http://www.electroclub.info/invest/tda7294/TDA7293.pdf
here is the datasheet
i have 3 things that i want to know
1) what does æ symbol mean at quick reference data
2) are the 120v the maximum supply voltage? and if i get it right, the norman supply voltage is 50V dc
3) if i want to convert 220ac to dc, do i have to first transfer it to 72vac? if i am right, then after diode bridge and caps, it should be about 50v dc, am i right?
here is the datasheet
i have 3 things that i want to know
1) what does æ symbol mean at quick reference data
2) are the 120v the maximum supply voltage? and if i get it right, the norman supply voltage is 50V dc
3) if i want to convert 220ac to dc, do i have to first transfer it to 72vac? if i am right, then after diode bridge and caps, it should be about 50v dc, am i right?
Maximum supply voltages are absolute max ratings with no signal. Less is better for normal use 
Somewhere around -/+ 40 volts DC would be ideal. That means you need a 25-0-25 volt AC transformer. The 25 volts AC will be a little higher than that at light loading, say nearer 27 volts. That will give around 38 volts DC per winding after rectifying and smoothing. So that gives a total of 76 volts.
(You have to look and consider what the max power dissipation in the chip will be when driving your speakers. Thats why lower supply voltages are used in practice. Reliablity improves dramatically too)
Somewhere around -/+ 40 volts DC would be ideal. That means you need a 25-0-25 volt AC transformer. The 25 volts AC will be a little higher than that at light loading, say nearer 27 volts. That will give around 38 volts DC per winding after rectifying and smoothing. So that gives a total of 76 volts.
(You have to look and consider what the max power dissipation in the chip will be when driving your speakers. Thats why lower supply voltages are used in practice. Reliablity improves dramatically too)
You've alot of reading to do
The 25-0-25 denotes a transformer with a "centre tap" between its two 25 volt windings. In other words its like a 50 volt winding with a connection in the middle. That point becomes the amplifiers "zero" or ground point.
Rectifing means using diodes to change the AC voltage from a transformer into DC voltage.
Rectifier - Wikipedia, the free encyclopedia
The 25-0-25 denotes a transformer with a "centre tap" between its two 25 volt windings. In other words its like a 50 volt winding with a connection in the middle. That point becomes the amplifiers "zero" or ground point.
Rectifing means using diodes to change the AC voltage from a transformer into DC voltage.
Rectifier - Wikipedia, the free encyclopedia
"Boot loader" seems to be some odd term they use. I've never come across that before in amp design. What it refers to is the "Bootstrap" part of the circuit (within the chip) that allows the output voltage to add to the supply voltage and so allow (internally in the chip) a higher voltage to be ued for the output driver stages. Its just for efficiency and to squeeze the most voltage swing out of the design. Its an old technique and uses those small electrolyitics to work.
You have to understand the power supplies...
The amp normally runs on a split or dual supply. That means an equal DC voltage ABOVE and an equal voltage BELOW a zero point.
A 38 volt winding, thats 38 volts AC and would give 38* root 2 which is 53 volts DC. That is just ONE rail. All you could do with that is make the "single rail" version of an amp which is AC coupled (big cap to couple the speaker to the amp). Its to high to double up on and make a dual supply.
For dual rail you need the 25-0-25 type transformer like this
MCTA250/25 - MULTICOMP - TRANSFORMER, 250VA, 2 X 25V | CPC
You have to understand the power supplies...
The amp normally runs on a split or dual supply. That means an equal DC voltage ABOVE and an equal voltage BELOW a zero point.
A 38 volt winding, thats 38 volts AC and would give 38* root 2 which is 53 volts DC. That is just ONE rail. All you could do with that is make the "single rail" version of an amp which is AC coupled (big cap to couple the speaker to the amp). Its to high to double up on and make a dual supply.
For dual rail you need the 25-0-25 type transformer like this
MCTA250/25 - MULTICOMP - TRANSFORMER, 250VA, 2 X 25V | CPC
oh... tnx for the info...
actually didnt know what the +/- at the supply voltage ment... and i think it would be better if i used 30-0-30 transformerr? on the other hand... the min voltage is +/- 12 volts... if i use 2x24v (2.08 amp) transformers... i would not be able to run 2 of the chips in parallel, because of the amp limit... i would need to get 2 transformers, for each chip, right?
actually didnt know what the +/- at the supply voltage ment... and i think it would be better if i used 30-0-30 transformerr? on the other hand... the min voltage is +/- 12 volts... if i use 2x24v (2.08 amp) transformers... i would not be able to run 2 of the chips in parallel, because of the amp limit... i would need to get 2 transformers, for each chip, right?
You are better setting out what the design goals are first.
What is the max power you want to aim for and into what impedance ?
For example 80 watts RMS into 6 ohm or 100 watts RMS into 8 ohm and so on. From that you can calculate the supply voltages needed and then move on to decide what transformer to use
What is the max power you want to aim for and into what impedance ?
For example 80 watts RMS into 6 ohm or 100 watts RMS into 8 ohm and so on. From that you can calculate the supply voltages needed and then move on to decide what transformer to use
w8... if i use 24x2 (2.08 amp) transformer, and the actual supply voltage is +/- 24v, not 24v, doesnt it mean, that the full voltage is 48v, and if i put a 100w amp it uses 100/48 wich is about 1.04A, so if i put 2 of the 100W amps the total amperage is 2.08A, and it shouldent burn...
am i right?
am i right?
