I am building an amplifier based on instructions found in “A Complete Guide to Design and Build A Hi-Fi LM3886 Amplifier.” I am designing my own PCB, since I have not found a commercial one that will fit my existing heatsink and chassis. The design calls for a 4.7 µF input coupling capacitor. I am debating between using a quality electrolytic (Nichicon UFW) or a film type (MultiCap) mounted vertically – horizontal mounting is not a option due to board size constraints. The film type is probably preferred, but I am concerned about the vertical mounting. Any thoughts or advice would be appreciated.
Cheers,
ceulrich
Cheers,
ceulrich
You can vertically mount it, but it´s good Engineering to "fix" it to the board with some kind of glue (hot melt/contact cement/electronics grade silicone) to protect it against vibration.
Since it´s a relatively heavy component, and mounted on edge hanging from just one flimsy leg, vibration may eventually break it, so the glue avoids that.
Since it´s a relatively heavy component, and mounted on edge hanging from just one flimsy leg, vibration may eventually break it, so the glue avoids that.
If you do mount the cap vertically, add a spacer under the end with the short lead.
Use around a 1/4" spacer.
Use around a 1/4" spacer.
You should not consider a 4.7uF electrolytic and a 4.7uF film cap as necessarily alternatives. It is quite possible that a film cap could have a smaller value, and so be easier to mount. What LF rolloff are you aiming at? What is the input resistance of the circuit?
Thanks everyone for your comments.
JMFahey: Yes, I will definitely do that.
rayma: I do not understand the reason for the spacer. My first thought is that this would make the component less stable. Could you please clarify?
scottjoplin: I never thought about that. Would it make any difference if that lead was wired to be the input or the output of the capacitor?
DF96: Yes, good thought. The design calls for 4.7µF with an input resistance of 20K, which puts the -3dB point at 1.69Hz, probably a bit of over kill. I happen to have some 3µF MultiCap units in my parts collection, so I was going to use them. That would put the -3dB point at 2.65Hz, still quite low. I could go down to 1µF for a -3dB point of 7.96Hz, but I still have a component length problem, at least with the parts I have.
Cheers,
ceulrich
JMFahey: Yes, I will definitely do that.
rayma: I do not understand the reason for the spacer. My first thought is that this would make the component less stable. Could you please clarify?
scottjoplin: I never thought about that. Would it make any difference if that lead was wired to be the input or the output of the capacitor?
DF96: Yes, good thought. The design calls for 4.7µF with an input resistance of 20K, which puts the -3dB point at 1.69Hz, probably a bit of over kill. I happen to have some 3µF MultiCap units in my parts collection, so I was going to use them. That would put the -3dB point at 2.65Hz, still quite low. I could go down to 1µF for a -3dB point of 7.96Hz, but I still have a component length problem, at least with the parts I have.
Cheers,
ceulrich
Have you considered a stacked film rather than a wound one? They're generally a lot smaller, particularly the polyethylene or polyphenylene sulfide ones.
0.47uF for a rolloff around 15Hz might be better.
Alternatively, just use the electrolytic. If you are worried about distortion then use a slightly higher value, say 10uF or 22uF.
Alternatively, just use the electrolytic. If you are worried about distortion then use a slightly higher value, say 10uF or 22uF.
JeffYoung and DF96: Good ideas, I would consider that if I did not have these MultiCaps laying around.
Thanks again for your suggestions.
Cheers,
ceulrich
Thanks again for your suggestions.
Cheers,
ceulrich
