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100W Audio Amplfier By Smart Kit


faizanbrohi
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Hello ,

my name is faizan brohi ,

There is a 100W Audio AMplifier Project in the Audio Section of the projects By SmartKit. The PRoblem That i am facing is that the power supplies neutral wire goes red and then breaks in the PCB Board. Ofcourse this means that the amplifier circuit is short , but i have checked everything and nothing seeems to be short. please can you help me with this , any help on this would be greatful . i have worked on this for 7 days and still no results ..plzzzz...help.......  :'( :'( :'( :'( :'(

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The Power Supplies neutral rail is getting burned out , not the amplifier's neutral connection. i think that there is something wrong at the amplifier end , but the thing is i have double checked every short connection , only one transtor Q6 seems to be short , but otherwise i have checked the DC Input stage . everything seems to be fine... what could be the problem ...  ??? ??? :'( :'(

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There are only a few parts connected to the amp's 0V (neutral):
1) The speaker. Disconnect it and measure that the amp's output is close to 0V.
2) C1 and C9. Maybe one or both are shorted or backwards.
3) R13 through C8. Maybe C8 is shorted or backwards.
4) R28 but it is 1.2k.
5) C6 but it is through R21 which is 220 ohms.
6) R6 but it is 2.2k.

Even if Q6 is shorted, very little current will flow in the neutral without a speaker.
Isn't your power supply +44V, 0V and -44V? I guess you call its 0V the "neutral".

Your power supply should have fuses or circuit breakers for the first tests of a high power amp. I would put 60W/120V lightbulbs in series with both voltages. If the current is normal, they will be a very low resistance when cold. If there is a short, they heat and increase their resistance which limits any fault current.

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I have disconnected the 0V neutral lead , nothin heats up except the goddamn 0.47 ohm (5W) R2 And R16 Resistors but the amplifier loads up perfectly , not even the transistors heat up . maybe i shoould place 1K resistor of 1 Watt in parallel with them  ??? as written on the manual.
But is this heating up of the 0.47ohm (5W) resistors normal when everything is fine. ??? ???

I made a discovery that the transistors body where the screw is mounted and touches the heat sink was shorted, so the transistors collector was actually shorted with the heat sink . i corrected that problem by applying a plastic washer in between them . Could this be the reason that the neutral wire actually burned up ????  ??? ???.

now i am putting the goddamn 1 k 2W resistors in parallel with the R2 And R 16 .. ok

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Hello again ,

When i add a bulb in series with both the +40 And -40 of 100W/220V , the bulb heats up and there is no voltage drop across the amplifier and only the bulbs , i did also one careless mistake that i put a AC ammeter in series which burned  one capicator at the input . But what does the bulb shows that something is short in the circuit . i think the two resistors have more current flowing , so they may be virtually short , i am going today to buy the stuff ,

1 ohm 2W x 2
1K pot x 2
10uF / 63V x 2
2A x 4 Fuses
3A x4 Fuses
BC548 x 2
BC546 x 2

and by the way i connected the neutral wire , it's working now with the neutral wire plugged , and the problem was that the heatsink was shorted with the transistor's body

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I think the parts list of this project is a mess. Read the note at its bottom: "For R2 and R16 if you don't find a 0,47Ohm place two of 1 Ohm parallel". So the parts list is wrong with 1 ohm/2W for R16.

Use 0.47 ohms/5W for R2 and R16 or two 1 ohm/2W in parallel for both to make your own 0.5 ohm/4W resistors.

The bulbs light with no voltage across the amplifier, so the amp is drawing a current much too high. Make sure that the pot is set to its highest resistance.

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Hi faizanbrohi !

If the pot wiper is at it's end position all pins will be shorted, check if Q7 is shorted between B-E pots don't usually get shorted, when resistors goes bad the value increase or they just go open circuit.
Q7 is supposed to work as a variable zener diode and rotating P1 will set quiscent current

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I just want to confirm that when i apply the 1 ohm in parallel with 0.47ohm . it will not heat up and i can set the pot . because i have tried a DC millimeter but it didn't give any reading and it's fuse was broken . this can mean there is alot of current flowing through 40V lead


No, don't add 1 ohm resistors. The confusing parts list says to use a 0.47 ohm/5W resistor for R2 and another 0.47 ohm/5W resistor for R16. Four 1 ohm resistors are used by people who can't find 0.47 ohm resistors.

Your amp's very high current is caused by a shorted P1 or Q7.
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Today i am going to the electronics market . I think iwiil buy two pots . and by the way q6 is short so that might be the problem . what do you think , i will change the pot today and will change q7 and q6 ok , but i forgot to tell you that i am using BD825 and BD 140 in place of BD829 and BD830 and BDW84A and BDW84A instead of BDW84D and BDW84D , because i could not find the original. ok

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but i forgot to tell you that i am using BD825 and BD 140 in place of BD829 and BD830 and BDW84A and BDW84A instead of BDW84D and BDW84D , because i could not find the original.



What more is there to say? If you are going to substitute parts, you need to compare the specs.

MP
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The BDW84A will blow-up in this circuit because its voltage rating is too low.

Go to www.farnell.com and look for your country's flag. They have online electronic parts ordering in many countries.
Can't you buy a Smart-Kit there? They are from Greece but I can buy them here in Canada, nearly on the other side of the planet.

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Hello ..

I am really worried , i am going to buy tommorow , the orignal transistors . but please reply soon audioguru that is the high current of R2 And R16 because of the Transistors . and if i replace them will it work . Plzzzz .. help .. and lastly will it give any signal if R2 And R16 are hot . thnxx plzz ....  ??? :'( :'( :'( :'(

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I am really worried , i am going to buy tommorow , the orignal transistors . but please reply soon audioguru that is the high current of R2 And R16 because of the Transistors, and if i replace them will it work? .. and lastly will it give any signal if R2 And R16 are hot?

R2 and R16 will not get hot if the pot is adjusted for an idle current for the amplifier of only 50mA. They will heat normally if the amp is playing loudly.
Many parts affect the current through R2 and R16, and the current through Q1 and Q9. The current source Q10 is supposed to provide 7mA so see if you measure 0.7V across R25.

Use the proper high voltage darlington transistors BDW84D for Q1 and BDW83D Q9 then maybe the amplifier will work properly. BDW84C and a BDW83C darlington transistors will also work fine.
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Forget about making an another amplifier . i will make this again , i will buy new components. ok and will make new PCB and please tell me the site where i can get info on getting the Inductor Value of 0.5mm wound around a resistor of 1W with 10 turns . is there a calculation , please i need to know the value in order to get the inductor right. now please help me on the inductor plzz ... i will do all the PCB Again. plz help on the inductor , i want it's value. and if possible a very
equivalent substitute for BD829 BD830 and BDW84D and BDW83D

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