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hello,
I have an amp that has a 1.5KVA transformer with a single Bridge rectifier. It has 2 caps the original cap values were 33,000uf/100V each cap. I have been having a hard time finding good quality caps in this valuse that will fit in the original spacing. I orginally was going to buy 5 (2 aside) 15,000uf/100V until I found out about the Mundorf HC caps at parts connexion. They only had 22,000uf and 47,000. I bought the 22,000uf/100V caps (2 only). The original caps drew too much inrush current and I kept having to replace the power switch which was a 16A/250V. This amp puts out 170w@ 8ohm and close to 400W@ 4ohms. Class AB quasi-complimentary NPN output.
My question here is would it be ok to use these these new Mundorf HC 22,000uf/100V caps and be safe or would I need to go higher with the 47,000uf/100V caps? using 4 22,000uf/100V caps is out too cause there is no room in the chassisfor the to fit. From what I have read the 22,000uf/100V should be ok but all those transformers were smaller in VA too. I just want to make sure and mess the amp up. the reason why Im replacing the caps is that I found one of the original caps cracked on top. Before that it blew the main fuse. It was working fine except for a bigpop/thump at turn off. Checked all the other circuits seems ok. I will use the Lamp technique when I do power up the amp slowly with a variac. Any ino would greatly be appreciated.
Follow Ups:
As far as I know, you could use 2 different values in parallel to ADD to the correct, as-issued, value. I wouldn't exceed that if possible due to inrush issues....which you are apparentlly already having!
Make sure voltage ratings for any different caps are AT LEAST the 100v of current caps and you may consider finding 105c rated........they'll take the heat better in a crowded chasis....
Too much is never enough
An inrush limiter is what you need.
Hi djk,
Thank you for the reply and info. I forgot to mention this Edge M8 (original Black version) has an in-rush limiter inline between the AC plug inlet and switch. Maybe I will have to put one that limits the in-rush more? everytime I would flip the switch sparks would come out the front of the switch. Changed it to a new switch (same exact value) same thing happen again 8 months later.
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)
___
So you are going from 33,000uF to 22,000uF?
Under "normal" listening levels you probably will not notice the difference.
But if you like to crank it you might notice a reduced transient response and the amp might clip sooner. Because the large filter caps, also act like an energy reserve for transients. A smaller reserve will be drained faster causing dips in your B+ thereby causing poorer transient response more frequent clipping at high volume levels.
Of course if you go to the 47,000uF you will increase this reserve and you might notice better transient response. But at the cost of higher inrush currents that will shorten the life of the power switch and ultimately the transformer it's self.
Hi Tweekeng,
Thank you for the reply and info. when the 33,000uf caps when working fine the amp on turn woukd dim the lights in the house and I could hear the tranny straining for the first few seconds, that's why I said it seems like the that power supply was near its limit/s with just the 33,000uf caps. This amp had lots of headroom and a very wide soundstage and could drive speaker that were difficult for other amps to drive. This amp had no problem driving the Carver amazing Silvers I have have. never once did it breakup.
I seen on the Partsconnexion website that these Mundorf HC caps can put out very high amounts of current but I was wonering if I could use these caps in my amp without hurting it. My goal was and still is to get the exact same cap value and voltage.
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