HELP with making two mono amps in to one stereo amp (with more output power)

[GooseElectro]

I have made a small 7w mono amp using a TDA2003 audio amplifer IC, it work really well, however i wanted to make it stereo so i made another one (same circuit). but when i linked the two it makes a nasty noise and it draws more and more current. i have linked it by conecting all grounds and power supply, i have linked the audio in and outs to the seperate amps. should i be linking the audio and power ground seperatly or using caps in powers lines. I can work it out can any one help ??

 

[Nigel Goodwin]

Post the circuit, and a picture of how you've built it.

 

[GooseElectro]

will do

ok i will do do you think you will be able to help?

 

[audioguru]

The two amplifiers can use the same power supply positive voltage and ground only if the power supply can provide enough current for the two amplifiers. Each amplifier circuit needs to have its own supply bypass capacitor.

Of course the amplifier inputs and outputs must not be connected together.

 

[GooseElectro]

Yes I have thought about the current. Could you explain more about the bypass cap ie what it will be doing and what sort of cap? I will be posting the circuit soon. Thanks for ur help so far

 

[audioguru]

The recommended circuit for each of your TDA2003 amplifiers is in its datasheet.
The very important supply bypass capacitors are shown.
Each of your amplifier circuits should have both supply bypass capacitors mounted very close to pin 5 and pin 3.

 

[Grossel]

I have an old tda2003 datasheet and the quality is (sorry to say) not good, but here's a picture of the schamatic for two tda2003 bridged.

 

[Hero999]

So you used four TDA2003s, two for each channel, right?

Or have you got your terminology wrong and want to build a mono bridged amplifier?

 

[audioguru]

Now there are two people saying they made amplifiers with TDA2003 ICs.
They are not matched so they might draw up to 400mA due to their offset voltages if they are bridged. Bridged amp ICs like the TDA2005 or TDA7240A should be used because their offset voltages are matched.

 

[Hero999]

If the speaker is AC coupled via a capacitor, the DC current won't be a problem.

 

[GooseElectro]

**broken link removed**
this is my circuit i will have to check my prototype

 

[Hero999]

It depends on how you've wired it.

Is the return for each input is connected near the each IC and not via a few 100mm of wire?

Please post of a picture of the assembled circuit.

 

[bountyhunter]

I have made a small 7w mono amp using a TDA2003 audio amplifer IC, it work really well, however i wanted to make it stereo so i made another one (same circuit). but when i linked the two it makes a nasty noise and it draws more and more current. i have linked it by conecting all grounds and power supply, i have linked the audio in and outs to the seperate amps. should i be linking the audio and power ground seperatly or using caps in powers lines. I can work it out can any one help ??

I don't see a problem with the schematic, but I do remember this part was sensitive to having a separate power ground for the load return. The ground sides of R2 and R4 must be tied directly to the ground pin on the TDA2003 device.

The load ground needs to have a short path to the source power ground.


BTW, this part is an antique: I designed it back at fairchild in 1979. I used some leftover 2003 parts as bridge amplifiers to make a power amp I used in my old car. They worked OK.

 

[bountyhunter]

Now there are two people saying they made amplifiers with TDA2003 ICs.
They are not matched so they might draw up to 400mA due to their offset voltages if they are bridged. Bridged amp ICs like the TDA2005 or TDA7240A should be used because their offset voltages are matched.

Good point. When I used 2003 for a bridge, I did put a trimmer in it to zero out the DC offset. Schematic attached.

 

[Hero999]

Is it wired like the first or second schematic in the picture attached?

 

[GooseElectro]

I will post a picture of how I have wired it. Both amps work fine on their own

 

[audioguru]

Good point. When I used 2003 for a bridge, I did put a trimmer in it to zero out the DC offset. Schematic attached.

Your offset adjustment is in a positive only direction. What if you need a negative offset adjustment, swap the amp ICs?

 

[GooseElectro]

I will have to post my wired circuit I am making a stereo amp not a briged amp ! Bothe circuits work fine on there own. Somthing to do with connecting them. Thanks for your help so far everyone I will post ciruit soon.

 

[Hero999]

Did you look at my previous attachment?

It makes a huge difference how the return lines to the audio channels are connected.
**broken link removed**

 

[GooseElectro]

Did you look at my previous attachment?

It makes a huge difference how the return lines to the audio channels are connected.
**broken link removed**

I don't want to bridge the amps I need seperate channels I just link the power supply and ground