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Old 13th January 2004, 02:02 AM   #1
Hitz is offline Hitz  Canada
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Unhappy P3A amplifier output trans and Prob

Hello,

I'm building the P3A for the first time and I'm using the mje2955 and mje3055 output transistors and the bd140 and 139 as drivers and all the small signal transistors are BC546
if you look at Rod's original schematic on this page, http://sound.westhost.com/project3a.htm I've replaced the mjl4302 with the mje3055 and the mjl4281 with the mje2955 is this a problem at all? Right now all the amplifier does is hum and I can't get a signal through it so I obviously have some wiring problems or something. But when I test it with the safety resistors as soon as I reach about 20 volts the output voltage quickly drops below 1V. but really I don't know what could be wrong. As far as components are concerned I've used all the detailed parts on rod's site other then that I just used whatever I had. If anybody has any tips on the transistors or my hum problem it would be greatly appretiated.
thanks
Ryan
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Old 13th January 2004, 11:52 AM   #2
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I think what you might have done here is substituted in the wrong transistors. I say this because the mjl4281 and mje3055 are NPN devices and the other two are PNP. What you have described below is the changing of a NPN for PNP device nad vice versa, so that could be you main problem here.
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Old 13th January 2004, 06:14 PM   #3
Hitz is offline Hitz  Canada
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thanks for the help, ya I had the NPN's and the PNP's switched I'll change that and see if it works!
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