OK, so 100 watts RMS into 4 ohm means you need to develop 20 volts RMS at the amp output. Thats worked out as V = square root (100*4).
20 volts RMS is 28.28 volts peak and 56.56 volts peak to peak (that's Vrms * root 2)
So we need at least 28.28 volts DC as a rail PLUS losses which are losses in the chip and general resistive losses. So around 35 volts DC would seem suitable. Thats 35-0-35 volts. If you built a single rail amp then that would be a single 70 volt rail. Yes
So the transformer needs to be 35 divided by root 2 which is 24.75 volts AC. So a 25-0-25 volt transformer should cover it.
The VA rating of the transformer needs to be determined.
Ipeak = Vpeak/R so that is 28.28/4 which is 7 amps
Iaverage is Ipeak/pi which is 7/3.142 which is 2.23 amps.
That's for one channel, so you are looking at a 160va transformer for mono and over 300va for stereo. Build in a good margin and that means using a 500va transformer (as a standard off the shelf part)
Next question.... do you really (really really) need 100 watts RMS ?
Have a read at this
http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html
20 volts RMS is 28.28 volts peak and 56.56 volts peak to peak (that's Vrms * root 2)
So we need at least 28.28 volts DC as a rail PLUS losses which are losses in the chip and general resistive losses. So around 35 volts DC would seem suitable. Thats 35-0-35 volts. If you built a single rail amp then that would be a single 70 volt rail. Yes
So the transformer needs to be 35 divided by root 2 which is 24.75 volts AC. So a 25-0-25 volt transformer should cover it.
The VA rating of the transformer needs to be determined.
Ipeak = Vpeak/R so that is 28.28/4 which is 7 amps
Iaverage is Ipeak/pi which is 7/3.142 which is 2.23 amps.
That's for one channel, so you are looking at a 160va transformer for mono and over 300va for stereo. Build in a good margin and that means using a 500va transformer (as a standard off the shelf part)
Next question.... do you really (really really) need 100 watts RMS ?
Have a read at this
http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html
well... actually the 100w arnt the important ones... i just picked the chip, and one of the reasons was the flexability it provides...
i have a 24x2 toridial transformet, wich i could use it would provide 24*sqrroot of 2... wich is around 33,6 DC volts to each of the windings. the transformer has a 2.08A limit, so if we squeeze all that we can, then 33,6*2*2,08=140W... am i right?
i have a 24x2 toridial transformet, wich i could use it would provide 24*sqrroot of 2... wich is around 33,6 DC volts to each of the windings. the transformer has a 2.08A limit, so if we squeeze all that we can, then 33,6*2*2,08=140W... am i right?
It doesn't quite work like that in practice. Transformers are rated for their max current into a resistive load. A bridge rectifier and reservoir caps draws "a lot of current for short time" on each cycle as the bridge only conducts at the tops of the sine wave to bring the caps back to full voltage. For most of the cycle no current flows.
So in practice... its a bit on the small side for two channels.
So in practice... its a bit on the small side for two channels.
heh... was looking for a chip, and came across this one
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1565.pdf
and i think this one could work
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1565.pdf
and i think this one could work
oh yeah...
http://lv.xn--sondae-tpb.com/_y/agifapcgompaleinebeijohgphcaecli_/bo1.jpg
what is this called... i just dont know the term... and the main question was, can i use nail polish to draw the lines, or the acid would just burn througs...
http://lv.xn--sondae-tpb.com/_y/agifapcgompaleinebeijohgphcaecli_/bo1.jpg
what is this called... i just dont know the term... and the main question was, can i use nail polish to draw the lines, or the acid would just burn througs...
The TDA7295 looks to have a lower max supply rating.
Making PCB's is something you have to learn by doing. Nail varnish is probably etch proof but the end result won't be pretty. You can get etch resist pens and transfers. The board in your picture looks a fibre glass roller tinned board.
Why don't you get a PCB ready made, I think they are advertised from the usual suspects
Making PCB's is something you have to learn by doing. Nail varnish is probably etch proof but the end result won't be pretty. You can get etch resist pens and transfers. The board in your picture looks a fibre glass roller tinned board.
Why don't you get a PCB ready made, I think they are advertised from the usual suspects
well thats not what i ment... well nevermind that
only now i realize, how bad i know english terms
actually the transformer i was talking about is 2x24V 2x2.08A and i found a datasheet with graphs Here
http://www.datasheetcatalog.org/datasheet2/9/0ozxelyhtgfl5jsx9108fj3sqq3y.pdf
it seems that with 8 ohm speakers, and +/- 34V power supply the max output power is somewhere around 80w, that means, that i can safely put 2 of the chips with the transformer, cant i? it doesnt have the 4ohm speaker supply vs power output graph though...
only now i realize, how bad i know english terms
actually the transformer i was talking about is 2x24V 2x2.08A and i found a datasheet with graphs Here
http://www.datasheetcatalog.org/datasheet2/9/0ozxelyhtgfl5jsx9108fj3sqq3y.pdf
it seems that with 8 ohm speakers, and +/- 34V power supply the max output power is somewhere around 80w, that means, that i can safely put 2 of the chips with the transformer, cant i? it doesnt have the 4ohm speaker supply vs power output graph though...
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