grounding question

[catnine]

I am building a AA764 BF champ circuit in an allen amps champ tweed style chassis .

On my other builds I have used the brass plate between the front and the pots and jacks . I grounded the PT secondary CT and the heaters CT plus the power cord and cathodes of the power tubes to the PT bolts . all the other grounds even the filter caps I grounded at the brass plate and the amps were quiet .

I have read about star grounding but don't like that method and I read about hoffmans buss bar method which seems very similar to the brass plate other than the first and second filter caps are grounds at the PT bolts rather than the brass plate .

What is the best method , the brass plate as I have done or the buss bar .

Is the main point of grounding to keep the power rail and the output tube and preamp separate from eachother so there are no ground loops .

I have a SF champ that used the chassis for all grounding and it was quiet too .

On mission amps I have read all grounds including the Center taps go to the brass plate other than the green power cord ground .

In that case where do you connect the center taps , are they a wire soldered to the center taps then to the brass plate ?

The champ is not a complicated amp circuit , I just want it to be quiet , so far the way i have been doing my builds is the brass plate for the filter caps and all the eyelet board grounds , all the pots and jacks are to the brass plate and all the center taps and output tube cathodes and the green power cord are bolted to the PT studs . All have been quiet .

[Paul P]

I have read about star grounding but don't like that method and I read about hoffmans buss bar method which seems very similar to the brass plate other than the first and second filter caps are grounds at the PT bolts rather than the brass plate .

What is it that you don't like about star grounding ? The idea behind star
grounding is that there is only one path to (real) ground for every node
that needs grounding. This way there are no ground loops. This does not
necessarily mean a separate wire from every ground point to a single point
on the chassis. I think 'snowflake' ground would be a better analogy since
you can collect other grounds on your way to the chassis ground. Like a
tree with the trunk attaching to the chassis ground.

On my amp I plan to ground each stage at its decoupling filter capacitor
ground and connect those together leading to the single chassis ground.
There will be a few other wires going to the chassis ground like the
transformer center taps.

Paul P

[catnine]

What is it that you don't like about star grounding ? The idea behind star
grounding is that there is only one path to (real) ground for every node
that needs grounding. This way there are no ground loops. This does not
necessarily mean a separate wire from every ground point to a single point
on the chassis. I think 'snowflake' ground would be a better analogy since
you can collect other grounds on your way to the chassis ground. Like a
tree with the trunk attaching to the chassis ground.

On my amp I plan to ground each stage at its decoupling filter capacitor
ground and connect those together leading to the single chassis ground.
There will be a few other wires going to the chassis ground like the
transformer center taps.

Paul P

I didn't like the star grounding because I built two amps with it , both champs from kits and did run each of the grounds that went together into one wire from each node and all to the one ground point but both had hum and noise . The amps where I used the brass plate even with all the filter caps grounded to the plate were quiet right off .

I understand why some say filter caps should be separate to each section of the amp but I never had a problem when they were all grounded to the same plate and it takes alot less work and wire to jump from the eyelet board to the plate . I did jumper the first 2 filter cap grounds together and the 3rd cap with the preamp and cathode . I used the layout weber has up on their site for reference . I think there were four or five ground wires from the board to the plate and i grounded the input jacks to the plate with a wire even though they were bolted through the plate . All the center taps I bolted to the PT studs as well as the cathode for the output tubes since I used an adjustable fixed bias instead of a cathode resister bias and grounded the bias board to the PT studs too .

[tubeswell]

Star grounding idea

I thought star grounding could be done the way PV does it; i.e; run all the preamp grounds to a 47R, and run all the power amp grounds to another 47R and then attach the other ends of the 47Rs to the chassis. The input sockets and speaker sockets ground to the chassis as does the PT and OT grounds.

[Enzo]

That is not quite what PV did. If you measure some of those 47 ohm resistors, you will find they are shorted. Those separate ground sections are bound together at the chassis by jacks. The resistors are there - some of them - to make sure the grounds are connected in the absence of a secure ground at a jack. That is not a plain star ground system anyway. I think in the C30 only one 47 ohm resistor actually measures out.
COmpared to a Marshall 100 watt, the gain of a CHamp is a lot lower, so to me the hum issue is diminished by that.

It is not like there is a wrong way and a right way. People get good results using a number of systems.

[Sir Cuitous]

My understanding is that star grounding works, but works best when each component/stage can be physically layed out around the grounding point so that there are fewer long wire runs. I may be way off here but I believe that the power rail and pre-amp stages should take a separate path to ground. If you are using some kind of grounding buss (brass plate or copper wire), the grounding should follow the signal. I personally like star grounding because as Paul says

The idea behind star
grounding is that there is only one path to (real) ground for every node
that needs grounding. This way there are no ground loops.

Star grounding may not always practical in long chassis. Also, I might point out that a single-ended amp is going to hum no matter how you ground. It may be a lot or it may be a little. The only SE amp I have ever heard that didn't hum was the Matchless Little Monster. Anyway I trust that the pros here will correct my errors or corroborate.

[PRNDL]

Grounding is a big issue in tube amps because a lot of current flows through the chassis, and a poor grounding scheme causes all kinds of problems, most notably hum.

Star grounding is used primarily in HiFi amps where they have heated discussions and debates about extremely expensive components and special techniques used to lower noise and improve quality.

The simple truth is that most skilled builders copy grounding schemes because someone else has already worked out the issues. Some builders warn that making a minor change in Leo's schemes will lower the tone and cause more headaches than its worth.

As for your tweed Champ, I'd go with the copper or brass plate to give it a more vintage accurate look.

[dai h.]

hi, here's some stuff if you feel like reading:

http://ampgarage.com/forum/viewtopic...220&highlight=

[Bruce / Mission Amps]

This conversation always amazes me but again, if done correctly, the brass plate IS a star ground, just a big one.

[dai h.]

this is a bit like Sisyphus, lol