Integrated dual mono lm4780

[SoIL4x4]

Originally Posted by AndrewT

Hi.

It looks to me that you measured an output voltage of 22Vac when the mains voltage was 125Vac.

Check that again.

Now correct the output voltage to predict what it would be if the rated voltage of 115Vac was fed into the transformer.

Output voltage = measured sec voltage * Rated primary voltage / measured primary voltage.

I am measuring 24.1Vac from the secondaries when the mains voltage is at 125V. The problem is my transformers are supposed to be 22V. The label on the transformers wiring diagram is marked 115V. My cheap easy math tells me that these would put out 22Vthe @ 115v. So right now I am getting a rise on the secondary side of roughly 1V for every 5.2V seen by the primaries. I am not concerned with this difference too much in relation to the chips capacities, the national data sheet rates these well beyond what I would be supplying them. Thanks again Andrew.

[AndrewT]

Your secondary voltage when fed with the rated 115Vac is
24.1 * 115 / 125 = 22.17Vac.

That is well within tolerance of any transformer winder.

That is the open circuit voltage.

If you know the transformer regulation you can also work out the rated full load voltage.

Let's assume the regulation for this transformer is 9%.

The full load rated voltage will be 22.17 / (1+0.09) = 20.3Vac.

You probably have a 20Vac transformer even though you measured 24.1Vac.

[pacificblue]

Typically the voltage at nominal current is given as nominal voltage. It seems however that Antek specifies the no-load voltage as nominal.
Is that normal in the US? Or is it only normal for Antek?

[SoIL4x4]

I think we have been chasing the question of transformer output around in a circle. I think antek rates their output voltage based on 115V mains that being said my mains being 125V are causing a higher output.

Anyways I was able to make some more progress on the amp today! I finally connected the transformers to the rectifier boards and with my light bulb tester fired them up. I am pleased to report that the bulb lit for a second and then went out. I am a chicken so I shut everything off and then turned it all back on. This time the bulb barely lit up for a second, I assume the caps were charged so I took some measurements.

Both pg+ v+ and pg- v- on both channels measured 31Vdc. Good.

When I flipped everything off and pulled the plug from the iec the leds stayed lit for a long time and even several hours later the caps are still charged. Before I connect the power supply board to the amp board I will definitely have to discharge the caps!

I am getting excited now!

[pacificblue]

Originally Posted by SoIL4x4

I think we have been chasing the question of transformer output around in a circle. I think antek rates their output voltage based on 115V mains that being said my mains being 125V are causing a higher output.

I am refering to something different than that. I understand that your amp is up and running, so you are not interested in the transformer anymore. Therefore I started a new thread.

[SoIL4x4]

Originally Posted by pacificblue

I am refering to something different than that. I understand that your amp is up and running, so you are not interested in the transformer anymore. Therefore I started a new thread.

Sorry I did not intend to sound like I had dismissed the topic, just to report progress. I had planned on using antek again for future projects so I do want to understand their specs, especially if I need to make some changes to my current project.

[SoIL4x4]

How can I calculate the actual load being placed on these transformers when connected to the amp? Or are they delivering the 6.8A 300va at all times?

[AndrewT]

The output of the transformer is connected via a rectifier to a capacitor input filter.
The current specifications no longer apply for this special loading operation.

It's I^2 * R that takes over and limits the power that can be drawn.

[pacificblue]

The actual load depends on the music signal and varies all the time.

The transformer (re)charges the smoothing capacitors. You cannot derive the charging currents as easily as e.g. the current that flows through a resistor directly connected to the secondaries. As long as the transformer rating is greater or equal to the average amplifier power draw and the smoothing caps are able to buffer the peak power draw, there is no need to worry.

[SoIL4x4]

Originally Posted by AndrewT

The output of the transformer is connected via a rectifier to a capacitor input filter.
The current specifications no longer apply for this special loading operation.

It's I^2 * R that takes over and limits the power that can be drawn.

Okay.its been a long time.
I= input value? To the second power? Multiplied by rectifier value?
Is I 300va? Or another value derived from multiple factors
How do I determine rectifier value(diode values and cap values?)

I know that the input signal will vary causing all these values to change but is there way for builders to establish a baseline, or minimum parameter to shoot for? Thanks all for the hand holding.