100v or 63v capasitors for the Aleph??? - diyAudio
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Old 1st February 2006, 09:06 AM   #1
folkeb is offline folkeb  Norway
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Default 100v or 63v capasitors for the Aleph???

I am in the process of buying parts for my Aleph 1.2 project. Apart from the apparent heatsink issues (this is not a new thread on this issue), there is the issue of capasitors. As I'm quite new to the DIY arena, I have some questions regarding capasitors:

Is 63v sufficient for the Aleph 1.2, or is it better (as in safer) to have 100v. Isn't 63v pushing the limits a bit? As in; will the 63v do for my Aleph 1.2 or not? I have seen several projects with 63v. The cost of quality caps with 100v is much higher than 63v.

If I'm not mistaken the original has 4x25000uF 75V capasitors. Why then has almost every Aleph 1.2 (and even 2) have over twice this amount? What is the "just right" value to go for?
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Old 1st February 2006, 09:14 AM   #2
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As a rule of thumb I go for the first higher value available.
35V rails gives 40V capacitors, 50V rails would be 63V capacitors and so on.

/Hugo
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Old 1st February 2006, 09:31 AM   #3
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Default Re: 100v or 63v capasitors for the Aleph???

Quote:
Originally posted by folkeb
What is the "just right" value to go for?
As much as you can afford.
Dropping ripple is the most important on the Aleph powersupplies.
Volume and cost of capacitors is a prominent issue with commercial amplifiers, for DIY it generally is not.
If you are investing so much in all other parts of a 1.2 it's better not to be to economical on the capacitors.
Even 200kuF per channel for an Aleph 1.2 is squeemish in my book.

The voltage rating depends on which transformer voltage you pick. If you use a 50Vac toroid i'd go for at least 75V for the capacitors.
Using 100 volt capacitors is blowing cash for nothing. Sensible practice is to use a CRC or CLC powersupply. The high bias of the 1.2 will make the nominal rated voltage of the transformer drop.
A CLC or CRC configuration will drop the voltage even further for the second capacitor bank. You will not even get near 100 volts, and 100V capacitors are relatively very expensive.
Up to 80volts capacitors there is a reasonable linearity between price and the product of capacity times voltage rating.
Above 80 volts they become more expensive, spend that money on more capacitance.
If the rail voltage never reaches 100V, 100 volt capacitors will behave like lower rated capacitors after some time, only advantage remaining is the voltage safety but the current rating wil be the same.
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Old 1st February 2006, 10:03 AM   #4
folkeb is offline folkeb  Norway
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The problem I face is that the caps I'm after, either the Evox-Rifa or the Fischer and Tauche, are only supplied for 63v or 100v.
I think 63v is running a bit close, and 100v is overkill! Are there any other recommended capasitors that have 75v and that can compare both with regard to price and performance?
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Old 1st February 2006, 10:12 AM   #5
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A number of people here share the view that you can't get better than Rifa.
An option would be to use lower transformer voltage, you may get away with 45Vac on 63 Volts Rifa169.

If you desire to stick to higher transformer voltage, order a load of NOS capacitors from a surplus store in the US. As economical as you can get and you end up with the same capacitor brand as the original ones use.
In these amplifiers a big can is worth more than a fancy weeny one.
(they stick a US engine in a Volvo, not the other way around)
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Old 1st February 2006, 10:19 AM   #6
folkeb is offline folkeb  Norway
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So if I go for 45V instead of 50V then it may be possible to use the 63v capasitors? I was thinking of the PEH200 as this is easily available, and cheaper. How does this compare with the PEH169?

What is the consequence of 45v versus 50v, and what risk is there with regard to the capasitors?
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Old 1st February 2006, 10:28 AM   #7
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imho, the Rifa PEH169 has been the top notch capacitor.
And the most expensive of the 2, to obtain them i had to pay silly prices overhere 15 years ago.
But the PEH169 is being dumped, i got me 20 NOS 33KuF/63V for a lot less than the MSRP.

If you use inrush protection and CRC/CLC, no risk.
Under constant load the regulation factor of the transformer is of no consequence.
The bias load will drop the nominal secondary transformer voltage well below sqrt2*45.
A CRC/CLC drops the voltage even more for the second capacitor bank.
Both effects are large enough so compensate for voltage surge.
With a 45Vac transformer the voltage after the rectifier is likely not to go above 55Vdc.

The effect of lower rail voltage for the amplifier is lower max output power, but you have the advantage of being able to increase the bias with the same setup.
Personally, i believe high bias on these amplifiers is far more important than having it do 150 or 200 watts.
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Old 1st February 2006, 10:39 AM   #8
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Hi, Folkeb

I recommend you to read this, (c) Excessive Voltage.

I think if the max. rail voltage is 60V, the 63V rated caps are useful.

Regards
jh
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Old 1st February 2006, 11:24 AM   #9
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Another thought is to check the ripple current rating of the caps, particularly the capacitors immediately following the rectifier.

Higher voltage tends to offer higher ripple current rating as a rule.
Size is a good indicator of ripple current rating.

They should be rated 3 x the ripple current (if parrelleled with will double the total rating).

The Aleph ones were rated at 15 amps as I recall, they were large bottles.

Mr Pass did not skimp on his power supplies. I recall seeing the capacitors and transformers at the factory..greater care is taken with the power supply and the newer models feature a clever improvement to reduce noise (a secret) .

macka
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Old 1st February 2006, 08:43 PM   #10
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Quote:
Originally posted by macka
the newer models feature a clever improvement to reduce noise
I love the model on the right, Macka.
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