Please comment my P3a PCB

Joku · 10:16 PM

Hi,

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.

CBS240 · 10th March 2011, 11:15 PM

Hi

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.

Joku · 11:32 PM

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

MJL21193 · 10th March 2011, 11:33 PM

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.

10th March 2011, 11:15 PM	#2
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Hi 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......

10th March 2011, 11:24 PM	#3
Joku diyAudio Member Join Date: May 2009	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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10th March 2011, 11:33 PM	#4
MJL21193 Account disabled at member's request Join Date: Mar 2007	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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