Reflection on grounds

[jfutral]

Maybe. Up until something like this happens (I heard it so I know it is true). Electrician about to do a 400 amp, 3 phase power tie-in "Black is ground because it is the colour of dirt, right?" All at once about 10 techs did this slow motion style run to the disconnect.

I do like the European colour convention of yellow/green for AC ground.

Joe

[jfutral]

There seems to be an awful lot of confusion surrounding the term GROUND.
In most cases it is a misnomer.
In a VAC circuit, there is not a ground.
Think of a transformer secondary.
In a VDC circuit the proper term is the reference of the circuit.
In most cases it is ZERO VOLTS.
Not ground.

I think this is an important distinction. I come from an AC/electricity background. The venture into DC/electronics has upended a lot of my thinking. Male connectors on the working end of cables was my first mind blowing moment.

Joe

[Wilder Amplification]

Yep - it's that think-of-the-currents stuff.

Yep. For a preamp with dual can style caps I take the "grounded legs" of the Volume/Master pots, Mid and Presence pots and I lift them up then turn the eyelets 90*. I then run a piece of 18 gauge buss wire through those legs. Due to the pot legs being lifted, this lifts the ground buss off of the chassis. All of the preamp cathodes join on their common turret, then I run a wire from the cathode turrets to a central point on the ground buss (usually on the pre-volume pot grounded leg) and solder them at that central point. The input jack sleeve runs directly to the grounded end of the 1st gain stage's cathode resistor.

I then take another wire and run it from that central point to the preamp filter cap negative. On the grounded leg of the Presence pot I run a wire from there to the phase inverter filter cap negative, then take the PI filter cap negative to the chassis.

Power valve cathodes/suppressor grids come straight off of the screen filter cap negative as does the sleeve connection of the speaker jack. OT secondary common also ties to the sleeve connection of the speaker jack itself.

For my high gain channel switching stuff, the negative path of the circuit has its own path that is not the chassis. The ONLY two connections the circuit itself has to the chassis on these is the input jack sleeve and the AC mains safety ground. All shielded cables get one end of the shield referenced directly to the chassis with the opposite end lifted.

[Steve Conner]

I think this is an important distinction. I come from an AC/electricity background. The venture into DC/electronics has upended a lot of my thinking. Male connectors on the working end of cables was my first mind blowing moment.

Joe

I've not seen anything in electronics as bad as those crazy Camlock connectors. Now that is mind blowing, a 3 phase 400 amp outlet made of five separate and identical connectors that all fit any of the five holes. I'm guessing the earlier "black is ground" emergency involved a set of these.

The standard colours in the UK for 3 phase power used to be red, yellow, blue for the 3 phases, black for neutral and green for ground. Then we changed to the European colours. There was a lot of confusion and things got blown up.

I suspect Americans still don't understand the difference between neutral and ground, because they spent so long with 2 pin outlets.

[Wilder Amplification]

I suspect Americans still don't understand the difference between neutral and ground, because they spent so long with 2 pin outlets.

Neutral is the return path (or the source path if we're speaking electron flow). Ground is just the "emergency ciruit" that allows surge current to bypass the neutral path back to the source neutral should mains hot short to the appliance casing.

Ooh ooh ooh...did I get it right? Did I? Did I?

[jfutral]

he standard colours in the UK for 3 phase power used to be red, yellow, blue for the 3 phases, black for neutral and green for ground. Then we changed to the European colours. There was a lot of confusion and things got blown up.

I suspect Americans still don't understand the difference between neutral and ground, because they spent so long with 2 pin outlets.

The legs and connectors are SUPPOSED to be colour coded—hot is red, blue, black, and white for neutral, green for ground. Neutral and ground USED to be reversed. Then sometimes only ground was reversed. I have no idea why that changed.

Joe

[Wilder Amplification]

The legs and connectors are SUPPOSED to be colour coded—hot is red, blue, black, and white for neutral, green for ground. Neutral and ground USED to be reversed. Then sometimes only ground was reversed. I have no idea why that changed.

