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Old 2nd March 2002, 04:10 AM   #1
PedroPO is offline PedroPO  Portugal
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Default 600.000uF SOZ

Hi guys!

My SOZ (under construction, but already playing) have 4 capacitors 150.000uF each (2 per channel). I I plug the SOZ directly to the mains, the 16A fuse blows....

So, I connected the amp to a extension chord of My PC (it has some kind of protection, varistors and suppresion capacitor) and works fine!

If someone is getting any trouble on the switching on try one of these things.

I guess their not audiofile approved, however I have seen a review of one of these babies on HIFI-CHOICE

Pedro
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Old 2nd March 2002, 10:56 AM   #2
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Default Big cap turnon

What is most likely happening is that the additional resistence of the cord is limiting the peak turn on current. You need to put a soft start circuit with about a 10 ohm resistor in series with the AC feed to the transformer. This resistor can then be bypassed with a relay when the filter caps have charged completely. Your bridge rectifiers will probably not last long if you don't use a soft start circuit.

H.H.
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Old 2nd March 2002, 11:53 AM   #3
PedroPO is offline PedroPO  Portugal
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HarryHaller

Can you be more specific in the soft start circuit? I'm not familiar with that kind of devices. Nelson Pass talks about thermistors in the SOZ project also, but I don't know how to use them...

My power chord as several components that I can't identify, but I can see 3 Varistors, one of them is in paralell with the mains.

Coul´dn't be it that limits the inrush? the resistance of the chord with the device mentioned is only 0.3 ohm.

Pedro
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Old 2nd March 2002, 12:56 PM   #4
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a varistor serves to minimize voltage spikes that get thru to your equipment but still allow extremely high currents in the order of hundreds or thousands of amps to be drawn from the mains .... if you place a high power high current thermistor in series with the mains, it will minimize the current that is drawn @ turn on while causing minimal voltage drop during normal operation.
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Old 2nd March 2002, 03:06 PM   #5
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You have too much inrush current due to large capacitance and big transformers. You need a delay circuit or some thermistors like in the aleph amps, to limit the current on turn on. Probably the computer power cord or multipower cord supresses this current.
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Old 2nd March 2002, 05:04 PM   #6
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Old 2nd March 2002, 05:31 PM   #7
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I would be carefull with using thermistors with big capacitance. In my A75 monoblocks (I have 6 of them) I used 100,000uF per channel with 2 bridges 35A ea. channel. I used thermistor as per original design and still have bridge failure from time to time (usually once a year). Using thermistors is convenient but I think that a power resistor (10 to 20 ohm) with a relay would be more reliable.
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Old 2nd March 2002, 08:53 PM   #8
PedroPO is offline PedroPO  Portugal
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Paulb

Thanks for the project, but since that I am a ZEN kind of guy I'll try the aleph aproach (thermistors).

Pedro
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Old 2nd March 2002, 08:59 PM   #9
PedroPO is offline PedroPO  Portugal
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promitheus

Do you really think that the chord resistance is enough to take the inrush? shouldn't it melt or at least become warm?

I believe that in the chord switch must be something like a suppresion capacitor or even thermistor, but I cant figure it out by the shape and the markings...

This remind me that my Audionote Kit one Has also a 0.1u
F Suppresion cap in paralell with the mains before the power transformer, but at 450V the capacitance is a little bit less that 600000uF....


Pedro
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Old 2nd March 2002, 09:40 PM   #10
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Default Be Careful of the Current Limiting Resistor Wattage

If you opt to go with the series resistor switched in and out of the AC input, be sure to consider the wattage of the resistor.

If you use a 10ohm resistor on a 120VAC input (240VAC in Europe), the initial inrush current through the resistor will be 12Amps (24Amps in Europe) and will decrease as the supply caps build voltage. A typical amp with a 40VDC supply and 100kuf of supply capacitance will draw nearly the full 12 amps for the first few seconds. Your amp, with 600kuf of capacitance will draw high current for a much longer period of time.

So what

This means that 120VAC @ 12Amps requires a 10ohm resistor capable of absorbing 1.44kW (Nearly 3kW in Europe)! This current is passing through the transformer and the bridge to get to the capacitors. What's even worse is the current coming out of the transformer is multiplied by the secondary-to-primary ratio, so you could be looking at 36Amps of inrush current through the bridge.

This is a lot of power. This is one reason I leave my equipment on 24/7 (I also don't like waiting for everything to warms up).

I use a central power box (I built myself) with 2 - 100ohm @ 200W resistors for current limit of 2.4Amps for 15 second. Then I switch in the straight-through by-pass with 3 poles of a 4 pole relay with each contact rated for 30Amps.

Something to think about.

Good luck
Rodd Yamashita
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