Just wondering why a 4.7uf input coupling cap would also have a .1uf cap in parallel with it. Both are film caps.
That is often done (small C in parallel with big C) to enhance high frequency performance of the combo. Small cap bypasses stray inductance (a limiter of HF performance) of the larger one. With some larger caps, that may not be necessary because of their design which would minimize the inductance.
IMHO this is over kill, but two things:
1. Capacitor self-resonance due to internal inductance.
https://article.murata.com/en-us/article/impedance-esr-frequency-characteristics-in-capacitors
2. Capacitor distortion. This shouldn't be a problem with film capacitors, but people will CYA design to please/impress their customers.
In reality, such a capacitor is in series with a high impedance so a few ohms of misbehaviors will make about zero effect.
1. Capacitor self-resonance due to internal inductance.
https://article.murata.com/en-us/article/impedance-esr-frequency-characteristics-in-capacitors
2. Capacitor distortion. This shouldn't be a problem with film capacitors, but people will CYA design to please/impress their customers.
In reality, such a capacitor is in series with a high impedance so a few ohms of misbehaviors will make about zero effect.
Good thread here about Bypass Capacitors: https://www.diyaudio.com/community/threads/science-of-bypass-capacitors-in-crossovers.396996/
That's what I was thinking. Doesn't seem like it could be a problem at audio frequencies.
What led me to look at this was because I was considering reducing the size of the 4.7uf cap to 1uf. I'm tight on space where this amp board is going and the 4.7 is huge. 1uf would still be good down to about 3hz
Ha! Very different... Usually these bypass capacitors are seen in loudspeaker crossovers. They allow for the use of a more economical main capacitor, complemented by a high-quality 0.01 μF bypass capacitor. This approach has improved performance in my experience, although your mileage may vary. However, I have yet to encounter the use of bypass capacitors in amplifiers or preamps.
Here is an example from the NAD C 320beee. The tone control circuit has polarized caps in the input and output bypassed by 0.1uf. C325 has rather big because the tone circuit is less than 4k.
Hi. If electrolytic capacitor would dry, you still have high frequencies sound , and by symptoms you know what you need to do - replace caps. But in your case, shunt one film cap with another film is not frequent. Probably it reduces overall ac resistance of capacitor, at wider frequency range.
Thanks for all the feedback.
Another curious thing is why they would spec a huge 250v version when it barely even fits. Max supply is +-45v.
Another curious thing is why they would spec a huge 250v version when it barely even fits. Max supply is +-45v.
That was my initial thought but the board has 4.7 250v stenciled on it. Pretty sure I could find at least equal spec 100v's that would fit better. Prefer to keep lead length as short as possible and these are sitting well off the board because they're too wide for the holes.
If holes don't match actual part, only one idea - initially it should have different part, but for some reason changed to different. Again, price - film capacitors are expensive , especially higher capacity and small size combination, but for lower voltage.
http://kit-amp.com/amplifier-audiophile-100w-en
I'm retromodding an old 70's stereo and needed a RTR board and something very space efficient and this fit the bill. Unlike most of the cheap Chinese boards with suspect parts, this one showed full test specs. Plus the company is located in Kiyv which I found intriguing.