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Old 6th October 2004, 06:19 PM   #1
diyAudio Member
 
Join Date: Mar 2004
Location: Prince George, BC, Canada
Default P27 Output Voltage

Hello all.

Link to ESP P27 http://www.sound.westhost.com/project27.htm

Schematic is attached.

I mounted my P27 board to an anodized aluminum heatsink using arctic alumina thermal adhesive. There is no conduction between the transistors and the heatsink, but the tabs of all transistors have very little resistance between them. Looking at the schematic, this is ok since they are connected together with the two 0.22 ohm resistors correct?

I powered it up from +/- 12 volts and there was no current draw, fuses were fine, but the amp side of the negative fuse read -7 volts instead of -12 volts. Measured directly at the bench supply it is also -7 volts, when the amplifier is disconnected it is -12 volts. This voltage appears on the output, but there is nothing heating up. I checked for solder problems but don't see any, is there any area that I should be focusing on? I have used NTE semiconductors in place of BC549 & BC559 as that is all I could find, and I managed to put the NTE 123AP in the wrong way for Q4 and Q12, as it is opposite orientation of the transistor that is supposed to be there. I switched those two around, and the same problem occurs. The BD transistors are installed correctly.

Then I upped the voltage to maybe 15 volts and the bench supply hits the current limiting (I think I had it set at around 1-2 amps) and the output transistors heat up right away. Must be a soldering issue somewhere? Again I see no problems, when I look again is there any area I should focus on? I plan to take the multimeter and trace the circuit to test for any problems.

Thanks muchly

Ray
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