hi,
If i would like to try on this quasi-complementary circuit shown below,what rate of transformer should i choose? in a way of VA. The link of this circuit is as below
http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html
thanks.
If i would like to try on this quasi-complementary circuit shown below,what rate of transformer should i choose? in a way of VA. The link of this circuit is as below
http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html
thanks.
how do u actually calculate that value?or by experience?
But the circuit label a +30V ,isnt it needs +30V?
thanks.
But the circuit label a +30V ,isnt it needs +30V?
thanks.
If the amp is 10watt then you need a bit more in VA due to losses into heat in the heatsink. I usually allow 50% for that so I reckon a 15-20VA transformer would do the job.
By experience + calculation.
A 10W amplifier usualy means 10 watt sinewave (RMS) power. But music is not sinewave, it has less power.
A 10 watt amplifier with 50% efficency wastes 10 watts in heat.
For an IC (chip) amp, transformer VA ~ 2 * amplifier watts is a guess.
The amplifier will work. If it gets hot, we put in a fan and buy a bigger transformer for next one. If it's a hot day, maybe the transformer goes bang anyway, so often we make it too big, just in case.
+30V is +30V, but transformer VA is ~. Approximate.
w
Do u mean that we dont have to follow the circuit which mention +30V as input power?
thanks.
after survey around the shop, i decide to buy a 24VA transformer with secondary voltage equals to +30V. Can it be?
thanks.
thanks.
sorry, i really not understand this. how could a 22Vac gives +30V?
ok this is my plan for the power supply part. I plan to use a +30V 24VA transformer and connect to a bridge rectifier(1N4007 will be use) and filter cap(not sure what value to put,any idea?) to get +30Vdc. Am i correct?
thanks.
NO!
30v AC gives ~ 30 * 1.41 = ~42V DC with capacitor filter.
Look here:- Explaining rms voltage and current | Practical Physics
Like Aldotin says: 22v AC * 1.4 = ~30V DC peak.
w
thanks for all the advices.noted. really helps a lot. Can i use 1/2 watt for all the resistors? except for R1, R4 and R5 i use 1/4watt resistors.thanks.
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what value should i turn to for R10(potentiometer) and R9(potentiometer) to bias both of the transistors? Is it by tuning it slowly and observe on the output?
thanks.
thanks.
ok.this makes me understand how the calculation is. But how do u know that, the +30V mention in the circuit is a Peak Value but not a RMS voltage?
thank you.
Mot.
go and read/research your subject.
The schematic shows a single polarity power supply of 0v to +30V.
A 20Vac transformer will give about 30Vdc after rectification and smoothing.
The maximum signal from a 30Vdc supply is ~8Vac to 10Vac.
If the supply voltage drops during high output power delivery then the maximum signal will be even lower than that estimated range.
The PSU voltage will drop. Maybe between 1Vdc and 10Vdc depending on how the PSU is assembled.
10W into 8r0 is the same as 8.944Vac into 8r0. That is exactly the same as 12.647Vpk into 8r0.
To get a 12.65Vpk sinewave, the actual output signal is 25.29Vpp.
The PSU, after the voltage has dropped to it's high power demand level, must have more than +25.3Vdc, about 2V to 5V greater would be about right.
The mains voltage varies. This must result in a variation of the output voltage of the PSU. This will then result in a variation of the DC supply voltage from the PSU.
In addition the VA rating of the transformer and the connections and the rectifier and the smoothing capacitance will all vary the output voltage of the PSU.
Finally as the circuit demands varying current, this too varies the supply voltage.
DO NOT expect the PSU voltage to measure 30Vdc all the time. It could vary from 29Vdc to 32Vdc +- the mains voltage tolerance. In the worst case supply and loading conditions it could vary between 27Vdc and 34Vdc from a 20Vac transformer.
go and read/research your subject.
The schematic shows a single polarity power supply of 0v to +30V.
A 20Vac transformer will give about 30Vdc after rectification and smoothing.
The maximum signal from a 30Vdc supply is ~8Vac to 10Vac.
If the supply voltage drops during high output power delivery then the maximum signal will be even lower than that estimated range.
The PSU voltage will drop. Maybe between 1Vdc and 10Vdc depending on how the PSU is assembled.
10W into 8r0 is the same as 8.944Vac into 8r0. That is exactly the same as 12.647Vpk into 8r0.
To get a 12.65Vpk sinewave, the actual output signal is 25.29Vpp.
The PSU, after the voltage has dropped to it's high power demand level, must have more than +25.3Vdc, about 2V to 5V greater would be about right.
The mains voltage varies. This must result in a variation of the output voltage of the PSU. This will then result in a variation of the DC supply voltage from the PSU.
In addition the VA rating of the transformer and the connections and the rectifier and the smoothing capacitance will all vary the output voltage of the PSU.
Finally as the circuit demands varying current, this too varies the supply voltage.
DO NOT expect the PSU voltage to measure 30Vdc all the time. It could vary from 29Vdc to 32Vdc +- the mains voltage tolerance. In the worst case supply and loading conditions it could vary between 27Vdc and 34Vdc from a 20Vac transformer.
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