Thank you! But I mean, amplifiers that uses transformer as a power supply, the same calculation of current needed to supply as of car amplifier?

 

Thank you! But I mean, amplifiers that uses transformer as a power supply, the same calculation of current needed to supply as of car amplifier?

 

A car has a voltage that is 14.4V when the engine is running. The voltage drops to 13.2V when the engine is turned off. You were talking about using a 12V power supply so the output power will be a lot less from the amplifiers.

The average of 14.4V and 13.2V is 13.8V. You need a 21V center-tapped transformer with 2 rectifiers or an 11V single winding transformer with a bridge rectifier.

The transformer must have a current rating that is 1.414 times the DC current used by the amplifiers.

 

Thank you Mr Audioguru! However if I have a 13.8V 15A power asupply, how would I know the output of an amplifier that this kind of power supply can handle?

 

Thank you Mr Audioguru! However if I have a 13.8V 15A power supply, how would I know the output of an amplifier that this kind of power supply can handle?

13.8V x 15A is 207W from the power supply. The output from the amplifiers will not be 207W because some of the power supply power causes heating in the amplifiers.

I showed that a TDA7240A bridged amplifier IC with a 13.8V supply and driving a 4 ohm speaker has an output of about 13.5W when it is barely clipping with low distortion and it produces about 11W of heat so its total power from the power supply is 13.5W + 11W= 24.5W.

Then you can have many amplifiers driving speakers: 207W/24.5W= 8 of them.

If you add a voltage stepoup circuit then a higher power amplifier can have more output power than only 13.5W.

 

How about if I only use two amplifiers (left and right channel), what is the output of each amplier using a 13.8V 15A power supply? thanks Mr Audioguru...

 

How about if I only use two amplifiers (left and right channel), what is the output of each amplier using a 13.8V 15A power supply?

Nobody can answer this question because all the details about the type of amplifier and the load impedance are missing.

If each amplifier is a single-ended TDA2003 IC driving an 8 ohm speaker then the output power is only about 2.4W for each channel.
If each amplifier is a bridged TDA7240A IC and the load is 4 ohms then the output power is 13.5W for each channel.
If a voltage stepup circuit is used with a class-D amplifier circuit then the output might be 93W for each channel.

 

No luck with the OP eh ! Guru ?

He is stuck with 15A supply. All he think is that the supply is totally responsible for amp power.

Any Idea what the OP has as a power amp?

 

Oh yes! thats what I mean. what op amp suited for that power supply? tnx!

 

Most opamps operate from a 13.8V power supply.

What will you use an opamp for? An opamp is low power and cannot drive a speaker.
A power amplifier is used to drive a speaker. The datasheet for a power amplifier IC shows its output power and distortion at various supply voltages and various speaker impedances.

 

I'm sorry. I mean power amplifier. tnx!

 

Look at post #25.
I already mentioned using a TDA7240A power amplifier IC.

 

I always thought a crossover was for speakers by themselves, routing the output of the power amp to the speaker best able to handle the sound. I'm still trying to catch up on this thread, about the idea of powered crossovers.

 

I always thought a crossover was for speakers by themselves, routing the output of the power amp to the speaker best able to handle the sound.

Good sound systems use an active crossover using opamps to make the filters. Then the woofer has its own filter and power amplifier, the mid-range speaker has its own bandpass filter and power amplifier and the tweeter has its own filter and power amplifier.

Then if the woofer amplifier is driven too hard causing clipping distortion, the resulting harmonics do not go to the mid-range or tweeter to destroy them or cause very bad sound.

Ordinary speakers have coils and capacitors to make passive crossover filters but the resistance of the coils cause problems.

 

How are the power levels maintained with op amps? From what I'm reading, I think the OP may be having problems with this too. If a amplifier outputs 25 watts, and (for the sake of argument) the mid range is 10 watts, are the op amps outputting 10 watts too, along with the power amp (at those frequencies)?

 

How are the power levels maintained with op amps? From what I'm reading, I think the OP may be having problems with this too. If a amplifier outputs 25 watts, and (for the sake of argument) the mid range is 10 watts, are the op amps outputting 10 watts too, along with the power amp (at those frequencies)?

Audio levels fluctuate very much, maybe 100,000 times from low level to full level.
The opamps in the active crossover filters follow the level fluctuations.

The active crossover filter opamp drives the input of its power amplifier. The power amplifier drives its speaker.

The full power input level to the power amplifiers (and also the max output level of the active crossover filters) is only line level (a few hundred milli-volts RMS) because the power amplifiers have a voltage gain of about 30 times and the volume control which is in between attenuates enough to avoid the power amplifiers to have clipping.

 

I still do not get all the confusion by the OP.

An OPAMP is not desgned to drive heavy loads. Except those Power OP amps dedicated as Power amps.
The opamps are used at the crossover which has power levels in mW range.

An active crossover is far better than a passive one

 

So the active crossover is at the input of the power amp? Or if it is at the output, how is it steering the frequencies?

Time for google.

*************

That was quick, several power amplifiers, each for it's own frequency range. Somehow I get the feeling the OP only has one power amp per channel. In such a case, active crossover networks do not apply.

 

They are 2 types of 'em.
Active & passive.

The passive type is more common and is used in consumer goods. They are wired internally, inside the speaker. Bunch of Caps and Resistors and Inductors form a typical network.
The design and type depends on one's need plus the cabinet types.
Passive networks wastes lot's of power and is somewhat unreliable. There values are calculated to the desired cutoff and pass frequencies. The type too plays in important role in how well the network blocks the unwanted band.

As power of the speaker increases so does the network sizes, meaning the caps voltages and Inductor sizes.
All in all they are pretty useless for High end audio reproduction.
Passive can only be used between the amp out and the speaker.
Each driver has it's own network.
The tweeter's don't like bass, so the HP cut's off base at a predetermined value.
The mid and low ranges also has the same setup.

On the hand, an active network cut's off the frequencies at preamp level and can be made less expensive and far better to operate in the desired frequencies.
But the draw back is that an Amplifier is needed for each driver ( speaker).

The Amp sums to the no. of speakers desired by the individual.
The tweeter amp can be small and of Hi end. Meaning low distortion type to produce those highs. The amp can be designed with the load and power in mind, which makes it better and reliable.
So does the mid if used and bass drives.
The bass drive is the one which users the power. Alt least around 80% of total power of an active 3 way system is used in producing the base

Eg: Values are figurative.
A 100W 3 Way, will have a round 5W of power for Highs, 15W mid and the 80W of power is used by bass unit.
The tweeter will have a 5W amp, 15W for the Mid and a powerful 80W for the base.

U might say that the 80W can be used to power a full range speaker. True but an active system will sound just heavenly. Is more reliable and produces sounds without any distortion at the maximum level.
An active 100W system can outcast a system powered @ 500W full range anyday. Count on it.

 

I think I said that, using many less words.