Stereo Audio power amplifier 2 x 40W - 80W

[audioguru]

The SMPS for a car amplifier that I posted operates at about 65kHz so it uses extremely fast Mosfets. Transistors are much too slow for the high frequency. The article mentions the IRF540 Mosfet which is very common, and hundreds of other suitable Mosfets are available.

The article says how to make the transformer, changing the number of turns for its secondary to get the voltage output that is desired. I haven't seen high frequency, high power transformers like this for sale anywhere.

[faizanbrohi]

Actually it seems like i have to make a toriodal transformer which it says about 4cm Dia , Isn't there any simpler schematic please for god sake..

[audioguru]

Isn't there any simpler schematic

You could make a simple low-frequency inverter with an ordinary huge and heavy power transformer.

[faizanbrohi]

As the Site says

'' A good starting point is using 4 turns for each primary (that is, 4 turns, centre tap and another 4 turns IN THE SAME DIRECTION). To calculate the number of turns of the secondary winding, multiply by the turns ratio. For example, if you want to build a +/-30V supply, the turns ratio is 30/13.8=2.2 approx, so wind 2.2 x 4 = 8.8 turns (better 9 turns, to overcome the diode losses) for each secondary (that is, again, 9 turns, centre tap and another 9 turns IN THE SAME DIRECTION). ''

And

''Another possibility is using a toroid. You can extract it from a BIG power inductor. As a guide, a 4cm diameter toroid with a section of about 1cm2 can be used for a > 250W SMPS. Winding is a little bit more complicated than with ETD cores but with a little practice is not too difficult either.''

Now

THe Idea is we can use it to make a >250W power supply using 4cm toriod and some wires. For my Output i would require

55/13.8 = 3.98 which is 4 turns and 4 x 4 = 16 turns . the problem is do i require a biggger toriod than the 4cm one ? If yes how big.

[audioguru]

His power supply makes about half the power you need. So maybe the core for the torroid should be bigger so it doesn't saturate, and use thicker wire to handle the higher current.

[faizanbrohi]

I think about 6 to 7cm toriod but be fine and 20SWG Wire gauge would be adequate , what abou u

[audioguru]

I think about 6 to 7cm toriod but be fine and 20SWG Wire gauge would be adequate , what abou u

The torroid will be good if you can find one, but 20 guage wire is too small for the primary winding, even if you parallel 6 strands. The max current will be about 62A in the primary.

[faizanbrohi]

So how muc gauge do i need any idea . 12 or 10 maybe.

[audioguru]

You were close before. 20 gauge wire can carry nearly 10A so 6 pieces of 18 gauge in parallel will be fine for the primary.

[faizanbrohi]

Hello Audio Guru , i have almost built the PCB and refined it , for the 80W Stereo That i posted the first time . i am making only a mono version for the university project. so i also need to make a preamplfier . So i had a preamplfier i made some time , but it had very bad distortion , it was made using a AN7116 Power amplfier IC , had awful distortion. I also tested it with the Power amp . didn't work good for my need.
SO here is another schematic . THere is a graph for THD also . I am making a PCB for it . Will this work for my Power Amplfier ?

[audioguru]

The distortion is quite low, but the voltage gain of the two transistors preamp is also low.
How much preamp gain is needed? What provides the input?
Why not use an audio opamp (TL071) as a preamp?

[faizanbrohi]

LM386 is also an audio opamp . well the input is from a electret mic , i toook both diagrams from the PDF . Both the documents agree that each of them might be used together.
I only want simple volume control and less bulky circuitry , how can i impelmet TL071 in it

k17.pdf

kit98.pdf

[audioguru]

The LM386 is not an opamp. It is a low-power speaker amp that is cheap and noisy.
You already have a speaker amp.

If you connect a microphone to an amplifier and speaker, how are you going to stop the acousical feedback? They will howl if the microphone can hear the output from the speaker.

There are no measurements shown for the two-transistors preamp so I think an audio opamp circuit will be much better. Here is one with a volume control:

[faizanbrohi]

IF i only use the Circuit that you have posted in and connect it to my power amp , it will have volume control . but will it have enough power to drive my power amp , and do i have to use the LM386 for that , or just use your TL071. One more thing i have made the PCB's for the LM386 and two transisitor op amp. Now will make for the TL071.

[audioguru]

The input transistors look like they are mounted backwards in the parts layout of the 1st amplifier you posted. I didn't see its schematic nor spec's so I don't know its voltage gain.

The LM386 is a cheap and noisy little speaker amp that isn't needed to drive your 40W amp. The two transistors and LM386 will work, but the TL071 preamp is much better.

[faizanbrohi]

Thanks Audio Guru i think i am making both LM386 one and the TL071 amnd then compare quality .. going to buy parts todays , thanks

[faizanbrohi]

I have tested the TL071 opamp preamp it is working great , but the sound when i connect it to the speaker it is really low, i mean it is behaving like a headphone , i think maybe the power amp would increase it .today i will build the Power amp and update you.

[audioguru]

An opamp doesn't have enough output current to drive a speaker. The opamp is designed for a load not less than 2k ohms. Also the output coupling capacitor's value is way too low to pass low frequencies to a low impedance speaker.

Post the schematic of the power amplifier. On your layout drawing it looks like its input transistor is backwards.

[faizanbrohi]

The Power amplifier uses bipolar capacitors , and they were hard to find . why are bipolar capaictors , why not use simple polar capacitors when there is an option.
and the input transistors are okay , i have a assembled version of the power amp which i bought as a guide and it is working. no problem with the input tranisitors . Just Hope the amp works .

One more thing i tested the assembled version of the power amp with a computer and it ran fine. don't know if it will work with the TL071 Preamp

[audioguru]

The Power amplifier uses bipolar capacitors

The 80W stereo amp you 1st posted? It uses polarized caps except the 56pF ceramic cap.

and the input transistors are okay

The audio input to a transistor is usually its base. Your pcb layout has the emitter as the input.

[faizanbrohi]

Hello Audio Guru , i have built the units together in one PCB they are complete . there is only one problem , the speakers are howling because of the microphone. is there any method i can apply to remove it

One more thing is that the volume when set to zero . i mean 100Kohm , it is still giving a amplified output at the speaker . i want volume at zero to be implemented where at zero no voice is there at the output what should i do , see the figure i think i should should add a resistor.

[audioguru]

the speakers are howling because of the microphone. is there any method i can apply to remove it?

Provide distance between the mic and speakers and point them in opposite directions. Turn down the volume.

One more thing is that the volume when set to zero . i mean 100Kohm , it is still giving a amplified output at the speaker . i want volume at zero to be implemented where at zero no voice is there at the output what should i do , see the figure i think i should should add a resistor.

The 100k pot in the preamp circuit is a gain control. It adjusts the gain from 1 to 22. Add a proper volume control (with an audio taper) between the preamp circuit and the power amp circuit.

[faizanbrohi]

i have a point where the preamp put out a connection between a preamp and power amp where i can implement it ?

Can i apply it like this , the first circuit shows the actual volume control circuit.

[audioguru]

Use a 47k audio taper (logarithmic) pot for a volume control. Use a dual pot with a single shaft for a stereo volume control.
The preamp output and power amp input have coupling capacitors so the pot won't mess their DC bias.

[faizanbrohi]

I have a Pot Rated at 50KA x 2 meaning 50K at both ends and A represents that it is LOg i guess , here is a picture of it.