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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: RE: Safe Change In Main Caps In Power Amp posted by Cougar on February 7, 2013 at 14:31:21:
It sounds like it may need a higher ohm value.
Do you know what it has now?
the Hafler DH500 had no inrush limiter originally, it ate power switches for breakfast (lunch and dinner too). They then added 0.5Ω, and still had problems. I changed the speaker relay to a three-pole type and used the third set of contacts to short out a 2.5Ω inrush limiter, that solved the problem.
I use the same 2.5Ω inrush limiter on the DH200/220 with no relay, they're OK even without the relay bypass.
A McIntosh MC2300 uses 1Ω, the MC2125 uses 2Ω, neither use a relay.
The 2.5Ω (cold) at the link below is only 0.03Ω (hot) at 15A, you could use that without a relay.
How much capacitance do we really need?
The values for power supply capacitance can be realistically determined by a consideration of the numerical value of W C R where W is the line frequency (377 rad/sec), C is the power supply capacitance, and R is the load resistance. An WCR value of 10 yields about 10 per cent ripple (pk.-pk. ) and a value of 100 has about two percent. Below 10, the power supply will have serious problems and values of about 100 will achieve diminishing performance returns. The minimum value then, for each of the four power supply capacitors should be about 3,000uF and the maximum about 30,00OuF. Capacitances above this value may cause diode bridge failure due to turn-on surges and are not recommended.
(http://www.passdiy.com/pdf/a40.pdf)
3,300µF x2 for one channel at 8Ω with 60hz line (3,900µF for 50hz), double for 4Ω, double again for 2Ω.
Example: Crest CA9 has a tiered supply and 120,000µF total capacitance. This is 15,000µF per channel, per tier, the 10% ripple point (for a 2Ω load with 50hz).
Remember, stored energy increases with the square of the voltage, so a 3,300µF cap with 100V on it stores 4x the energy that a 3,300µF cap with 50V on it stores.
radian per second = W
f*2Pi=W
377 (60hz)
314(50hz)
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Follow Ups
- RE: Safe Change In Main Caps In Power Amp - djk 00:05:11 02/08/13 (0)
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