Post by Owen Y on Jan 1, 2021 15:42:28 GMT 12
Every now & then, most audio (or HT) enthusiasts have Grounding issues. eg: - Complex systems (eg HT and/or Home Entertainment systems with lots of devices hooked up) - Phono systems (ultra-low signal level signals, un-shielded tonearm wiring, TT motor in proximity, etc.) - Valve/tube systems (high voltage / high impedance ccts tend to pick up noise more easily) - Digital & other set-ups where RF noise can be especially problematic, This is a thread to explore, air, explain & discuss such problems. Below is a Typical System Grounding diagram - which can be simplified if you happen to have, for example, an integrated amplifier. You can immediately see the potential for 'Earth loops' or 'hum loops'.  (GBC - 'Ground lifts' are not advisable, but modern consumer audio devices (in most major parts of the world) incorporate a 'Ground-Loop Breaker Circuit' between the circuit Ground & Earth - a small resistor, say 10 ohms in parallel with a 0.1uF capacitor, that reduces Ground currents but ensures that RF noise is always bypassed to Earth.)
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Post by cartridgeguyonline on Jan 2, 2021 7:35:14 GMT 12
Nice Diagram Owen !
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Post by Owen Y on Jan 2, 2021 14:04:47 GMT 12
With a valve/tube amplifier, things can get a bit more complicated. Aside from the higher voltage/impedance circuit, there is usually an Output Transformer (OPT) 'coupling' the amp to the l'spkr. In my case, I have also a Transformer Volume Control (TVC). And, a Step-up Transformer (SUT) if using a MC cartridge. It is recommended practice to connect the 'Grounds' of a SUT from Primary (input) side to the Secondary (output) side of a SUT. I was to discover that this is beneficial too for a TVC & also for the OPT of a tube amp. (More later in a separate thread - Noise chasing) 
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Post by colinf on Jan 2, 2021 22:13:07 GMT 12
Hi Owen, nice diagrams but I’m finding them a little confusing. In theory there’s no ground loop with your first diagram as the grounds are all floated with a resistor-cap combo. The second diagram has ground loops as each component ground is connected to the 3 pin power supply earth, creating two earth paths for the signal ground. Is that what you were meant to indicate?
AMR-iFi R&D
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Post by Owen Y on Jan 3, 2021 15:27:29 GMT 12
Ah no, sorry - 1) The first diagram was just indicating the *possible* Ground/hum loops - which the GBCs effectively break. 2) In the 2nd diagram, I was lazy & did not show the GBCs (thanks for pulling me up on that  ). The cct Gnds are all connected to the chassis via GBCs & the chasses of course are Earthed. With my own set-up, I had this idea that the TVC & amp OPT (& later also preamp Line OPT) were providing me with a good measure of Gnd loop isolation - and, the Prim-Sec Common Gnds of each of the above 3 were not connected. As mentioned above, I discovered later that system noise was significantly reduced when I did Gnd connect these TXs (2* & 3*). (I also now do not usually use a SUT / MC cartridge.)
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Post by RdM on Jan 3, 2021 20:08:45 GMT 12
A slight tangent perhaps, since Owen is writing about connected home audio equipment each with own power leads, but from my bookmarks: www.aikenamps.com/index.php/groundingThis is from a guitar amp maker, and for the home constructor, also valve amp oriented, but may be of interest.
