TDA7294 + Power Transistors AMP (TDA7293 to come also)

Hi all. Great work iv seen here and plan on building something myself with a little help...

I have a few tda7293 and the transistors needed.
I'm looking for a PCB layout I can open in sprint or eagle to save me the hard work if I plan to edit my work. I need something I could print.


I have brought this transformer is it any good. what power could I get with two tda7293 chips two or three pairs of transistors



Product Features

  • 300VA TOROIDAL 2X35V
Product Details
Power Rating: 300VA Secondary Current Nom: 4.28A Secondary Voltages: 2 x 35V Transformer Mounting: Chassis AC Power: 300VA Approval Bodies: EN / UL Bolt Hole Diameter: 6mm Bolt Length: 60mm Current Rating: 4.28A External Diameter: 119mm External Length / Height: 49mm Mounting Type: Chassis Output 2 Voltage Max: 35V Output Voltage: 35V Primary Voltages: 115V, 230V Regulation: 6% Secondary Power: 150VA Temperature Rise: 50°C Transformer Type: Toroidal Weight: 2.8kg




Thanks in advance

Pls. I'm planning to use this as home subwoofer amp
 
The maximum output power is determined by the transformer voltage and a bit less by the transformer VA.
You could get upto 300W total from a 300VA transformer.
With supply rails of +-50Vdc from your 35Vac transformer the maximum you can get into 4r0 is ~200W, into 3r0 ~ 290W, into 2r0 ~360W

Using a 2ohms speaker will severely stress your transformer.
 
So what would be the best transformer size to get?
Iv just brought this one ....

200watts is that rms
It is probably a 200VA. Transformers are rated in VA, not watts.
And Watts is not rms. Just watts when referring to averages.
You can use an instantaneous power value by taking the instantaneous current through a component and multiplying by the instantaneous voltage drop across that same component at that same moment in time, otherwise just watts.

The 200VA transformer can be used to power upto a total maximum power output of 200W.
 
It is probably a 200VA. Transformers are rated in VA, not watts.
And Watts is not rms. Just watts when referring to averages.
You can use an instantaneous power value by taking the instantaneous current through a component and multiplying by the instantaneous voltage drop across that same component at that same moment in time, otherwise just watts.

The 200VA transformer can be used to power upto a total maximum power output of 200W.

Unless your components dissipate any power as heat.

That would probably be close to the maximum average input power. But the max avg output power would be that times the efficiency, which would probably end up being more like 2/3rds of that.

And that's the maximum average output power. What about the peaks? They might be OK. But you could think about leaving more headroom, probably at least the square root of two times the final max avg power. So another factor of about 2/3rds. That takes it down to about 1/2 or a little less, of the transformer's max VA rating.
 
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Gootee,
I stand by my usual recommendation that for a specific total maximum output power: use a transformer VA that is rated from 1 to 2 times the watts.

i.e. for 100W of total maximum output power use a transformer from 100VA to 200VA.
For 200W of total maximum output power use a transformer from 200VA to 400VA.

My statement earlier
The 200VA transformer can be used to power up to a total maximum power output of 200W.
fits exactly with the general recommendation.

This takes account of music reproduction in a domestic environment including the occasional party, where average power output is many dB below the maximum that the amplifier is capable of, provided all the drunks at the party are NOT allowed to fiddle with the controls.
 
AndrewT,

I will agree that for most music, most of the time, 1X should be sufficient. And it should be theoretically "perfect" up to about 1/3rd of max volume, even wth a worst-case non-music signal. So it could be "good enough", in most cases. However, it seems that the max output power rating of such an amplifier would need to be lowered, to make it technically correct.
 
Meh, been reading Philips data sheets and they recommend 16x the normal listening level for head room. If I could afford capacitors like that...

I've had an epiphany though on protection of our precious stereo amp and speakers. Just use an 800V florescent light ballast wired to an aluminum volume knob that kicks in whenever some knucklehead turns the volume past 8. You could also set it so it is triggered to be on after you set the volume where it should be or just to a dummy volume knob that had no other function other then to persuade people not to touch your stereo w/o asking.

Idea of defeating knuckleheads isn't original to me of course. I was reading a Crown amp manual and they make them such that you can pull the volume control knobs off and replace them with a hard rubber plug.
 
reading Philips data sheets and they recommend 16x the normal listening level for head room
16 times what?
Voltage? or Power?, or Loudness?

It is normal for us to listen to average music levels that are one tenth of the maximum power available from the amplifiers.
Many will listen at one hundredth of maximum and during quieter periods we can be listening at one thousandth of maximum power.
These are equivalent to -10dB, -20dB and -30dB relative to maximum power.

This normal listening does not require any listener to change capacitors.
 
I took it to mean power output i.e. if you like to listen to music at say 5 Watts/channel, you should have an amplifier capable of delivering 80 Watts.

Seemed to be unique view of the problem. I literally can't stand it when distortion gets to steady state ~3%. I don't care about volume that much, sum of everything that can go wrong from an over taxed amp at 3 Watts or old cassette player. They seemed to be targeting that one note or drum beat that will spoil the whole experience for them.

I don't think I will change but I can see their point. Mona Lisa with a mustache would kind of kill the rest of the painting.

I trend towards power supplies that are just good'nuff. Transformer output geared at minimum requirements and capacitors just enough to make the hum go away. I don't worry about distortion on a single rim shot >3% in a few hours of listening.
 
Listening to 5W/channel will be described by some or many as too loud. Especially if they only had an 80W/channel amplifier for that 5W listening session. That leaves just 12dB for transients over the average level.

I generally listen at less than 1W and use amplifiers of ~60W to 170W
 
Is it suitable for a subwoofer amplifier?
I plan on building the version with the TDA7293 as a subwoofer amp, the subwoofer is 2ohm ~1200W RMS, how many output pairs per amp would you recommend for that kind of power (or ~1000W RMS is more than enough)? Something along the lines of 3-4 pairs per amp?

Thanks in advance.
T.C.
 
I made this amp, and like I said before it's amazing. Low cost, few components and it kicks.
My first one blew up when power went down because of lightning storm( I think, it just didn't work after that day), so I made new one. I made everything the same like last time, but this one has a problem. It's like sync resistor doesn't sync good. There are popping sounds and short term dc signals or something (speaker moves out like it plays really low and high volume bass) and generally speaker doesn't play what it should. Everything is wired properly, and values are the same? Any ideas what's wrong?