good grounding
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good grounding
hey i have had some debates with several people about the best way to ground using a chassis. what are y'alls opinions?
-skyy amps
Re: good grounding
I'd have to do a drawing to do it any justice.
my method is unorthodox by amp standards, but very normal by EMC/signal-integrity engineering standards.
my amps are dead quiet.
my method is unorthodox by amp standards, but very normal by EMC/signal-integrity engineering standards.
my amps are dead quiet.
Great lets see
Love to see what you do.
Re: good grounding
I think there a bit of magic in that answer.....I think we each do what we personally have found to work.
I like the 2 chassy point system. 1 near eic, goes to ps ground, via 2 wires, 1st to totem pole, 2nd to rest of ps string, and also connect power tubes ground here. The other chassy connection is very close to the input jack, and this gets all pre-amp grounds. I guess technically there is a 3rd point, as I use metal output jacks, which grounds the OT at the jack.
works for me.
theres a lot dependent on how you choose to route your wiring.
I like the 2 chassy point system. 1 near eic, goes to ps ground, via 2 wires, 1st to totem pole, 2nd to rest of ps string, and also connect power tubes ground here. The other chassy connection is very close to the input jack, and this gets all pre-amp grounds. I guess technically there is a 3rd point, as I use metal output jacks, which grounds the OT at the jack.
works for me.
theres a lot dependent on how you choose to route your wiring.
it really is a journey, and you just cant farm out the battle wounds
Re: good grounding
well unfortunately I don't have a drawing.
however in a nutshell it's like this.
let's say we are talking about 18W "Lite" kind of amp... one channel, 2x cathode bias EL84.
There are two ground points: the input jack, and a ground lug on the power-supply/power-stage end of the board.
the power supply up to the B+3 or the plate supply for the PI are all grounded together sort of "bus" style on the turret board. I use the front (control panel) edge of the board for grounds, with +V on the other side. So I just run short wires from one turret to the next one that's ground, and the last turret on that corner has a wire coming off to the ground lug.
The rest of the grounds of the amp on the turret board (downstream PS stages, cathodes, grid leak resistors, etc.) are connected together bus-style to the other front corner turret on the board, which is the V1A input stage cathode C/R ground side. This has one wire coming off going to the input jack.
The vol and tone controls are grounded to the input jack. I don't use a ground from the body of the pots like in many amps. Instead I just use the terminals of the pots with short wires running from one pot to the next, and from there to the ground terminal on the input jack.
The output jack(s) are grounded mechanically through the chassis, no ground wire. They are connected to the OT secondary and nowhere else.
There is one "safety" ground lug near the power inlet with the green wire connected to it.
and that's it, ladies and gentlemen!
now of course many of my amps have more complicated circuits than this with many more places where I need a ground including shielded wires and that kind of thing but basically it works the same. PI plates thru the power stage and their associated PS caps etc are all going to the ground lug on the PT end of the chassis, and the preamp all the way to the PI input and tail resistor are all grounded bus-style terminating at the input jack. Simple, effective, clean.
however in a nutshell it's like this.
let's say we are talking about 18W "Lite" kind of amp... one channel, 2x cathode bias EL84.
There are two ground points: the input jack, and a ground lug on the power-supply/power-stage end of the board.
the power supply up to the B+3 or the plate supply for the PI are all grounded together sort of "bus" style on the turret board. I use the front (control panel) edge of the board for grounds, with +V on the other side. So I just run short wires from one turret to the next one that's ground, and the last turret on that corner has a wire coming off to the ground lug.
The rest of the grounds of the amp on the turret board (downstream PS stages, cathodes, grid leak resistors, etc.) are connected together bus-style to the other front corner turret on the board, which is the V1A input stage cathode C/R ground side. This has one wire coming off going to the input jack.
The vol and tone controls are grounded to the input jack. I don't use a ground from the body of the pots like in many amps. Instead I just use the terminals of the pots with short wires running from one pot to the next, and from there to the ground terminal on the input jack.
