Power Amplifier Vcc

[ecestudent]

The rectifier diodes?

Oh yeah... I forgot that very important stage... He3.. Thnx..

 

[Nigel Goodwin]

24-0-24 will give you too much voltage, about 36-0-36 DC - you want a 20-0-20 or a 22-0-22 transformer.

 

[ecestudent]

I'll check if 22-0-22 is available. when i used a 12-12 i did get above 30. Anyway in case the 22-0-22 is not available, i'll just adjust the resistor values to give me 30V.

 

[Nigel Goodwin]

I'll check if 22-0-22 is available. when i used a 12-12 i did get above 30. Anyway in case the 22-0-22 is not available, i'll just adjust the resistor values to give me 30V.

What resistor values?.

 

[audioguru]

There are no resistors in the transformer circuit. If you use the wrong transformer then the voltage will be wrong.

A 22V-0V-22V transformer will produce +29V and -29V at its rated current and will produce about +31.5V and -31.5V with low current.

The max allowed supply voltage for the TDA7295 is 80V.

A 22V-0V-22V/3A transformer is rated at 44V x 3A= 132VA. when the amplifier has a 50W output then it heats with about 40W so its total power from the transformer is 90VA and the transformer will not over-heat. A 2.5A transformer will also be fine.
you don't listen to music at full blast all the time so a 2A transformer will be fine.

 

[ecestudent]

The 22-0-22 transformer is not available in our area so i'm using a 24-0-24 transformer. it's giving me about +-36 V and its a 3A transformer. Wouldn't it hurt my power amp?

 

[ecestudent]

i removed the regulator and had a supply about +-35V. The input is reaching 2Vrms from my preamp but the output of the power amp is zero. I made use of the test circuit shown in the datasheet (http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1565.pdf).

 

[Nigel Goodwin]

Post a picture of how you've built it.

 

[ecestudent]

Am I supposed to supply some voltage to the mute and standby pins?

 

[audioguru]

Am I supposed to supply some voltage to the mute and standby pins?

The datasheet for the TDA7295 is confusing.
The text spec says the Standby and Mute functions occur when their pins are 1.5V or more more positive than pin1. But the Turn-on Sequence graph shows the Standby and Mute functions turned off and the amplifier plays when their pins voltages are positive.

 

[ecestudent]

I think the mute and stndby pins need some voltage above 3.5V so that they won't be in mute and standby... Would the +35V be ok for that?

 

[audioguru]

I think the mute and stndby pins need some voltage above 3.5V so that they won't be in mute and standby... Would the +35V be ok for that?

The circuit in the datasheet shows the Mute and Standby pins having capacitors to pin1 which is grounded and series 22k resistors to a positive voltage that is not specified. The positive supply might be OK.

If you don't follow the recommended sequencing then the output of the amplifier will probably POP when it is turned on and turned off.

 

[ecestudent]

Is the tda7295 suppose to gain heat when it's operating?

 

[Hero999]

All amplifiers get warm when working properly.

 

[audioguru]

Is the tda7295 suppose to gain heat when it's operating?

Don't you have its datasheet?
It shows a dissipation of 32W of heat when its output is 29W into 8 ohms with a plus and minus 34V supply. 32W is a lot of heat and the heatsink must be pretty big or the IC will fry itself to death.
Its output at clipping is about 60W then its dissipation is 26W

 

[ecestudent]

I see. It worked but i haven't tried connecting it to a speaker. I need to look for a big heatsink first.