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Old 3rd February 2003, 01:28 PM   #1
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Default Silence audio o/p

In audio circuits, the control circit invariably produces some sort of hum. No matter what you do, getting silence at the

output is very difficult.
What are the different ways to obtain silent o/p? I autoroute my boards having control and power sections on the same board

using Layout Plus.

I am using amps in bdg configuration in the final stage. Instead of bridging it in the amp circuit itself, I plan to invert

the final control signal and feed the complementary signals to two identical amps.
I hope that this will eliminate the common mode hum. I also hope that this will eliminate the need to have a turn- on delay

circuit along with the bulky relay.

All comments and views welcome.

bimbla.
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Old 3rd February 2003, 10:08 PM   #2
halojoy is offline halojoy  Sweden
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Default bimbla - gives us a diagram?

Hello bimbla

Quote:
In audio circuits, the control circit invariably produces some sort of hum. No matter what you do, getting silence at the
output is very difficult.
What are the different ways to obtain silent o/p? I autoroute my boards having control and power sections on the same board
With control you mean Volume control ..
Or do you mean Protection Cicuit?

If you draw a simple Picture of your circuit
or the way you plan to do,
I think you get some good advice.

/halo
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Old 4th February 2003, 11:05 AM   #3
EC8010 is offline EC8010  United Kingdom
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Default Re: Silence audio o/p

Quote:
Originally posted by bimbla
In audio circuits, the control circit invariably produces some sort of hum. I autoroute my boards having control and power sections on the same board using Layout Plus.
Well, there you are. Letting an autorouter loose is asking for trouble. Any software that you or I can afford will not be as good as thoughtful human layout and invariably uses tracks that are too narrow, too long, and too convoluted. When you lay out a board, you can consider factors of which the software is ignorant.

Try widening tracks, shortening tracks, avoiding mixing control and audio currents in tracks, and adding grounded guard tracks between noisy and sensitive areas. Realistically, PCBs are a production method, and require a huge amount of thought to achieve optimum performance. When I use them, I lay mine out manually...
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Old 4th February 2003, 11:42 AM   #4
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I second that: never autoroute audio circuits!

First, identify your signal path, any high impedance nodes, low level, high level and your power path. Next, try to layout your circuit so that the signal follows a "smooth" route from in to out (like in on one side, flowing stage after stage to the other side where the output is). Also try to keep high impedance nodes away from high level circuits, power from low level.....Then layout each stage for minimal loops inside (like feedback....) Next, choose a grounding scheme that will simplify your routing while eliminating loops. Then get power to each component keeping the loops that carry a lot of current small and out of the way.

Next stage is putting it all in a box, keeping all the above in mind.
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Old 4th February 2003, 02:08 PM   #5
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I third that. Do it manually.

Quote:
originally posted by bimbla
In audio circuits, the control circit invariably produces some sort of hum. No matter what you do, getting silence at the output is very difficult.
I use speakers with about 105dB sensitivity, and my system is tube from MC cart to poweramp output, and I don't get any hum. It's about getting the detail of the layout right, and if you're not very experienced at it, unfortunately it might take a few attempts.
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Old 4th February 2003, 06:06 PM   #6
e96mlo is offline e96mlo  Sweden
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If its LF-hum you are experiencing then it might be bad grounding and insufficient decoupling.

Well, I too have to agree what the other guys said about autorouting. It sucks! I've seen experienced(?) engineers in the industry trying to autoroute, for example PSUs, only to have to rip it up and do it by hand.

/Marcus
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