Ground Scheme

[C Moore]

A friend of mine bought a (used) Marshall clone....The 1986 bass circuit.
It was making noise, so he asked me to look at it.
Was a complete mess inside...beyond repair, so I stripped it to bare switches and sockets.

It is a mesh-mash of an "old style" Ceriatone chassis and their newer version 1986 board.
It has 2 different brands of trannies.

Anyway.....looking at the Ceriatone layout. Should I put the amp back this way.?
They ground the:
PI
NFB
Presence
Neg Bias
all with the preamp grounds.

If somebody were to ask me, I would have thought those circuits would be better grounded with the power amp circuit.
I assume Ceriatone has used this scheme thousands of time with success...but I am still a bit leery.
If I am going to change the ground scheme, it would be much easier to do it now.
So what do YOU guys think about this layout below.?
Thank You

http://ceriatone.com/images/layoutPic/m ... iatone.jpg

[C Moore]

Nobody would like to venture an opinion.....

[xtian]

There's more than one way to ground a cat. I've had good luck with a single ground point at the input jack for everything, everything. Also, one point at the input jack for everything forward of the PI, and another ground point near the reservoir cap for everything else.

Wire it up so it's flexible, and modify if you have noise.

[C Moore]

You do not know how true that is.
This amp was built so incredibly poorly, that I would have sworn it would have barely been playable.
Not just heater wires on top of grid wires...but wrapped around the grid and cathode wires.
Horrible soldering...worst I have ever seen. Wires spliced together...just tack soldered...and NO insulation to cover the splice.
If I had built this amp, it would have been a buzzing, humming, arcing nightmare.
Oh yeah...this guy used 1-1/2 screws for the PT.
The screw was so close to the Pilot Light, that it had black, arc marks on it.

...And this amp just kind of buzzed a little...like maybe it had a bad preamp tube.

I guess I will just ground it the way it is set up now...and hope for the best.....otherwise, there is a ground buss I will need to deal with.
Thanks Again

[Phil_S]

I'll echo, no one wants to say how. This is not a high gain amp like an Express and it's my impression that allows some leeway in construction. There are so many ways of constructing a ground scheme that works, it's really hard to say one way or the other. There are guys who swear by placing the ground at the input jack, but I've only used that one time.

I like a buss ground all the way to the PI and then taking that to the single chassis ground used by the first filter cap. In this model, all the high potential grounds go straight to the single bolt provided for the first filter cap. High potential grounds include power tube cathodes, OT secondary common, plate and screen filter caps, and a wire from the ground buss. Think of the ground buss as a linear star. Define the grounds for each preamp stage by the cathode ground. Each cathode is the end of a stage. If more than one stage is supplied by the same filter cap, assume ground potential is the same and enlarge the definition of the stage. Keep moving down the line on the buss from the input jack and V1 to the PI. I can tell you this works. Guys everywhere tell me I've grounded at the wrong end. Go figure. That's why I think no one wants to say whether what you post works well or not.

I'm thinking he wouldn't have posted a known bad ground scheme. Give it a try and let us know. I'm sure we'd like to hear about it.

[C Moore]

I hear you.
Nobody wants to be wrong on another guys amp.
I will just wire it the way it is set up and go from there.

Like I say...this amp was total mess, and it almost worked 100%.
If it had not been for some minor noise, I never would have pulled the chassis.
As you say, we have all had success with one thing or another. This layout is not what I usually do...so I was a bit apprehensive.

To think I MIGHT have ground issues while taking care...and this guy got away with murder.
You feel like the guy that drove carefully for 25 years, and then gets a ticket the first time he rolls through a stop sign.

It should be fine
Thanks

[Bob S]

Yeah - the quietest amp I've ever built (as in totally silent) broke a few of the normal conventions. I do like individual ground points for each supply node.
But that's just me. A bus for B3, 4 & 5 works too.
Be Lucky. If that doesn't work, be good.

[labb]

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

Take a look at this from the EL34 world (Hoffman)site. It generally works. I don't solder to the back of the pots. I just use a buss bar to connect the pre amp, pots and input jacks to instead of soldering to the back of the pots. Works for me.

[romberg]

This is the only thing I have ever read about grounding amplifiers that did not sound like black magic, voodoo and pure superstition . It is worth a read in my opinion.

http://www.valvewizard.co.uk/Grounding.pdf

Mike

[C Moore]

I appreciate all the Responses/Links.
I have never really had a problem using the "my type" of ground scheme when I Build, or Assemble an amp.

If THIS amp had been a new kit from Ceriatone or Metro, and I were following their layout, I would not hesitate to ground as they indicate.

But this amp was a collection of 2 different Ceriatone Revisions, and a PT and OT that did not follow a Metro or Ceriatone diagram.
So THAT is why I was hesitant to follow Niks layout. But like I say, at this point, both Nik and George have sold Thousands of these amps...so I am sure their scheme works.
I was just not confident using it in an amp that was kind of a parts build...so I asked you guys.

I had had to desolder anything this guy touched...including the In Jacks. He cut a lot of the wires pretty short, and then just tacked them on to a surface. So I either had to replace the wire(s)...which can be hard when they run up inside a turret that shares leads with 2 other components.
So more often than not, I have cut back the wire, and spliced in a length to fit. Endless checking and rechecking .

I could have built a brand new kit by now...would have been much easier.
I am sure you guys have tried to fix an amp that was really F'd Up by somebody who should not have taken on the project.
It just takes forever to scrutinize every connection, to make sure you are not falling into any "traps".
I do not want to do this again...that is for sure....!
Thanks

[EL34]

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

Take a look at this from the EL34 world (Hoffman)site. It generally works. I don't solder to the back of the pots. I just use a buss bar to connect the pre amp, pots and input jacks to instead of soldering to the back of the pots. Works for me.

Thanks for the link labb.
That grounding scheme I use is tried and true.
It's nothing new and it's not fancy, it just works.

[roberto]

I always ground each part of the pre/poweramp to the relative power supply cap, then connect all caps together from power tubes' up to the first stage, grounded at the input jack. Sometimes geounded at the plates' node.