| fedde |
Hi DIY fellows,
usually, I use a 220 ohm resistor parallel with a 220 nF capacitor to connect the case with the ground of my opamp circuits. I wonder if any theory exists why these (or similar) values should be used !?
The result on two variables can be considered:
- The amount of noise that is added to the ground
- The shielding properties of the case (Faraday cage)
Any information would be appreciated!
Fedde |
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| fedde |
Anyone, p-p-p-please !?
Fedde |
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| Peter Daniel |
| It seems like 220ohm is a bit high. Usually 10ohm is being used. |
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| breguetphile |
| A step further than just a low resistance would be what alephs use. If you use a thermistor which will only be resistive when current is flowing, otherwise its close to 0 ohms. This is described in one (if not more) of the aleph service manuals. |
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| fedde |
Guys, you have no idea how thankful I am !!! :)
I will come back soon with a full report, but I think my amp is twice as chilling as before... ;)
(just solved one of the biggest problems I still had)
Fedde |
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| uvodee |
| quote: | Originally posted by fedde
(just solved one of the biggest problems I still had)
Fedde [/B] |
DIYaudio does it again.... if everything would be this easy .....
J-P
ik hou van Holland, landje aan de Zui...... |
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| Mad_K |
| quote: | Originally posted by breguetphile
A step further than just a low resistance would be what alephs use. If you use a thermistor which will only be resistive when current is flowing, otherwise its close to 0 ohms. This is described in one (if not more) of the aleph service manuals. |
Yup, I always do it like this. EXCEPT that you must use a NTC, not a PTC. This means that it should be about 5-10ohms when little or no current is flowing throug your ground, but it drops to a very low value when conducting any significant current. Another elegant solution would be to use a std rectifier bridge as in ZV4. |
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| fmak |
| quote: | Originally posted by Peter Daniel
It seems like 220ohm is a bit high. Usually 10ohm is being used. |
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Theses things sre done in 110V areas. Be careful in 220V region. I don't believe one should connect reoung to chasis via any resistor!
Even the Japanese have abandoned this practice, but still seems to take place in Taiwan.
:( |
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| fedde |
I have a tiny bit of hum if I don't connect the case to ground (the transformers are in the same case). I now connect the case directly to ground. I'll try 10 ohm too...
Fedde |
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| pinkmouse |
| Just a quick note, but using anything in line with the connection between chassis and the ground is bad practise, and, AFAIK, against IEE wiring regulations as being unsafe. It is also not really needed, if you think about your wiring and earth loops properly. ;) |
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| mskeete |
unsafe ?
Are you talking about putting a resistor in between the mains earth and the case
OR
connecting the case directly to mains earth and linking the circuit earth (e.g. transformer centre tap) to mains earth via a resistor
If you mean the second case (no pun intended), please explain why you think this is unsafe |
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