EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: dexters_lab on December 20, 2016, 08:06:08 am
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just replacing some badcaps in a 'audiophile' amp for a friend and saw these.... i guess someone goofed somewhere in the design process... :-DD
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I think the goof up is to need 100uF non-polarized electrolytics in a place like that?
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I believe, correct me if I am wrong, that non-polarized electrolytic capacitors are usually bigger than the polarized variants. I remember having a couple of the non-polarized ones that were the same value and voltage as a couple of polarized electrolytics and they were physically bigger.
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I think the goof up is to need 100uF non-polarized electrolytics in a place like that?
Yep, footprints are completely adequate for 100uf 16V or 25V normal electrolytic capacitors. Also there is polarity on the silkscreen. The question is, who decided to put such caps into there.
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I think the goof up is to need 100uF non-polarized electrolytics in a place like that?
Yep, footprints are completely adequate for 100uf 16V or 25V normal electrolytic capacitors. Also there is polarity on the silkscreen. The question is, who decided to put such caps into there.
1) There is nothing wrong in using non-polar elcaps in audio. I actually prefer non-polar electrolytics in a signal path if you can not avoid using a capacitor and a good P/P or P/S type are not suitable size-wise. Non-polar electrolytic caps have considerably lower measured distortion comparing to most polarized types (and yes, I did measure distortion on a number of capacitors including non-polar elcaps similar to the used in that amp).
2) If these caps do work better that the originally planned polarized type, I see nothing wrong with the solution as shown on the photos - it is perfectly safe on a PTH board and even if it looks somewhat ugly, it does the job.
Cheers
Alex
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Possible "upgrade" by previous owner?
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Possible "upgrade" by previous owner?
no i don't think so, i'm fixing it for a friend who bought it new about 8 years ago
All the caps in it are the same Tepco brand, i am replacing three in the power supply section
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The trouble is that there is no mechanical support of these capacitors except via their leads.
Vibration may not be an issue (depending on the volume setting ;D) and the leads look quite 'chunky" but I would be worried about solder joint cracking over time.
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At least they used a TL072, not a JRC version, so there might be slightly lower noise. Likely there was originally a 47uF 16V cap specified, but they found it hard to source. So instead went to the next value, which is very common.
100uF non polarised caps on an audio output are useful though, but you need to use a 100uF 63V unit, so as to avoid damage if it is connected to a mixing deck and somebody turns on the phantom power. You saw that in the damage done to the outputs of Mark's Sony Betacam player teardowns, which all had signs of replaced capacitors from that, and capacitors failing from applied voltage when the unit was retired.
In an audio amplifier just having a polarised 100uF 63V unit on the input is fine, the thicker foils on high voltage units means any leakage at audio levels is negligible. For interstage coupling it is fine as well, providing you have a defined bias, or the voltage across it is under 1V at most, as the stages are referenced to the common rail.
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I read "Teapo" there - reasonably common middle-of-the-road caps. They're half-decent when not stressed (ripple or temperature wise), but still far below Japanese brands.
Possible "upgrade" by previous owner?
no i don't think so, i'm fixing it for a friend who bought it new about 8 years ago
All the caps in it are the same Tepco brand, i am replacing three in the power supply section
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I think we are looking at a Shenzhen market availability error here. They fit for the right price sort of thing.