I recently acquired a set of Bose Roomate speakers from the mid to late 80's. Basically the right speaker cabinet is completely passive, and the left one has the power transformer and amplifier circuit in it. Out of curiosity, I opened it up to see what the circuit looked like. Looks like they used all Nichicon VX (2x 4700uF/16v for smoothing off the bridge rectifier), a couple random Nichicon SE series sprinkled on the board, and what really caught my eye - 2 yellow sleeved Nichicon caps (both 1uF/50v with no real series marking. Below are pictures of the caps. The only thing not shown in these pics is a "(M)" that is also printed on the sleeve. I thought Nichicon was always 2 letters series, and the (M) is marked on all caps next to the series.
From what I've read, usually an orange or yellow colored cap from back in the 70s/80s could indicate a special cap with lower leakage or possibly even low ESR. No schematic exists that I can find, so I traced out the yellow caps. I believe they are just there to bock DC on the audio path for each L/R channel. The negative of each cap goes to a different output on a LS404CB quad op amp. And the positive of each goes to an input of a different LF411N op amp (along with a resistor in series, and some other components also connect to the input of each LF411N).
Assuming I am correct in this 1uF cap acting only as DC blocking, then I believe it would stand to reason that the yellow sleeve indicates it is low leakage. As I've read that a low leakage cap would be ideal, as it would cause the least amount of noise/hiss on the audio signal, correct?
Also if my assumptions are correct, would a film 1uF cap be ideal in this position? Obviously back in the 80's a 1uF film would have been quite large. But now days you can get a 1uF/50v film that is about the same size as the electrolytic is. Or what about a Nichicon KL series, which is supposed to be "ultra low leakage"? Or how do those supposed "audio grade" caps Nichicon sell fit into something like this? According to their data sheets, the leakage doesn't look any better than regular caps, and no where near the KL cap.
TIA,
-Nick
Edit: for some reason the IMG tag doesn't seem to be working, or I'm doing something wrong. So here are the URLs.
https://ibb.co/xSz3m1v
From what I've read, usually an orange or yellow colored cap from back in the 70s/80s could indicate a special cap with lower leakage or possibly even low ESR. No schematic exists that I can find, so I traced out the yellow caps. I believe they are just there to bock DC on the audio path for each L/R channel. The negative of each cap goes to a different output on a LS404CB quad op amp. And the positive of each goes to an input of a different LF411N op amp (along with a resistor in series, and some other components also connect to the input of each LF411N).
Assuming I am correct in this 1uF cap acting only as DC blocking, then I believe it would stand to reason that the yellow sleeve indicates it is low leakage. As I've read that a low leakage cap would be ideal, as it would cause the least amount of noise/hiss on the audio signal, correct?
Also if my assumptions are correct, would a film 1uF cap be ideal in this position? Obviously back in the 80's a 1uF film would have been quite large. But now days you can get a 1uF/50v film that is about the same size as the electrolytic is. Or what about a Nichicon KL series, which is supposed to be "ultra low leakage"? Or how do those supposed "audio grade" caps Nichicon sell fit into something like this? According to their data sheets, the leakage doesn't look any better than regular caps, and no where near the KL cap.
TIA,
-Nick
Edit: for some reason the IMG tag doesn't seem to be working, or I'm doing something wrong. So here are the URLs.
https://ibb.co/xSz3m1v
Attached Files
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