Buss grounding question (TOS build)

[daveyajd]

I am a little confused on how to do my grounding buss in my new build. I see some that have a floating buss along the pots and others that have a buss bar down the side of the turret board. What I can't see from any build pictures on here is where that buss bar connects to ground. I am building a Tweed Overdrive Special using Doug's board so I have been planning on bussing all ground turrets on the board to one spot and connecting that to my buss bar running along the pots. Does that just bolt to a spot on the chassis? Thanks.

Aaron

[TIMBO]

Hey Aaron, just find a spot near the input jack and bolt it to the chassis 

[tubenit]

I would be concerned that what Timbo suggested might  create a ground loop and unwanted buzz.

Instead follow Hoffman's grounding scheme which I always use and my amps are quiet.

http://www.el34world.com/charts/grounds.htm

In other words, the input jack and pots are grounded to each other and NOT a bolt into the chassis.

With respect, Tubenit

[Tyrannocaster]

I have used that setup with good results too, but there's one ting I really didn't like about it; that buss wire soldered to the back of the pots makes it a real pain in the butt later if you have to replace one of the pots. I find it's more work to run the buss wire alongside them and jumper to them but later it's much easier as far as repairs go.

[Fresh_Start]

I have used that setup with good results too, but there's one ting I really didn't like about it; that buss wire soldered to the back of the pots makes it a real pain in the butt later if you have to replace one of the pots. I find it's more work to run the buss wire alongside them and jumper to them but later it's much easier as far as repairs go.

That's why I went with a bus wire running along the edge of the turret board.  A short lead from the bus to the chassis at the input jack end is the only ground connection for the preamp.  No loop.  I ground the power amp separately at the other end of the chassis.  My grounding scheme is almost identical to Hoffman's except for the location of the ground bus.  I actually got my idea from his photo here:



You can see the bus and the bolt to the chassis in the lower, left corner of this pic.  Also, note the short wires for grounds from the pot lugs.  Pot bodies are just grounded to the chassis with lock washers.



BTW radial filter caps actually look cleaner and are a bit easier to use with this approach.

Cheers,

Chip

[TIMBO]

Hi guy's, the reply answer i gave Aaron is how Fresh Start has posted. I do much to same.A heavy gauge solid wire that runs along above the pots, with the ground lug on the pots bent up and the loop on the end of the lug nipped so that the buss wire does not run through the loop but notched for the wire to sit in, this makes unsoldering the pot easy. The buss also has any grounds from the preamp circuit soldered to it ,the buss then picks up the ground of the input jack and because the jack is plastic (cliff jack) the only connection to ground  is made close to it via a bolt to the chassis, much the same as Fresh Start has posted.  I don't see why the pot bodys need to be grounded as they are already grounded when they are firmly bolted to the chassis. 

I'm sorry if i gave some wrong info but this grounding seems to me as a "bit of a hit or miss" thing and as i have had my problems when it comes to evicting these buzzes. 

[jazbo8]

The "bus across the back of pots" method may work in many cases, as in "if Fender did it, why can't I..." It may not be the way to go if you want to control the ground loops, OTOH, grounding the input jack ground to the chassis close-by as Timbo "jokingly" put it, is usually a good practice in general.

From Aikenamp:

"What about volume and tone control grounds?
The ground connections for the volume and tone controls should not be connected to the potentiometer case, for two reasons. First, it destroys the star ground scheme and can contribute to ground loops. Second, when the nut that holds the pot in place becomes loose (and it will, eventually), you will get a bad ground connection and noise or intermittent operation. You should always solder a wire from the grounded pot connections back to the common local ground of the stage the pot is used in. For example, the grounded pin of the volume pot, if it is located at the grid of the second tube section, should go to the local common point for that second tube section's cathode resistor and bypass cap. Don't use the Fender style brass plate and connect the grounds there. The pot cases will be grounded to the chassis via the mounting nut, so they will have the benefit of shielding, but you don't want the circuit connection to go to that point."

Merlin also has a good "how-to" on his site.

Of course, like many things in amp building, YMMV...

Jaz

[tubenit]

Grounding schemes has always been a lively discussion/debate on this forum.

 

   With respect, Tubenit

[Fresh_Start]

Grounding schemes has always been a lively discussion/debate on this forum.

 

   With respect, Tubenit

You think it's lively here - try having a reasonable discussion about viable grounding alternatives on 18-Watt.com.  That's one mistake I won't make again. Ooops, it's still down.

Hoffman's fundamental scheme works every time.  We're just niggling over the mechanical aspects of how the preamp bus is implemented.

Cheers,
Chip

[daveyajd]

Thanks for all the help. Lots of good minds at work around here.  Here is what my layout plan has looked like so far:



All pot lugs and my input jack (not cliff) with short runs to the buss wire. As well as the grounds from my board and the caps for the preamp section. I will ground my power section caps and power tube cathodes to one of my PT lugs. Should I still connect all the pots with a buss on the back?

Aaron

[Fresh_Start]

Aaron - that looks nice and neat.  The other (left) end of the bus should be mechanically secured but NOT grounded.  Bolt to board maybe?  I really like the idea of bolting the bus directly to the chassis and the shrink wrap is a nice touch.

One thing I learned the hard way: you need to tin a copper wire like that at each connection point to get the best solder joints and flux helps.  A bad solder joint on a ground connection can drive you crazy during debugging.  That pre-tinned bus wire from AES that I used was easier for me to use.

I don't think you need to have a bus wire to ground all of the pot bodies but YMMV.

Cheers,

Chip