faizanbrohi Posted July 15, 2006 Report Posted July 15, 2006 I found a commercial audio power amplfier and i have just finished it's PCB mapping . although some parts need a little image enhancement. because some connection were broken when i mapped the PCB. When i am finished i will place the corrected PCB , and details, also the preamplfier module. so here is a little not so god , under improvement , reverse engineered PCB layout Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 So here is the PCB layout and PCB silkscreen for PCB toner transfer the image is mirrored . AUdio guru please i require your help with the schematic . and one more thing , there are two channels , can you draw it for one channel seperately. Quote
audioguru Posted July 15, 2006 Report Posted July 15, 2006 It looks like an old design, not very good performance and uses mostly Oriental transistors.The input transistors look like they are mounted backwards.Draw a schematic, cut its pcb in half and make it if you want, but there are many newer and better amplifiers designs on the internet. Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 Well this amplfier is goood for starters Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 Can you tell me which class of amplfier is it . Class B or AB or not likely A Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 How is this POwer amplfier of CLass AB i found on the web Quote
audioguru Posted July 15, 2006 Report Posted July 15, 2006 This amplifier produces a little more power than the other amplifier you showed and both operate in class-AB.Class-A creates too much heat and class-B has crossover distortion. Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 So what is the final verdict , which one should i make for my project , the commercial amplfier that i showed you first which has easy to find components , or the other which has high power , but have just found it on the internet . One more thing , will the power increase , if i replace the 2N3055 with MJ15023 or MJ15022 in my first amplfier . Quote
audioguru Posted July 15, 2006 Report Posted July 15, 2006 Make the 1st amplifier if its power output and distortion are acceptable to you.Changing its output transistors won't increase its power output.The supply voltages for the 1st amplifier from a dual 24VAC transformer are about plus and minus 32V while they are plus and minus 36V for the 2nd amplifier. Therefore the power output from each amplifier are nearly the same.Changing the output transistors won't affect the max power output of an amplifier when the transistors are in the same package and have good cooling. Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 If we increase the input voltage upto +-40V on the first amplifier i posted , will it then effect the power output. if not is there any way to increase the power to 100W per channel or 60W per channel . ??? Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 :P Hmm if we add a darlington current amplifier at the end of the 1st amplfier , it will increase current , wouldn't it . so this can increase overall power and if we increase the voltage up to say 50V or 60V plus and minus both. What do you think :o Quote
audioguru Posted July 15, 2006 Report Posted July 15, 2006 Even if you used high voltage output transistors with a dual 60V supply, the peak current into an 8 ohm speaker is only about 7A which all power transistors can pass.But transistors will melt due to the high power in them, so need to be paralleled.Here is a pretty good 150W amplifier (into 8 ohms) that uses high voltage transistors with a dual 56V supply. The transistors are paralleled.The same site has a 1.5kW amplifier with 18 output transistors. Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 But there is one problem , the transistors used cannot be found easily , can u suggest a replacement , for them like the MPSA and the MJL series transistors Quote
audioguru Posted July 15, 2006 Report Posted July 15, 2006 Find an amplifier designed for parts available in your country.In Canada, I can buy any transistor I want, except some Oriental ones are hard to get. Quote
faizanbrohi Posted July 15, 2006 Author Report Posted July 15, 2006 hmm , now let me give you another amplfier . to play with . i have a good felling that these parts can be found. How is this amplfier Quote
audioguru Posted July 16, 2006 Report Posted July 16, 2006 The M250 looks like another good modern amplifier. It has enough paralleled output transistors to produce high power in a 4 ohm speaker. Quote