The output jack(s) are grounded mechanically through the chassis, no ground wire. They are connected to the OT secondary and nowhere else.
There is one "safety" ground lug near the power inlet with the green wire connected to it.
and that's it, ladies and gentlemen!
now of course many of my amps have more complicated circuits than this with many more places where I need a ground including shielded wires and that kind of thing but basically it works the same. PI plates thru the power stage and their associated PS caps etc are all going to the ground lug on the PT end of the chassis, and the preamp all the way to the PI input and tail resistor are all grounded bus-style terminating at the input jack. Simple, effective, clean.
Re: good grounding
so the idea would be to keep them far enough apart that you end up with as little potential difference as possible?
-skyy amps
Re: good grounding
the idea is to know where your current is flowing and eliminate the opportunity for a loop.
in the case of my amp, the preamp stage HAS to have a ground connection at the input jack, so if I ground it elsewhere, it forces a ground loop opportunity. So they ground in a bus/series and then terminate at the one ground that is required for that circuit. the power amp does not have to be grounded at the front panel so I ground it local to the protective earth/ground inlet to reduce ground impedance and again use bus/series to prevent ground loops. current does not try and flow through the preamp stage to the power amp/PS ground since it is referenced at the front panel, and any current that needs to flow from the PS can come from the PS decoupling cap. current in the power amp does not try to flow from the front panel since clearly the low impedance path is from the power end of the chassis near the PE connection.
reducing noise from ground problems is all about designing in current flow.
in the case of my amp, the preamp stage HAS to have a ground connection at the input jack, so if I ground it elsewhere, it forces a ground loop opportunity. So they ground in a bus/series and then terminate at the one ground that is required for that circuit. the power amp does not have to be grounded at the front panel so I ground it local to the protective earth/ground inlet to reduce ground impedance and again use bus/series to prevent ground loops. current does not try and flow through the preamp stage to the power amp/PS ground since it is referenced at the front panel, and any current that needs to flow from the PS can come from the PS decoupling cap. current in the power amp does not try to flow from the front panel since clearly the low impedance path is from the power end of the chassis near the PE connection.
reducing noise from ground problems is all about designing in current flow.
Re: good grounding
Here is my "go to" schematic for amp grounding philosophies.
http://www.el34world.com/charts/grounds.htm
It has worked flawlessly for every build/repair (about a dozen or so) that I have done.
Although I only scanned the previous posts, I believe that this chart embodies the principles that are presented there.
Good Luck,
Dave O.
http://www.el34world.com/charts/grounds.htm
It has worked flawlessly for every build/repair (about a dozen or so) that I have done.
Although I only scanned the previous posts, I believe that this chart embodies the principles that are presented there.
Good Luck,
Dave O.
Re: good grounding
no that drawing doesn't represent my grounding scheme.
I do not use the "back of the pots wire bus" method that is so popular. That would be more like a multi-point rather than my quasi-single-point ground method.
The way my method is sort of similar is ON THE BOARD the grounds are bussed together, then with a single wire connection to the chassis ground, at the input jack for the preamp circuit grounds, and at the ground lug on the other end of the chassis for the power amp and main PS circuit grounds. but with the back-of-the-pots method you have multiple ground connections and clearly loop area between the pot bus wire and the chassis in front of it, through to the input jack, and back around the board back to the ground bus with multiple connections.
I'm not suggesting you can't make such a method work, or that it won't work nearly every time without fail. It's just not really the best way in my mind.
I do not use the "back of the pots wire bus" method that is so popular. That would be more like a multi-point rather than my quasi-single-point ground method.
The way my method is sort of similar is ON THE BOARD the grounds are bussed together, then with a single wire connection to the chassis ground, at the input jack for the preamp circuit grounds, and at the ground lug on the other end of the chassis for the power amp and main PS circuit grounds. but with the back-of-the-pots method you have multiple ground connections and clearly loop area between the pot bus wire and the chassis in front of it, through to the input jack, and back around the board back to the ground bus with multiple connections.
I'm not suggesting you can't make such a method work, or that it won't work nearly every time without fail. It's just not really the best way in my mind.
