TDA7265 for multimedia speakers

[pra3718]

Is attached circuit will work ?

[pacificblue]

Add the snubbers C7 + R8 and C8 and R9 as per datasheet.
Make yourself aware that an 18 V transformer will give more than 25 V DC.
Do us a favour and get yourself a decent software to draw schematics with. There are enough freeware programs available.

[pra3718]

Thank you pacificblue.

Make yourself aware that an 18 V transformer will give more than 25 V DC.

I have used 18-0-18 transformer (25 -+ DC) split supply for tda2050. If I am right 18VAC*1.4 = 25.20 VDC. Please remark if I going beyond the absolute maximum ratings. I am going to use all capacitors rated 25v. In fact I was confused with mute pin. I want the Amplifier should be mute at least 2-3 seconds when I power ON.

Do us a favour and get yourself a decent software to draw schematics with. There are enough freeware programs available.

Yes, I will try my level best.

I want to know minimum gain for tda7265. If I used (18K/560R)+1=33 Gain @THD=10%. What about (22K/1K)+1=23 Gain @THD=????%

Best Regards.

[thetube0a3]

I used two samsung tablet 19V switching supplies with my TDA-7265 amp. Seems to work great, and I don't notice any noise from the supplies. its been in use for a few months.

[pra3718]

thetube0a3, How did you handle mute pin ?

[pacificblue]

Originally Posted by pra3718

If I am right 18VAC*1.4 = 25.20 VDC.

Transformer voltages are given at nominal load. If the load is lower, the voltage is higher. E. g. when you listen to music at low level or when the amplifier is on with no music playing at all. This is called transformer regulation. The smaller a transformer is, the bigger is its regulation. E. g. an 80 VA transformer will have ~15 % regulation, which means with no load the voltage will be 15 % higher, with 80 VA load the voltage will be exactly 18 V. A 160 VA transformer will have ~10%, the voltage will be 10 % higher, with 160 VA load the voltage will be exactly 18 V.

Assume a 160 VA transformer is used, so you get 18 V + 10 % and your DC voltage will be 19,8 V*1,41 = 27,92 V, more than 10 % above specs.

Originally Posted by pra3718

I am going to use all capacitors rated 25v.

You should not use capacitors with such a tight voltage rating. Mains voltage will fluctuate several percent up and down and the secondary voltage will rise and fall accordingly. Capacitors also have to cope with ripple. As a rule of thumb capacitors should have at least a 25 % higher voltage rating than the nominal voltage of your power supply.

Originally Posted by pra3718

I want to know minimum gain for tda7265. If I used (18K/560R)+1=33 Gain @THD=10%. What about (22K/1K)+1=23 Gain @THD=????%

The datasheet specifies gain to be >= 25 dB, which is 17,78 times. Both your gain settings comply with that. THD is given for certain power levels, not for different gains, e. g. 10 % @ 25 W, 1 % @ 20 W, 0,02 % @ 1 W.

[sangram]

@pb, I suspect the TS has access to locally made transformers only, where it is the fashion to quote open terminal (unloaded) voltage so that they pass casual tests with multimeters at the point of sale. These are usually poorly made EI-frame transformers with up to 10% copper loss alone. For a given AWG, we get about 6 grades of wire locally - the most expensive being 5x the cost of the cheapest, and the only one with copper content over 90%. Guess which ones manufacturers like to use. Third world tends to be a little different The cost of a '200VA' transformer is between $4 and $5, so you can take a pretty good shot at guessing the quality of the parts and workmanship!

I've used the locally available transformers and the only solution is to get them custom-wound. A 90VA 18V transformer measures in at about 23VDC in this part of the world - though I do agree that 25V capacitors is cutting it too close.

Mute pin in TDA amplifiers requires to be maintained at a small positive voltage (as opposed to LM series chips that need current to be drawn out of a pin). A simple resistor from the positive supply will do this, and a capacitor to ground will add a small time delay. If you look at the datasheet, attenuation reaches zero when the mute pin is 6V or so below the positive supply voltage. In your circuit, there needs to be one more resistor from Pin 5 to ground, depending on the value of the supply voltage and the mute resistor you already have. Alternatively, a zener may be used to maintain pin 5 voltage 6V below V+.

High gain usually raises the noise floor. If you have a high gain setup and use a high signal level, you will generate excess THD. Typical sources have a voltage output level between 1 and 2VRMS. Your chip can put out a maximum of 30W into 8 ohms at 1% THD. This is a maximum voltage of 15V under any circumstances, so a voltage gain between 7 and 15 is adequate to achieve maximum undistorted output for this chip even though the minimum stable voltage gain is specified to be 18. If you have a source that is known to put out low voltages the additional gain may come in handy. I would use 18K/1K or even better, 1.8K/100 ohms. The lower resistor values result in lower noise, specially when using locally available parts.

TDA7265 is used in the very popular and now obsolete MX5021 from Altec Lansing, a pretty good sounding multimedia system.

[pra3718]

Pacificblue, I am using local non-branded trafo so I think it should be below to printed specification i.e. 18-0-18 5 Amp. Accepted, I will use all caps rated 63v accept input caps 25v.

Sangram, Please look at attached picture's mute pin added resistor to ground compare to 1st post picture.

[sangram]

That's better, pin 5 will now be at 1/2 Vcc, which should be adequate as long as your rails are over 12V. You can experiment with the capacitor to create slightly longer turn-on time.

Remember that with a bridge circuit you cannot use 25V, you will easily exceed the dissipation of the chip. The bridge circuit is rated for a maximum of 16V rails (from a 12V transformer) and only into a rated impedance of 8 ohms. The ST chips are exceedingly fragile and if you exceed SOA you have a fried chip, so you have been warned.

If you've given this only use this for a reference to the mute pin and plan to use single-ended, I would use 20V rails to be safe. You can get that from a 15V transformer.

[pra3718]

Remember that with a bridge circuit you cannot use 25V, you will easily exceed the dissipation of the chip. The bridge circuit is rated for a maximum of 16V rails (from a 12V transformer) and only into a rated impedance of 8 ohms. The ST chips are exceedingly fragile and if you exceed SOA you have a fried chip, so you have been warned.

In fact, my future plan was to build bridge for sub. Then, I will not be able to use single trafo for two chips. And if single trafo, should be 12-0-12 only.

Short story, I build several chips but still not settled.
1. TDA1554Q Build=Easy, Mute=Yes, Loudness=Poor, Price=Expensive
2. TDA2030 Build=Very Easy, Mute=No, Loudness=Poor, Price=Very Cheap
3. TDA2050 Build=Very Easy, Mute=No, Loudness=Good, Price=Cheap
4. LM3886 Build=Easy, Mute=Yes, Loudness=Very Good, Price=Very-Very Expensive
5. TDA7294 Build=Not Easy, Mute=Yes, Loudness=Very Good, Price=Very Expensive
5. TDA7265 Mute=Yes, Loudness=Don't know, Price=Cheap Rs.48 per chip

You have written in another thread, when +- voltage properly balanced then tda2030,2050 does not POP, but practically not possible to me.

By suppling the 12-0-12 trafo to TDA7265 and the loudness is equal to tda2030 then my purpose does not solve. Only advantage is MUTE.

What to do ?

Today, I have purchased everything required to tda7265 (easily available to local indian mkt) and going to build.

Thank you & Best Regards.