Star vs. Bus ground

[Slartibartfast]

I was reading the website of one amp builder who said he did not like wiring up a star ground, but used a bus ground instead. His bus ground looked like all the amps I see here with the single copper conductor, that everything is grounded to. People on here refer to this as star grounding. Is this nothing more than a semantics issue?

[TomMcNally]

I use a bus ground system in my amps ...

pix at http://tmamps.com

Important things to remember for any ground system

* single point of connection to the chassis

* keep the centertap of the high voltage transformer
connected right where the first capacitor off the
rectifier comes off

* keep input stage grounds close together and away
from power supply grounds

It's not really tricky, and can be nice and quiet.

... tom

[SDS-PAGE]

I like bus ground better, mostly because it make wiring passive components easy. I don't like the extra wires going all over the place as you do in star ground. -Min

[EWBrown]

As long as you ground to the chassis at a single point, either method is good...

I use a combination star / bus ground approach generally.

/ed B in NH

[Slartibartfast]

Well it sounds like I have done all the right things on the first iteration of my JE 2A3 amp. I used a ground bus. It is quiet, when there is no input signal. So that is good. It is not the prettiest of wiring jobs, and the need for version 2. Yellow_Light_Colorz_PDT_02

I am in the process of rebuilding the 2A3 on a spare ST-70 chassis and while building the ground bus, I was wondering the differences between bus and star.


Ed,

I did not ground the bus to the chassis, well except at the RCA inputs, they make physical contact. The ground bus is on standoffs from the chassis. Its there a requirement to ground the chassis to the bus?

[Geek]

Hi,

I use star grounds in HiFi and bus grounds in guitar amps. I have experienced no problems with either.

Cheers!

[EWBrown]

Grounding the bus at the RCA jacks is probably the best practice, and seems to be a fairly standard method. The center "ground" terminal of one of the standard means of connecting the ground star / bus to the chassis, I usually connect to one of the terminal strips in the input VA stage, but after the volume pot if one os present, the two RCA ground terminals connect to this point and then every other ground bus ends up at the same point. But then this "ground plane" is anathema to goo d audio circuit design practice :o

No matter your grounding approach, the main "prime directive" is to not run any current through the chassis, this can and will cause some nasty hum, noise and other ground loop situations - I've learned from hard experienc in some of my earlier amp builds. Chassis ground is good and fine for RF, and is sometimes necessary - hence those four ground lugs on a lot of 9-pin sockets.
Sometimes one can get away with having the amp circuitry not directly grounded to the chassis, but most often, nOT.

If you don't have a hum situation, then it is more than good enough.
Even with insulated RCAs, I'l lselect a nearby chassis ground point and "star" any ground buss to that point, so I guess my combined star / bus approach could be called a "tree ground" Yellow_Light_Colorz_PDT_04

I have found in some cases that if the amp's circuitry is totally isolated form the chassis, some weird hum and noise problems can crop up.

In some situations, I find that the chassis ground point is best done at one of the power transformer mounting screws, rather than at the input RCAs. . YMMV, etc...

As a co-worker here used to say, "the only consistency is the inconsistency..."

I find that the tried and true engineering practices are good about 90% of the time, but every so often, I run into a real puzzler, and have to hget creative .

/ed B in NH

[SteveH]

Interesting thread...Timely for me too !

So on my 'new' ST70; here is what I was thinking...

Bend my buss bar in a 'U' shape, with the open ends facing the input jacks. Connect the ground of each jack to the ends of the 'U', and along the way connect each ground connection off of the tubes (cathode resistors) to it. Wire a lead from the PCB ground to the center of the 'U', as well as the ground lead off of the SDS board, and the CT from the Power Tranny. Then connect this singular point to the chassis (Star washer off of the Tranny bolt).

[Slartibartfast]

Interesting thread...Timely for me too !

So on my 'new' ST70; here is what I was thinking...

Bend my buss bar in a 'U' shape, with the open ends facing the input jacks. Connect the ground of each jack to the ends of the 'U', and along the way connect each ground connection off of the tubes (cathode resistors) to it. Wire a lead from the PCB ground to the center of the 'U', as well as the ground lead off of the SDS board, and the CT from the Power Tranny. Then connect this singular point to the chassis (Star washer off of the Tranny bolt).

Here is the Bus ground in my 2A3 ST-70 Yellow_Light_Colorz_PDT_09 I had to bow it out at the front to make room for the volume pot.