Transistor/opamp circuit - Page 2

soundNERD · 11th September 2004, 01:16 AM

Can somebody at least tell me how well they think that this amp will perform with a 3875, mj15003/4 transistors, +/-30VDC supply, and an 8ohm 12" sub (sealed box)?

And, I still want to know, 400W RMS or Peak?

djk · 11th September 2004, 06:45 AM

"And, I still want to know, 400W RMS or Peak?"

Maybe you should learn something about your hobby.

400W avereage power, what the great unwashed refer to as 'watts RMS', is 40V RMS across 4 ohms. That would be 56.56V peak.

The suggested supply was 75V.

The 75V is obtained from a 55V AC transformer, rectified and filtered under no load you will have about 75V, as you load the supply by driving the amplifier this voltage will drop.

The transformer should be about 800VA, the main filter cap about 6,800~10,000µF at 80~100V, the rectifier about 25A at 200V.

soundNERD · 15th September 2004, 02:16 AM

When building this, would it be a bad thing if I use short wires to connect the transistors to the PCB? Its hard to connect both 2 to-220 devices and 4 to-3 devices to a heatsink if they are all soldered to a board.

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11th September 2004, 01:16 AM	#11
soundNERD diyAudio Member Join Date: Sep 2003 Location: Illinois	Can somebody at least tell me how well they think that this amp will perform with a 3875, mj15003/4 transistors, +/-30VDC supply, and an 8ohm 12" sub (sealed box)? And, I still want to know, 400W RMS or Peak?

11th September 2004, 06:45 AM	#12
djk diyAudio Member Join Date: Feb 2001 Location: USA	"And, I still want to know, 400W RMS or Peak?" Maybe you should learn something about your hobby. 400W avereage power, what the great unwashed refer to as 'watts RMS', is 40V RMS across 4 ohms. That would be 56.56V peak. The suggested supply was 75V. The 75V is obtained from a 55V AC transformer, rectified and filtered under no load you will have about 75V, as you load the supply by driving the amplifier this voltage will drop. The transformer should be about 800VA, the main filter cap about 6,800~10,000µF at 80~100V, the rectifier about 25A at 200V.

15th September 2004, 02:16 AM	#13
soundNERD diyAudio Member Join Date: Sep 2003 Location: Illinois	When building this, would it be a bad thing if I use short wires to connect the transistors to the PCB? Its hard to connect both 2 to-220 devices and 4 to-3 devices to a heatsink if they are all soldered to a board.

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