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Old 30th September 2005, 09:23 AM   #21
pinco is offline pinco  Croatia
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Quote:
Originally posted by Ipanema
Hi Roly3055 ,

I just complete one channel of blameless amplifier. Would like to know how you mirror one channel to get two channel side by side on eagle?

r!sc!,

Your input and decoupling caps sharing the same ground, will it generate hum?

Thanks.
Is it advisable to add electrolytic capacitor 100-220uF parallel to 100nF decoupling capacitor and separate grounds with 10 ohm res.,

Mr. Leach:


"I have seen some circuits in which the values of the decoupling capacitors are far too small. When I first started designing the Low TIM amplifier, I used a single 0.1 uF capacitor to decouple each power supply rail at the points where they connect to the circuit boards, i.e. in place of C21 through C24. I used that value because I had seen it used in so many other circuits. In taking measurements on the amplifier, I found a very large AC signal would appear on the power supply rails when I tested the amplifier at high frequencies. At 1 MHz, the AC signal on the rails had the same amplitude as the amplifier output signal. When I removed the 0.1 uF decoupling capacitors, the AC signals on the rails would almost disappear. Replacing the 0.1 uF capacitors with 10 uF capacitors eliminated the problem. I settled on 100 uF capacitors to be on the safe side."
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Old 30th September 2005, 11:26 AM   #22
r!sc! is offline r!sc!  Serbia
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Another layout with Pinco's suggestions

Click the image to open in full size.
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Old 30th September 2005, 03:38 PM   #23
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Hi r!sc!,
Actually Iím wrong, which is good! J You swapped the - + voltage rails, I see it now.
With your present layout your input and output are too close, is wise to have some distance between them. R9, R10 and R15 must be Ĺ watt. Provide more space around Q4 for air cooling or place for heatsink. C4 and C6 didnít like heat too. Rest is very good.
Pozdrav!
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Old 30th September 2005, 11:05 PM   #24
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Yes that NFB takeoff point is better. Good luck with building this amp :)
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Old 1st October 2005, 12:23 AM   #25
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Hi r!sc!

I think you have done an excellent job on this PCB. I have recently gone through the same process, starting with Rod Elliott's original PCB and spending a few hours tidying things up. Your's looks a lot better than mine BTW.

I like what you did around VR1, the original was ugly. Also your earthing scheme looks better. I do think it would be nicer if the power feeds for the first 2 stages come of the main feed just once, closer to the original. That being said, it probably won't make any difference.

I have built an ESP P3A which is quite a compressed layout and the gap between the output and input shouldn't be an issue.

You have D1 on the silkscreen as a diode but it is really a led. I notice Rod did the same thing. On such a nice layout I think you should put on a led symbol.

I found reversing Q5 and R11 improved the track layout but obviously upset the Q5 and Q6 symmetry.

C4 and C6 need to be close to the transistors and if you use polystyrenes you could move the pads closer together.

It will be interesting if adding C8 and C9 make any difference.

Regards
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Old 1st October 2005, 02:17 AM   #26
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Hi Greg Erskine,
Pls explain how you will move C4 and C6 closer to transistors???
We all know that any, I mean any capacitor donít like heat and take another look at pcb. Capacitors are stick to transistors!?!
Possible solution is soldering under the board, or at least 5mm far from Q4 and Q6?
r!sc!, scrap 10 ohm resistor to ground; we talk about ESP amp, not AKSA one.
C7 must go to power ground, not signal ground.
C8 and C9 canít do any harm, so Iím for them.

Best regards,
Chicco
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Old 1st October 2005, 04:01 AM   #27
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hi chicco_36,

Sorry if I didn't explain myself properly. When I said, "C4 and C6 need to be close to the transistors" I was meaning, leave them where they are, don't move them further away. Sticking them under the board as you suggested, directly on the transistor pads would be good IMO if you like having components underneath, some people don't.

I had the impression that polystyrenes or ceramics were not sensitive to temperature like electrolytics, but I could be wrong. Next time I have the lid off my P3A I'll check the two transistors and capactiors because I think the caps were actually touching the transistor.

Lots of amps have a resistor between grounds. From memory Rod Elliott never does. Six of one, half dozen of the other?

Regards C8 and C9 - I always wondered why Rod doesn't use them, so it will be interesting to find out what improvement results.

Regards
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Old 1st October 2005, 05:31 AM   #28
djQUAN is offline djQUAN  Philippines
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Quote:
Originally posted by Greg Erskine
hi chicco_36,

Lots of amps have a resistor between grounds. From memory Rod Elliott never does. Six of one, half dozen of the other?

Regards
nope, he used one on both P68 and P101.
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Old 1st October 2005, 05:34 AM   #29
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Cats didn't like water, caps also.
Regarding C8 and C9, i'll be happy when main capacitors will be on pcb.
Components underneath are best bet when you have single sided board!
Chicco
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Old 1st October 2005, 05:40 AM   #30
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To be precise, caps and heat in amps are enemys!
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