questions about grounding

[jeff]

 1) Should the ground lug of a pot be soldered to the back or have its own wire to ground? I've seen examples where its grounded to the pot and there is a buss connecting all pots together to ground. Isn't this setting up a ground loop?  

2) On the board can you daisy chain all grounds and ground to a single point or should each stage(cathode, grid and filter cap) be grounded at different points on the chassis?

3) Should each filter cap be connected to ground with its own wire? Should those wires be grounded to the chassis at different points?

http://www.ceriatone.com/images/layoutPic/fenderLayout/5F6A-BassmanCeriatone_100508.jpg shows pots and caps going to a star ground

http://thenormster.com/DumbleLite/DumbleLite16x8Layout3.JPG has things grounded at different points

http://home.comcast.net/~zjcsiplon/pwpimages/TBS%20layout%20II.jpg shows everything daisy chained

[Rich]

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

[jeff]

Awsome, Thanks

     Jeff

 Should the pots be isolated from the chassis? If everything is grounded to the buss wire which is grounded to the back of each pot and jack isn't it being grounded in 8 different places? Isn't that what a ground loop is?
 I have a steel chassis that's painted. Should I only sand where the jacks(input and speaker) makes contact with the chassis or for all pots and jacks.

[J Rindt]

Randall has some good info on grounding.
Good Luck

http://www.aikenamps.com/

[stingray_65]

Awsome, Thanks

     Jeff

 Should the pots be isolated from the chassis? If everything is grounded to the buss wire which is grounded to the back of each pot and jack isn't it being grounded in 8 different places? Isn't that what a ground loop is?
 I have a steel chassis that's painted. Should I only sand where the jacks(input and speaker) makes contact with the chassis or for all pots and jacks.

No, the pots should make good contact to the chassis. the case makes a shield around the wiper and resistive  element and keep hum out.

it is good practice to "sand" where ever there is an electric contact with the chassis. this would include studs or screws that are used for ground.

Many people have soldered a bus wire to the back of the pots and then to the ground  of the input jack(s).
This has worked for many (myself included) but I have changed my ways. It is difficult to insure a good connection to the back of pots and it creates a potential for a ground loop.

I will on occasion run a bus for shielded cable shield to ground on. This is mostly on high gain amps in tight quarters where good lead dress isn't possible. When I do run this extra buss, I terminate it on the other side of the chassis far away from any signal grounds.

Ray

****opinion alert****

study Doug's grounding schemes first, ask questions here, apply it to an amp project, then look around to other places like Aiken and the other sites to expand on grounding schemes.
I have yet to hear of anyone saying Doug's schemes are noisy.
PRR will school you the virtues of using a proven design

[LooseChange]

Everybody has thier way of doing things. My way...

I run all my grounds in succession on the board. All grounds from pots and jacks run to the board. The board is grounded to the chassis with one wire.  (Except for the earth groung which has it's own.)
This method is called a galactic ground made popular by Kevin O'Connor and is also discussed in Merlin's book.  I have built and modified MANY amps to use this grounding scheme and it has always been sucessful.

[samato]

Can someone please direct me to some photos of Doug's grounding scheme in an actual amp?

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

The diagram is great but photos are much better for me.  I'd like to see photos of the other methods too.  Thanks.

[Fresh_Start]

I've used Hoffman's approach with a couple of tweaks very successfully.  If you study his notes and layouts carefully, you'll see that it's very close to O'Connor's "galactic ground".  The idea there (and in Merlin's book IIRC) is that each subsection of the circuit is grounded with its corresponding power supply cap, and then those are all tied together.  IOW it's a collection of star grounds, hence "galactic"   Hoffman's deviation from the "galactic ground" is to separate the power amp ground from the preamp ground.

I found it really helpful to study Hoffman's current flow diagram:
http://www.el34world.com/charts/currentflow.htm

Look at the following layout and photos of a Super Reverb build I did.  It's hard to see in the photos, but there is one ground for the entire preamp very close to the isolated input jacks.  There's a preamp ground bus (gold line in layout), but it's attached to the board instead of running along the back of the pots.  On the board, grounds for each subsection of the circuit are grounded together.  Except for control pots - those are mostly tied to the ground bus at the closest possible point.  There's a separate, very short bus for the power amp filter caps at the poweramp end of the board, and that bus is grounded at the same point as the power tube cathodes, the bias supply and the PT center tap.  Guess that's a star ground of sorts.  In hindsight, I would prefer to ground the PT center tap directly to the negative terminal of the first reservoir capacitor.  Heaters are grounded separately at that tag strip on the far right.  Speaker jack also is isolated and grounded where the NFB is returned to the circuit.  Reverb grounding gets a little touchy for me - I'm still not sure this is the best way to do it.  The tremolo circuit is grounded with the power amp via under-board wire.  Again, that may not be the best way to do it.

preamp guts

poweramp guts

Please understand that this is NOT the best way, or the only way, to ground an amp.  I simply took Hoffman's approach, and tweaked it a little bit based on lots of reading.  It does work well though.

Hope the photos & layout drawing help.  BTW there are small discrepancies between the actual amp and my after-the-fact amendmended version of the layout based on things I learned during construction &/or testing.

Chip

[Merlin]

  I've seen examples where its grounded to the pot and there is a buss connecting all pots together to ground. Isn't this setting up a ground loop?  

Yes

2) On the board can you daisy chain all grounds and ground to a single point or should each stage(cathode, grid and filter cap) be grounded at different points on the chassis?
3) Should each filter cap be connected to ground with its own wire? Should those wires be grounded to the chassis at different points?

See:
http://www.freewebs.com/valvewizard2/grounding.html

[jeff]

 That makes sence to me.

[Champ_49]

Everybody has thier way of doing things. My way...

I run all my grounds in succession on the board. All grounds from pots and jacks run to the board. The board is grounded to the chassis with one wire.  (Except for the earth groung which has it's own.)
This method is called a galactic ground made popular by Kevin O'Connor and is also discussed in Merlin's book.  I have built and modified MANY amps to use this grounding scheme and it has always been sucessful.

I have also used Kevins method from TUT3 aka galactic grounding. I was and am very happy with the results. I couldn't fully understand it at first but I ended up contacting Kevin and he is a real good guy. Very passionate about his thing.
After implementing it I was so happy with the tone and feel of the amp.
And ended up pretty much getting a lot of his other kits for the fx loop, rbx bias supply and the sv1 power scaling. I also implemented an extra gain stage with help from Kevin. The amp is phenomenal right now.  I couldn't be happier. For a high gain amp it has very low noise issues.  I'm in the process of selling off a bunch of gear now and am thinking of selling my most prized soldano  slo. That's how happy I am with my build inspired by Kevins books and ideas.

[SoundmasterG]

Everybody has thier way of doing things. My way...

I run all my grounds in succession on the board. All grounds from pots and jacks run to the board. The board is grounded to the chassis with one wire.  (Except for the earth groung which has it's own.)
This method is called a galactic ground made popular by Kevin O'Connor and is also discussed in Merlin's book.  I have built and modified MANY amps to use this grounding scheme and it has always been sucessful.

I use the galactic grounding method too and it has always been successful for me.


Greg