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Old 12th July 2006, 08:49 AM   #11
Did it Himself
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I have already told you the answer, as has Andrew in post 7. The C5 across the whole transformer does need to be rated higher... because it's across the whole thing.

I'm not sure what your confusion is now, please can you explain?
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Old 12th July 2006, 09:13 AM   #12
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head_spqaz says i need 80v caps!!but i have +-35v and the caps are connected between voltage and ground, but he says that they see the whole differential voltage, so 70v, is it true?i think maybe during transient could be true...
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Old 12th July 2006, 09:15 AM   #13
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ups...i'm an idiot!
c5!!ok,that's right!!sorry guys!!!i thought the other big filter caps!!!
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Old 12th July 2006, 11:22 AM   #14
folkeb is offline folkeb  Norway
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Sorry to barge in on the discussion, but I have a similar issue that has to be delt with! I have several (16) Mallory (org) 66000uF caps rated at 60v with a surge capability of 75v. I intend on using these in my Aleph 1.2 project. However, this amp should have approx. 60v on the rails. I am thinking of bringing the voltage down to just under 60v by the use of resitors. Is this safe, an how big a margin should I use? I would prefer to get as close as possible to 60v. What does surge actually mean? Peak value? For how long etc.

Thanks for any help!

Best regards,
folke
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Old 12th July 2006, 11:36 AM   #15
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No you can't use resistors. They will be hot, waste power and make regulation even worse.

Aren't Aleph's class-a? With 60-0-60 volts and class-a that will be some monster heat machine. Are you sure on the rail voltage there?
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Old 12th July 2006, 11:41 AM   #16
folkeb is offline folkeb  Norway
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The aleph 1.2 are 200w class A amplifiers and they are monsters with a rail voltage of 60. The resistors are ment to be after the rectifier bridge and before the caps. Why can't I use resistors?

Tnx
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Old 12th July 2006, 11:51 AM   #17
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I don't think regulation is much of a problem since it is a class A amp, but the resistors will be hot. Make sure they can handle the power required, with margin, and mount them so they get sufficient cooling.
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Old 12th July 2006, 12:47 PM   #18
AndrewT is offline AndrewT  Scotland
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Hi,
not sure I can help, but try to help me.
Is the A1.2 a single ended ClassA amplifier?
Is the standard PSU a rectifier followed by smoothing caps? i.e. an RC PSU.

or

Is it an RCRC supply with some resistance built in to reduce ripple being fed to the amplifier?

BTW. in both the above cases that first R might just be the resistance of the transformer secondary + cable.
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Old 12th July 2006, 01:39 PM   #19
folkeb is offline folkeb  Norway
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The following link show the principle of the PSU supply. My main question is whether or not it will be safe using capasitors close to their nominal rated limit, when their surge limit is somewhat higher. In my case - 60v VDC nom. tolerance and 75VDC surge. I was hoping to bring the voltage down to 58-59 volts with the use of power resistors. Hope the link will enable you to see what I 'm getting at. The resistors will be connected in series with the + and - out of the rectifier before the caps.

http://www.kk-pcb.com/power-12.html

The Aleph is Class A single ended.
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Old 12th July 2006, 02:10 PM   #20
AndrewT is offline AndrewT  Scotland
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Hi,
you have an RCLC supply with a very small R.

The problem is slightly worse than you described.

Have you measured the secondary voltage of the transformer when the mains input is exactly at the nominal specified voltage?

You need to correct for any variation here first.
Now add on the +6% mains voltage variation that is permitted in the UK.

You could end up with a considerable overvoltage when doing it this way.

BTW the Vsurge rating would take account of the +6% on the mains and other glitches that get fed into your house wiring.

Some spike attenuation can be added to the primary side of the amp or directly to the room wiring or even back at the distribution board. If your sound quality assessor approves of such things.

Part 2 to follow ( I just lost it when trying to preview)
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