Help deciphering schematic for hobby circuit I want to build

[HandyMan]

Hi all,

I want to build myself a little amplifier as part of my hobby, which I will then use to power a couple of speakers. I like the idea of it as it'll be small and I could transport it around so it'd be ideal for use with my other hobbies.

I want to use parts I already have on old chassis and things in the shed, so I got an old TV chassis and found the stereo amplifier IC - TDA2615 - which seems perfect for my basic needs; it seems simple and needs few external components.

My needs: stereo amplifier circuit to take outputs from, say, tape recorders, computer sound cards, etc. Amplifier to take around 9 to 12V DC, and to output to a couple of 8 ohm speakers. Circuit to be small and not require components I don't have here already.

All I can find is a datasheet for the TDA2615 which shows a test circuit. I was going to copy this test circuit since I don't know how to design one around the TDA2615 myself. Trouble is, part of the test circuit doesn't make sense to me.

Here is link to datasheet, page 8 has the test circuit I wanted to copy:

https://www.electro-tech-online.com/custompdfs/2005/01/TDA2615_3.pdf

However, to save trouble, here are the relevant images:

**broken link removed**
**broken link removed**

Here's what confuses me: the input voltage's negative -Vp goes to the negative of a 2200uF capacitor, with the positive of said capacitor going to 'ground'. It also shows pins 3 and 8 of the IC going to ground and the negatives of the speakers, etc. So, if -Vp isn't ground, since it is kept apart via a capacitor with the positive of the capacitor going to ground, what exactly is ground? Are the parts that are shown to go to ground actually going to the negative of the audio inputs, so the whole 'ground' network is based upon the input ground, with the voltage -Vp ground being kept separate? If I haven't explained this well, please ask, as you'll need to understand my confusion in order to answer to it, and others may see nothing confusing in the circuit at all...

Another thing, what is "INV1,2" - stated as: inverting input 1 and 2 - it shows it being grounded, but what exactly is an inverting input? What should or normally would go there? It confuses me as the audio inputs are named 'non-inverting inputs'.

Lastly, I want a volume control on here. I know it would require two potentiometers so as to keep the stereo channels separate, but where would I place them? In line with the audio inputs, so when the resistance is high enough, no audio input goes into the amplifier IC and hence no sound comes of of its outputs?

Thanks to anyone who answers this! Also, if you think the design could be improved, changed to make is easier, please go ahead.

Thank you,

James

 

[Styx]

1) the good-old GND debate. Groud is basically a philosophy in electroics. All it depicts is a reference point.

Take a battery, it has a positive terminal and a negative terminal. IF I label the negative terminal GND and connect a volt-meter across it, I would see a positive voltage. IF I labeled the positve terminal GND adn connected a volt-meter across it I would see a negative voltage.

All GND is used is a common reference point, you can reference against anything you like.


2) INV 1,2 (or pin8 on the IC) if you look at the red outline, pin 8 goes to both OPAMPS, they go the the inverting input hence they are just stating that.

As to the volume control I would put it on the output.

 

[TheOne]

Since it is a (directly coupled) DC amplifier with no cap in series with the speaker, you will need a split supply for this to work. +Vp GND and -Vp. Like two batteries in series with the middle point taken as GND. If you have only a single supply available you will have to look for another IC.

Because it is basically a power opamp, the one input is referenced to GND as the output will swing +ve or -ve (with gain set by the resistor ratio) from this reference point according to the input signal.

Styx, looks like we posted at the same time!

 

[audioguru]

The datasheet says the IC operates with positive and negative 12V supplies and also shows how to use a single 24V supply and output capacitors. It is not made for car radios so won't work with only a 12V supply (minimum 15V with very low output power).

Don't put an expensive, huge, and hot volume control on the output!
Use a small 10K audio-taper volume control with its slider to the amp's input capacitor and its input capacitor-coupled from your audio source. The remaining end of the volume control connects to the amp's ground.
The ground of your audio source connects to the amp's ground through the shield of the connecting cable.

 

[HandyMan]

Thanks to Styx and TheOne for your info, it helped me to understand what's going on. Thanks Audioguru, I overlooked what you discovered and appreciate the help. Unfortunately, I don't have a 24V supply, I'm limited to 12V and that would be easiest for me to use, as I have 12V available around all the applications I have in store for the amplifier when it's built.

I've now looked through my shed and found that I have an old car cassette-radio player. Inside, there is TDA7386, the datasheet for which can be viewed at:

https://www.alldatasheet.com/datasheet-pdf/view/STMICROELECTRONICS/TDA7386.html

It seems ideal since it only needs a 12V supply as used in cars. I'd only be using 2 of its 4 outputs. I wonder if anyone could give me some advice with using it, though?

Referencing the datasheet, here's what's stopping me at the moment:

Page 7 - It says that "if the standby and mute functions aren't to be used, a straight connection to Vs of their respective pins would be admissible." Since I don't need standby or mute, they will remain unused, but I don't understand what it suggests I do with the related pins?

Page 2 - the pin connection drawing: P-GND1, P-GND2, P-GND3, and P-GND4 are clearly supposed to go to ground and are associated with each output, and I suppose S-GND also connects to common ground, although I don't know what it's for, so in essence, all the above are interconnected via ground. But why is AC-GND coupled to ground via a capacitor in the test circuit? Would the audio input negatives go to ground as well? I suppose they must do? Maybe S-GND is [input] Signal Ground. HSD on newer datasheet which I found and then lost shows it has no connection in any circuit.

Thanks again for any help,
James

 

[Exo]

Page 7 - It says that "if the standby and mute functions aren't to be used, a straight connection to Vs of their respective pins would be admissible." Since I don't need standby or mute, they will remain unused, but I don't understand what it suggests I do with the related pins?

Connect them to GND

 

[HandyMan]

Thanks