Brass grounding plate

[Jarvini]

Hi all can anyone tell me what the purpose of the brass grounding strip that the two stroke amp im building has? I can't work out what benefit it would have over a ground buss, is it to make soldering the ground leads easier? does it do a better job than a buss? and I suppose the main question is can I create a ground buss instead or would that create an earth loop?
Thanks
Scott

[mikepukmel]

Hi all can anyone tell me what the purpose of the brass grounding strip that the two stroke amp im building has? I can't work out what benefit it would have over a ground buss, is it to make soldering the ground leads easier? does it do a better job than a buss? and I suppose the main question is can I create a ground buss instead or would that create an earth loop?
Thanks
Scott

Scott Im still very new to this stuff too, so with that pound of salt : I'm just finishing building a Fender Deluxe style amp as well. The best I could determine: the pots on this amp are all mounted to this plate, from inside the chassis, as are the input jacks, so makes a very good ground contact for the pots and jacks. A few ground wires from the eyelet board that are on the preamp end of the circuit are also grounded here. Its very conductive, easy to solder to, and they also (back in the day) tucked the relatively low signal wire bundle leading to the vol, bass, treble, etc, controls down into the corner of this plate (Im guessing as well) for shielding. If you don't put the plate in, and use a buss, the grounds should be fine, but the FRONT (side mounted to chassis) of the pots, and input jacks won't have as good a conductor to mount to, since the Fender style steel chassis, with some oxidation that forms naturally, won't be as good a ground path. Also, look at the Marshall style chassis builds, they run a bus wire across the back of all the pots. Re grounding, all of the low signal stuff grounds to the brass plate, then all of (most of) the power filter stuff grounds in a different spot, on the chassis, over by the power transformer. At least for fender style builds. Cleaner/audio signals grounded in one area, dirty/power signals in another area. I don't think you need to worry about a loop unless you build one in: i.e. say you ground both ends of a shielded input jack wire. There are a whole LOT of great threads on this site regarding improving grounding schemes. (lots of great gurus here) check some of them out. Check out some of the great comments on grounding schemes on this thread: http://music-electronics-forum.com/t44744/ (and look at the build quality, its a work of art)

[soundmasterg]

Hi all can anyone tell me what the purpose of the brass grounding strip that the two stroke amp im building has? I can't work out what benefit it would have over a ground buss, is it to make soldering the ground leads easier? does it do a better job than a buss? and I suppose the main question is can I create a ground buss instead or would that create an earth loop?
Thanks
Scott

The brass grounding plate is easy to solder to and it worked fine with vintage amps like Fenders. However, when using that, your grounding is just random to the chassis, which can cause problems with noise and hum and oscillations, depending on the circuit and gain levels you are using. A ground buss isn't really any better if it is also random chassis grounded, such as to the back of pots for example. Using a ground buss does allow you to control your grounding a bit better, but it has to be done correctly. With any grounding design, the safety ground should have it's own ground to the chassis within about an inch of where the power cord comes into the amp, and it should be made a little longer than the hot and neutral wires so that if the power cord is pulled out of the amp, the safety ground is the last thing that would be connected. It should use a bolt with two keps nuts and a terminal soldered to the wire. It should be a green wire with a yellow stripe, or a green wire, depending on your jurisdiction. You can look up what the code is for your country. In the US it is a green wire with a yellow stripe.

Your buss bar should be ground for the signal grounds and should not connect to the same point as the safety ground. In order for the buss bar to be used correctly, it needs to be connected to the chassis at only one point, usually near the input, but it can also work if your connection point is near the power transformer....as long as there is only one chassis grounding point for the buss bar. This means that you need to use isolating jacks so that those will not ground on their own. Switchcraft makes longer shaft jacks that you can use isolating washers with. These are better quality jacks than Neutrick or Cliff plastic jacks. Do not ground to the back of the pots. They can ground fine with a star washer to the chassis. Any grounds off the terminals of the pots can go to the buss. All grounds should go to the buss in order....meaning that the cap that supplies your first preamp stage should have a local summing point where all grounds for that stage go. Then that summing point should go to the buss bar. Think of it as little streams leading into a river. The next stage would also have it's own local supply cap and a summing point, then ground to the buss in order after the first stage, etc. Do not ground anything to a transformer bolt either...that is a potential safety hazard. You should lay out the supply caps for each stage near the stages they supply rather than all in one spot like Fender did. If it is a kit that you building with a pre-determined layout that mounts all the caps in one place, then that isn't ideal but it will work. For more on the proper grounding with a buss bar, look up Kevin O' Conner's galactic ground (In his books) and/or Merlin's buss bar system in his books and on his website. I highly urge you to get Merlin's book if you don't have it already. It is VERY good. The Valve Wizard

