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TDA7297 and TDA2822M with the same supply

danielgpsalmeida
Associate II

‎2012-12-24 09:14 AM

Posted on December 24, 2012 at 18:14

Good afternoon,

I've mounted 2 amplifiers using the same power supply using 3 breadboards, one is for a TDA7297 power amplifier which is running perfectly with some changes to the specified circuit, like 470nF input capacitors instead of 220nF, and 100nF capacitors between pins 3 and ground and pin 13 and ground, 100uF standby/mute capacitor, two 470uF rail capacitors instead of only one, a 10kohm potenciometer at the inputs.

The second breadboard is used for a 15V/4A regulator LM338T based, the power ground pin and the signal ground pins are both connected to the 2*470uF supply filtering, and the signal from the audio source is connected to the same path as signal ground and so the potenciometers.

In the third breadboard I've a TDA2822M headphone amplifier, when this amplifier is running alone with TDA7297 with the potentiometer at the cut position the sound is very good, but if I turn the volume up at the TDA7297's potentiometer the sound coming from the headphones become distorted, both amplifiers share the same audio source but the signal ground reference is only connected to TDA7297, the TDA2822M also have a potentiometer of the same type but it's connected to the TDA2822M ground path, for TDA2822M is used a L7806 linear regulator. The power supply itself is unregulated and as 45VA.

Can anyone help me solving this problem?

Thank you very much for your atention,

Best regards,

Daniel Almeida
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2 REPLIES 2
bosco.stefano
ST Employee

‎2013-01-08 03:39 AM

Posted on January 08, 2013 at 12:39

Dear Daniel,

as mentioned in Online support, for this type of problem, it is mandatory to have detailed information such as schematic, block diagram or a photo of the system to verify wich is the problem.

Best regards,

Stefano

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danielgpsalmeida
Associate II

‎2013-01-08 08:16 PM

Posted on January 09, 2013 at 05:16

Good night Mr. Stefano,

Thank you very much for your repply.

Attached to this email is a draft of the circuit diagram.

I'm sorry for not making a better diagram but I can't find the libraries to use with orcad or ltspice.

I've changed the breadboard mounting and now the noise and interfeerence was reduced, the only problem that presists is due to signal injection on the ground plane, but it only can be perceived if one of the potentiometers, is completly ''closed'', and the other one is set with a very high volume, it's heard the sound on the device with the potentiometer ''closed'' like a whisper, I'm working on a good PCB layout to solve this problem.

I've other question to do, I've used a TDA7375V but it has some problems with current limiting, the device when the volume is raised to maximum and it's drived into clipping beggins turning on and off making strange noises, I don't know if there's some problem with the IC or the problem is the ground plane because I've also tested it on a breadboard.

I think the problem is caused by high impedance of the breadboard conductor materials and by the parasitic capacitance.

Thank you once more for your attention,

Best regards

Daniel Almeida

________________

Attachments :

digitalizar0001.bmp : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006Ht1U&d=%2Fa%2F0X0000000aIv%2FRUxXA3JqJU09P93QWuqY2I1ZGuXrd7.9GCa4YBBE9Y0&asPdf=false
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