers were selling them by the thousands for TTL logic bypassing, and often came in with incomplete envelope and metal showing, for example. Price was very important in that application. The Aerovox gold ceramics cost over $6 each with the closeout symbol by the price; not a jellybean part.
While I can buy NP rated caps, they come with no life specification and are probably sealed with red gum rubber for at least 500 hours of trouble free service. I use my main entertainment amp 2000 hours a year, so I look down at my nose at NP. However, polyprophylene won't fit in the chassis in the 68 uf size in an Allen S100 amp I'm upgrading. That amp will only be used 20 minutes a week, so cheapo NP would not a problem I suppose.
So do the experiment. Not totally stupid. I think some of J Curl's prejudice against ceramic comes from the *****y quality of the average ceramic cap in his prime years. Manufacturers were selling them by the thousands for TTL logic bypassing, and often came in with incomplete envelope and metal showing, for example. Price was very important in that application. The Aerovox gold ceramics cost over $6 each with the closeout symbol by the price; not a jellybean part.
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Thanks for the replies. It's encouraging to know that the idea of using high-K ceramics is not immediately and automatically rejected. I'm going to try them out.
However, this is a hobby project and it will take some time to get all the parts together. I live in a very remote region and mail order for electronic components has never really taken off in the country, before or after the advent of the internet. I've come to rely more and more on AliExpress for my requirements in recent years.
I'm not in a big hurry to complete the project but I'm asking early before commiting my circuit and pcb designs to using ceramics.
However, this is a hobby project and it will take some time to get all the parts together. I live in a very remote region and mail order for electronic components has never really taken off in the country, before or after the advent of the internet. I've come to rely more and more on AliExpress for my requirements in recent years.
I'm not in a big hurry to complete the project but I'm asking early before commiting my circuit and pcb designs to using ceramics.
To put a finer point on it, the article in Linear Audio #12 referenced MLCC caps. I believe that for their tests they used SMT 1206, but leaded types are available. Searching Mouser's website the available values appear to range from 1 pF to 100nF with 2.5mm lead spacing.
A-10 was initially manufactured by Fairchild. Fairchild Camera and Instruments Company -- one of the early pioneers in electronics was a subsidiary. Sherman Fairchild had the foresight to hire a bunch of guys away from William Shockley in 1957 and thus was the semiconductor industry born. (Shockley would have killed it.)
A-10 was initially manufactured by Fairchild. Fairchild Camera and Instruments Company -- one of the early pioneers in electronics was a subsidiary. Sherman Fairchild had the foresight to hire a bunch of guys away from William Shockley in 1957 and thus was the semiconductor industry born. (Shockley would have killed it.)
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