There is also the Hoffman system which uses a buss bar and rather than random chassis grounding, it uses controlled chassis grounding. It works ok too, but for high gain amps it may have issues. To me it is also more work than doing things the other ways I mentioned above, so I don't use it myself. You can find the Hoffman grounding system on his website. Tube amp parts, Guitar amp parts, Tube amp for guitar

Greg

[Jarvini]

Thanks guys I think I shall buy a copy of the valve wizard I've got dave hunters the guitar amp handbook and the aspen pittman book but there's not much at all on grounding in either of those.
I'm new to amp building myself but after 30 years of playing guitar I seem to have become obsessed with building my own valve amp and I am trying to learn as much as I can before I start the build!!
I have been gradually selecting and purchasing the various components required (an expensive route i know) and trying to understand each stage of the amp rather than just chucking it together and hoping it works at the end!!
i chose the two stroke amp (The revised version with only 1 6v6) from dave hunters book as it has some building instructions and it seemed like a fairly basic amp for me to start with
So I also apologise for some of my questions which must seem like very obvious things to you experienced builders but we all had to start somewhere and I'm just trying to avoid any silly and perhaps costly mistakes
Thanks
Scott

[Jarvini]

[mikepukmel]

Thanks guys I think I shall buy a copy of the valve wizard I've got dave hunters the guitar amp handbook and the aspen pittman book but there's not much at all on grounding in either of those.
I'm new to amp building myself but after 30 years of playing guitar I seem to have become obsessed with building my own valve amp and I am trying to learn as much as I can before I start the build!!
I have been gradually selecting and purchasing the various components required (an expensive route i know) and trying to understand each stage of the amp rather than just chucking it together and hoping it works at the end!!
i chose the two stroke amp (The revised version with only 1 6v6) from dave hunters book as it has some building instructions and it seemed like a fairly basic amp for me to start with
So I also apologise for some of my questions which must seem like very obvious things to you experienced builders but we all had to start somewhere and I'm just trying to avoid any silly and perhaps costly mistakes
Thanks
Scott

Good books. Also, check out some of the great posts by gurus like Aiken, this is a very good one: Grounding

We sound like kindred spirits, same here, except Im not much of a guitarist but enjoy playing.

I did almost the same thing, but tried really hard, and partially failed, to minimize the number of orders and hence shipping costs. Arrghh, forgot the 1 ohm resistors, blatt, forgot the 100 ohm resistors for the 6.3v heater line artificial ground, akkk, forgot the lamps for the pilot light, that sort of thing.

Check out Rob Robinette's site, lots of great build info, and links.

Good luck on your build, post lots of photos. Lots of real gurus here to learn from.

[Jarvini]

I've added a picture of the layout that I'm using so I can ask you all another question ?
Should the wire from the 1.5k on the far right of the board go to the top lug of the input jack and have a wire connecting the middle lug to the top lug and should there be a wire connecting the top lug to the brass grounding plate as there is no mention of this in the build notes but the earth symbol leads me to believe the top lug should go to earth ?

[mikepukmel]

The brass grounding plate is easy to solder to and it worked fine with vintage amps like Fenders. However, when using that, your grounding is just random to the chassis, which can cause problems with noise and hum and oscillations, depending on the circuit and gain levels you are using. A ground buss isn't really any better if it is also random chassis grounded, such as to the back of pots for example. Using a ground buss does allow you to control your grounding a bit better, but it has to be done correctly. With any grounding design, the safety ground should have it's own ground to the chassis within about an inch of where the power cord comes into the amp, and it should be made a little longer than the hot and neutral wires so that if the power cord is pulled out of the amp, the safety ground is the last thing that would be connected. It should use a bolt with two keps nuts and a terminal soldered to the wire. It should be a green wire with a yellow stripe, or a green wire, depending on your jurisdiction. You can look up what the code is for your country. In the US it is a green wire with a yellow stripe.

