Amplifier earthing query

[bigal_scorpio]

Hi to all,

Just wondered if anyone can clarify something for me on the subject of earths in amplifiers?

I have just had my amp for the surround speakers on my tv pack in, so having a 9 pin amp IC handy I thought I would just make a new and smaller one, the surround is only used at low volumes usually and ther isn't much room behind the chairs where it lives, so I thought the stereo 11 watt amp would do fine.

After building the circuit on a small piece of veroboard, I hit a snag, the diagram refers to both power earth and signal earth, not having much experience with audio circuits this puzzled me!

I understand the need for the earths to be kept separate, but I don't understand where I should get a signal earth from! The 12v power supply I'm using provides me with an earth for the power side but how do I get an earth for the signal side of the amp?

I have attached the pdf file with the diagram I used (fig 6) and wondered if anyone can clarify things for me? EG which of the earths shown should go to the power supply earth and where to get a signal earth from so as to not get the dreaded hum!

Thanks in advance for looking.............Al

 

[TrevorP]

The Power Earth from the Substrate is most likely the one you want to connect to your Ground pin on your power cable. The Signal Earth probably is just connected to your negative side of your power supply.

At least that's what it seems like to me.

 

[bigal_scorpio]

The Power Earth from the Substrate is most likely the one you want to connect to your Ground pin on your power cable. The Signal Earth probably is just connected to your negative side of your power supply.

At least that's what it seems like to me.

Hi Trevor,

Substrate? Sorry but I don't know what it means?

Maybe I should also have mentioned that the PSU is a SMPS that just has a 2 pin plug that goes to my amp, so the Neg on my cable is also the ground, so can I connect all the earths to this or will I get interference? I remember reading about the importance of different ground planes but I never had to use this before and didn't quite understand it.

Regards...........Al

 

[CynicalMan]

I think that the signal ground refers to the ground from the inputs.

Power ground is the ground from the supply that you are using to power the IC.

 

[bigal_scorpio]

Strange problem with earths

Hi again,

Tried the amp with all earths from PSU neg and seems ok but a bit buzzy then tried without signal earth connection to neg and the IC gets hot very quickly!

Any ideas?

Al

 

[audioguru]

The inputs to the amplifier IC are shielded audio cables that connect to the inputs and their shields connect to pin 2 of the amp ICs which is the Signal Ground Pin.
Don't use RadioShack garbage-quality shielded cables. Maplin in the UK?
The 0V from the power amplifier connects to the pin 5 which is the power pin.

The buzz you hear is probably a high pitched whine from the SMPS.
If the buzz is at your mains frequency then you have a ground loop problem.

Maybe the buzz comes from the output of the signal source.

 

[bigal_scorpio]

Oh well problems problems

Hi again,

Right an update. The amp does not work at all unless I connect the signal earth to the power earth! When it is connected the amp seems to perform ok but the IC gets very hot!

I am not playing at high volume through the amp (testing with sons Ipod) and I have a heatsink on the IC the sink is about 3" by 1" and about 2mm thick copper. I am now wondering if I should start again and build a new amp?

I have another amp IC which is the 1560q, but thats even higher powered and I just wondered if it will run even hotter?

Any suggestions would be good, I don't need a HiFi quality amp, its just for the rear surround speakers after all, a few watts would probably be adequate, but it does need 2 channels, it doesn't need a volume control or tone or balance, just a bog standard amp!

Any ideas?

Thanks in advance.........Al

 

[things]

The amp i use for my home stereo has a huge heatsink, and it still gets hot enough for me to worry about the dvd player sitting ontop of it. I burn't my finger on the top of my amp case!

 

[audioguru]

The TDA1519C has an idle power dissipation of only 1W. When it has a 4 ohm speaker, is bridged and has a 14.4V supply its max power dissipation is almost 17W. Your tiny heatsink is too small.

The TDA1560 has an idle power dissipation of 2W and is much more powerful.
When it has an 8 ohm speaker, is bridged and has a 14.4V supply its max power dissipation is almost 30W. It reduces its power dissipation when the music level is low.

Since your amp is hot when it is not working hard then it is oscillating at a high frequency. It has a high voltage gain of 100 so maybe the output wires are too close to the input wires. If you made it on a breadboard then it will probably oscillate. it needs a properly layed out pcb.

Most audio amp IC datasheets show a recommended pcb design. Not this one.

 

[CynicalMan]

The signal ground is connected to the power ground inside the IC.

What must be happening is if they are not connected externally, the little wire that connects them internally overheats.

This also means that there shouldn't be any difference whether you connect them or not.