Coincidence.
1) The transformer has its current rated in AC amps but the amplifier operates from DC amps.
2) The rectifiers produce peak voltage that is filtered. The peak voltage is 1.414 times higher than the RMS AC voltage and the power cannot be changed so the DC current rating is 0.707 times the AC current rating.
3) You need to calculate the RMS DC current not guess at the peak DC current.
If the transformer was more powerful then the woofer gets 120W and each satellite gets 38W for a total of 196W. At 70% efficiency the total power required is 280W. Then the RMS current in the 40.2V transformer is 280/40.2= 6.07A.
But nobody plays their sound system at full blast all the time except you at your house party. (smilie)
The sound system in my car has a total continuous output of 288W RMS. I have played it very loud but I have never heard it clipping. It has a real sub-woofer that might be clipping a little but it and the rear seat filter out the distortion harmonics then I don't hear the clipping distortion.
My home stereo has a total continuous output of 140W RMS and I have had it loud enough to clip more than a few times. My dog runs away.
I live in a brick home, not a cloth tent so it doesn't bother the neighbours.
Thanks audioguru for the helpful insight.
**broken link removed**
Finally I got hold of how my Z-2300 works.
Principles of Z-2300 Operation:
1. A stereo audio signal comes in through the green 3.5mm connector.
2. Signal passes through the remote’s (control pod in the picture) main volume potentiometer for attenuation.
3. Signal is then fed down to the subwoofer enclosure for pre-amplification. A
JRC-4565 operational amplifier is used. Two voltage regulators a
78M18 and a
79M18, making positive and negative 18 volts respectively is used to feed the JRC-4565 op amp.
4. The pre-amplifier distribute the audio into two places:
a) To the left and right satellite power amplifiers each using a
TDA7296 (and subsequently to the 2 satellite speakers)
b) Back up to the remote.
5. Inside the remote, the signal is split again:
a) To the headphone jack
b) To the subwoofer bass volume potentiometer (where it is combined to mono at this point)
6. Output from the subwoofer potentiometer finally gets fed back into the sub enclosure and last, into the
bridged TDA7296 subwoofer power amplifiers.
The power train consists of a 150.9 VA TenPao center tapped toroidal transformer as below:
150.9VA --> 20.1V X 2, 3.75A
Two CapXon
10,000 uF, 35V capacitors for smoothing the DC output are used.
My question is why JRC-4565 op-amp is used? Does it have any role in improveing the on audio quality. Where do you think the crossovers for the satellites & subwoofer are used?