okay guys im a bit confused down here.
i have a 25-0-25 200va transformer.
how do you calculate how much can this amplifier put in 4,6,8ohm loads with my transformer. i posted this earlier. but since this is not a 100% efficient amp i dont understand how can it put 200w in any load?
astute guys, guide me.
i have a 25-0-25 200va transformer.
how do you calculate how much can this amplifier put in 4,6,8ohm loads with my transformer. i posted this earlier. but since this is not a 100% efficient amp i dont understand how can it put 200w in any load?
astute guys, guide me.
he uses the casing of a psu. see pics carefully he has a torrroidal stacked beneath :-l
The ring-transformer is inside the ATX-PSU Case, i just went with the ATX-PSU Case as it "fit" the purpose
, also there are 2x 5600uF capacitors in thereI been busy with a lot of projects etc so i have not made any more amps recently, but im planning on making one with an SMPS instead of the heavy ring-transformer, also it takes ALOT less space in the case, so would be cool to completely transform a ATX-PSU case to a 4x AMP for Surround/BI-AMP/Bridge purpose, always nice to have a versatile amp
Power calculation is easy. With dual Power supply of 25V, the max. power is given by this formulas:
U = I * Z (Ohms law)
P = U * I = I^2 * Z = U^2 /Z
For audio power in this case:
P (RMS) = (U-1)^2 /Z /2
-1V (theoretically - 0,7V) due to the rail clipping and saturation of the powertransistors. With some MOS FETS it is possible that -1V is around - 0,25V.
And /2 due to the fact that a sinus wave will give half the power of a block wave.
With a BTL circuit you double the voltage so the power is times 4. But note the current limits!
So with +/- 25 V and 4 Ohm in a single ended amp you have 24^2 /4 / 2 = 72Watt.
Note that chipamps have a current limit of e.g. 6A.
With 24V and 4 Ohm the max current = 6A, so this will just do the work.
With BTL you cannot allways double the power because the current limit is allready reached. You need a chipamp with 12A current limit to push 4 * 72 = 288W into a 4 Ohm speaker from a BTL feeded with 25V.
If you use a 2 Ohm speaker you will get less power. The voltage is enough, but you cannot put enough current through the speaker. In that case the calculation is as follows:
P (RMS) = I^2 * Z /2.
So with 2 Ohm speaker and 6A current limit the P(RMS) = 6*6*2/2 = 36 W only. And not what you would perhaps expect 2 * 72W = 144W.
In Caraudio with 4 Ohm speakers in BTL you can obtain max
(14,4 - 2)^2 / 4 /2 = 18W RMS and 36W with 2 Ohm speakers.
Do not believe people who say it gives 50W and even more!! It is impossible, unless you transform the car voltage to a higher level with an inverter.
The most powerfull chipamps that I know have a 7A current limit only. You can boost that by additional powertransistors.
U = I * Z (Ohms law)
P = U * I = I^2 * Z = U^2 /Z
For audio power in this case:
P (RMS) = (U-1)^2 /Z /2
-1V (theoretically - 0,7V) due to the rail clipping and saturation of the powertransistors. With some MOS FETS it is possible that -1V is around - 0,25V.
And /2 due to the fact that a sinus wave will give half the power of a block wave.
With a BTL circuit you double the voltage so the power is times 4. But note the current limits!
So with +/- 25 V and 4 Ohm in a single ended amp you have 24^2 /4 / 2 = 72Watt.
Note that chipamps have a current limit of e.g. 6A.
With 24V and 4 Ohm the max current = 6A, so this will just do the work.
With BTL you cannot allways double the power because the current limit is allready reached. You need a chipamp with 12A current limit to push 4 * 72 = 288W into a 4 Ohm speaker from a BTL feeded with 25V.
If you use a 2 Ohm speaker you will get less power. The voltage is enough, but you cannot put enough current through the speaker. In that case the calculation is as follows:
P (RMS) = I^2 * Z /2.
