900W H-class PA Amp with Limiter

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#1,966
donpetru said:
STEP 1:
A = 4.5 inch = 11.43 cm;
H = 3 inch = 7.62 cm.

STEP 2:
Then calculate the coefficient a = A / 6 = 1.9 cm.

STEP 3:
After step 2 is calculated active section of the core:
- first: b = 2 *a = 3,8 cm;
- second: S = b * H = 3,8 * 7.62 = 28.95 cmp (square centimeters).

STEP 4:
Now calculate the apparent power of the transformer (primary winding):
P1 = S * S = 28.95*28.95 = ~850VA.
Efficiency of such a transformer is about e=85%. In this case secondary power will be:
P2 = P1*(e/100) = 0.85*850 = 722.5VA.

STEP 5:
Knowing secondary electrical transformer voltages we can determine secondary winding current value using the following formula:
I2 = P2 / U2.
For example, you have two DC voltage of 100V (filtered with capacitors). Now, I refer to a symmetrical voltage of + / - 100Vdc, this means 200Vdc. The secondary voltage will be effective:
Vs = 0.707 * 200 = 141.4 VAC.
In this example, the secondary winding current will be maximum:
Is = P2 / Vs = 5.1 A.
So, if those 141.4 VAC are given by two voltages of about 70V each then current calculated above will be given by each winding.

I hope you understand me and I hope I was helpful.
Click to expand...
thank u very much sir.....
 
#1,967
nazirdigi said:
hi apex sir,
here is h900.
supply dc votage is 100-50-0-50-100. sound is excellent.
one question , without load i increase the volume ,and i see the clipping led is blink, but i checked the out with dmm ,ac voltage is 26vac. is there any mistakes from me.
thanks.

one question for tony, can u tell me what is the exact ampere of this transformer.
40 into 4 transformer,
core size is 40mm by 79mm.
thanks
Click to expand...

Nice work. DMM can measure only 50Hz sine wave ac voltage, you need scope for ac measurements.
Regards
 
#1,969
question about resistors getting hot

Dear Sir Apex,

Just I want to ask if it is normal that these resistors with the red arrows are getting really hot.
2.2k 2 watts very hot
22k 1 watt very hot
3.3k 1 watt very hot
6.8k very very hot, it is like you will get burn if you touch it with in 1 0r 2 seconds
but the sound is very clear with good bass and treble, I'm using a full range Jamo S606 tower speakers for sound test.

the supply voltage are: 112 - 56 - 0 - 56 - 112 Volts DC from 40 40 0 40 40 Volts AC



APEXaudio H900 PCBMON V2 resistor getting hot.jpg
 
Last edited:
#1,970
mj777 said:
Dear Sir Apex,

Just I want to ask if it is normal that these resistors with the red arrows are getting really hot.
2.2k 2 watts very hot
22k 1 watt very hot
3.3k 1 watt very hot
6.8k very very hot, it is like you will get burn if you touch it with in 1 0r 2 seconds
but the sound is very clear with good bass and treble, I'm using a full range Jamo S606 tower speakers for sound test.

the supply voltage are: 112 - 56 - 0 - 56 - 112 Volts DC from 40 40 0 40 40 Volts AC



View attachment 268882
Click to expand...

This resistors must be hot, it's normal don't touch it 🙂
 
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