Your buss bar should be ground for the signal grounds and should not connect to the same point as the safety ground. In order for the buss bar to be used correctly, it needs to be connected to the chassis at only one point, usually near the input, but it can also work if your connection point is near the power transformer....as long as there is only one chassis grounding point for the buss bar. This means that you need to use isolating jacks so that those will not ground on their own. Switchcraft makes longer shaft jacks that you can use isolating washers with. These are better quality jacks than Neutrick or Cliff plastic jacks. Do not ground to the back of the pots. They can ground fine with a star washer to the chassis. Any grounds off the terminals of the pots can go to the buss. All grounds should go to the buss in order....meaning that the cap that supplies your first preamp stage should have a local summing point where all grounds for that stage go. Then that summing point should go to the buss bar. Think of it as little streams leading into a river. The next stage would also have it's own local supply cap and a summing point, then ground to the buss in order after the first stage, etc. Do not ground anything to a transformer bolt either...that is a potential safety hazard. You should lay out the supply caps for each stage near the stages they supply rather than all in one spot like Fender did. If it is a kit that you building with a pre-determined layout that mounts all the caps in one place, then that isn't ideal but it will work. For more on the proper grounding with a buss bar, look up Kevin O' Conner's galactic ground (In his books) and/or Merlin's buss bar system in his books and on his website. I highly urge you to get Merlin's book if you don't have it already. It is VERY good. The Valve Wizard

There is also the Hoffman system which uses a buss bar and rather than random chassis grounding, it uses controlled chassis grounding. It works ok too, but for high gain amps it may have issues. To me it is also more work than doing things the other ways I mentioned above, so I don't use it myself. You can find the Hoffman grounding system on his website. Tube amp parts, Guitar amp parts, Tube amp for guitar

Greg

Hi Greg, I found photos of a few Marshall style builds, where they put a big ground buss wire across the back of all the pots, but also put little rubber or plastic rings to isolate the pots where they mount to the chassis. If hte bus wire is then run to one point on the chassis, would that fix the random ground point issue?

[mikepukmel]

I've added a picture of the layout that I'm using so I can ask you all another question ?
Should the wire from the 1.5k on the far right of the board go to the top lug of the input jack and have a wire connecting the middle lug to the top lug and should there be a wire connecting the top lug to the brass grounding plate as there is no mention of this in the build notes but the earth symbol leads me to believe the top lug should go to earth ?

Check with the gurus, but I believe the middle and top lug on your input jack (in your diagram) get wired together and then to ground. If you look at a shorting switchcraft jack, it will make sense to you. If you use an isolated input jack grounding scheme like Greg wrote about above, you'll need a ground wire. For Fender style, that is bolted to the brass plate, it will get grounded there.

[Jarvini]

Does that mean that if I use the brass plate method I don't need to run a wire from the top lug of the input jack and solder it to the brass plate ?

[mikepukmel]

Ahh, this is what I was looking for:
https://www.tubesandmore.com/sites/d...2a_drawing.gif

The "tip" is your input signal, clockwise tab as viewed from the bottom.
The shunt is the middle tab. You wire the jack so that when there is no guitar plugged into the jack, the shunt connects the tip connection to ground, which is the counter clockwise tab (top tab in your schematic). This is so you don't get garbage signal going into your amp when nothing is plugged in.
The ring is the outer tab that goes to the shield on your guitar cord. it will get grounded somehow, depending on your grounding scheme, either to the brass plate, or for the isolated jack scheme, a wire to ground.

[mikepukmel]

Does that mean that if I use the brass plate method I don't need to run a wire from the top lug of the input jack and solder it to the brass plate ?

Yes, you won't need a wire if you bolt the jacks and pots to the brass plate. See
http://www.tjadamowicz.com/amps/gall.../BFamps048.jpg
for the isolated w ground bar case. There, he has the little red isolators behind the input jack, then wires the counter clockwise most lug (the "ring") to his ground bus.
in the standard old style fenders, the jack is screwed tightly to the brass plate, so the ring is grounded that way, so no wire needed on the counter clockwise most lug.

[Jarvini]

Thanks I see now, the top lug is already grounded as it's in contact with the brass plate already and adding a wire from the top lug to the brass plate would create an earth loop is that right?

[Jarvini]

Just like to say thanks for your help Mike helped me a lot and as for the photos you posted some super neat workmanship out there
Scott

[mikepukmel]

Ooh, another tip I got from the gurus: the 68k resistor leading from your input jack to V1 is a grid stop. Its there to help prevent radio signals and other garbage from getting into your amp, and also to help prevent parasitic oscillations. They didn't have shielded wire in the old days, so they put the resistors right on the input jacks. I was told by several gurus to move the grid stop resistors to the pin on the preamp tube, and also ground the shield on the shielded cabe to the other side, the side nearest the jacks. The former will let the grid stop work better, and the latter will be in keeping with the grounding scheme.