So with 2 Ohm speaker and 6A current limit the P(RMS) = 6*6*2/2 = 36 W only. And not what you would perhaps expect 2 * 72W = 144W.
In Caraudio with 4 Ohm speakers in BTL you can obtain max
(14,4 - 2)^2 / 4 /2 = 18W RMS and 36W with 2 Ohm speakers.
Do not believe people who say it gives 50W and even more!! It is impossible, unless you transform the car voltage to a higher level with an inverter.
The most powerfull chipamps that I know have a 7A current limit only. You can boost that by additional powertransistors.
thanks for your replies zanden! i always knew the ohms law. the basics of power transmission and losses.v=i*r and p=V*I*R but your posts made it clear about /2 sine wave concept! thanks a ton!
very informative post. a 25-0-25 transformer rectified will give a higher voltage?
i know it might sag under load.
i have a small confusion down here-
i plan on driving two subwoofer each measuring 6ohm. connecting them in parallel will yield 3ohm resistance. now, according to the calculation you mentioned, assuming i have exact 25v(due to rectification of transformer output and filtering then again -1 your clipping and saturation voltages)
the max power transferred is (25^2 /3 )/2=104w RMS.is this doable on 25v voltages and 4amp current(transformer)? can you kindly tell me how do i find out the effect of current limit you mentioned about in this circuit?
say i make a bare simple tda7293 circuit using the above transformer. will it still put out the same amount of power? i believe from the datasheet's graph it only tells me that you can put out 45w with 26v to a 8ohm load?
i am bit confused with all the stuff. are the transistors at all required?
very informative post. a 25-0-25 transformer rectified will give a higher voltage?
i know it might sag under load.
i have a small confusion down here-
i plan on driving two subwoofer each measuring 6ohm. connecting them in parallel will yield 3ohm resistance. now, according to the calculation you mentioned, assuming i have exact 25v(due to rectification of transformer output and filtering then again -1 your clipping and saturation voltages)
the max power transferred is (25^2 /3 )/2=104w RMS.is this doable on 25v voltages and 4amp current(transformer)? can you kindly tell me how do i find out the effect of current limit you mentioned about in this circuit?
say i make a bare simple tda7293 circuit using the above transformer. will it still put out the same amount of power? i believe from the datasheet's graph it only tells me that you can put out 45w with 26v to a 8ohm load?
i am bit confused with all the stuff. are the transistors at all required?
Last edited:
I forgot: a 25V AC will give times SQRT(2) DC. So about 35V. With load it will easily decrease to 30 - 33V, depending on size of capacitors.
TDA 7293 has a 6,5A current limiter on chip. So the max power into 3 Ohm with this chip is only
6,5*6,5*3/2 =about 60W.
With 35V and no BTL the rail can deliver (35-1)V/3Ohm = 11,3A. So: the voltage is high enough, but the max current of the chip will limit the performance by giving ugly distortion.
With 25V the rail still delivers 24V/3 Ohm = 8A. Enough for 104W, but too much for the poor TDA. It will clip at 6,5A and give ugly distortion.
If the transformer delivers 4A continu, this means that if you have big capacitors, your Amp can for some short period of time deliver more than 4 A. But not continuously of course. Note that the sinus wave is only a short time of its cycle on the top. But if the chip clips or the powersupply, due to too small C, fails at this maximum, you will get distortion.
The graph tells 8 Ohm 26V --> 50W 10%D and 40W 0,5%D.
My calculation tells you: (26-1)*(26-1)/8/2 = 39W. Pretty good!
The transistors are required if you want more max current than 6,5A. You can choose: lower impedance ==> more current and lower voltage, use transitors.
higher impedance ==> less current higher voltage use BTL, no transistors
The TDA goes up to +/- 50V. But mind the heat production!
TDA 7293 has a 6,5A current limiter on chip. So the max power into 3 Ohm with this chip is only
6,5*6,5*3/2 =about 60W.
