I’m building a TDA7293-based power amp according to Fig. 1 on the datasheet.
* What is the recommended V+s/V-s for roughly 100W output at 8 ohms and 0.1% THD? The datasheet says anything up to +/-60V, but I tried 45 and it blew up and caught fire (at the voltage supply inputs).
* How much supply current will it draw at full volume? The datasheet only says 100mA quiescent.
I really can’t figure this out, I need your help.
* What is the recommended V+s/V-s for roughly 100W output at 8 ohms and 0.1% THD? The datasheet says anything up to +/-60V, but I tried 45 and it blew up and caught fire (at the voltage supply inputs).
* How much supply current will it draw at full volume? The datasheet only says 100mA quiescent.
I really can’t figure this out, I need your help.
Did you isolate the tab?
Did you make a PCB as per the data sheet?
For 100W output using +- 29v with 10% THD. There is no measurement of 0.1% THD. They are designed to work into 4R for maximum power output. At a load of 8R it will provide around 40Watts.
These amplifiers, if used correctly, with lots of damping to stop them taking off into the MHZ range are very reliable but must be kept cool on a large heatsink.
Did you make a PCB as per the data sheet?
For 100W output using +- 29v with 10% THD. There is no measurement of 0.1% THD. They are designed to work into 4R for maximum power output. At a load of 8R it will provide around 40Watts.
These amplifiers, if used correctly, with lots of damping to stop them taking off into the MHZ range are very reliable but must be kept cool on a large heatsink.
Pardon my ignorance as inexperienced and under-educated, but when calculating current draw for an amp, you’d use Ohm’s Law with the input voltage and the impedance of the output speaker as factors? It seems a bit counter-intuitive to me.
Checked and double-checked the tab.
Best ways to keep them from going into MHz?
no....no!!
The relation of the input voltage to output voltage is the Gain of an amplifier!
power and current :
on your output terminals you put your load.
what angryfatcat wrote is for AC applications - 30V rail supply...end up about RMS 16...20V into the load (approx, ). 20/8R (load)=2.5A Irms.
" I guess 2x25VAC*5A will be more than enough.And yep, 20000-30000 uF per rail don't forget."
so a 250VA or 300VA transformer will do 2x 25VAC on the secondary is fine
kr
chris
I used a 28-0-28 trafo. This gives me 40V rails good for about 80 watts. Even with a fairly chunky heatsink the chips get crazy hot when pushed. I wouldn’t go that high again, I’d stick with a 24 or 25V transformer. You really won’t miss a few watts.
Typical output power for normal domestic listening in a small room is about a 1-3 watts for me with plenty of headroom to shake the furniture for the loud bits.
Typical output power for normal domestic listening in a small room is about a 1-3 watts for me with plenty of headroom to shake the furniture for the loud bits.
Oh, and by the way I bought a few chips from China. All of them exploded on power on. The ones I bought from RS or Farnell didn’t.
The Chinese ones were clearly fakes and not the bargain I thought they were.
There is a thread on here somewhere that shows how to check before you solder them.
The Chinese ones were clearly fakes and not the bargain I thought they were.
There is a thread on here somewhere that shows how to check before you solder them.
ok, sorry I'm confused here. I have no idea whatsoever what the load of a TDA7293 is. All I know is that I'll be using an 8R speaker.
So if I use +-30VAC, how do I calculate the current draw for a chip amp at full volume, in order to know how to dimension the power supply?
I presume the 20-30mF refer to smoothing caps?
Yes, I do realise that you don't use the full blast. However, I'd rather overdimension the power supply to be able to cater for the full power potential of the amp plus a little more, than finding myself putting out a trafo fire.
I've taken care of the heat problem already, so that isn't an issue. However, you using 40V interests me. In that case, why can't I use 45V?
That won't happen unless it's an incredibly crappy transformer.
Usually the supply voltage will sag a little more and eventual onset of clipping will indicate the limit.
The data sheet says absolute max is 50V, so 45V is very close especially when you take into account mains voltage tolerance.
You can easily protect against cooking the trafo by using one with a slightly higher current (hence VA) rating.
In practice you will not be able to tell the difference at full volume between 80 and 100W, you’d need to go to about 250W for it to sound much louder.
My Farnell sourced chips have been running daily for about 2 years including some brief spells of VERY LOUD playing 😀.
I turn it down when the heatsinks are too hot to touch as I don’t have external thermal protection and I think someone calculated that the thermal resistance in the chip is actually too high to sustain full power indefinitely.
My advice is to stick at 40. I can stand over that because I know it works well and keeps working. I have read many threads counseling against maxing these out.
80W into 8ohms is 25V RMS or 35V peak.
Current is about 3.2 amps RMS.
Amp is 75% efficient at full power so your transformer needs to be rated higher than your max output power.
Many transformers are rated at 8 to 10 % regulation or sag at full power and bridge rectifiers make this look worse, so you need to over rate again to minimize this sag.
On the other side of the coin, music has typically a 30% duty cycle so the peak power isn’t used as often as you think.
Current is about 3.2 amps RMS.
Amp is 75% efficient at full power so your transformer needs to be rated higher than your max output power.
Many transformers are rated at 8 to 10 % regulation or sag at full power and bridge rectifiers make this look worse, so you need to over rate again to minimize this sag.
On the other side of the coin, music has typically a 30% duty cycle so the peak power isn’t used as often as you think.
I use 4 of the project 127 amps in my speakers at 40 V and use a 240VA transformer.
I can get way with this because my speakers reach their excursion limit before any of the amps clip as I use small drive units with lots of EQ.
The maximum observed power draw from the mains I have seen at outrageously loud volume is 130W per speaker. At that level the trafo only gets warm.
If you are making a general purpose amplifier under rating would be a bad idea.
I can get way with this because my speakers reach their excursion limit before any of the amps clip as I use small drive units with lots of EQ.
The maximum observed power draw from the mains I have seen at outrageously loud volume is 130W per speaker. At that level the trafo only gets warm.
If you are making a general purpose amplifier under rating would be a bad idea.
All the current going into the speaker load comes from the dc supply and thus from the secondary of the transformer.
On the mains side the current is less as the voltage is higher by a factor of 6 in my case. So at 80W the draw would be about half an amp.
Does that answer your question?