Going in loops about grounds

[mbratch]

I am about to embark on a 5e3 build (from kit) and have been researching how to properly make the ground connections in the circuit.

I've read about star versus buss and various mixes. I believe I understand them. But what's really messing me up is that there are some reputable builders who say you should solder a ground buss (heavy wire) on back of the pots and connect pre-amp grounds to that. Then another reputable build who says to absolutely not take this approach.

I've studied pics of vintage amps and they seem to to exactly what everyone says not to do: solder the pre-amp grounds to the chassis and the pot ground lugs directly to the back of the pot.

So what's the right answer? Can someone provide pics of what they've done for grounding that has worked really well?

Thanks! I hope this doesn't start a ground flame war.

[Enzo]

Some people think you should order lobster from the menu, others think steak. SOme people don't think you should eat red meat at all, while others think anything that came from the sea will be poisonous. Salad or cole slaw? WHICH ONE IS RIGHT????

This argument and the one you proposed is based upon the notion that there is a right and wrong, that there is some sort of absolute. There is not. Some ideas are based upon sound principles, while others are based upon, I did this and it worked (or didn;t).

If you chose a "wrong" grounding scheme, the amp can still wind up working just fine. We worry about center taps on the heaters and elevating the heaters, and even DC heaters, yet some older amps simply grounded one side of the heaters at each socket and ran a single 6VAC wire socket to socket, and the amp came out OK.

Ground bus across the pot backs? As opposed to basically the same thing by using the Fender brass sheet? Not all pots are made the same. SOme pots with metal construction will naturally ground their shell to the chassis. This forms a little shield for the pot innards. Other pots do not make a ground conection for thier covers. In those cases, a volume control on a high gain stage can pick up hum from this ungrounded cover. In THAT case, it needs to be grounded. WHether you use that ground also for your circuits is a separate issue.

Just because someone successfully uses one particular method doesn;t make other ways wrong, even if that successful fellow says so.

[mbratch]

OK, so it's just, "pick one and if it doesn't work out, try something else".

[tubeswell]

OK, so it's just, "pick one and if it doesn't work out, try something else".

Works for me (although a little discussion, when it is forthcoming, can help with motivation). This can be a blimmin' tricky aspect of amp building.

There are lots of different forces at work in the ground return path. Some ground return points are referencing high voltages, and others not so high. My theoretical understanding of this (limited as it is - and I welcome discussion) is that this can have the effect of creating localised micro-rises in ground potential, which interact/react with other parts of the amp's ground return path which have slightly lower ground potential, and bingo, you have a source of hum. If you can get all the ground return points at the same potential, you will reduce (or even 'eliminate') the hum. As we know, the things that affect potential, are current and resistance (E=IxR). The best way to manage this equation is by managing the resistance - (if you make R really low, you will keep E low no matter what). Different metals have different resistance, as do different thicknesses and/or lengths of wire. Thick brass, copper or aluminium will provide very low resistance, thereby ensuring that potential differences at different ground return points are minimised. I prefer (and this is where the 'I tried it and it works for me' part of the discussion comes into play ) running each ground return point by its own separate wire to a common ground return point;- but I typically have two ground return points (one for the pre-amp grounds, including the pre-amp filter caps grounds; and the other for the power amp grounds, including the heater CT (in situations where I do not have the heaters elevated)). The separate wires helps avoid creating a situation where you are introducing a margin for localised rises in chassis potential. To-date I have used 1.2mm (16 gauge) aluminium sheetmetal for my chassis. My amps have all been very quiet. Other peeps will say different stuff (as Enzo said).

[mbratch]

Thanks tubeswell.

Both of you guys have given me more education on grounding.

It's a funny thing though: I'm learning more and more about grounding, but still I suppose there will be a level of uncertainty as to where to start with my particular project.

My initial thinking was to take a piece of 14 or 12 gauge copper wire and run it across the back of the pots, tying the pre-amp grounds and pot/jack grounds to it, and then soldering the end near the jacks to the chassis. That more or less lines up with the Hoffman methodology. The power amp and output section I was going to keep separate.

Then I read somewhere that tying grounds busses to the back of the pots wasn't such a good idea, so I thought I'd do something similar, keep the buss, but somehow make it separate from the pots. Perhaps running it along one side of the eyelet board or suspending it with insulated tie points fastened to the chassis. I would in that case otherwise connect the grounds to it as planned.

I thought I'd look at pics of other peoples' builds but the funny thing is, of all the detailed pics out there of the innards of a 5E3, you rarely see how the grounding is done. It's usually obscured in the photos. :-O

I'll give this some further thought.

[dai h.]

basically anything that you do which considers what is happening in the grounds and is wired accordingly regardless of whether you use stars, buss, plane, etc. will work. Lots of info if you search.

[mbratch]

basically anything that you do which considers what is happening in the grounds and is wired accordingly regardless of whether you use stars, buss, plane, etc. will work. Lots of info if you search.

Oh yeah, I've been searching, finding, reading, and studying. That's what led me here.