With 35V and no BTL the rail can deliver (35-1)V/3Ohm = 11,3A. So: the voltage is high enough, but the max current of the chip will limit the performance by giving ugly distortion.
With 25V the rail still delivers 24V/3 Ohm = 8A. Enough for 104W, but too much for the poor TDA. It will clip at 6,5A and give ugly distortion.
If the transformer delivers 4A continu, this means that if you have big capacitors, your Amp can for some short period of time deliver more than 4 A. But not continuously of course. Note that the sinus wave is only a short time of its cycle on the top. But if the chip clips or the powersupply, due to too small C, fails at this maximum, you will get distortion.
The graph tells 8 Ohm 26V --> 50W 10%D and 40W 0,5%D.
My calculation tells you: (26-1)*(26-1)/8/2 = 39W. Pretty good!
The transistors are required if you want more max current than 6,5A. You can choose: lower impedance ==> more current and lower voltage, use transitors.
higher impedance ==> less current higher voltage use BTL, no transistors
The TDA goes up to +/- 50V. But mind the heat production!
according to what i understand, i actually dont need any transistors in my case when my supply is giving only 4amp current which the chip can handle itself.. whereas on the other end, i should use the transistors when i am dealing with currents higher than 6.5amperes(bigger transformers)?
so should i go the simple minimal tda7293(or maybe BTL) way with a LPF?
i have already given you what i have with me already.. kindly suggest which way should i go ^_^ (sorry for the noobish questions)
so should i go the simple minimal tda7293(or maybe BTL) way with a LPF?
i have already given you what i have with me already.. kindly suggest which way should i go ^_^ (sorry for the noobish questions)
Last edited:
Your first sentence is partly right. As I wrote: if the trafo supplies 4A contiously, nevertheless with good (and necessary!!!) capacitors the amp can provide temporarily far more current through the load. So take care.
The simple TDA will do normally in home applications as 10W RMS will do......
The simple TDA will do normally in home applications as 10W RMS will do......
i believe i can do with better way to drive subs. but sadly in my part of the world, there is nothing called class D/class H. importing pcbs is like importing a bomb huge duties aswel as bad uneducated customs department. if i use TDA only for subs, ill be wasting most of the energy in heat :-| damn even paypal is so restricted that you cant even buy anything with it online. but the good part is.. i know certain chip suppliers in my place. i can get genuine chips for cheap. fabrication of two sided pcb aswel as soldering the chips(provided that i can get cheap class d chips) is not my piece of cake... choose your poison if you may.. only left with old class AB chips :\
on the other hand when you mention 10w rms. i believe my tda2050 can put out that much easily than complicating it with bigger ICS
huge duties aswel as bad uneducated customs department. if i use TDA only for subs, ill be wasting most of the energy in heat :-| damn even paypal is so restricted that you cant even buy anything with it online. but the good part is.. i know certain chip suppliers in my place. i can get genuine chips for cheap. fabrication of two sided pcb aswel as soldering the chips(provided that i can get cheap class d chips) is not my piece of cake... choose your poison if you may.. only left with old class AB chips :\on the other hand when you mention 10w rms. i believe my tda2050 can put out that much easily than complicating it with bigger ICS
The 2050 is at its max with half the power of the TDA729x and gives distortion at its max.
If you use TDA729x you will not work on the edge of its capacity which results in very low distortion! That is the advantage. In Europe LM3886 is very low priced and comparable to TDA729x for your goals. It does not require many components like the 2050.
Good luck with your choice!
If you use TDA729x you will not work on the edge of its capacity which results in very low distortion! That is the advantage. In Europe LM3886 is very low priced and comparable to TDA729x for your goals. It does not require many components like the 2050.
Good luck with your choice!
you don't hear the smoothing capacitors except when they supply current to the load for low frequency signals.
You never hear the transformer, because most of the time it is not connect to the load. The few times it is connected to the load, the Builder has put in an intervening set of filters to remove the transformer influence on the sound emanating from the load.