220uF capacitor rating for Aleph 30? - diyAudio
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Old 26th January 2007, 11:52 AM   #1
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Default 220uF capacitor rating for Aleph 30?

Hi!

No I don't mean the PSU capacitors, but C9-C11 being 220uF. What do I need here at least?

Thing is I'm thinking of using Silmic caps, but only 25V types would fit.

I guess C11 gets max 2V (sits at the input), but I'm not so sure about C9/C10.

Of course I want to stay away from stupid riscs, so if a higher rating is necessary I will different caps with higher ratings, that's sure.

Thanks a lot for your help!

Have fun! Hannes

PS: I mean for standard +-25V rails.
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Old 26th January 2007, 12:33 PM   #2
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Well I found this thread about the input coupling cap C11, which confirms that even 6.3V is enough.

What about C9+C10?

Higher rating needed?

Have fun! Hannes

PS: funny that most times people only want to replace parts spatially close to the input or output, but ignore the rest ;-))
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Old 26th January 2007, 06:24 PM   #3
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this should help:
http://www.diyaudio.com/forums/showt...730#post846730
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Old 26th January 2007, 07:07 PM   #4
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Great thanks a lot!

I thought I read the whole thread, but seems I missed that post!

So Peter's measurements are without signal, could the values change upwards when operating?

Sorry if this is a stupid question, but I prefer making sure over blown caps.

So, are these the max values or can they increase with a music signal?

Cheers, Hannes

PS: all info is of course added to the wiki!
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Old 28th January 2007, 10:36 AM   #5
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So C9 is the crucial one as far as voltage rating is concerned.

Mr. Pass writes

Quote:
R20 serves to sense the current running through Q6, and feeds that to the base of Q5,
forming a loop that holds the output current at 2 amps.
and

Quote:
The PN junction drop of Q5 forms the
reference voltage for the system.
Which is about 4 to 5V.

So is it correct to deduce that the 15.3V across C9 that Peter measured (see above link for his post) are constantly the same, since the voltage drop of Q5 stays the same?

If yes, any >20V cap is sufficient for the 3x 220uF that are needed.

I hope somebody can confirm this!

Thanks a lot! Have fun, Hannes
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Old 31st January 2007, 07:35 AM   #6
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Nobody?
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Old 31st January 2007, 11:07 AM   #7
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Hi,

yes 20V is enough for an Aleph 30. I´m using 25V for an Aleph 5 with 32V supply for years now without any problems.

The input and feedback cap can be much lower as they see no dc voltage in these positions.

William
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Old 31st January 2007, 02:16 PM   #8
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Thanks for your reply!

Yes I also think so - however I hoped somebody with more knowledge could confirm my above thoughts.

Usually I really want to stay away a bit from the max rating - so I would take say a 63V cap - but 25V seem to be quite close to the worst case.

Since I do not want to depend on the manufacturer quality (exceeding specs), I want to go absolutely sure!

Anyway thanks a lot for your kind reply!

Have fun! Hannes

May I copy my original thoughts here
Quote:
So C9 is the crucial one as far as voltage rating is concerned.

Mr. Pass writes
Quote:
R20 serves to sense the current running through Q6, and feeds that to the base of Q5,
forming a loop that holds the output current at 2 amps.
and
Quote:
The PN junction drop of Q5 forms the
reference voltage for the system.
Which is about 4 to 5V.

So is it correct to deduce that the 15.3V across C9 that Peter measured (see above link for his post) are constantly the same, since the voltage drop of Q5 stays the same?

If yes, any >20V cap is sufficient for the 3x 220uF that are needed.

I hope somebody can confirm this!

Thanks a lot! Have fun, Hannes
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Old 31st January 2007, 02:45 PM   #9
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The main role of C9 is bootstrapping (follow-the-leader action).
Therefore, if the measured V across C9 is 15.3V, the C9 will see the maximum voltage of 15.3V during its life time if the amp works without any trouble. But, if there is any trouble with "open" or "short" circuits around C9, there could be a possibility for C9 to see the supply voltage of 25V.

To take a good sleep with no worry, if I were you would use 35V-rated cap.
Or to forget all, would use 50V-rated cap.
Or to keep smiling even during sleep, would use 100V-rated cap.
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Old 31st January 2007, 04:25 PM   #10
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Quote:
Originally posted by Babowana

To take a good sleep with no worry, if I were you would use 35V-rated cap.
Or to forget all, would use 50V-rated cap.
Or to keep smiling even during sleep, would use 100V-rated cap.

Good advise and safe thinking...
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