nap 250 power supply info
Posted by: Simo on 31 July 2003
This question is for nap 250 first serie:
i see an inside photo of this amp were there are 2 new main capacitor (BHC 15000 uf) smaller that i usualy see in a nap 250.
May be the new one are less bigger compared to the old, but this value is the right one?
If yes, why a nap 140 have 4x10000 uf and a 250 "only" 2x 15000 uf?
Sorry for my english....
thanks
Simone
Posted on: 31 July 2003 by Manu
Replacement capacitors 15,000uF, 63v are the same size as the old ones.
As for 140 vs 250, one explaination can be: in a regulated PSU, capacitors can be smaller as ripple is removed by the regulation.
Emmanuel
All opinions are my own, and reflect those of the organisation i work for, even if not stipulated.
Posted on: 01 August 2003 by John Luckins
Big isn't always better!
The capacitor has its own resonant frequency. Above this frequency it no longer filters the incoming supply or supplies current at a low impedance for the Power Amp Acting. It is rather like a tuning fork being regularly tapped, the capacitor is being hit with a pulse of current 100 times a second. If it resonates anywhere near the audio range then the circuits downstream are in trouble.
The larger the capacitance the lower this resonant frequency. I've measured as low as 8kHz on some so called supply capacitors.
Also the regulator circuit in the 250 is as good a quality as the amp itself, even using the same custom power transistors. This regulator takes care of the large low frequency filtering demands of the amp that normally require large filter capacitors. It is in effect a DC power Amp replacing and buffering the filter capacitor.
John