Joe

This is true of the old school 120/240 "high leg delta" 3 phase, with red being the "B" phase/high leg. On a 480/277Y it's brown, orange, yellow for the phases and grey for neutral. Not sure about 208/120Y.

[jfutral]

On a 480/277Y it's brown, orange, yellow for the phases and grey for neutral. Not sure about 208/120Y.

Right. I have only come across that once when I lit a boat show in Portland, ME. I was glad we hired someone else to deal with power tie-in.

Joe

[Wilder Amplification]

Right. I have only come across that once when I lit a boat show in Portland, ME. I was glad we hired someone else to deal with power tie-in.

Joe

I run into it all the time as I do commercial electric and lighting so most of their lighting stuff runs on the 277V line.

[jfutral]

I run into it all the time as I do commercial electric and lighting so most of their lighting stuff runs on the 277V line.

Yeah. Life is simpler for us theatre folk! :-) Simple things for simple minds. All I remember is portable theatrical dimming really hates that Delta leg.

Joe

[MikeM]

On this topic, does anyone have opinions on using a cap pan underneath and grounding / interference from there? I am using solens so no space for the caps upstairs. Had some ideas from reading Merlin's article on it but am not sure it will work so going to give it a bash on my next build. Basically using mini-busses to ground each section to the cap that's powering it. Good/bad idea?

[Wilder Amplification]

Yeah. Life is simpler for us theatre folk! :-) Simple things for simple minds. All I remember is portable theatrical dimming really hates that Delta leg.

Joe

LOL...the delta leg was never meant to power anything phase to neutral. Only the A and C legs are to be used for powering phase to neutral for 120V devices. The fact that the B leg ended up being a phase to neutral "high leg" was a byproduct of center tapping one of the 3 coils in the delta and using it as the neutral reference.

The whole reason for high leg delta 3 phase was to be able to obtain 240V 3 phase power while still being able to power 120V single phase devices without having to have a dedicated single phase 120/240V service in addition to the 240V 3 phase service. Plus the power company only had to use two transformers to get that kind of service.

[soundmasterg]

On this topic, does anyone have opinions on using a cap pan underneath and grounding / interference from there? I am using solens so no space for the caps upstairs. Had some ideas from reading Merlin's article on it but am not sure it will work so going to give it a bash on my next build. Basically using mini-busses to ground each section to the cap that's powering it. Good/bad idea?

Its best to locate each cap close to the stage it is filtering if possible. That stage and it's associated circuitry should ground to the same point that cap grounds, and then all of these local nodes should ground to the main circuit ground with a seperate wire. Using them like Fender did on the blackface amps with a cap pan isn't the best way to do it but it might work ok depending on your gain levels.

Greg

[dai h.]

I think it can work okay to put the filters further away since the frequencies bypassed are low(i.e. not RF or whatever point is considered high freqs.--audio freqs. I think are not)--that's my understanding(something I recall reading in an op amp app. note IIRC). One time, I tack soldered filters(re-located them) on the underside of the PCB to make the smallest loop, most ideal position across the plate and cathode ends (this was in a Marshall 50W w/basically run-of-the-mill 1987/1959 5F6-A Bassman-type circuit) and (at least as far as by ear) I could not detect any difference (so I put them further away again for easier access). Possibly, under different conditions (ultra high gain or whatever) could be different(?).

[Steve Conner]

Yes, because guitar amp circuits are high impedance and low frequency, the placement of the filters isn't so critical. In the old Selmer T'n'B 50 that I modded, they were practically at the other end of the chassis to the preamp stages they were filtering. I think the designer placed them there because they were large cans that he wanted to keep far from the power tubes.

If you're building a hi-fi amp and aiming for 90dB+ signal-to-noise ratio, maybe that placement is a bit more critical.

The physical explanation is that the loop formed by the wires between filter cap and filtered stage can have noise induced in it by magnetic induction. So, if you have to site the caps far away, you can twist the HT wires with their respective grounds to minimize the loop area.