faizanbrohi Posted July 16, 2006 Author Report Posted July 16, 2006 The power supply suggests a toriodal transformer of 2x38V = 76V total . and a power 500VA , but i have a transformer of 2 x 28V with a current of 8A . now calculating the current required , Watt = power factor x VA = .5(typical) x 500 , so i get 300W and divide by 76V , i get 3.94A , which is the current it needs , right , and there is also a fuse of 4A . and a bridge of 35A / 250V ???? ??? , one more thing will m 2 x 28V transformer rated at 8A , work with the M250 power supply , does it fullfill the needs . Quote
audioguru Posted July 16, 2006 Report Posted July 16, 2006 Making a high power amplifier with high voltage transistors and with them paralleled for high power is a waste if you use your little transformer that has a low voltage. The amp will have the same low power as the other amplifier that uses this little transformer. Quote
faizanbrohi Posted July 16, 2006 Author Report Posted July 16, 2006 But i can produce a DC 55 and -55 from the transformer that i have because it has reserver power of 4A , and 8A is the total , the circuit uses 4A @ 2 x 38 , and i have 2x28 V but 8A . so the voltage can be tackeled , because it is a multiple V=IR Quote
audioguru Posted July 16, 2006 Report Posted July 16, 2006 Your transformer has a sine-wave RMS value of 28VAC.Its peak voltage is 28 x 1.414= 39.6VDC.The two rectifier diodes in series will drop it to about 37.6VDC at full output which is far less than 55VDC.At clipping, the amplifier will make a sine-wave at its output of about 69Vp-p which is 24.4V RMS. Therefore it produces 74W RMS into 8 ohms.The 38VAC transformer will have a peak voltage of 53.7VDC. After the rectifier diodes it will be 51.7VDC at full output.At clipping, the amplifier will make a sine-wave at its output of about 96Vp-p which is 34V RMS. Therefore it produces about 144W into 8 ohms. Nearly double the power of the smaller transformer. Quote
faizanbrohi Posted July 16, 2006 Author Report Posted July 16, 2006 ok you are right but how much ampere should i have , a transformer of 2x38VDC @ how many amperes ??? A . what i think it would 500VA so if i multiply by power factor which i don't know , but assuming , it to be 0.5 , it is 300W that is 4A , so the transformer should be rated at 2x38VDC @ 4A , or else .. what do you suggest ??? Quote
c3r14l.k1l4 Posted July 16, 2006 Report Posted July 16, 2006 Hi,you'll need a supply with the voltage the schematic was designed to. About it's current, the more the better (the circuit will only use the required amperes). The problem is that if your transformer has less power, the circuit will cause the transformer to dissipate more power (incresing it's temperature) and therefore... kaput :PDon't forget to have a rectifier bridge with support for more than 1.5x the maximum current you'll need. Quote
audioguru Posted July 16, 2006 Report Posted July 16, 2006 A class-AB amplifier is about 50% efficient at clipping, so a stereo amplifier with 144W output from each channel will have a supply power requirement of 576VA which is a current of 7.6A. Amplifiers don't work at full power continuously so a smaller transformer with a current of 5A will be fine. Quote
faizanbrohi Posted July 16, 2006 Author Report Posted July 16, 2006 i have studyed just now that Class AB is about 79% efficient and Class A transformer coupled have 50% efficiency. However as far as the transformer is concerned , i have decided , a transformer of 2 x 38VAC @ 6A , with 2 x 12VDC @ 1 A for something(the other winding is seperate for from the first BUT IN THE SAME HOUSING) other then powering up a amplfier . i mean for the Detector circuits and the 10 band VU LED meter that i will insert in it . i will also need a bridge of 35A @ 230V , well i will begin in it later , seems like a tough project and a little expensive too . i will keep it as a mega audio project and now i will make the First Audio AMplfier i posted with PCB . i am going to draw a schematic and post it sooon. Wish me good luck in the exams , tommorow is my Solid state Devices and Basic Electrical Engineering paperz. Quote
c3r14l.k1l4 Posted July 16, 2006 Report Posted July 16, 2006 Good luck man!I'm just waiting for the results of one disciplin (DataBases 2), the others are done. (I'm from informatics engineering). Quote
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