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-   -   Crown Studio Reference I: beefing up the power supply (http://www.diyaudio.com/forums/power-supplies/156198-crown-studio-reference-i-beefing-up-power-supply.html)

elac310 5th December 2009 08:36 AM

Crown Studio Reference I: beefing up the power supply
 
I've finally found an SR I to buy from the uS and I'm almost done with the conversion to 230V.

Since I had to put my hands in the amp, I was considering beefing up the power supply. The toroid transformer is among the biggest I've seen so far in a commercial amp so there's no worries on that side. I do not intend to replace the bridge rectifiers with fast diodes either.

Also because of the natural ageing process and to be on the safe side for the next few years, I see a good opportunity to replace the two 6800uF caps. Because of the limited space left, I could use a bank of smaller computer grade capacitors of 12x2200uF on each channel.

The current 6800uF caps are rated about 8-10A according to manufacturer datasheet and this is easily handled by any bridge rectifier of the uper range such as those currently installed in. But a bank of the caps I intend to mount would draw theoretically about 36A and the toroid can easily release a large amperage at firing up even though it would not reach that amount of current;

My questions, especially to those who are possibly familiar with this amp: 1) Would the bridge rectifiers (because of the way they are mounted I can't read their current rating or identify the part used but they're the size of classical 20-30A) and the PCB they are mounted on handle the extra surge current ? 2) anything else (especially possible surge limiters) I need to upgrade as well, besides perhaps the wiring between the PCB where the bridge rectifiers are mounted and the caps?

Thanks for any tips and advice.

Chris.

microsim444 28th December 2009 04:47 PM

Why you need to do that man?

elac310 29th December 2009 11:47 PM

Quote:

Originally Posted by microsim444 (Post 2026880)
Why you need to do that man?

Because I found the original value a bit "short" 1) to handle the current needed by this amp; 2) to provide the energy required by fast musical impulses on medium and high frequencies.

As regards 1), contrary to my initial thoughts, I have ordered capacitors with "only" twice the current capacitance (and lower ESR) and that are not too large so that they can fit in lieu of the current ones (if someone is interested, I'll report back on this as soon as it's done); It could be that the reasonable value of the existing caps is one of the reasons for the extra-ordinary bass slam of this amp; I will thus not alter this element of the amp's personality and will avoid modifying anything else.[EDIT: the bass slam concerns the upper bass rather than the first one or two octaves]

On 2), in the meantime, I have now added 20uF MKP caps in parallel to the existing electrolytics: the amp has definitely a smoother sound on voices and certain accoutic instruments (used for instance on classical/ancient music). Until now, I usually had better experience with larger decoupling high voltage caps of up to 100uF than the 0,1uF or less that is sometimes recommended for the decoupling of power supplies in amplifiers (small values are probably OK for lower consumption circuits, e.g. preamps, digital circuits etc.).

Chris.

OMF 18th April 2010 05:54 PM

Hi!

Currenlty I have 2 Studio Reference I in my set up. I would be very interested in you opinion of this "mod/upgrade"!

Thanks!

Best regards
OMF

Th3 uN1Qu3 28th April 2010 12:50 AM

There is a general rule on filter caps - any higher than 10000uF and the law of diminishing returns starts to apply.

10000uF caps would be a good idea. More, i don't think so. Anyway the only thing that larger caps will do in a class AB design is better transient reproduction, as the supply voltage sags less under momentary high load peaks. They will not magically bring more power or anything like that, but since this is supposed to be a "studio" amp they probably don't need to either.


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