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Old 13th January 2009, 08:30 AM   #1
Buhl is offline Buhl  Denmark
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Default Aleph PSU design thoughts

After finally pulling my self together and finishing my long running A30 project, I am having some thoughts on how to do the PSU the best possible way. Having build the amp it self based on Peter Daniels wonderfull boards (which does not leave much up to thought - thank god ) - this part troubles me more...

Inicially I had thought to use four 20-0 trafos - 150 VA each - so each A30 channel has 20-0-20 trafo of 300VA total - followed by 10 pcs. 22.000uF Nichicon caps - with a 0R1 resistor after the first cap forming a CRC filter - meaning completely dual mono setup.

But- dual mono has troubled me before - giving noise in amps, where I have always ended up using a single transformer for all channels. So - should I use a 2x17Volt, 750 VA Transformer for both channels, but still keep the capacitor bank "dual mono" - 220.000 for each channel - the alephs dynamic current source means that the power draw wil be dynamic so I'm thinking that seperate capacitor banks are best?

Or should I go with a single bank for both channels for lowest possible ripple?

I suspect that using a 17 volt or 20 volt unretrified supply wont mean any difference to the circuit?

Kind regards
Hans
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Old 13th January 2009, 08:38 AM   #2
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I had very good results with 22+22V trafo,dual bridge rectifier, 20000uF "common" cap and then a R-C per channel (R = small value, depending on the voltage level you want, I used 0.47 Ohm, C=30000uF).

And star ground (actually a piece of copper board) , with every gnd (input and speaker return included) going to the star point.

Ciao

Andrea
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Old 13th January 2009, 01:23 PM   #3
Buhl is offline Buhl  Denmark
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Ok - so you went for the sigle Transformator - single pair of bridges - and dual supply banks - I will maybe go that way....

So you actually did not connect your RCA's etc to the amp board - but all of them direct to a star? Maybe I should try that also - I just think it gives a bit "messy wirering" But who cares, as long as the amp is silent

Kind regards
Hans
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Old 13th January 2009, 03:09 PM   #4
h_a is offline h_a  Europe
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I give you a few ideas:

Don't put the power resistor after the first cap; the caps in front of the R are always the most stressed ones as they have to load the caps after the R.

Honestly, with 220000uF I wouldn't bother with a power resistor at all. It just increases power supply impedance and ripple is already tiny. It's "just" an A30 after all, that came with 120000uF stock. Further due to the current source power supply ripple rejection should also be rather high.

Regarding 17V vs. 20V AC: it will probably will have little effect on sound, but more on power dissipation.

Hum is in 99% of all cases a grounding problem. Think of a proper grounding scheme, ideally with signal and power ground separated.

Have fun, Hannes
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