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Post by RdM on Jan 10, 2021 22:48:53 GMT 12
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Post by Owen Y on Jan 11, 2021 10:23:44 GMT 12
Valve Wizard's site is often quite useful. Internally, inside amps etc, I do not fanatically adhere of 'star grounding' or whatever philosophy. I think what works best is minimising Grounding routes/runs (star grounding often results in long Gnd wires), which usually means a combination of a heavy Ground 'bus' with local 'star' Grounding. Secondly, consider where the highest Gnd current are (eg. AC currents around the PSU first filter capacitor) & minimise these Gnd runs. Thirdly, I keep in mind Sakuma's '2-point' Grounding method - generally a separate PSU Gnd & signal Gnd (coming together near/at the chassis Earth point. All IMVHO of course
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Post by colinf on Jan 28, 2021 21:15:01 GMT 12
(Copied from valve push pull implementation thread) Ah, a grounding of convenience on this chassis then. The concept is good, use a low impedance ground plane to connect all circuit grounds to. It’s not quite as simple as it seems though. Magnetic eddy currents from the power transformer circulate through the chassis and a result in potential differences at each ground point. RF interference today is very high with mobile phones, wifi, bluetooth etc and the UHF RF potential at different points across an unshielded ground plane can be high, low impedance as it is forming high Q resonances. Ideally the chassis should be grounded at one point only, generally near the input socket, and all circuit earths wired to it (star grounding), or in series as the circuit goes from input to output. The output earth should not be far from the input earth so that any RF on the interconnect shield and speaker earth goes straight to the chassis, the closer to the single point connection the better. The chassis then acts as a large shield for the circuit inside. Mains earth goes there as well. If there’s a potential for a ground loop from connected equipment the star ground can be lifted with a ground lift circuit, but the main chassis containing the power transformer is earthed directly to mains earth.
AMR-iFi R&D
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Post by Owen Y on Feb 13, 2021 14:25:17 GMT 12
Ground Loop Breaker Circuits (GBC): Just to recap - the idea of a GLBC / GBC is to " minimise the ground loop current" - whilst still maintaining a safe Earth connection to divert any hazardous fault currents. The small resistance " could be increased to 33Ω to reduce ground currents still further without violating CE design rules". ( moleculardevices.com) The small capacitor is there to ensure that RF currents are always connected to Earth.  (Notional amp schematic.)
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Post by Owen Y on Feb 13, 2021 14:54:21 GMT 12
This is an update on my system: - The devices that I have built have a GBC Earth connection installed now. - Except for the SUT (which is Grounded through the Phono stage (Lounge Audio) to my Line Preamp. - The Phono Stage is 'floating' as it is supplied with low voltage AC from an outboard PTX (Power Transformer). In my search to track down & minimise noise (hum mainly) in my system with high-sensitivity l'spkers, I have experimented with system Grounding - as noted (asterisks) - 1* - The primary & secondary (input / output) sides of SUTs usually must be Ground connected (to provide a ground connection to the Phono stage for any noise picked up). 2* - Line Preamp - in my case, I have a TVC (Transformer Vol Control) at the input & a 'Line OPT' at the output. So my preamp circuit was 'isolated' inadvertently at 2 ends. When the Ground connection 2* was made, there was a significant reduction in noise. 2a* - I found that this Ground connection was of no benefit noise-wise (& was deleted) - because I think, the sec. side of my Line OPT is already connected forward to my Power Amp Ground cicuit. 3* - Power Amp(s) - Grounding the -ve side of a tube OPT speaker connection, also reduced noise. So, in the end, only the Line Preamp & the Power amp(s) are Earthed - important as they are high-voltage (tube) devices. 
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Post by Owen Y on Feb 13, 2021 15:33:41 GMT 12
I had actually made some crude investigations beforehand on the bench with an old-school o'scope: Looking at the output of my tube Line Preamp (inputs shorted, outputs loaded 100k..... - I had 6-7MHz RF noise, riding on top of 50Hz hum - around 1.0V pk-pk, quite significant level. - When the TVC was Ground-connected both sides, this reduced to only 20mV pk-pk (1/50th). 
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Post by Owen Y on Feb 13, 2021 15:54:09 GMT 12
Similarly, my tube power amp: - I found that I had 650kHz RF on top of 1.2V pk-pk 50Hz hum - only when the mains cord is connected & regardless of whether the amp was switched on or off. (I think this is telling me that such noise is present in the mains Earth line AND makes its way across the to the OPT secondary winding.) Surprising & interesting. - When the OPT sec is Grounded, the noise reduces to 48-50mV (1/25th). 
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Post by colinf on Feb 13, 2021 20:42:51 GMT 12
Aha, welcome to the weird and wonderful world of RF! Remember your scope is also grounded. Measuring these sorts of things is best done with a battery-powered scope and/or spectrum analyser.
AMR-iFi R&D
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). The cct Gnds are all connected to the chassis via GBCs & the chasses of course are Earthed.