voltage ok?

[troublecomes]

Hello.

ive just measured the voltage on my transformers that i plan to use for my brianGT 3886.

They are supposed to be 22V but when i measured them they are actually

23.5-23.6V
and
23.3-23.4

are these going to be ok for a speaker with a nominal load of 6.1 ohms? Even for peak lower ohmage? What about the slight difference between them, will this be a problem/noticable?

At least they work, i stupidly thought they were broken when i put the secondries (with no resistance) into the mains and the circuit breaker tripped. I thought about it after i measured the resistance (dunno why i didnt do this first) then felt really stupid. Especially since i posted in the parts section about it. Learning...


Thank you.

[peranders]

Up to +- 42 volts is OK, technically speaking and around 22-25 V is perfect. Remember also that the voltage will drop when you play loud.

I recommend that to take a look at these docs:

http://www.national.com/appinfo/audi...gn_Guide13.xls
http://www.national.com/appinfo/audi...sign_Guide.pdf
http://www.national.com/an/AN/AN-1192.pdf
http://cache.national.com/ds/LM/LM3886.pdf

[boholm]

Usually you can measure a little more voltage on a unloaded transformer, so your measurements fits.

Adding a resistor should lower the voltage to - well, close to - 22V.

I take it, you were measuring without anything connected and you measured AC?

[peranders]

Originally posted by troublecomes
At least they work, i stupidly thought they were broken when i put the secondries (with no resistance) into the mains and the circuit breaker tripped.

If you have a toroid transformer of more than 300 VA or so you'll get pretty large inrush currents. A inrush current limiter may be a solution.

Notice that you'll get this huge current even with a transformer alone, nothing connected at all at the secondary side!

[peranders]

Originally posted by boholm
Adding a resistor should lower the voltage to - well, close to - 22V.

Not a good idea, quite meaningless.

[lineup]

Originally posted by boholm
Usually you can measure a little more voltage on a unloaded transformer, so your measurements fits.

Adding a resistor should lower the voltage to - well, close to - 22V.

I take it, you were measuring without anything connected and you measured AC?

One LM3886 has supply current like +-40 mA at +-25 VDC.

To simulate this and see what final voltage will
you can load the power supply with 2 resistors.
I am talking here after rectifier bridge and capacitors.

To get around 40-50 mA you should use two resistors
2 Watt rated, 680(for 40 mA) or 470 Ohm( for 50 mA)

One between V+ and 0V and the other between V- and 0V.

This will simulate one LM3886, and you see what DC voltage supply will be
when LM3886 is idle.
When you put out power it will sink, as mentioned.

If you will use same supply for both, two LM3886
then you should add two more resistors in parallell with the first two.

[boholm]

Originally posted by peranders

If you have a toroid transformer of more than 300 VA or so you'll get pretty large inrush currents. A inrush current limiter may be a solution.

Notice that you'll get this huge current even with a transformer alone, nothing connected at all at the secondary side!

Originally posted by peranders

Not a good idea, quite meaningless.

Quite a good idea for testing the transformer alone.

[troublecomes]

thanks for the replies

yes measuring AC voltage with no load.

If you have a toroid transformer of more than 300 VA or so you'll get pretty large inrush currents. A inrush current limiter may be a solution.

Yeah, actually the large inrush of current was me applying 240 V directly to the secondries instead of the primaries. So it was effectively just shoving a loop of wire into the mains. Thats why the breaker tripped. I guess i was just a little exited and didnt think about it first. I learned something though.

I havent recieved the kit yet, so ill have to wait to set up that resistance circuit to measure voltage at simulated load.

Thanks again
-matt