hi,

this would be the quasi-complementary amplifier that i try to build it and observe it how it works.


http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html

When constructing the circuit there are a few doubts.
What rate of transformer that i should use for my power supply part which is not mention in the tutorial. Any idea everyone?

And what is the watt rating that i should choose for all the resistors? Could 1 watt be a good choice?

thanks.

 

R4, R5 around 2W
R6, R7 around 5W cement.... do not use wire wound type
R8 2W
others low wattage

as for power... u can suffice with 1 amps. but do check the voltage for sagging.

 

A few tips:-

To get your 30V power supply, use a transformer with a 24VAC secondary and connect a bridge rectiifier and smoothing capacitor. Transformer and rectifier at least good for 1A or a bit more. Capacitor about 4700uF, 35V to 50V DC.

Before you first power it up, make sure that R10 is adjusted so that the base of Q1 is connected to the collector.

I would advise temporally connecting a wire-wound resistor of say, 470 ohms in series with the power supply when you first switch on. This will limit the current and save your transistors if there is a fault.

The positive end of C4 should be at about half supply voltage. Adjust R10 until you get a small continuous current through the output transistors (about 50mA).

When you are sure that everything is OK, then short out the 470 ohm resistor and try it with some audio.

 

A few tips:-

To get your 30V power supply, use a transformer with a 24VAC secondary and connect a bridge rectiifier and smoothing capacitor. Transformer and rectifier at least good for 1A or a bit more. Capacitor about 4700uF, 35V to 50V DC.

Before you first power it up, make sure that R10 is adjusted so that the base of Q1 is connected to the collector.

I would advise temporally connecting a wire-wound resistor of say, 470 ohms in series with the power supply when you first switch on. This will limit the current and save your transistors if there is a fault.

The positive end of C4 should be at about half supply voltage. Adjust R10 until you get a small continuous current through the output transistors (about 50mA).

When you are sure that everything is OK, then short out the 470 ohm resistor and try it with some audio.

I hear ya.... but I still say he will blow the output before he can hear anything

 

hi,
thanks for all the replies. I would use a transformer with 24VA and 22Vac at the secondary voltage to get my 30V power supply.
After calculating the watt for resistors R1 and R2 i will choose a 1/4 watt resistor for them.
But what about the R3? how to calculate the watt across R3? Is it ~1.76mW?

thanks.

 

R3 is 470KΩ 0.25W will be OK

 

how do u actually calculate the watt across R3?

thanks.

 

experience

 

how do u actually calculate the watt across R3?

Ohms Law will help.

 

since the speaker i use is a 8ohm speaker. Can i connect the output to a 8ohm resistor to try before i connect the real speaker on to avoid any damage to my speaker?

thanks.

 

You want damage any thing if you do exactly what post 3 says.

 

You want damage any thing if you do exactly what post 3 says.

u mean which part? the 470ohm resistor after power supply that part?

thanks.

 

exactly that

 

View attachment 17357
http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html

hi,

Does the potentiometer R9 use to control the volume? When i turn on the power. The volume is too high till the audio sound become very terrible.

thanks.

 

If the volume control R9 is wired correctly then it should adjust the volume smoothly from zero to maximum.

 

Yes... I would use an 8ohm 20 watt resistor at a minimum. Many surplus outlets have hi-powered resistors at decent prices.
dmccormick84

 

R9 is the volume and any 0.5W pot would suffice.
R10 is a trip pot which is used to adjust the biasing of the drivers and power stage.
The noise could be that your bias is too low which is heard as distortion

 

hi,

i change the R9 potentiometer from 4k7 to 5K7. then i manage to tune the volume lower.but still when i tune the volume to the lowest point the volume still too loud for me. Is it because of the bias part?

thanks.

 

Are u hearing any thing from the speaker

 

yes.i input the audio sound from a DVD player to the input point.But it seems like the volume is too high even i tune the volume POT to the lowest.

thanks.