Symmetrical vs unsymmetrical supply for an audio amp - Page 1
Forum section: electronics / beginners

author: Marulo
author_rank: Newbie
timestamp: April 21, 2019, 06:26:39 pm
content: Hey!I've recently bought my first set of components, breadboard, cables, etc. for my DIY synth project. Only problem is, I didn't think about the actual audio output that much. Meaning I bought an 8 ohm 10 W speaker, but had no actual way to power it. So, I've been looking to make a second round of buying stuff, mainly a soldering tools and an "audio amp pcb diy component kit thingy". But most of them are marked as "unsymmentrical supply". So, my question is, can I power it with a symmetrical supply (the same I'm using for the synth thing itself). What I'm trying to say is that I've hooked up two 9v batteries in a way like: +9 0 -9So can I take the output the synth section and plug it into the amp using it in a way, that the supply is: +18 0; where the -9v is considered the input ground.ThanksI should also note that the amp IC is TDA2040V. Even though there are no schematics on the shop page, there's a picture of the thing its self:https://www.svetsuciastok.sk/out/pictures/z1/7214-1-stavebnica_kmj2040_sx_zos_nesymetricke_nap_.jpg.Please I'm new to this whole thing, so if something's not clear please ask me

author: Zero999
author_rank: Super Contributor
timestamp: April 21, 2019, 07:04:38 pm
content: The supply voltage is high enough, but two 9V batteries will not provide enough current to get 10W of power output.A total supply voltage of 18V could be used to power the TDA2040V, in single supply configuration.Assuming the schematic for the amplifier module is similar to the one in figure 15 of the datasheet. Connect the ground to -9V and +Vz to +9V. The output from the synth should be connected to the input via a 2.2µF capacitor, with its positive to the synth output and negative to the amplifier input,https://www.mouser.co.uk/datasheet/2/389/stmicroelectronics_cd00000130-1204115.pdfThere are better suited amplifier ICs available to this application. The TDA2040V will draw about 30mA, even when no music is playing. A typical 9V battery has a capacity of about 500mAH, so it will last about 500m/30m= 162/3hours, with just the amplifier hooked up to it, with no music playing!If you must use the TDA2040, connect a large capacitor (1000µF or more, rated to at least 20V) as near to the amplifier PCB as possible.

author: mariush
author_rank: Super Contributor
timestamp: April 21, 2019, 07:34:44 pm
content: Like Zero above says, you can configure your TDA in split power supply mode.See the datasheet :https://www.st.com/resource/en/datasheet/cd00000130.pdfBrowse to page 8 and you'll see there example circuit which shows schematic and circuit board layout for mono aplifier with simple power supply.On page 7. you have example circuit and schematic for split power supply... so you could use your -9v, 0 , +9v power supplyKeep in mind that the TDA2040 chip MUST be heatsinked, as it's only around 60-70% efficient (if you get 10w of audio, it probably dissipates around 2-3 watts as heat)Also, the maximum audio power will vary depending on input voltage.Look on page 5 at figure 4 and 6 and you'll see that with +/-9v (or 18v if single power supply), the output power will be around 4w @ 8 ohm and around 7-8w @ 4 ohmHere's an example amplifier with 2 TDA2050 :http://www.electronics-lab.com/project/audio-power-amplifier-with-tda2050/You can look at that to make your power supply using a transformer with two secondary windings.... if you want to use transformers. If you want just DC voltage... 9v batteries won't work for long time, they're too lousy (small energy amount, resistance, can not output a lot of current etc)