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Old 10th October 2012, 04:52 PM   #41
jcx is offline jcx  United States
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+/- pwr runs on opposed edges of the board is one of my gripes - really the worst for Class AB

+/- pwr trace should be on top of each other - as close to common centroid design as possible so that the "half wave rectified" currents magnetic fields "add up" to reflect the mostly linear load current

with pwr gnd/speaker out also nearby the fields even cancel to a degree

I wouldn't put the output inductor on the board - open cylinder solenoid coil radiates mag field badly too - hang them from the speaker terminal

how are you mounting to heatsink? aren't the MJL TO-264 flat plastic packages - not TO-3 metal cans your layout appears to show

do the boards have to be so small - hobby builds don't have the mass market price pressure, can improve some layout issues with added empty board space

thinking about multichannel operation - if you have a preamp/input buffer board then you could make the amp circuit front end a differential receiver to reject pwr gnd common impedance noise

I would always use the "beta enhanced" VAS today with some variant of 2-pole compensation given the design info we have - at least make it board stuffing option

Last edited by jcx; 10th October 2012 at 04:59 PM.
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Old 10th October 2012, 07:35 PM   #42
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I'm not entirely sold on the cancellation of the fields produced by the power supply traces, they occur at different times and therefore are not in exact opposition. I had entertained the idea of feeding the DC supplies directly to the metal mounting flanges of the outputs and just 'fingering in' the power to the rest of the circuit. I had also entertained the idea of putting the coil off board at the speaker terminal but felt I wanted a sort of all-in-one PCB. The emphasis I put on this one was on improving my grounding scheme.

The devices listed on the schematic are what I had in the library for simulation purposes that were close to the MJ15003/15004 or MJ15024/15025 that I have handy. The outputs will be TO-3 metal cans. The small signal will be 2N5551 and 2N5401 and there are some other options in my parts box for drivers, VAS and CCS but the drivers will be TO-220 and VAS/CCS will be TO-126 or TO-225.

This is a rebuild of a much earlier project (like over 10 years ago) and I wanted to improve it some but would like it to retain the same dimensions, hence the rather small board. Also I can etch two from a standard 6"x4" pre-sensitized piece of board. For a true clean slate design the board would be probably be much larger. Attached is the old artwork from well before I knew better (note also that the circuit is not the same, nor the pinout of the small signal devices).

I did entertain the beta-enhanced VAS but the board was getting tight! TPC or TMC is also definitely recognized as having beneficial properties and again the real estate I was hoping to use was getting tight.

Thanks for the input.
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File Type: jpg Old Amp Layout.JPG (488.1 KB, 282 views)
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Old 11th October 2012, 07:01 AM   #43
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Some discussion of how to avoid the "opposite sides of the board power layout" that JCX (and I) dislike starts here.

Best wishes
David
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Old 11th October 2012, 04:20 PM   #44
jcx is offline jcx  United States
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and keeps on going on...

good to see the discussion, drawings
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Old 11th October 2012, 05:08 PM   #45
dadod is offline dadod  Croatia
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Originally Posted by Dave Zan View Post
Some discussion of how to avoid the "opposite sides of the board power layout" that JCX (and I) dislike starts here.

Best wishes
David
According to that discussion, I am trying to layout the PCB for my TT amp were big and small C multipliers are on the same board with the amp. On the attached PCB I started the layout and the OPS and plus side C multipliers are on. I have big problem how to layout the output and I can not find good enough solution for that part according what Charry suggests Has anyone seen this front-end before?.
dado
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Old 12th October 2012, 03:44 AM   #46
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Hope its not too late to join the show and tell

Here are the ideas for OPB
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Old 12th October 2012, 01:18 PM   #47
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I'm working on rearranging things a little, but I'm not fast like Alex MM, so I'll have something to show shortly to see what folks think. A short synopsis will be delivering the PSU rails directly to the TO-3 mounting flanges and fingering out to the low current areas on the PCB from the outputs.

Does the grounding scheme in post #40 look OK? I was shooting for star-on-star with the audio star isolated by a 10 ohm resistor from the main ground on the PCB.
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Old 12th October 2012, 02:22 PM   #48
AndrewT is offline AndrewT  Scotland
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Originally Posted by jkuetemann View Post
........ Any constructive comments or criticism welcome.
never drop the leading zero of values <1
eg 0r22 or 0.22 is much less ambiguous than .22
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Old 12th October 2012, 03:05 PM   #49
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Quote:
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never drop the leading zero of values <1
eg 0r22 or 0.22 is much less ambiguous than .22
Yes, this is true. I'll work on making component markings more succinct. Good tip for everyone, thanks.
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Old 12th October 2012, 06:17 PM   #50
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So here's a version that has no large high current traces on opposing edges of the PCB, fusing will be off board on the PSU instead. Some components are a little better spaced and more distance between many of the traces. Any comments? Better or worse than the one on post #40 and why?
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