| whitelabrat |
| I need a sanity check folks. What would happen if I attach the center tap of the high voltage secondary of a power transformer to Earth ground? Pat on the back or smoke and flames? Should Earth be used to ground the chassis and the center tap for the circuit? |
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| dave_gerecke |
You're still sane, at least in regards to this design. If you look at most classic tube amp designs, the center tap is grounded to the chassis, thus establishing it as the relative zero volt point. With modern design philosophy, I would suggest that instead of connecting it directly to your chassis earth, you use a NTC thermistor or a bridge rectifier between the transformer center tap and the earthing point. This will help keep hum off of your circuit zero volt path. Also, attach your earth safety wire of your power cord directly to your chassis, then bring all of your circuits grounds together at one star ground point near the point where you attached your safety wire.
Peace,
Dave |
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| whitelabrat |
| I never thought about using a thermistor. Good idea. Any suggestions for an appropriate value? The transformer I'm using is 250-0-250 (500VCT). I see one that can do 180 ohms. Typically I've used 10k resistors for closing ground loops which are effective, but may not give the best results as far as safety is concerned. |
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| dave_gerecke |
Hello labrat, I don't know of the top of my head what value thermistor to use. I got the general idea from one of Nelson Pass writeups about his ZEN amps. If you go to www.passdiy.com and take a look at the ZEN amp series, he shows using Thermistors. That's also where I got the idea of using a Bridge rectifier.
Basically you want some sort of device that keeps the circuit ground isolated from the earth(safety) ground in normal operation, but allows any excess current to flow to the safety ground when necessary. That's why a Bridge rectifier will also work.
Peace,
Dave |
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