grounding

[Toxophilite]

In a previous posting I was shown some pictures of a circuit board with the filter cap for each stage attached at that stage rather than  sequestered off in their own area. This seems to agree with the concepts merlin espouses
I can't seem to find the post with those pictures
I wonder if anyone has an example? I know how it's supposed to work but an actual picture of an actual amp would be hugely helpful
Thanks

[sluckey]

This is how Doug does it...
http://el34world.com/Hoffman/images/Dscn0295.jpg

I usually like to put the first two caps in a can and put the remainder directly on the board...
http://home.comcast.net/~seluckey/amps/dual_lite/bottom.jpg

[EL34]

This page shows the most common ground setup and a bunch of info

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

[Toxophilite]

Thanks very much, the both of you!
That's just what I needed as I was hoping to improve on my previous efforts

[EL34]

My stuff is all linked on the library page here.

http://el34world.com/schematics.htm

[vibrolax]

Here is an illustration of my variation, which is closer to slukey's than Doug's.  I don't use can caps, and I don't use an off-board buss wire behind the controls.   I ground controls to the turrets in the ground buss turret row on the board.  I think all the presented variations can give good results.

http://www.frontiernet.net/~jff/TrainwreckExpressCombo/Trainwreck%20Express%206V6%20in%20combo%20amp.html

[Fresh_Start]

This was my second build using a modified version of Doug's layout. Bus wire mounted on edge of board, galactic grounding like Merlin/O'Connor which is surprisingly close to Hoffman's actually, and preamp filter caps mounted along edge of board.



Here's the layout - it's an AB763 Super Reverb with considerable changes to the Normal channel:




One nice thing about this approach is that it works equally well with radial or axial filter caps.

Cheers,
Chip

[Toxophilite]

I was checking out Doug's scheme and the various variations


Preamp grounded near input jack or at it.


Power amp and PI at star ground with earth PT etc


What happens with circuits like the Harmonic vibrato which shares the B+ source of the power amp,  has it's own dropping resistors and filters, but is part of the early signal path
Should i group it's grounds into their own star and run them to the main star

And the reverb circuit which shares both the power amps B+ and the preamps B+ and their accompanying filters,
would I split up the grounding? sending the 12at7 grounds to the star point and the 12ax7 to the input ground?


Checking out one of Melin's ideal grounding scheme he has a chassis earth and then Everything else seems to be on the buss bar with each circuit grounded near the filter cap for their B+ section. This seems like it could work with my set up except I'd run lines to my preamp filter for the half reverb section?


It;s a little confusing
Perhaps I'm making it too difficult?

[Fresh_Start]

I found Hoffman's current flow diagram really helpful:


My answer to reverb grounding was to add a new node on the power rail just for the reverb Transformer. I figured that a little more filtering couldn't hurt there, and it allowed me to ground that filter cap on the preamp bus. Note that the phase inverter is on the preamp bus too. The tremolo circuit is grounded on the power amp bus (if you can call it that) because its supply is the screen grid node.

I must confess that I am puzzled by the output transformer being grounded on the preamp bus.  A lot of current travels through that wire and I can't figure out years later why I put it on the preamp bus.  It worked fine though.

One advantage of using a single bus for everything is that you can add a ground lift switch. If you look at the Uberverb layout above, you'll see that it would be very easy to tie the power amp filter capacitor grounds onto the preamp bus.

There are only three circuit ground points in my layout:
1) preamp bus
2) power amp bus, bias, power tube cathodes, and power transformer
3) heater winding center tap

I do remember working hard at getting the physical current loop for the power amp as small as possible.

Cheers,

Chip

[Toxophilite]

THanks!

(Quote from Fresh Start)
"I must confess that I am puzzled by the output transformer being grounded on the preamp bus.  A lot of current travels through that wire and I can't figure out years later why I put it on the preamp bus.  It worked fine though."


From my recent reading of Merlins article on grounding he recommended that the if you're not using global feedback (neagitive feedback0 then teh PT secondary should be grounded to the power amp star, if you are using Global feedback it should be grounded to the stage the global feedback is sent to (usually the PI)


Maybe that explains that some?

[EL34]

Reply #2 shows the OT grounded at the main ground

[Willabe]

With NF, you tap off a small amount of acv from the OT's secondary and bring it back to some earlier point, tube, in the signal chain.

So you ground back to the same point, tube, in the signal chain. It's the other 1/2 of the NF loop.   

[jojokeo]

From my recent reading of Merlins article on grounding he recommended that the if you're not using global feedback (neagitive feedback0 then teh PT secondary should be grounded to the power amp star, if you are using Global feedback it should be grounded to the stage the global feedback is sent to (usually the PI)

Here's a layout example of this.

[mresistor]

Chip that is a nice looking Super Rev you have there.  ;-)  Can you put up a pic of the PT side of the guts?

[Toxophilite]

I second that emotion!

[Toxophilite]

ON my board/layout, the reverb circuit is right beside the PI
It goes like this:


preamp
harmonic vibrato
reverb
PI
POwer amp


the section of the reverb that uses the same B+ node as the preamp is faaaaaar away from the preamp
Is it worthwhile creating another node for this section ? and if I do I need a dropping resistor to seperate it as well as a filter cap
I also have a couple of tiny 1 henry chokes from the power supply (they were in series) of a hammond amp that had 2 amps, 2 6L6s,a couple of ECL86s and easily a half dozen 12ax and 12au tubes)could I use one of those in lieu of a dropping resistor in this application??


oooooor  should I just run the (D) B+ of the reverb circuit to the preamp section, put the filter at the preamp and then run the reverb grounds to there.
I'm wary of that because then I'm running ground wires down the chassis which I'm given to understand one is supposed to avoid if possib;e

[Willabe]

What B+ node does Fender pull the B+ for their reverb?

The preamp B+ node is the lowest in an amp.

[Toxophilite]

Fender uses two B+ nodes for their reverb


-The 12AT7 via the reverb transformer gets B+ from (B) the same as the power tubes


-The 12AX7 recovery and the 1/2 gain stage after both get B+ from (D) the same node as the preamp

[Fresh_Start]

Chip that is a nice looking Super Rev you have there.  ;-)  Can you put up a pic of the PT side of the guts?

Thanks!  Since the OP apparently asked for it as well here's the other end. You can't see the power amp ground except for the top of the nut just "above" the power amp filter caps, but you can follow the PT center tap. Also, the negative feedback rationale for locating the OT ground on the preamp bus rings a bell. 

[mresistor]

Thanks Chip.