Power supply questions
Jul 4, 2002 at 8:30 PM Thread Starter Post #1 of 3

mizterbob

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I am planning to build a meta42 and a linear psu for it. A few questions:

1. The meta42 PCB can be used with a TLE2426 rail splitter for virtual ground. However, if I build a psu, I could just make the psu have positive, negative, and ground connections so the rail splitter would be unnecessary. Which is better (with rail splitter or without)?

2. I will probably use a metal case which will be connected to the mains ground. Many psu designs use a ground loop breaker to also ground the signal ground. But many people build battery or wall-wart powered amps, so it doesn't seem that the signal ground needs to be connected to the actual earth ground. So what is the purpose of connecting the signal ground to the mains ground at all (even through a ground loop breaker)? Also, looking at schematics of the ground loop breaker, it seems that if a live wire somehow came into contact with the metal chassis then the mains voltage would be able to enter directly into the amp circuit through the signal ground to mains ground connection, possibly blowing up amp/headphones etc. Is that true? So ultimately the question is, is it better to connect the signal ground to the mains ground or not? Or if I made DIY interconnects I could connect the shield to mains ground and still have a floating signal ground. Would that be a worthwhile solution?

3. This is actually unrelated to the psu, but if I were to make interconnects, is there a minimum length? I would figure it would be best to make the interconnects as short as possible but I think I remember reading that if they're too short there can be problems. Anyone have advice on this?

Thanks for your help on all these questions.
 
Jul 6, 2002 at 2:26 PM Post #2 of 3

Tomo

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Hello,

1. Personally, I believe that will improve the behaviors of your amp when it uses two 9V batteries or something. Especially when the voltage on those two batteries aren't garranteed to be the same. Considering the ease of designing and construction of rail splitter/driver, I believe it is definitely worth having.

2. Ground Loop Breaker is essential. For sound quality, you should separate signal ground and power supply ground. However, by doing this, you will promote ground looping. You must keep this from happening.

Your chasis should be connected to ground line of our outlet. Live wire leakage will be swept back into the outlet rather thru you, entirely bypassing the amps or the headphones. In that case, fuse will blow preventing further damage. (You must have fuse) Note if your signal ground is connected to PS ground, you might want to use faster fuse.

3. Interconnect building still belongs with DIY area. Shorter interconnects are better always. This is because longer the interconnects higher the capacitance and the resistance the it present to the line driver. Of course, if you make it too short you can't reach the amplifier input. (which did happened to me.)

You should pay more closer attention to the grounding and the shielding of the interconnects depending on applications. My amp PSU ground is completely separate from signal whatsoever. So my amp signal ground share signal ground with CD player, but with nothing else. This way there is no unnecessary ground looping, but easier construction of interconnects. (It isn't ideal so I keep interconnects "decently" short.)

If I can choose, I prefer using BALANCED in/out amplifiers specifically because of better grounding solution. However, currently it isn't much of a choice for me. Most of my equipments have UNBALANCED in/out. I would really love BTL solutions like I can do with speaker amps.

----------------------------------------------------------------------------------

To be honest, decent battery PSUs are very hard to beat. It has been ongoing desire to build as good linear supply, but it isn't quite alike. But then convenience and necessity decides what one should use. Please note, that opamps come with pretty decent power supply ripple rejection. So you don't have to go wary of building this "perfect" PSU people talk about. (Benefits are far less than money spent. I say, be practical at least until economy is better. But I must admit it is fun to talk about that.)

Tomo
 
Jul 6, 2002 at 5:12 PM Post #3 of 3

morsel

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A true dual regulated supply is better than using virtual ground. Virtual ground is better than splitting two batteries.

Do not connect your case to AC ground, that is a really bad idea, and the cause of many ground loop problems. Make the case signal ground if you must. You can not connect signal ground to AC ground if you are using a virtual ground or you will short the negative rail to ground. You can if you are using a dual supply.

Cases are tied to AC ground for electrical safety reasons. If the hot AC side were to connect to the case due to a fault it would be shorted to ground and blow the breaker instead of shocking the user. This is generally more appropriate for power tools than your headphone amp. Many pieces of audio equipment use ungrounded power plugs, and they are generally happier for it. Every piece of audio equipment beyond 1 (ie 2 or more) hooked up to your stereo that does not use balanced inputs and outputs, but does have the case tied to AC ground, creates a ground loop several feet in diameter between the power strip, power cords, chassis, and signal wires between the units. This ground loop functions as a giant loop antenna, picking up 60Hz hum and other nasty stuff which gets injected straight into your signal path.

For more information on ground loops and how to correct them, read the Sound Reinforcement Handbook published by Yamaha. This is the industry standard text for pro audio and has the best treatise on ground loops I have seen.

-Morsel, Goddess of Ground Loops
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