Picking out parts for this schematic

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Seb1929

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Mooly said:
This shows something like you should see on either pin 5 or pin 8.

Notice how the notional centre line is biased to 1.5 volts. This allows the sine to swing up to +3 volts (your supply) and down toward zero.

So we have here a peak voltage of 1.2 volts and peak to peak of 2.4 volts. The rms value is Vpeak*square root of 2 so that becomes 1.2*1.414 which is 1.7 volts.

On your amp, because the speaker is driven by two antiphase signals it would see in this example 2.4 volts peak and so the rms value becomes 2.4*1.414 which is 3.4 volts. That would be a power of 1.4 watts rms into 8 ohm.
Click to expand...

Before i start again you are helping me so much, thank you! :)

So the power is 1.4 watts. So i bought wrong speakers again? :p Also i got a multimeter not a scope. I'm not English so i thought a scope was a multimeter sorry :|
 
Mooly

Mooly

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Think of it like this. Here are the two output stages with one being inverted. The scope trace in green is one output and the blue the other. The speaker sees the combined voltage of the two.

Have to leave it for today... hope it makes sense.
 

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Mooly

Mooly

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Seb1929 said:
Before i start again you are helping me so much, thank you! :)

So the power is 1.4 watts. So i bought wrong speakers again? :p Also i got a multimeter not a scope. I'm not English so i thought a scope was a multimeter sorry :|
Click to expand...

Its no problem :) and it might make more sense seeing it drawn as a scope trace.

So with your meter, whatever AC voltage you measure across the speaker is the rms value. You multiply that by itself and divide by 8 (ohms) to get the power.

For example 28.3 volts rms is 100 watts into 8 ohms. Change the load to 2 ohms and would be 400 watts and so on.

Have to leave it for today.
 
S

Seb1929

Member
Joined 2015
Mooly said:
Its no problem :) and it might make more sense seeing it drawn as a scope trace.

So with your meter, whatever AC voltage you measure across the speaker is the rms value. You multiply that by itself and divide by 8 (ohms) to get the power.

For example 28.3 volts rms is 100 watts into 8 ohms. Change the load to 2 ohms and would be 400 watts and so on.

Have to leave it for today.
Click to expand...

Okay i will try to understand this, thank you again :)
 
Mooly

Mooly

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Seb1929 said:
I think so it says VAC. Also across the speakers is one pin on the one side and one pin on the other right?
Click to expand...

Easy one first, yes that's correct.

Mooly said:
This shows something like you should see on either pin 5 or pin 8.

Notice how the notional centre line is biased to 1.5 volts. This allows the sine to swing up to +3 volts (your supply) and down toward zero.

So we have here a peak voltage of 1.2 volts and peak to peak of 2.4 volts. The rms value is Vpeak*square root of 2 so that becomes 1.2*1.414 which is 1.7 volts.

On your amp, because the speaker is driven by two antiphase signals it would see in this example 2.4 volts peak and so the rms value becomes 2.4*1.414 which is 3.4 volts. That would be a power of 1.4 watts rms into 8 ohm.
Click to expand...

I thought this didn't sound right when I typed it.

1.2 volts peak is 0.848 vrms (its divided by root2, not multiply). That would be what you would see on a conventional single amp.

Now for your bridged amp that becomes double that or 2.4 volts peak and 1.7vrms.

1.7 vrms develops 0.36 watts rms into 8 ohm. That's the maximum power available.

Sorry about that.
 
Mooly

Mooly

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To increase 5 volts to 8.4 (or another voltage) you need a switching type power supply. Lots of ways to do that although pure diy from scratch won't be very easy.

Boost converter - Wikipedia, the free encyclopedia

Chip manufacturers will have worked examples and probably even evaluation boards available.

You can also buy off the shelf small switching convertors, say 5 volt to 9 or 12 volt and so on. Connecting batteries (to charge them ?) involves more than just connecting them to a voltage source... if that's what you are thinking.
 
Mooly

Mooly

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You're going to have to look at the battery technology and requirements. I'm guessing your going for Li-On batteries which mean you have to follow the manufacturers directions carefully. NiMH and NiCad are much more forgiving. Don't underestimate how much current a Li-On type may want to draw on its main charge sequence.
 
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