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Old 15th June 2012, 05:30 AM   #1
ccheung is offline ccheung  United States
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Default Home made Cyrus PSX

Hi, I'm planing to build a home made PSX for my cyrus 767 LFAU amp (similar to Cyrus II). I know that the perfect transformer is 28-0-28v that could produce DC 40-0-40v. However, 28-0-28v transformer is a bit hard to find. I find 30-0-30v transformer in parts express. Will it overload the transistors, or do I need to tune up the amp for that? Will an underpower 25-0-25v transformer be safer for my case?

Besides, what VA of the transformer do you suggest? and what capacitor size will you put in?

Thank you.
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Old 15th June 2012, 12:07 PM   #2
AndrewT is offline AndrewT  Scotland
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Is this a clone of the early type of PSX that has fixed output voltages?
or the newer type that senses the equipment and adjusts the output voltage to suit the equipment being supplied?

Use a fairly high VA transformer, that is the philosophy that Cyrus have adopted. I think they use 300VA, but 500VA would do no harm.
Using a 25+25Vac or 30+30Vac transformer makes little difference since both can easily be modified to give 28+28Vac by adding or removing a few turns to/from the existing windings.

Capacitance is not critical. Cyrus use relatively expensive caps designed specifically for good audio performance. You would do well to source the same caps. Again uF can be varied, I would go for at least +-10mF/ch amounting to 40mF in the PSX. But since I would be custom building I would probably increase that to +-20mF/ch
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Last edited by AndrewT; 15th June 2012 at 12:11 PM.
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Old 15th June 2012, 03:22 PM   #3
ccheung is offline ccheung  United States
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The old version fix +-40v voltage output will be made. I'm beginner and don't know how to change premade transformer voltage. Would like to know whether using 30-0-30v transfomer may hurt the amp?
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