Aleph 5 inrush current protection

[vossie]

Hi,

I'm in the process of building an Aleph 5 and the BOSOZ preamp both at the same time (got a serious bite from the diy bug). I have a dear friend who recently build the Aleph30 but had problems with the startup inrush current to get the psu caps charged. He blew a few fuses until eventually putting in another thermistor in the primary winding circuit on the toriod.

I am using a 625VA 28-0-28 toriod (with 120000uF caps) for the Aleph 5 and two 50VA 30-0-30 toriods for the revised BOSOZ. My question is this: What is the best way to handle the startup current. (you will have to give me a circuit or explain slowly please)

Thanks in advance,
SV

[Peter Daniel]

The best way is thermistor. if one is not enough, put 2 in series. I'm using 2 x CL-70 on my Aleph X and they work fine. The reason I used two, was that I had some bridge failures before and I wanted to be sure that this time my discreet soft recovery diodes won't blow.

I tried fixed resistors, but because of the nature of the amp (constant high current draw), the higher the resistor's value the higher voltage drop on a resistor which prevents the full charge on PS caps. Thermistors, OTOH, behave more dynamic and seem to be a perfect solution for the inrush problem (and the easiest as well).

Some people use a relay to short thermistor later, I don't think it's necessary though.

[Philo]

I had heard that just adding a thyristor based soft start in the circuit adds noise both up and down the power path and using a relay circuit in conjunction with the thermistor will help prevent the noise. I am building a Borberly DC100 and putting the power supply together right now so this would be nice to know.

[Philo]

Sorry, ...is nice to know.

[blank527]

I'm thinking building one of these..

http://mitglied.lycos.de/Promitheus/...or_toroids.htm[/URL]

Any comments?

[Philo]

pretty slick, that one is much more of the KISS line of thought than the one described in Randy Slone's sourcebook. That one has twice the amount of parts and much larger. What is the duration of time delay with C2 and C3 at 470uF?

[blank527]

I don't know..
Check it out..
I'm still in processing state..
But the bigger the longer you have to wait..

[jwb]

The problem with thermistors is they don't work if they are already hot. If the thermistor is cold is supresses the inrush. But if the thermistor is hot, and you turn the amp off, and the power filter drains, and you restore power, the thermistor does nothing. I am partial to the solution of a relay which shorts out a resistor bank.

You may say that you should just avoid turning the amp on and off, but sometimes the power company doesn't give you the choice.

[Philo]

Oops, upon further review, the circuits are very similar. Slone's merely adds several other circuits for speaker protection and an aux power circuit for a balun circuit.

[Philo]

Oops, upon further review, the circuits are very similar. Slone's merely adds several other circuits for speaker protection and an aux power circuit for a balun circuit.