Safety thought regarding low voltage caps for DC-decoupling - diyAudio
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Old 24th April 2004, 11:55 PM   #1
roibm is offline roibm  Romania
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Question Safety thought regarding low voltage caps for DC-decoupling

I am tweaking an older DAC that has 2 decoupling caps on the analog signal path.
One is just before the I/V opamp(is it called like this?) and the other one is after the opamp. They are rated 10uF/25V and I replaced them with some 4.7uF Wima. The sound is much better, but there is a high pass filter in place now(it was there before, but not like it is now) that cuts pretty much under 60Hz(@ 40Hz it is -2dB).
Not good at all

I was thinking about replacing these caps for some Black Gates(I do believe in Black Gates since I tested them) 22uF/6.3V NX hence my question: is it something I should be avoiding at all cost considering that they are rated only 6.3V(instead of 25V)? I measured the voltage that is going through the caps: before the opamps I have 4V DC(comes from the DAC chip) and after the opamps I have ~1mV DC and 5-300mV AC, and never more than this values. The 4VDC doesn't really look good, but the other I find it ok.
Other alternative, would be BG 10uF/50V N, but double the score.

So now you got the oveview... what do you think? am I crazy to even put this question?
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Old 25th April 2004, 04:00 PM   #2
boholm is offline boholm  Denmark
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Well, it would work perfectly, but if anything goes wrong it will go too.

One concern: You should measure the maximal voltage over the caps during switch-on and switch-off. It is in these two situations where big voltages can occur. To be on the safe side you should choose a cap that withstand the entire voltage swing possible - from V+ to V- (in other words the power supply).

One thing you can test: Put back the original caps and also put in the 4.7 F parallel with the caps. You will get your bass back, but maybe also a better sound. Compare that sound to that you heard with the 4.7F alone (not focusing on the bass, but the rest), and let's hear your verdict (if you do the test).
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Old 25th April 2004, 08:01 PM   #3
roibm is offline roibm  Romania
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Quote:
Originally posted by boholm
Well, it would work perfectly, but if anything goes wrong it will go too.

Oh Murphy, where are you?

Quote:
One concern: You should measure the maximal voltage over the caps during switch-on and switch-off. It is in these two situations where big voltages can occur. To be on the safe side you should choose a cap that withstand the entire voltage swing possible - from V+ to V- (in other words the power supply).
Ok. I will do just that.
The way I see it, at least the caps right at the output from the DAC are never receiving more than 5V since the DAC is supplied with 5V(or 4.8V, I forgot it).
The opamps are running on +/-12, so I must pay special attention to the caps after the opamps.

Quote:
One thing you can test: Put back the original caps and also put in the 4.7 F parallel with the caps. You will get your bass back, but maybe also a better sound. Compare that sound to that you heard with the 4.7F alone (not focusing on the bass, but the rest), and let's hear your verdict (if you do the test).
Thanks for the tip.
I did just that, but not with the original caps(they were very cheap elcos), instead I used Pana FC 10uF/50V. So instead of a 10uF/25V I have 4.7uF+10uF. Needless to say the bass is fully back(linear down to 16Hz), but the quality compared to the Black Gates is a far cry.
Worth saying is that the Black Gates(4.7uF N) have their own sound coloration, but they do sound much much better, it's like it brings the dynamics alive(I don't know the right description, sorry... maybe not laid back? someone that helps me here?). There might be some people that don't like any sound coloration, I won't say everybody must like them, but this is me, and I don't really care about others since I am listening to the device

Now I wish I had some 22uF NX

None the less, thanks boholm for your feedback, much appreciated.

Edit: The Black Gates alone felt punchier(more bass, nicer bass) than the 4.7+10uF(altho this one brings more bass)
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Old 25th April 2004, 11:07 PM   #4
boholm is offline boholm  Denmark
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If you like it best with BGs, then go for it.

BHW: Another thread got us this: http://diyparadise.com/cap/dare_to_compare.html
On that page the caps job is different from that in your situation, but it does make go "hrm . . . "
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Old 25th April 2004, 11:46 PM   #5
roibm is offline roibm  Romania
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Quote:
Originally posted by boholm
If you like it best with BGs, then go for it.

The matter of fact is that I like BG best from what I have, and that ain't much: OSCON, Pana FC, Wima 4.7uF, BG 4.7uF(only 2 from a Brian GC kit which is not yet assembled), Elna Silmic and Elna Starget. There might be some other caps, maybe for an even better price that do a better job, but I don't know which ones. I am a beginner in this field and it will take some time to build a stock(small).

Quote:
BHW: Another thread got us this: http://diyparadise.com/cap/dare_to_compare.html
On that page the caps job is different from that in your situation, but it does make go "hrm . . . "
I will take a look. Thank you.
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