-
David Root
- Posts: 3540
- Joined: Fri Aug 04, 2006 3:00 pm
- Location: Chilliwack BC
Re: good grounding
I have used multiple star points to an isolated buss wire that is grounded at the input end only. Filter cap grounds run to the star point for that part of the circuit that the filter cap feeds. If using NFB, the OT common goes to the same star point as the PI ground. I also isolate the input jacks and the output jacks from the chassis using fiber shoulder washers. Pots are not isolated so the casing shields the pot, but I never use the pot casing as a ground either.
Works great, dead quiet too. The logic for the two ground system is sound too. Like someone else said, you have to eliminate any possibility of a ground loops. If you do that, it will be quiet.
Another refinement is an internal hum shield on the PT, connected to the same star point as the PT center tap. Copper flux band on the PT doesn't hurt either.
Works great, dead quiet too. The logic for the two ground system is sound too. Like someone else said, you have to eliminate any possibility of a ground loops. If you do that, it will be quiet.
Another refinement is an internal hum shield on the PT, connected to the same star point as the PT center tap. Copper flux band on the PT doesn't hurt either.
Re: good grounding
I would consider earth ground on the input jacks to be a safety necessity.
In fact it would most likely be a requirement for regulatory safety compliance, I would think. I am not familiar with the standard they use for guitar amps but if it were a telecom device (with which I am extremely familiar), then any accessible metal parts would be required to be grounded.
In fact it would most likely be a requirement for regulatory safety compliance, I would think. I am not familiar with the standard they use for guitar amps but if it were a telecom device (with which I am extremely familiar), then any accessible metal parts would be required to be grounded.
Re: good grounding
Bus wire suspended from the ground lugs of pots (not the back of pots)
Green from power cord to chassis
local stars on the PS, PT center taps, FB wire, and power tube cathodes, terminate at power supply end of bus
local stars on main board terminate on buss nearest to pot grounds for same cicuit
all jacks isolated
input ground goes to closest place on bus wire, then wire from bus is bolted to chassis near the input jack.
No other connections to chassis
My personal belief is the chassis should be a shield and should not carry any current (although it saves wire to do it the Fender way) YMMV
Green from power cord to chassis
local stars on the PS, PT center taps, FB wire, and power tube cathodes, terminate at power supply end of bus
local stars on main board terminate on buss nearest to pot grounds for same cicuit
all jacks isolated
input ground goes to closest place on bus wire, then wire from bus is bolted to chassis near the input jack.
No other connections to chassis
My personal belief is the chassis should be a shield and should not carry any current (although it saves wire to do it the Fender way) YMMV
Re: good grounding
I agree with Tonegeekskyyamps wrote:hey i have had some debates with several people about the best way to ground using a chassis. what are y'alls opinions?
My opinion and my late fathers who was an engineer at Bell labs and a complete tube audio nut....
Never use the chassis as a connection for your grounds, Your audio and supply grounds should be separated from chassis. The closest thing I have seen to my fathers explanations are individual baby star grounds that go to a main buss bar which only connects to chassis at one place. each baby ground includes the filter cap for that section and ground preceding the stage like grid resistor. Basically the idea explained by O'Connor in the London Power book for Galactic grounds. The main bus bar connect at one place on the chassis right next to the input jack is good for RF or a cap from input jack ground to chassis will be a good idea fro RF, AC power input third pin wall ground also connects to the chassis preferably at least 2 inches away from circuit ground.
Phase inverter ground should connect at the same place as the OT secondary ground if there is feedback.
You will never have real control over the ground path if you use the chassis as a ground path even though it has been done successfully it is easy to make work that way on amps that are not high gain. With high gain things get more touchy. when using high gain add DC heaters for the preamp tubes (not needed on phase inverter) and you will have a silent amp EVERY time, no guess work, doesnt matter what circuit.
PS... FYI ....CE and UL do not allow the input jack itself to be the chassis ground for the circuit. Grounds must go to a staked threaded stud if you want to do it by the book.