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Thoughts on these audio amp circuits?

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Re: [moved] Query about VU meters (led bargraph)

The amplifier I bought recently for my build I dont think its as poweful as the specs say it is I want to build a class D amplifier on my own, something with some Mosfets.

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I am aware of the speaker set up, as I have done a couple of them over the years but building the amplifier is the part I want to learn.
 

Re: [moved] Query about VU meters (led bargraph)

The amplifier I bought recently for my build I dont think its as poweful as the specs say it is I want to build a class D amplifier on my own, something with some Mosfets.
Click to expand...

It is more demanding to design the power supply rather than the amplifier...
 

Re: [moved] Query about VU meters (led bargraph)

I plan to use a liner supply rather than switch mode since thats the one I can build.

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the power supply is the one I think I would have least problem with the amplifier is the unfamiliar task for me
 

Re: [moved] Query about VU meters (led bargraph)

Audioguru are you a member of a forum call Electro Tech online
 

Re: [moved] Query about VU meters (led bargraph)

I have seen your name here and there was just wondering if it was the same person.

Anyway I made mention that I wanted to build an amplifier of my own, I saw some versions that used pwm chips but I mostly see low wattage set ups I know that the amp can be built based up on mosfets could I get some assistance on how to start off
 

[Several posts have been moved here from the thread about making VU bargraph meters.]

Not sure whether I already posted this class D audio amplifier. It's vastly simplified, to illustrate the operating principle. It will need a power supply and various safeguards.



By raising supply voltage, and paralleling mosfets, you can gain more power.

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The class D amplifier is not my design. It is (or was) included in the menu of Falstad's animated interactive simulator. Free to download and use at:

www.falstad.com/circuit
 

Ok so In this case for example I could use a tl071 opamp with a pair of Irfz44n Fets and add a 4 or 8 ohm speaker just as the circuit is and it would work or would I need to make mods to opamp circuit and output circuit.
 

The 1kHz switching frequency will be audible and since the amplifier has no negative feedback its distortion will be awful.
 

class d.png

Ok I just did this drawing
 

Where is the saw tooth waveform coming?
 

I am just working from the example I got, is something wrong with my drawing?
 

Enzy said:
Ok I just did this drawing
Click to expand...

What waveforms are output from your schematic? If you want to make it into a class D type, then many details need to be filled in.

You need to make a sawtooth wave oscillator (as C_mitra points out).
The carrier frequency needs to be greater than 1 kHz (as Audioguru points out).
The frequency of the carrier depends on whether you are amplifying bass or midrange or treble.

The op amp needs a split supply. Your op amp has a single-ended supply. The rail-to-rail voltage cannot exceed safe parameters for the op amp.
 

class d.png

Update to the drawing based on what you guys just told me, how does it look now.
 

Enzy said:
View attachment 130432

Update to the drawing based on what you guys just told me, how does it look now.
Click to expand...

You schematic is shaping up.
Power supply to the mosfets is greater that the supply to the op amp driving them.
The op amp needs the same voltage power supply, or else it cannot turn the mosfets entirely On and entirely Off.

This raises the question whether you can find an op amp which is able to endure 48V to its supply leads.
 

I think you are confused with triangular wave with a sawtooth wave. Like in the oscilloscope horizontal scan, we use a sawtooth waveform. It takes the electron beam from left to right and then blanks it and rapidly comes back to left end. If you integrate a square wave, you will get a triangular wave. Divide the work in parts and check and then put it back in the main drawing. You will also need some input conditioning. Remember that if there is some overlap between bass and midrange, they must join smoothly in the two amplifiers (else you can guess the result) and if there is no overlap then the cut must be sharp so that they can be neatly spliced. You need to manage the input level uniformly in all the amplifiers.
 

Hi,

I didn´t follow the whole thread, therefore I may have missed a lot.

I just see the schematic of post#74 .. it has several big mistakes... no way to get any sound out of it.
It´s more likely it kills your speakers, or kills itself.

* The sawtooth/triangle will saturate at negative rail. --> But you need a sawtooth/triangle precisely swinging around zero volts. Else DC will kill your speakers.
* The TL071 is completely unsuitable here. It simply is not suited for switching circuits. And it suffers from phase reversal. --> use a comparator.
* I don´t think the capactive driving of the gates will work.
* No overcurrent, no overvoltage protection at the FETs. Maybe they burn soon after power ON.
* An undamped LC filter at the output is an undamped resonator.. As soon as you disconnect the speaker expect very high voltage and very high current killing your FETs almost immediately.

I recommend to use ready to buy class D amplifiers.

Klaus
 

KlausST said:
Hi,

I didn´t follow the whole thread, therefore I may have missed a lot.

I just see the schematic of post#74 .. it has several big mistakes... no way to get any sound out of it.
It´s more likely it kills your speakers, or kills itself.

* The sawtooth/triangle will saturate at negative rail. --> But you need a sawtooth/triangle precisely swinging around zero volts. Else DC will kill your speakers.
* The TL071 is completely unsuitable here. It simply is not suited for switching circuits. And it suffers from phase reversal. --> use a comparator.
* I don´t think the capactive driving of the gates will work.
* No overcurrent, no overvoltage protection at the FETs. Maybe they burn soon after power ON.
* An undamped LC filter at the output is an undamped resonator.. As soon as you disconnect the speaker expect very high voltage and very high current killing your FETs almost immediately.

I recommend to use ready to buy class D amplifiers.

Klaus
Click to expand...

I am only learning to build my own so far I am getting information and I make the corrections to the schematic based on what you guys say, Ill get there. all the improvements you says it needs I think the other guys know that already but just taking me through it in stages, I actually wanted to use a comparator but while I can find the function of a comparator I cannot find a part number for one and I dont know any but ill read some more.

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c_mitra said:
I think you are confused with triangular wave with a sawtooth wave. Like in the oscilloscope horizontal scan, we use a sawtooth waveform. It takes the electron beam from left to right and then blanks it and rapidly comes back to left end. If you integrate a square wave, you will get a triangular wave. Divide the work in parts and check and then put it back in the main drawing. You will also need some input conditioning. Remember that if there is some overlap between bass and midrange, they must join smoothly in the two amplifiers (else you can guess the result) and if there is no overlap then the cut must be sharp so that they can be neatly spliced. You need to manage the input level uniformly in all the amplifiers.
Click to expand...

Its actually a saw tooth generator circuit I did some reading and realized that triangle wave and saw tooth waves are different. Ill see if I can make changes as I go.
 

BradtheRad said:
You schematic is shaping up.
Power supply to the mosfets is greater that the supply to the op amp driving them.
The op amp needs the same voltage power supply, or else it cannot turn the mosfets entirely On and entirely Off.

This raises the question whether you can find an op amp which is able to endure 48V to its supply leads.
Click to expand...

I haven't found any opamps to manage 48v as yet, I changed the opamp to a comparator and removed the Cap from the output going to the gates of the FEts.
 

Attachments

  • class d.png
    class d.png
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Your schematic has MANY errors. Maybe you should first learn about comparators and Mosfets then learn something about class-D amplifiers from one of the many tutorials on the internet, like this one:http://www.irf.com/product-info/audio/classdtutorial606.pdf .

When the Mosfets are used as switches then the comparator does not need a high voltage output rating.

EDIT: I forgot to say that the lousy old 741 opamp design is 48 years old and is useless to try to make a high frequency triangle wave.
 

Attachments

  • class-D amplifier output.png
    class-D amplifier output.png
    15.1 KB · Views: 59
Last edited:

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