22 watt per chanel amp. Will this work?

[doug0147]

I am using one chanel bridged (11 + 11). With 12V. How did you get the 6 Watts? Not that I don't beleive you, I just don't understand.

[Ice-9]

If you are plugging your guitar into the input of the power amp (effect pedal or direct) you are only putting instrument level into power amp which expects a line level, ie there will need to be some preamp circuitry , in most amps this will be the gain treble mid and bass secions of the amp plus other buffers and preamp bits.

Check the link i gave you earlier for the marshall amp that uses these amp chips and you will see how the different circuit sections are built up to form the full amp.

[Tubebass]

Looking at the datasheet for the chip here: http://www.datasheetcatalog.com/datasheets_pdf/T/D/A/1/TDA1554.shtml
Each half of the bridged amp can swing within about a volt of the power rail and ground, or about 10 volts peak-to peak with 12 volt supply. So the bridged amp can swing 20v p-p between its output pins. To get RMS output voltage, divide by 2.82, equals 7.09 volts RMS. Square that, equals 50.3, divide by your 8 ohm speaker, equals 6.28 watts. It may be a little more than that, depending on just how close to the rails the chip can swing, and on what your actual supply voltage is. Note that the datasheet numbers are taken at 14.4 volts, and at 4 ohm speaker loads. Hope this helps!

[doug0147]

Tubebass-

That was an exelent explination, and it makes perfect sense, but since I've very uneducated about this stuff I need some explination of your explination. 

What do you mean power rail and ground can swing within a volt? How did you determine that?

What does peak to peak mean?

When you say bridged 20V P-P between the output pins, do you mean the actual pins that go to the speaker?

In the RMS voltage formula you described, where did you get the number 2.82?

Thank you for all your help!

[Tubebass]

What do you mean power rail and ground can swing within a volt? How did you determine that?

If the chip were "perfect", it would be able to swing its output all the way from ground to the 12v rail. However, each output of the chip has a pair of
transistors, one of which pulls the output towards 12v, and the other pulls it towards ground, not both at the same time of course!
If you have a look at the schematic of the chip on the datasheet, you can see those transistors, one between the 12v rail and the output, and the other
between ground and the output.When the signal swings almost to 12v  that upper transistor will be turned on fully (saturated), and in that state the transistor
will have a voltage across it of 0.6 volts or so. Same goes for the lower transistor. So the signal can only get within 0.6 volts of either the 12v rail or ground.
Pushing more signal into the chip after this point will only make the output signal clip.


What does peak to peak mean?

Just what it says. It's the difference in voltage between the highest positive peak of the signal, and the lowest negative peak.So if the signal starts at zero volts, increases
to positive 10 volts, then heads downward to minus 10 volts, that's 20 volts peak-to-peak.




When you say bridged 20V P-P between the output pins, do you mean the actual pins that go to the speaker?

Yes.



In the RMS voltage formula you described, where did you get the number 2.82?

Talking about peak-to-peak voltages is all very well if what you're doing is looking at signals on an oscilloscope, but they're
kind of awkward when it comes to calculating power. If you want to figure out how much power is going to your 8 ohm load (speaker)
you need to know the RMS (root mean square) value of your signal. If you have a sine wave going through your amp and measure, say,
10 volts RMS across
your speaker with your digital multimeter set to AC volts, then connect an oscilloscope across the speaker, you will see 28.2 volts
peak-to-peak. The RMS value is equivalent to DC when calculating power. Guys a lot smarter than I am figured out that 2.82 number....
I just use it!


Hope any of this is useful to you!

[doug0147]

Thanks  I appreciate you taking the time to answer my questions

[Tubebass]

No problem!