# 30W and 4x8W audio amplifier circuit?

Discussion in 'Audio' started by FilipSebik, Oct 12, 2017.

1. ### FilipSebik

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Sep 7, 2017
Hey, I want to make my own subwoofer amplifier that outputs 15V and 2A to output 30W of power to a 8ohm subwoofer and 4x8W amplifier that outputs 7V and 1.1A to output almost 8W of power to a 6 ohm speaker. Best would be class AB or class D. Transistor or IC? I don't care
For the 30W I found this
https://www.gme.sk/data/attachments/dsh.313-106.1.pdf The Figure 16 : Bridge Amplifier with Split Power Supply (PO = 34W, VS = ± 16V) which would be usable in my case.
Is that any good? What are the + and - of that amp.

For the 4x8W I didn't found anything yet, but it could be any combination of 2x 2x8W or 4x 8W amplifiers for 6 Ohm speakers.
Maybe a class D for this one?

Thanks for help

2. ### Audioguru

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Sep 24, 2016
VS = ± 16V is the + and - power supply for that 34W bridge amp.
The datasheet does not say its distortion or how much heat it produces.
There are many class-D 8W amplifiers available. Look at the Texas Instruments website.

3. ### FilipSebik

13
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Sep 7, 2017
Ugh, texas instruments has millions of ICs of amplifiers, but not the ones that suit me. Every sh#@% is SMD and the way you search for components is dumb. They are even expensive as hell for me.

I could use my 2 20W TDA2005 bridge amps (that blow up when used as bridge) to make it into 2 2x10W amp because the PCB that came with the kit, can be used for Figure 7 : Typical ApplicationCircuit
I could use input voltage of 14V for power of almost 8W with 3Ω load by connectng 2 6Ω speakers to parallel (using Figure 12 : Output Power versus Supply Voltage (Stereo amplifier))
http://pdf1.alldatasheet.com/datasheet-pdf/view/25037/STMICROELECTRONICS/TDA2005.html

EDIT: I have 2 TDA2005 bridge amps, that I can modify to 4x10W from 2x20W (they are on the same PCB) <--- this is to simplify the "spaghetti" I wrote up here

4. ### kellys_eye

4,277
1,146
Jun 25, 2010
That's an unusual way to specify an amplifier output (volts/amps) - the usual xx watts into yy ohms is normal. You then chose your class, decide on your power supply etc and go from there.

SMD is here to stay - either adapt to it or use devices that will, in very short order, become obsolete and hard to replace.

Are you looking for efficiency? clarity (low distortion)? what?

You already seem predisposed towards the TDA**** device(s) - nothing wrong with that - and there are a gazillion schematics for their application across the interweb.

Equally there are a gazillion ready-made amplifier modules of all 'class', all power output and all supply ranges available via your local friendly Chinese retailer (eBay being the usual culprit/source but Banggood and/or AliExpress etc also do them). Lots less hassle, LOTS cheaper etc.

5. ### FilipSebik

13
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Sep 7, 2017
Ebay for amps? No.
Ebay for parts? Uhh, yes
Why not for amps? 30W amp class D 4 bucks, blows up when you power it on or kills your speakers. I had an experience with it blowing up and then taking my speaker with it, so no ebay

6. ### WHONOES

784
174
May 20, 2017
Look up the LM1875 which is a Texas part and do as the data sheet instructs. They seem to be less than 4\$ each and are not surface mount. If that's not good enough you may have to construct you own power amps which is not as much of a nightmare as it sounds.

7. ### kellys_eye

4,277
1,146
Jun 25, 2010
If you're overly concerned for eBay products then you'd be wary enough to take precautions before connecting speakers and/or power.

Unless you've had multiple experiences of failure I think it's a little premature to be discounting such sources on 'one' example. It doesn't equate with my own experience either.

For the price of building ONE amplifier using propitiatory parts you could purchase three of four small 'eBay' modules to experiment with. Personally I wouldn't expect such modules to be the be-all and end-all of quality/functionality but certainly a good place to start and get something - even just the parts count - for very little outlay.

8. ### Audioguru

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619
Sep 24, 2016
You are looking at the exaggerated power ratings shown on amplifier datasheets. It says 10% distortion that sounds awful because the amplifier is clipping like crazy.

The old TDA2005 produces 2 x 8W into 3 ohm speakers (two of your 6 ohm speakers in parallel) at low distortion when its supply is 16V. It will need a pretty big heatsink to dissipate about 15W of heat.

9. ### Audioguru

2,742
619
Sep 24, 2016
The National Semi (now owned by Texas Instruments) LM1875 single amplifier is almost the same as each amplifier in a TDA2005 dual amplifier that you have.

10. ### WHONOES

784
174
May 20, 2017
As a point of interest, you can easily calculate power supply requirements for what ever power output you want.
First decide on how much RMS power you need then decide on the impedance of your speaker system.
Next multiply RMS power by speaker impedance and extract the square root of that sum. Easy to do on a calculator.
Example 50W RMS into 8 ohms = 50 x 8 = 400 extract SQRT = 20. So that is telling us that you need 20V RMS for 50W RMS at the onset of clipping.
Now for the power supply, assuming that you are going to use a split supply ie +V 0V -V, you need to calculate the peak to peak value of 20V RMS. To do this multiply by 2.84 which = 56.8V or +/- 28.4V. Next add another 6V to the total to allow for saturation in the output of a BJT amplifier or 10V or so (It may be more) for a FET amplifier.
Hope that's not too confusing.

11. ### Audioguru

2,742
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Sep 24, 2016
That was many years ago. Today most little amplifiers are class-D, use a single positive supply, are bridged and have no saturation voltage loss.

12. ### WHONOES

784
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May 20, 2017
Agreed. As I said it was a point of interest. Personally I would not use a class D for HI-FI as they are sonically inferior but, I am sure you disagree with that.

13. ### Audioguru

2,742
619
Sep 24, 2016
I have never used a class-D amplifier, all my hifi amplifiers are class-AB. The latest class-D amplifier ICs switch at hundreds of kHz and have very linear PWM so that their noise and distortion cannot be heard and can be barely measured so sure they are hifi.

14. ### WHONOES

784
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May 20, 2017
I have only ever used class AB or sometimes B. I have designed my own for the last 40 years or so with noise impossible to hear and distortion vanishingly small (at least in simulation). Preferring Fet O/P though they are a little more recent.