Amplifier testing

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?

:cool:
 
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,

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
 
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...
 
Eccu said:
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
 
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
 
Eccu,

use one fuse for the primary winding, yes it will protect the secondar too (sorry for that).

after the secondary you have the rectifier and the caps, I would suggest to place after the caps two fuses, one for each supply rail (+ and -). That's what I mean. If something goes wrong in the circuit there will no longer flow a current into it, because the caps will be isolated by the fuses. So components can't get fire anymore because of a short circuited device in the circuit, so the caps are also protected against these high currents.

HB.
 
wuffwaff said:

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

If so.... how I calculate this....
For Crescendo ME amp I have 2x38 VAC transformer -> about (+-)53VDC (total 106V ?).
And if I want about 80W in stereo, should I calculate that primary fuse like this:
160W / 106V = 1,5A

I have that soft start circuit. And I have only one transformer.
 
HI Eccu,

I think it`s easier just to test how big the fuse should be by measuring the amps at the primary side while delivering 160watts into some test load.

The correct calculation would be [email protected] = 0,7A but this must be corrected with the (in)efficiency of the amp so 1.5A wouldn't be that wrong after all.
Problem with a setup with one transformer is that one channel could be delivering 160watts and the other one 0 before the fuse blows but normally when something goes wrong it will deliver a lot more then 160watts:eek:

william