6G15 build ground loop hum question

[dai h.]

the second path through the safety grounds comes back through a section of the ground line which has a higher voltage drop because higher current returns are going through those points which is why I'm saying they should be moved out of the way so they don't share a common resistance. Like star grounding. A star connection is made to unshare common resistance paths.

[Enzo]

The ONLY currents flowing through the earth ground line is leakage currents. Zero operating currents flow down those wires. The operating currents all flow down the neutral (and hot of course), not the earth lead.

[dai h.]

but I'm saying it comes back through a section of the ground line where there are currents because part of the chassis is being used to return higher current portions of the ground line, and that (I think) is where a potential difference is (could be) developed and thus hum (difference is picked up). That's why I'm saying take that part off the chassis so that 2nd return through the safety ground doesn't pass directly through those points, insignificant as that might seem they are still going through the chassis and sharing resistance. We ARE in agreement that there is (has to be) some difference developed but you are saying you aren't sure where it is. And to my thinking the aforementioned is where I see it could happen hence again the proposed solution to where a loop still exists but it's sort of like making a redundant connection across the same segment of the ground line instead of making it loop backwards so it goes through the noisy end.

[dai h.]

(hopefully for more clarity) :

the diagram I made is not how things are (as described by TW with two-point, chassis being used, etc.) but how things should be

sorry (I still think the way things end up being hooked up is the problem, but) maybe I should be explaining it backwards, i.e. the heavier currents on that second group of ground points now can find its way back through the safety ground and through the quieter end (lower current end of the ground line) making a big hoop. By the heavier currents I mean things like the power tubes (think of them as a resistor across the B+ line, spk. return, noisier sections like the early filter caps leaking ripple through the ground line)

[Enzo]

And I have to keep asking, WHAT higher current ground returns? ALL the operating currents return to the power grid through the NEUTRAL wire, NOT the GROUND wire (the Earth wire.)

[dai h.]

yes I know and that was not what I said. *I thought* that was understood before when I said the safety ground wasn't needed for the circuit to work(since that isn't the return path). Specifically the higher current returns such as the power tubes, spk. out return, returns that are noisy like the B+ center tap and filament cnt. tap (if there is one), the early filter caps (ripple leaks back out towards the PT). If the chassis is being used as a return path for these points(if they are connected to a lug that is on a power transformer bolt), then they are sharing a path with the loop being made with the other amp(or reverb) via the safety ground. So I'm saying move those out of the way (off the chassis and not from the ground line obviously)so that when the loop is made when signal and safety grounds form a loop, all the points are the same super low current return segments of the ground line. And that is for BOTH amps (or reverb and amp).

[loudthud]

I think what Dai means is having a path within the amp where, for instance, the HV Ct has a common path with the power line safety ground. If the HV Ct and the power line safety ground go to the same transformer bolt, that could be the source. They should be separated as much as possible, the HV Ct closest to the circuitry and the safety ground on the opposite corner of the transformer.

I just noticed the the 6G15 schematic has no death cap. That would have been a nightmare

[dai h.]

yes! thank you! Not only if it's the same bolt but if both are on the chassis as well.The high current stuff which should go back towards the power transformer (because it's given another path back towards the input where the ground line is the lowest current via the safety grounds) returns in a way it shouldn't.



sorry for getting it sort of backwards. I still think the way I'm suggesting is right but my explanation should have focused on the higher current returns incorrectly traveling that way. Did something sort of like this before where I got the ground re-wiring locations right (i.e. did solve someone's hum problem) but when I looked back over what I posted I got the explanation wrong.

[Enzo]

And when the power is off?

[dai h.]

you mean the reverb (or another amp)? Still looks like a problem. The current comes from the amp that is on. If the powered off amp way can be seen as a wire, it still looks to me that you are connecting parts of the ground line that should not be connected.

[Enzo]

OK, but if you take away the reverb, and just touch a wire to the amp's frame and to earth, you no longer get the hum.

[dai h.]

I think that would depend exactly where. If you made the connection that was the same, then it shouldn't be any different (no hum). What I see is from the plug end safety ground back towards the input. The second point (two-ground point scheme)'s currents that come from the PT winding should go back there but a wire back towards the input gives another path through points it shouldn't be put through.

[tubeswell]

Hi Dai h. and Enzo

I really appreciate the thought you both have put into assisting me with this. Mere words cannot convey my gratitude. I trust that it has been as much fun for you both as it has been instructive for me.

I have a lot to think about.

Yours Sincerely

tubeswell

[dai h.]

well, I'm not sure if I'm just getting you more confused.

anyway, some basics as I understand

-electronic circuits are made of sends and returns. If something goes it needs to come back. So various AC and DC circuits, sends and returns, physical hoops

-they loops are not all the same magnitude

-current flows through the ground line (in general)

a. if no currents were present in the ground line it wouldn't matter how you hooked up the grounds (so in an ideal world, reverb and amp could be hookup up so the grounds are connected but there would be nothing happening, nothing flowing, no possible voltage drop to create voltages where they shouldn't be, no difference

b. current does flow in the ground line making it matter how the grounds are hooked up

as far as what enzo is thinking above, I guess he is sort of saying that big hoop that would be made back towards the input wouldn't matter (and since I'm not sure exactly the specific physical hookup that is in his mind) I'm not sure if it will be a problem but as far as a grounding scheme, if someone asked if a wire could be connected from a metal power strip housing(which had the safety ground connected to it from the amp) towards the guitar jack's ground, I would tell them not to do it because it looks wrong. If any of the heavier currents, ripple leakage do end up there by way of the safety ground wire back towards the input it shares a path with points of the ground line it shouldn't. Maybe I'm analyzing it wrong but it looks like a bad idea to make a big loop like that. My understanding is you want one way back to the source (the PT not the safety ground) for those currents and you want to keep them short since they are noisy unfiltered sections (the ground side of the B+ filter) and since you get more voltage drop across a resistance with more current flow, higher current flow returns with high amount of ripple don't make a good zero point(why my suggestion to take them off the chassis--they still need to be connected to the ground line. They will still be connected to the chassis but not in a way those heavy currents and ripple come back *through* the chassis).

[Enzo]

-current flows through the ground line (in general)

You see, here is exactly where I believe our problem lies. What we call Ground in a guitar amp is really its common. "Ground" should be reserved for Earth. Currents DO indeed flow in the common, but generally do not flow in the earth lead. If you connect one of the 6v green wires to chassis, and one side of each tube heater also to chassis, then indeed all that heater current flows through the chassis, through common. That voltage and current came from the power transformer. The origin of that current is the primary of the PT, And that does flow up and down the hot and neutral wires between your mains supply and the amplifier. But we don;t connect our chassis to either HOT or NEUTRAL. SO unless we DID connect our mains to our chassis, then there is no current to be flowing down the Earth lead. It only flows down the hot and neutral.

Sorta.

There are tiny leakage currents on the chassis, WITH RESPECT TO EARTH. Those are separate from currents down the main and neutral paths. They are the currents that remain when power is switched off.


Dai, I think what I am calling earth, you are calling safety ground For the record, I see three wires in the mains cord - Hot, neutral, earth.