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Old 10th March 2011, 10:09 PM   #1
Joku is offline Joku  Finland
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Default Please comment my P3a PCB


Just made a board for P3a, I made both versions for single pair one that has the emitter resistors on board for using two pairs. In the version with two output pairs the driver transistors are MJE15034/5 and the VAS stage is MJE350.

Thoughts? Personally I like the one with single output pair more, the one with two pairs feels like a mess.
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Last edited by Joku; 10th March 2011 at 10:16 PM.
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Old 10th March 2011, 11:15 PM   #2
CBS240 is offline CBS240  United States
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The orientation of the TIP3055 is backwards which would make it difficult to mount to a heatsink. Also it appears you are missing an output coil. Amplifiers with a global feedback loop taken from the output needs to have a coil in series from the output to the speaker to block RF from entering the feedback loop and causing instabilities. Wrap a 1/2W 10R resistor with 22Ga wire and attach it at both ends to the resistor. Place it in series with the output.
All the trouble I've ever been in started out as fun......
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Old 10th March 2011, 11:24 PM   #3
Joku is offline Joku  Finland
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Ah well, I haven't meant to mount the TIP3055/2955 directly to the PCB, I just used them as connectors for Eagle. The output transistors (usually TO-3) would be attached to heatsink and be connected to PCB via wires.

Also, this design is from Rod Elliott, and he didn't use a coil to block RF from speaker, I don't know why. Maybe the cap & resistor to ground take care of that? Anyways, I have built the amp, and it works.

60-80W Power Amplifier

Last edited by Joku; 10th March 2011 at 11:32 PM.
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Old 10th March 2011, 11:33 PM   #4
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The output inductor (coil) is a good idea. It also protects your amp from capacitive loads.

Not sure why you have the ground trace in a big "u" around the board - you might want to cut it back to the last component it picks up.
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