[Five_E35]

On mine, I used the brass plate, but experimented with the screen, main, and center tap grounds, and found very little difference in hum. I ended up with everything grounded to the brass plate, similar to what Bruce recommends in some posts on here and what Fender does on the '57 RI. BTW - The schematic on the Fender site includes complete wire by wire diagrams.

I suspect the 5E3 isn't that sensitive as long as the cathode resistor for the output tubes and the main cap are tied together. My guess is the Hoffman method probably makes more sense for fixed bias amps like a Bassman or Twin where the power tube cathodes are grounded to the tube sockets on the other side of the chassis. My impression is that more exotic grounding schemes are needed for higher gain amps and although there's probably some people here who can do it, I wouldn't have a clue when it comes to something like a Soldano.

[mbratch]

Thanks. I didn't think to look at the Fender schematic for their re-issue. It is a very helpful drawing.

What assumptions are made about the brass plate? It looks to me that it's assumed the brass plan makes good electrical contact with the chassis, and that the pots and jacks also completely ground to the brass plate by virtue of being bolted to it. I know these sound obvious, but I'm just confirming.

It's also interesting that for the 3 big filter caps, the old Fender layout ties grounds of the cathode bias cap with filter cap 1, and then ties the grounds of filter caps 2 & 3. In their new layout, they tie grounds of filter caps 1 & 2 together, but not 2 & 3.

[Five_E35]

I've read in several places that the brass plate acts like a giant buss ground, and with everything connected to it the mechanical connections to the chassis are less critical. Dave Funk says the same thing in his book and also talks about grounding parts of the circuit near or opposite from their power source - i.e. cathode resistor & input jacks for V1 opposite the 100K plate resistors, screen cap opposite screen supply, and this seems like what Leo was doing on most of his amps. My own feeling is it's also better to rely on soldered vs. mechanical connections.

I soldered up the ground wires, input jacks, and pots with the plate outside the chassis, included a ground wire from the transformer bolt, and used excess cap lead for jumpers between the caps above the board instead of underneath. I experimented with a 5AR4 & 5881 tubes in it, in a back room near an in-ground power company transformer where it's almost impossible to use single coil pickups. I tried both screen cap variations to the brass plate & to the transformer bolt & to a location closer to the power tubes suggested in the Hoffman method, and there really wasn't much difference. I did clean up the back of the brass plate & the inside of the chassis with electrical cleaner before assembly, so maybe with dirt & age there might be a difference.

[dai h.]

it's Bruce I think who said that the brass plate is sort of like a star (not a giant buss). When you star points, the purpose is to try to eliminate common paths, common resistance. If you have a big conductor in a central location which you connect the grounds to it can be like a star in the sense that the bigger the conductor is the lower the common resistance. Star connecting may look more physically obvious in reducing common resistance, but the big plane can be doing the same thing. The back of the pot buss can be the same as the plate in the multiple connections to the chassis and the pot backs (usually brass I think) to each other. You get an area of higher conductivity, lower R. There might, (with the wire across pot backs) be a way(s) of connecting the ground wires to the buss that is more correct or less correct.

[tubeswell]

It's also interesting that for the 3 big filter caps, the old Fender layout ties grounds of the cathode bias cap with filter cap 1, and then ties the grounds of filter caps 2 & 3. In their new layout, they tie grounds of filter caps 1 & 2 together, but not 2 & 3.

FWIW Out of curiousity I have tried both ways, and I found that if I tied '1' & '2''s ground returns together, it was slightly quieter than if I tie '2' & '3''s ground returns together ('3' being the pre-amp cap). Anyhow you can always change it afterwards. I ended up changing it to whatever was quietest

[mbratch]

I have a kit that doesn't come with a brass plate. So now I'm wondering whether I should go to a HW store and see if I can find a brass plate, or go to my plan A which is fuss with a 14 gauge copper wire method (al la Hoffmann).

As an aside, I'm also a little confused that the drawing shows the PT yellow/red strip center tap grounded whilst it also has the two 100 ohm resistors from the pilot light to ground. I thought these were mutually exclusive?

[tubeswell]

As an aside, I'm also a little confused that the drawing shows the PT yellow/red strip center tap grounded whilst it also has the two 100 ohm resistors from the pilot light to ground. I thought these were mutually exclusive?

Yes the heater winding only needs EITHER a 'real' centre tap connected to ground, OR the 2 x 100R 'artificial centre tap' connected to ground. Depending on how accurately the 'real' Heater CT is placed w.r.t. being in the middle of the winding, the 2 x 100R can provide a quieter method if the resistors are 1% tolerant (but it draws a wee bit more current than the 'real' CT method). But if the 'real' CT is exactly in the middle of the heater winding, then it will be really quiet (All other things being equal)

[mbratch]

Thanks tubeswell. I'm not sure why the drawing shows both hookups at the same time. I figured from prior experience working on vintage amps that they're supposed to be mutually exclusive. Unless I'm misinterpreting what the yellow/red wire is.