# Does this circuit work?

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#### dsp_redux

Joined Apr 11, 2009
182
I was under the impression that it didn't matter which way round they went, however if they are ordered as they are in the last diagram i attached the output signal amplitude reduces dramatically so it seems to be right that they were reversed.
The gain is given by $$G=\frac{V_{out}}{V_{in}} = \frac{R_3 + R_1}{R_1}$$. Logically, if you want a high gain, you better put R3 >> R1.

#### Audioguru

Joined Dec 20, 2007
11,248
The datasheet states in the main table that with 14V supply voltage it has an output power of 14W with 4Ω speakers or 9W with 8Ω.
No.
It says a plus and minus 14V supply which is a total of 28V.

I have 1x 4Ω 10W speaker and 1x 4Ω 5W speaker, if i hook them up in series they'll become and 8Ω RL, the amp supposedly will only have 8W output at 12V so shouldn't be enough to blow the speakers, right?
No.
The output power into 8 ohms when the supply is only 12V is 1W or less.
When the supply is plus and minus 13V (26V total) then the power into 8 ohms is 8W.

I'd like to add that i am just playing with this amplifier, i find making and doing a better way to learn than just reading about it
Then calculate that 8W into 8 ohms is an RMS voltage of 8V. Its peak-to-peak voltage is 22.6V and the amplifier output has voltage losses so the supply must be 26V.

If the supply is only 12V then the p-p signal is only about 8.6V then the RMS voltage is only 3V. Then the power into 8 ohms is only 1.1W.

#### MWG

Joined Apr 15, 2009
28
i'm confused now this is the datasheet i'm using

http://www.rapidonline.com/netalogue/specs/82-0628e.pdf

This is the part i'm looking at, am i reading this wrong then? that's saying ±6V in the first column or 12V, right? if you go down that column it says 12W or 8W (underlined) so thats wrong? it won't give me that with a 12V supply?

further down in the datasheet is a diagram for supply voltage Vs output power and they show the same values? if you could explain how it will only be 1W because i have no idea why it is

Edit: thats a bit bigger than i thought lol

just had a look at some other datasheets for the TDA2030, seems that the graphs are showing ±V along the bottom, not that i could make it out from that other datasheet

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#### Audioguru

Joined Dec 20, 2007
11,248
This is the part i'm looking at, am i reading this wrong then? that's saying ±6V in the first column or 12V, right?
yes. That is the minimum supply voltage where it barely works with a power output of 1W or less.

If you go down that column it says 12W or 8W (underlined) so thats wrong? it won't give me that with a 12V supply?
No.
It says at the top of the text that the supply is plus and minus 14V (28V total).

further down in the datasheet is a diagram for supply voltage Vs output power and they show the same values?
It shows an output of only 6W into 8 ohms when the supply is plus and minus 12V (a total of 24V).

if you could explain how it will only be 1W because i have no idea why it is

just had a look at some other datasheets for the TDA2030, seems that the graphs are showing ±V along the bottom, not that i could make it out from that other datasheet
ST Micro is Italian. Their graphs are extremely fuzzy due to the pasta all over the place.

#### MWG

Joined Apr 15, 2009
28
I can see it now I've looked at some better datasheets that actually have their graphs axis labelled clearly. Now i know how the datasheets work i won't be making that mistake again thats for sure

I haven't actually got a power supply yet so i can make it 24-30V. I'm still trying to work out how this works, then i'll start buying stuff to build it.

I'm still learning about electronics. My degree is in automotive engineering so this is not something i'm used to dealing with on a day to day basis, its just a hobby at the moment and thats only when i think of something to make