Amplifier testing

[Eccu]

Soon I will finish my Crescendo amplifier, so how I must test amplifier without that I burn some components on amplifier or on speakers?

Now I have one fuse in primary side, but do I have to add some fuses in secondary side? And

is there some disadvantages if I add those fuses in secondary side?

I have read something about testing with lamp (bulb) or resistor in series with primary? What are advantages it when testing amplifier?

[Samuel Jayaraj]

Which Crescendo are you referring to -Crescendo 140watt/8ohm, Mini Crescendo 70watt/8ohm or the Millenium Crescendo 90watt/ 8ohm?

[hugobross]

you have to place fuses in secondary windings too, otherwise your transformator can burn (!!!!) out when your transistor are damaged. I don't know the schematic of the crescendo, but for testing I would recommend to use first the lowest voltage at which the amp still works (easy if you have a variac) and use a big fixed resistor instead of a speaker. Then you can test the amp on DC-voltages, bias/quiescent current etc...

HB.

[Eccu]

Originally posted by Samuel Jayaraj
Which Crescendo are you referring to -Crescendo 140watt/8ohm, Mini Crescendo 70watt/8ohm or the Millenium Crescendo 90watt/ 8ohm?

Millenium Crescendo....

[fcel]

I think you do mean fuses on the sec side before the rectifier but if you meant rail fuses, here's something to read on that ... starting on post dated 7/28/02. My Aleph is freezing

[Peter Daniel]

Originally posted by hugobross
you have to place fuses in secondary windings too, otherwise your transformator can burn (!!!!)

HB.

It won't burn. Properly selected fuse in primary will protect it. One fuse for all.

[wuffwaff]

Eccu,

you could place small resistors in the plus and minus connections to the amp (10 Ohms/0.5watt), turn the bias to zero and fire it up. If everything is allright nothing will happen and you can adjust the bias current and wait......

If something is wrong you'll see one or two puffs of smoke and search for the fault.

This method was used on the original Crescendo and I wouldn´t know why you couldn't use it again.



william

[Eccu]

Which one I must believe, Hugobross or Peter Daniel?
Two fuses (before rectifiers ( I have two rectifiers in my psu)) to secondary side or not?

And if I use only one fuse in primary, how big this must be.... In my transformer is recommendation for 8A fuse in primary, but should I use that or little smaller?

Wuffwaff: Why you use 0,5W resistor? Will that resistor survive when current flows start?


Thanks anyway... I must read now that link... and I hope you diyers understand my language...

[jan.didden]

Originally posted by Eccu
Which one I must believe, Hugobross or Peter Daniel?
[snip]

What do YOU think? Try to reason, take into account current shapes (hint: sec current is huge to charge the caps, but only for a small portion of the wave. same as prim current, but that is lower by the transformer ratio). What do you want to protect?
If you don't do any thinking yourself (and fall flat on your face once in a while) you'll still be asking the same questions 20 years from now.

Jan Didden

[wuffwaff]

Hello Eccu,

the 0,5 or 0,25 resistor is only in place for testing!

You can accurately measure bais current with this in place. If everything is working and all your voltages are allright you have to remove them.

I only use a primary fuse in my crescendo, one 3,15A T per 500VA transformer.
I used to have fuses after the capacitors but I threw them out years ago.

If you've got a soft start circuit you can use a fuse wich is rated for the max power you want your amp to deliver.
(test amp with max. power into 4 (or2) ohms and measure the current on the primary side and choose the fuse)

william