Deluxe AB763 buss bar grounding

[7xa12]

the grounding t is confusing for beginner like me. If anyone can shed a bit of light I would be grateful

Deluxe AB763 build.

I use a buss bar for grounding. it is going at the back of pots and then through input socket ground lug. connected to chaisis right there in "one point"

1 schoud I solder the buss bar to all control pots including intensity pot. ?

2 I do not understand what is the point of isolating input sockets if ground lug of the socket is connected to chasiis right at the input jacks.

3 What I have seen in many photos - the input socket grround lugs are not soldered to anything. ( so the signal through a chasis is not a problem...?)

4 whats about reverb input/output/vibrato pedal sockets - is the buss bar and isolation to chasis necessery too ?

I am not trying to built super quiet HI fi amp.

[Randall]

Pot bodies are automatically grounded to the chassis just by tightening them. The cover over the back of them are now shielding the signal within. Don't solder the ground bar to the backs of the pots, that is defeating the purpose. Float the bar a bit away from the pots, and connect the pot lugs that are to be grounded with a wire or in some cases a resistor to the bar. This will support the bar in mid air. Also connect the preamp side grounds from the board to this bar. It's good to use aggressive toothed washers behind every pot and input jack (providing you are not using isolated inputs). It helps them to dig into the chassis and make a solid ground.

Do not connect any power amp grounds to this bus bar. There are various methods and opinions on all of this, but in general connect power amp grounds on the other side of the chassis at a common point.

Are you using isolated input sockets, or standard switchcraft type? Switchcraft chassis grounded jacks will work just fine, in this case, connect the end of the ground bus to the ground lug. That ties all the input and preamp grounds to one point, on the opposite side of the chassis as the power amp side. The resistance of the metal between those two points is your friend in this case.

If you are using isolated input jacks, which are better for real star grounding where everything is isolated and gets run back via it's own wire to a single star ground point, then you are mixing up the two schemes, which may be the source of some of your confusion. In this, connecting the ground lug to the chassis is simply negating the isolating jack function, but should be the same outcome. Personally, I like to drill a hole and install a chassis ground point close to the input jacks. that way, I don't lose my circuit ground if a jack becomes loose.

No buss bar connection on rev/vib pedal jacks. They are not important to your grounding scheme.

I just completed an AB763 build using these methods, and I could not be happier with it.

[Enzo]

Looks pretty good.

[7xa12]

Thanks a lot for a very good explanation and great picture. I will unsolder the buss bar from the pots completely and move it a bit. I said buss bar but actually I only have a tinned thick wire. I did not find anything thicker and beefier. Your buss is definietely a bar. If i find something like you have I will change it. That would be very helpful for me if you can post an input jacks picture.
the best place for the buss bar connection to chasis is somewher in front of input jacks?
I need to drill the chasis there so its better to do it once. I have Switchcraft jacks. it is a good news for me that i can leave them grounded, because I do not have isolating washers that fit the hole at the moment.

[7xa12]

no drilling is required if I use unisolated jack as grounding point.

[Randall]

Here is how I connected my ground bus, but it is not the only way to do it. I put it at the far end of the chassis near the Normal channel to put as much resistance I as could between the preamp amp power amp ground points. But, it's also not the channel I would normally use, so I suppose one could put it near the Vibrato channel input with good results. It was also easier and less cluttered to drill and install at the end of the chassis. It is very quiet.

"Looks pretty good."

Thanks Enzo, that really made my day!

[7xa12]

Randall Where did you ground the second Power amp ground (3X 16mF caps from doghouse)
I need to unsolder this wire from a buss wire where it is tied now in my buid.
Is it good idea to use a very long wire from “doghouse” and terminate it at PT at the same point whith the first 25mf cap ?

1 I have CT+ first 25Mf cap+Power tubes Cathodes connected together at one upper PT bolt

2 Heaters through 100 ohms rteference resistors grounded to chasis right at the Pilot lamp.

3 preamp section grounds connected to buss wire and terminated at input socket

4 AC mains ground at lower PT bolt(Left) near to AC input

[7xa12]

Thank you again

[ajeffcote]

http://www.el34world.com/charts/images/grounds.gif

This shows the buss wire across the backs of the pots, which is how I did mine. But it makes sense to lift it from the pots and ground at one point, which I am going to try myself.
All power section grounds to the transformer bolt, or at least to the end of the chassis.

[7xa12]

thanks ajecffcote
What I see on the picture the second part of the power amp section (3X 16Mf caps) is grounded to buss bar.
it t is confusing a bit. would it be ok with my grounded scheme?
Is it not very important to seperate the low currents grounds (preamp grounded to buss wire) from high current grounds (doghouse caps and cathodes) ?

[7xa12]

I have just read what you wrote under a link -so you meant everything like on the picture, except (3x 16mf caps)?

[ajeffcote]

The 3 16uf caps are the pre-amp supply and filter caps. The other caps are 1, the main power supply filter cap and 2, the screen supply cap. So it goes along with your scheme perfectly.
The caps in the cap can, or dog house, are separated.
Mine is a little different from the pic. I used a larger main cap and put it inside the chassis by the PT. The screen and pre-amp caps are all in the dog house with a long wire from the screen cap to the power rail in the appropriate place. I grounded the pre-amp caps to the buss, but I know guys who just grounded to the chassis at the can and that seems to work OK too.
Using the buss lifted from the pots and grounded to one spot is essentially a star ground, just an easier way of doing it. In another amp of mine, I went from a star ground to the scheme shown in the pic, with the buss on the backs of the pots, and the amp is now quieter. There are lots of ways to do it, but I know that this works.

Check out Doug Hoffman's site EL34World for tons of how to info, schematics, tools, parts, etc.

[Randall]

Ground the preamp node [D] to the ground bus. Everything else in the doghouse goes to your common ground, whether it be a transformer bolt or separate ground point near the power transformer. In my case it's simply HV CT, doghouse ground (without preamp), and safety ground. All jacks are connected to chassis. Quiet as a mouse.

Someone will have to explain to me the logic of soldering a bus wire to the back of pot shells that are already grounded to the chassis the moment they are fastened down. I think that is one of those internet misinformation things that has gotten passed along. It defeats the very purpose of what you are trying to accomplish with a ground bus in the first place.

[7xa12]

[7xa12]

the D node to buss bar.