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Old 16th January 2007, 07:31 AM   #1
Nordic is offline Nordic  South Africa
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Default Ground planes and solidstate?

I must have made like 5 PCB's now for the same circuit.... Nuuk's (Les Sarge) class-A buffer....

Invariably, there is noise from one channel...sometimes it seems to sound a bit better but the noise comes and goes, which leads me to think it could be oscillation...

Now the big question this morning.
were ground planes on the PCB's a bad idea for solidstate....? with chips they normally make things better.. no idea about stupid transistors... I just want to throw all of mine away...


I can't figure out if the problem is related to the sharing of the PSU or the ground plane....think I swapped enough transistors around to exlude ttransistors as the culrpits....
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Old 16th January 2007, 08:58 AM   #2
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Forgot to ask...

beside the above 2 questions.... what would be a good bias level for my transistors... using BD135.
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Old 16th January 2007, 09:08 AM   #3
cviller is offline cviller  Denmark
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Any chance you could post some pictures of your setup?
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Old 16th January 2007, 09:18 AM   #4
Electrons are yellow and more is better!
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Using groundplanes is an excellent idea _unless_ you don't want extra stray capacitance to ground but consider that 1 cm2 copper creates 3 pF so when it's sensitive below 1pF you must watch out, hardly a problem in not too extreme audio circuits.
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Old 16th January 2007, 09:51 AM   #5
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Maybe its not the groundplane... redid pcb without.. and still very noisy- was acceptale testing with headset, but unbearable with the actual amp. I have an opa2777 board set up for 2x gain, which I'm going to drop in there while I figure it out...

chips are just so much less stress.
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Old 16th January 2007, 09:53 AM   #6
Skorpio is offline Skorpio  Denmark
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Quote:
Originally posted by peranders
1 cm2 copper creates 3 pF
There must be something about distances and areas to the other pole?
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Old 16th January 2007, 09:57 AM   #7
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Indeed but if you have a 1.6 mm pcb you'll get 3 pF per cm2. Remember though that a small trace above a groundplane creates less capacitance.
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Old 16th January 2007, 10:12 AM   #8
Nordic is offline Nordic  South Africa
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Sorry to avoid confusion... it was a single sided pcb with groundplane....there is about 4cm/almost 2" diffirence in trace lenghts connecting v+ and v-... one being very close to the connector...and regulator (maybe 3cm)

I have not seen too many transistor pcb's (compared to all the chip based stuff I learned from...), so its pretty foreign territory to me...

I think what I will do is start from scratch..., yet again! maybe try some stripboard and use 2 equal length power cords to the connection points.

I never knew transistors will be so hard to implement... being able to read te schematic here is of negligible importance it seems.
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Old 16th January 2007, 10:16 AM   #9
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A groundplane should be as "whole" as possible and it's a challenge to make a good singlesided groundplane pcb.
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Old 16th January 2007, 10:24 AM   #10
Nordic is offline Nordic  South Africa
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Would this layout be ok on veroboard?

the original circuit is this one;

Click the image to open in full size.
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