I would like to build the LM4651/52 subwoofer amp, but have searched and seen many posts about the inductor. Do I need that inductor or can I use an active crossover? Also, if anybody has built this amp, how is the sound, reliability, and simplicity? Thanks, Mike
I do believe the inductor acts as a filter to remove any high-frequency from the switching on the OUTPUT (so no active xover here) and by doing so reconstructs the sine-wave. Not a wizz by any means on class-d amps, but I think you're going to need that inductor on the output.
So, I can't do away with the Inductor to save some money and space? It won't work without it? Also, my other question is how good is the sound and heat output?
Thanks, Mike
Thanks, Mike
YES, you do need the inductor for sure.
The output of a class-D amplifier is basically a square-wave. The LC-circuit on the output lowpass filter this into the "original" input signal, just amplified.
The output inductor on a audio calss-D amplifier is one of the more tricky parts to get right.
The inductor and capacitor togher with the load makes a lowpass filter, but since the load can change, the x-over freq. for your LC-filter also change. This means that you have to take different loads into the senario when you select the size of your inductor !!
Be also aware of the "RF-noise" a class-D amplifier can give. You should put the amplifier in some kind of metal-case.
Have fun
THomas
P.S. Check that everything works (squarewaves) before you mount the LM4652. I didn't first time around and it took me quite some time to get it going.
The output of a class-D amplifier is basically a square-wave. The LC-circuit on the output lowpass filter this into the "original" input signal, just amplified.
The output inductor on a audio calss-D amplifier is one of the more tricky parts to get right.
The inductor and capacitor togher with the load makes a lowpass filter, but since the load can change, the x-over freq. for your LC-filter also change. This means that you have to take different loads into the senario when you select the size of your inductor !!
Be also aware of the "RF-noise" a class-D amplifier can give. You should put the amplifier in some kind of metal-case.
Have fun
THomas
P.S. Check that everything works (squarewaves) before you mount the LM4652. I didn't first time around and it took me quite some time to get it going.
Yes, but it depends very much on the freq. range you want to cover and your load.
They are not that expensive; 4-5 $, so if you are locky you will only save a dollar or two.
There are some recommendations in the datasheet for the LM4651/52 somewhere.
By "size" you should not only talk about the induction of your inductor, but also of the amp-rating.
Thomas
They are not that expensive; 4-5 $, so if you are locky you will only save a dollar or two.
There are some recommendations in the datasheet for the LM4651/52 somewhere.
By "size" you should not only talk about the induction of your inductor, but also of the amp-rating.
Thomas
soundNERD
Always use double faced PCB.
My first attempt was on a breadboard and... my hi-fi started making some 'music'...
After that, in a pre-made PCB (those with holes and pads), the music was another: hot ans... puff!!
Some smoke...
So, I decided to make the double faced PCB that National has in the datasheet and... still work!
The high frequencies of the PWM are realy HIGH to use a single sided PCB.
If you check the DS (datasheet), the fsw goes up to 200khz.
Don't forget the output inductors!
You really need them!
Regards,
Pedro Martins
Always use double faced PCB.
My first attempt was on a breadboard and... my hi-fi started making some 'music'...
After that, in a pre-made PCB (those with holes and pads), the music was another: hot ans... puff!!
Some smoke...So, I decided to make the double faced PCB that National has in the datasheet and... still work!
The high frequencies of the PWM are realy HIGH to use a single sided PCB.
If you check the DS (datasheet), the fsw goes up to 200khz.
Don't forget the output inductors!
You really need them!
Regards,
Pedro Martins
One more question:
On the datasheet, the schematic says the type of caps and resistors used. can I just use any resistor and cap type?
Thanks again, Mike
On the datasheet, the schematic says the type of caps and resistors used. can I just use any resistor and cap type?
Thanks again, Mike
Hi Mike
Yes you can use any kind of resistor or capacitor as long as you use the same type as speceified. I.e. if they say 50 ohm/3 W you have to use at least a 3 W resistor.
It don't have to be a specific brand.
Thomas
Yes you can use any kind of resistor or capacitor as long as you use the same type as speceified. I.e. if they say 50 ohm/3 W you have to use at least a 3 W resistor.
It don't have to be a specific brand.
Thomas
Thomas,
My question was really referrring to the type of parts, not the brand. For example, when it says to use mylar, do I really have to use a mylar capacitor?
-Mike
My question was really referrring to the type of parts, not the brand. For example, when it says to use mylar, do I really have to use a mylar capacitor?
-Mike
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