More Grounding Questions
Thanks Heyraz. Let me provide more info. My main power amp has both AC ground and signal/circuit ground wired to the chassis. I don't think I've ever seen that in audio gear.If someone used a cheater plug that can reverse the neutral,and the hot phase line,that would give 120 volts to the chassis.Zap the user,plus fireworks possible.I can see them tying the green ground to the chassis.I don't think I would experiment either. |
Vett93 This new post of yours has a lot more going on than the original (ground rod placement and ways to minimize noise). And by the way, everything I suggested was from personal practice after consulting EEs and Union Electricians. Being a retail pharmacist has it's advantages, I get to know a lot of knowledgeable people and pick their brains. Why do you think your secondary power amp hummed when the signal ground was isolated from the chassis? If I'm reading you correctly, the chassis of your secondary power amp was internally connected to the input signal ground as well as the power ground. When you isolated the input signal ground from chassis (and AC ground), the hum disappeared. How did you do this? If I read you literally, you were able to do this while leaving the AC ground still connected to chassis. I have seen equipment with "ground lifting" switches, but never used one in practice, nor do I fully understand it. Perhaps another reader can explain further. Have you been able to obtain schematics of your equipment? Did you open it up to verify that the power was proper polarity with regard to hot and neutral? Have you checked for leakage? What equipment do you have exactly? Perhaps other readers have had personal experience. I read a post a few weeks back regarding a preamp/poweramp mismatch. Without getting specific, the two were literally oil and water, one passing DC to another unable to handle it. Perhaps your situation is basic design incompatibility. I'm no EE but I have built a few kits, fixed a few rigs, and can read schematics well enough to trace a circuit. Please provide more specific information, I'm intrigued. |
Hifihvn, yes, AC ground (not AC neutral) is wired to chassis. Heyraz, there was a ground loop between the preamp and the secondary power amp. (To be clear, I only use one power amp at a time). So it hummed. Then I isolated the signal/circuit ground from the chassis while keeping the AC ground wired to the chassis. The hum stopped because no ground loop is between preamp and the secondary power amp. I opened up the secondary power amp to disconnect the wiring. I did check the polarity and it was fine. The manufacturer wouldn't give out schematic. But it is a simple KT88 PP amp and is easy to trace. When I use the main power amp, there is still a ground loop between the preamp and this main power amp. But it does not hum. Maybe I should re-phrase my questions: 1. Will ground loops degrade sound quality even though it does not hum? 2. When you "float" your power amp, do you float the signal/circuit ground from the chassis or you float AC ground from the chassis? Thanks all. |
Will ground loops degrade sound quality even though it does not hum?In addition to producing hum, ground loops can also result in high frequency noise and buzz, by coupling harmonic distortion components and/or noise that is typically present on the ac lines into signal return paths. However, if you don't hear that when no music is playing, or if any low level buzz or noise that you do hear is the same whether or not the equipment is temporarily floated with a cheater plug, I doubt that it would have any effect on sound quality. I suppose it is slightly conceivable that inaudible ultrasonic noise that is introduced by a ground loop could somehow intermodulate with the music and have audible effects, but it's easy enough to rule out that possibility -- just compare the sonics with and without the ac safety ground temporarily lifted via a cheater plug. When you "float" your power amp, do you float the signal/circuit ground from the chassis or you float AC ground from the chassis?I would never isolate circuit ground from chassis, assuming the equipment was designed with them common. And I'm not sure how it would even be practical to do that, unless the design had them connected together at only one point, and the rca jacks were the type that has isolated ground sleeves. Assuming that circuit ground and chassis are connected at more than one point, isolating those connections would most likely result in significant impedances, especially at high frequencies, between circuit points that should be common. In other words, grounds at different points in the circuit would no longer be truly common. Also, stray capacitances between various circuit points and ground would be different than those which were present when the initial design and development was performed, in effect changing the design in unpredictable ways. Also, instead of the chassis functioning as a shield, it would very conceivably function as a path for emi/rfi to couple into internal circuit points. Of course, as you probably realize floating the ac safety ground is in principle not a good idea either, due to the safety risk it creates. Although a lot of people do it anyway. As far as I am aware the only way to break a problematic ground loop that is both effective and completely safe is with something like a Jensen Isomax. This Jensen paper will probably be of interest, if you haven't seen it already. Best regards, -- Al |
