Ground buss bar question...

[dehughes]

Hello again,

Quick question: If you're doing the star ground thing, does the location of the individual grounds on the ground buss bar matter? I mean, I understand that you only ground one point of the bar, and that at a certain location on the chassis, but does the individual positions of the grounds on the bar itself matter?

Thanks!

[Allynmey]

Hi Dehughes, There tends to be a lot of mojo style talk about grounding schemes. I find that just following best practices works out the best. I use 2W PEC or Clarostst pots on most of my build and solder doesn't stick very well to Stainless Steel! I bolt a buss bar to the chassis run up behind pots for asthetics and ground my preamp stuff to it. My screens, plates, Bias grounds are put on a separate ground lug. My Centertaps are grounded nearby on a lug or a separate lug on the same bolt and my chassis earth ground is terminated on a separate lug right where the cord comes into the chassis (or IEC connector). This usually yields a very quiet amp and stops ground paths from the input stage crossing the output stage and picking up noise. The TW's I've built as well as other amps are very quiet using this basic scheme! Your mileage may vary but, there is nothing special that I do.

Allyn

[dehughes]

Allyn,

Thanks for the reply...on both topics. Your amps look killer....and I'm sure they sound equally as nice...

[mhuss]

In keeping with the 'constellation ground' idea, I just connect all the grounds of a given stage (including the front panel controls) to the buss at roughly the same location (near that stage), and then connect the buss to the chassis at or near the input jack. This also makes it fairly easy, no soldering to pot backs or extra lugs and such required.

I connect the power grounds (transformer CTs, first two caps, and the cathode resistor, if it's cathode biased) together at one point near the PT.

This has resulted in very quiet amps, even for higher gain ones.

--mark h

[rfgordon]

I like to use the bus bar and star schemes.

However, in the Holland amp I just finished working on for a guy, things were grounded all over the place, but the amp was well behaved and quiet. For example, there was no bus bar, preamp cathode resistors went to whatever bolt was nearby, one grid load resistor went to the bolt holding that tube socket in, and the ground side of the OT secondary was anchored to the OT mounting bolt, with only one wire going to the output jacks.

So, clearly there's more than one way to do this "correctly."

[sharkboy]

Right, there are many paths, but a simplified rule of thumb like galactic (or star + buss) grounds works better for people like me than trying to figure out a bunch of different grounds, if I'm doing it from scratch. Oh, and maybe moreso if I'm working on an existing amp.

[dehughes]

Thanks guys. I've had the pleasure of gleaning a lot of star ground info from drz400 here, so I've learned a lot about ground paths, etc.. I guess I'm just curious to see if, using a buss bar, it matters how close things are grounded to each other ON THE BAR...being as the bar itself is one piece and (supposedly) grounded at one point on the chassis.

[Dai H.]

if you read some theory, things don't need to be so mysterious. Basically, you want to make yourself concious of what is happening in the grounds (the current flows). *IMO* it really isn't that hard to develop a basic idea of what is going on simply because there is zero heavy math involved. If you don't want to (which is okay) I would try to copy a scheme that is known to work for a given amp.

[mhuss]

The location on the buss bar is not critical, as long as the bar itself is chassis-grounded at a distance from the power grounds.

The underlying idea behind all the successful grounding schemes is to keep the "noisy" ground currents, e.g., between the center tap of the PT and the (-) side of the early filter caps, a far as possible from the low-level/input signal grounds, e.g., between the input jack and the first stage cathode.

--mark h

[drz400]

Thanks guys. I've had the pleasure of gleaning a lot of star ground info from drz400 here, so I've learned a lot about ground paths, etc.. I guess I'm just curious to see if, using a buss bar, it matters how close things are grounded to each other ON THE BAR...being as the bar itself is one piece and (supposedly) grounded at one point on the chassis.

But the current still flows, keep the star point and run one wire to the buss for each stage.
Yes it matters, keep them logically apart from each other and a heavy duty buss is not needed