Grounding schemes and disciplines

[pedro]

I was wondering about grounding in my build.
Ive set things up so the my power section, screens and main filter all go to earth point at first filter cap.

But I was wondering about preamp - I usually route a copper ground bus round the chassis and earth each preamp point in sequence following signal flow, I then earth as close to input socket as possible - sometimes with an RF suppression cap to ground from the input socket as well.

Looking at some schemes I see that people like to combine all the preamp earths and earth somewhere else away from main ground point

Anyone know what disciplines are used in the dumbles and what works well in general. I also try to use screened for the signal flow between board and pots/relays but see that not everyone bothers.

Any thoughts ?
cheers
Pete

Its evening here in Leeds now so I better go do some family stuff - Ive been checking this board all day between work commitments !

BFN..

[KyleJ]

I know this is an old posting, but since no one replied...

Check out the tech pages on

gtto://www.aikenamps.com

Lots of good stuff there

[Normster]

Based on the only reliable info I have, early Dumble amps were grounded as follows:
1. First filter caps, bias board, and CT's are grounded to the right rear transformer mount.
2. Preamp filter caps are grounded at the first power tube, rear mount (along with the 100R filament resistors).
3. Relay PS and footswitch grounded to the right front transformer mount.
4. Preamp bus bar grounded close to the input.
5. All preamp circuits grounded to bus bar in circuit order:
a) Ck1
b) Vol
c) Deep
d) Ck2
e) Mid
f) R/J cap
g) Bass 10k resistor
h) OD
i) Master
6. 390R NFB resistor grounded at "poweramp in" jack.

[groovtubin]

I was wondering about grounding in my build.
Ive set things up so the my power section, screens and main filter all go to earth point at first filter cap.

But I was wondering about preamp - I usually route a copper ground bus round the chassis and earth each preamp point in sequence following signal flow, I then earth as close to input socket as possible - sometimes with an RF suppression cap to ground from the input socket as well.

Looking at some schemes I see that people like to combine all the preamp earths and earth somewhere else away from main ground point

Anyone know what disciplines are used in the dumbles and what works well in general. I also try to use screened for the signal flow between board and pots/relays but see that not everyone bothers.

Any thoughts ?
cheers
Pete

Its evening here in Leeds now so I better go do some family stuff - Ive been checking this board all day between work commitments !

BFN..

[Bob-I]

I'm still figuring out the best scheme but here's what I used for my current 2 amps.

Amp 1 is a 6V6 Hybrid type amp.

All PS Filters are grounded at the PT mounting bolt using eyelet terminals.

All cathodes are strung together and grounded to a lug in the chassis near the PS

Pots are strung together and grounded near the input.

Relay is not grounded, it floats.

Heaters 100/100 fake centertap is on the last tube socket to a lug on the socket mounting bolt.

Amp 1 is a 3 channel 6L6 Hybrid style with a Fender channel and reverb.

PS is the same
Cathodes same
Pots are grounded to a bus bar made from a piece of brass rod. I soldered a eyelet tab on each end and bolted it to the chassis under the pots.
heaters same

I'm getting some hum on the reverb return. After much playing around it's minimized but still too much.

[ElectronAvalanche]

Hi Bob,

try to seperate the Reverb cathode grounds from the other grounds of the preamp, especially the ground from the Reverb Return amp!

Run this ground to the ground of the corresponding Reverb filter cap.


Cheers,

Dominik

[Bob-I]

Hi Bob,

try to seperate the Reverb cathode grounds from the other grounds of the preamp, especially the ground from the Reverb Return amp!

Run this ground to the ground of the corresponding Reverb filter cap.


Cheers,

Dominik

I think I'll need to seperate my filter grounds. They're all connected together now. My bus bar is grounded at both ends, this also may be an issue.

Thx.

[BobW]

Hi Bob, grounding the bus bar at both ends can invite ground loop noise, ie the circulating currents for each stage now have an alternate path for a return. Try disconnecting one of the grounded ends on the bus bar, one at a time to determine which is the better ground return.

I'm puzzled why a lot of the layouts solder the bus bar directly to the pots? Since most metal backed pots are also grounded to the chassis via the shaft threads, that sets up multiple chassis ground returns which are a potential circuit for noise. This is ok for the standard 2 stages of gain fender type amp, but for the 4 stage higher gain amps we love to build, it could be inviting trouble. For now, I'll bow to the, if it ain't broke don't fix it, logic.

[jazzyjoepass]

BobW, you've just pointed something that I thought about recently ... the shafts are already grounding the pots so there'll be chance of ground loops .... so, I've decided not to even ground my POTS.

Certain circuits sometimes require a grounded POT terminal and sometimes I see the them being soldered to the back of the POT.

Shouldn't it be soldered to proper common preamp star ground instead of using the chassis path to ground?

[dobbhill]

My experience only: I have always used the physical chassis connection to ground the pot bodies, and used a separate ground bus (12ga wire) run behind the pots but not connected for the preamp grounds.
D

[BobW]

BobW, you've just pointed something that I thought about recently ... the shafts are already grounding the pots so there'll be chance of ground loops .... so, I've decided not to even ground my POTS.

Jazzyjoepass, the labor involved in replacing a bad pot is another good reason to avoid soldering a bus bar to the pots. Either way will work, I'm just lazy and don't want to have to remove all the pots from the front panel just to replace one bad pot.