I`m just getting very faint ground loop. I have used chassis ground directly from the B+ Gnd. Now getting low level ground loop with 98db sensitivity speakers. Finally thinking to add a Bridge block rectifier 50A with + and - short use a 100 ohm resistor across AC inputs of the bridge and connect the AC terminal of the bridge to B+ Gnd and other to chassis earth just like how we usually do with amps. Now how far is this right when it comes to preamp. I`m using 6sn7 in Mu follower configuration.
Do I need to get the RCA -ve returns to B+ Gnd directly? instead of the on the preamp board signal ground?
Do I need to get the RCA -ve returns to B+ Gnd directly? instead of the on the preamp board signal ground?
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1. What frequency is the ground loop hum?
50/60 Hz power mains frequency?
100/120 Hz full wave rectified frequency (2X power mains frequency)?
2. Is there ground loop hum when all signal source(s) are Not connected to the preamp inputs?
Or, do you only hear the ground loop hum when signal source(s) are connected to the preamp input?
(Trouble shooting is like going to the doctor, symptoms lead to a diagnosis).
The answers to questions 1. and 2. above, will lead the doctor to ask for even more symptoms, based on those answers.
Find all the symptoms before going in for an invasive operation.
50/60 Hz power mains frequency?
100/120 Hz full wave rectified frequency (2X power mains frequency)?
2. Is there ground loop hum when all signal source(s) are Not connected to the preamp inputs?
Or, do you only hear the ground loop hum when signal source(s) are connected to the preamp input?
(Trouble shooting is like going to the doctor, symptoms lead to a diagnosis).
The answers to questions 1. and 2. above, will lead the doctor to ask for even more symptoms, based on those answers.
Find all the symptoms before going in for an invasive operation.
Well spoken,
i would like to add :
3. Is any devices connected direct or indirect to ground. ( a cable tv antenna is grounded but far away)
3.1 : will grounding the pre reduce hum ? ( temporary ground taken from <suitable source> )
3.2 : add a coarser interconnect between the chassies , fasten well on cover screws. Will this reduce hum
evaluating all points before taking permanent action. Just like a doctor 🙂
When I have hum I'll disconnect all the sources then use a phone or an mp3 player as the source instead of something that runs on AC. Its a way of demarcating the problem to sources side or downstream.
When I have a hum, I lift the ground to see if it goes away. If it does, I look for the loops. I've even resorted to optical coupling to avoid loops... When you get hum through optical, you know it's not a loop at least 🙂
I agree all the above statements but my generic question is that can we use the above bridge ground lifter for tube gear?
Yes even 10ohm should be fine to stop the ground currents flowing in the loop. If not more than 10ohm should also be fine as far as I know. Since if there is potential on the ground the diode bridge will anyway conduct.
Known terrain and what I often see is confusion what ground is. Many use Audio GND connected to chassis. Now someone turns up and says this was done like this 70 years ago and all was fine but granddad did not care about hum/noise as he was glad he had sound at all. Many also don't connect PE to chassis and still use 3 pin plugs?! A good thing would be not to call both Audio GND and PE "ground" as that is part of the confusion and it is simply stupid to call different things by the same name. Metal chassis should be connected to PE for safety solely and not be used as a conductor for audio.
Connecting Audio GND directly to PE in all devices is very safe (insert standard comment of a short circuit of L to Audio GND here) but it causes ground loops. This is not what many like as hum is not music. We would like safety AND no hum.
So, in sources/preamps it should be PE connected to chassis and Audio GND referenced with the 10 Ohm/100 Ohm/diode bridge/CL60 to a single PE point. When only the power amplifier has a direct (0 Ohm) connection between Audio GND and PE things won't hum and safety is still OK. The power amplifier then is "master" with regards to PE and even a short circuit of L to Audio GND in a source device will then not cause unwanted effects. When all devices are connected the Audio GND will be connected via the RCA shields to the power amplifiers PE. Safe + hum free. Solved.
As usual the advice to use correct fuses per device for selectivity/safety. It may sound trivial but I regularly see 6.3A 5 x 20 fuses in 230V 50VA devices.
Connecting Audio GND directly to PE in all devices is very safe (insert standard comment of a short circuit of L to Audio GND here) but it causes ground loops. This is not what many like as hum is not music. We would like safety AND no hum.
So, in sources/preamps it should be PE connected to chassis and Audio GND referenced with the 10 Ohm/100 Ohm/diode bridge/CL60 to a single PE point. When only the power amplifier has a direct (0 Ohm) connection between Audio GND and PE things won't hum and safety is still OK. The power amplifier then is "master" with regards to PE and even a short circuit of L to Audio GND in a source device will then not cause unwanted effects. When all devices are connected the Audio GND will be connected via the RCA shields to the power amplifiers PE. Safe + hum free. Solved.
As usual the advice to use correct fuses per device for selectivity/safety. It may sound trivial but I regularly see 6.3A 5 x 20 fuses in 230V 50VA devices.
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