Best grounding scheme

[loudthud]

Steve nailed it. Grounding is truely a Black Art Light the incense!

In ideal point to "jump grounds", going from the quiet preamp ground to the noisey output stage ground is where the signal is differential. At that point the push pull power tubes can reject the ground noise, it cancels at the output transformer. The power tube grid leak resistors can be "grounded" at either ground without much penality. In fixed biased amps, the bias supply ground performs that function with the added aggravation of the rectifier currents. Probably best to keep those currents with the power stage ground and not pass them between grounds.

mbratch: 60Hz hums usually come from lead dress or heater supply issues. 120Hz buzz type hums are usually ground related. Try a hum-balance control and/or elevating the heater supply.

[mbratch]

Thanks LT.

Interesting, after my amp has warmed up a bit, the 60 (or 120?) Hz sound subsides a bit. It's almost inaudible unless you are listening hard or the amp is turned up to nearly 12 on the volume. But, I've heard a couple people now say their amps are "dead quiet" so I am striving for that! It must be entering at the input stage somewhere, as it is controllable from the volume controls. If either volume control goes up, so does the hum. No volume, no hum.

I have some pics now of what my amp guts look like. First, is a quick drawn layout of where the grounds are, then the actual pics:

[stingray_65]

FWIW

There are so many grounding techniques.
each technique has it's do's and don't
pick one grounding style and follow the rules that govern it.

IF there is noise after it is built THEN worry about how to fix it.

each amp I have built so far has had a different grounding style and each one has been quiet as a wisper, even my SE princeton.

a lot of guys on here with so much more knowledge and experience have given you thier opinions, find one that suits you and follow thier good orderly direction and you'll be happy as a clam and your amp will be quiet as can be.

my .02 take it for what its worth

Ray

[mbratch]

There are so many grounding techniques.
each technique has it's do's and don't
pick one grounding style and follow the rules that govern it.

That's the trick. I've seen a few schemes, read of a few. Found some scattered do's and don'ts but haven't found a complete set of rules. With each scheme I have had questions.

IF there is noise after it is built THEN worry about how to fix it.

That's exactly where I am at now.

each amp I have built so far has had a different grounding style and each one has been quiet as a wisper, even my SE princeton.

I commend you for that Ray. I wish I knew the trick.

a lot of guys on here with so much more knowledge and experience have given you thier opinions, find one that suits you and follow thier good orderly direction and you'll be happy as a clam and your amp will be quiet as can be.

In another thread I layed out what I was going to do and got no feedback. My scheme matches that of one poster that I saw on the board here. So I proceeded and.... here I am.

my .02 take it for what its worth

I accept and much appreciate any advice you have given!

Mark

[tubeswell]

Well apart from grounding induced hum (and I prefer the Hoffman-style split-ground system - and my amps are very quiet), I note that the signal wires around your pre-amp sockets pass right over the top of your heater wires. Try moving the white wires up and away from the heater wires (and even shortening the white wires a bit)

[mbratch]

Well apart from grounding induced hum (and I prefer the Hoffman-style split-ground system - and my amps are very quiet), I note that the signal wires around your pre-amp sockets pass right over the top of your heater wires. Try moving the white wires up and away from the heater wires (and even shortening the white wires a bit)

So theoretically all the ground points I show in my diagram look OK a-la Hoffman?

I just made a change to bring the crossing heater wire through the middle of the socket, arched, so there is no more crossing. I did the same with both V1 and V2. I made the heater wires more direct from pilot light to the first power tube as well to avoid being around the OT wires.

Still the hum.

I had previously moved those white wires around everywhere, up and out of the way, and it didn't change the hum.

I did notice a very slight hum, but definite, when both volumes are down at minimum. When I touch the chassis, it goes away. Not sure what that means...

[tubeswell]

When you have the guitar cable unplugged and the amp on full vol, how much hum is there?

[mbratch]

When you have the guitar cable unplugged and the amp on full vol, how much hum is there?

Hard to describe. Using the bright channel volume, it's about moderate conversational level. The normal channel volume sometimes is more, but sometimes not.

[tubeswell]

Since the hum is still there without the guitar cable plugged in, it is related to grounding.

Your body acts as a large low reservoir capacitor when you touch the amp chassis, diverting the residual low-voltage swing in the chassis to ground reducing the hum. The hum is caused by localised micro rises in ground potential in different parts of the ground return path interacting with 'lesser' potentials - inducing an unwanted AC into the signal path.

You need to re-do the grounding first. I recommend a split-ground system (works for me)

I have all the pre-amp ground return paths going each by their own individual separate wire to one common chassis point (which I make at one of the input socket grounds). I include the pre-amp filter cap ground return with these.

I have the output stage ground returns, including the screen and reservoir filter cap grounds, and the HT CT and Heater CT going by their own separate wires to one of the PT bolts at the other end of the chassis.

[mbratch]

You need to re-do the grounding first. I recommend a split-ground system (works for me)

I have all the pre-amp ground return paths going each by their own individual separate wire to one common chassis point (which I make at one of the input socket grounds). I include the pre-amp filter cap ground return with these.

I have the output stage ground returns, including the screen and reservoir filter cap grounds, and the HT CT and Heater CT going by their own separate wires to one of the PT bolts at the other end of the chassis.

My grounding system is sort of split. I have all the power stuff going to one side, and the pre-amp stuff to the other (via the buss on the back of the pots). In your case then, instead of a buss, you are doing a star ground back to one input jack? Where do you run the grounds from the pots, to the same star location on the jack side? Is that jack then grounded to the chassis directly near by?

Is it necessary that the CTs, filter cap grounds go to the same PT bolt? Should the AC ground go to a separate one or the same one?

BTW the system I used fits one of the other members' scheme descriptions perfectly and theirs does not hum. :-/

[loudthud]

Is the first tube a 12AX7 or 12AY7 ? Comparing your ground diagram to the Fender, I noticed the middle filter cap goes to the main filter on yours and the preamp filter on Leo's. Which one is right? The one that makes the quietest amp. The second thing I noticed was the virtual center tap going to ground. Try moving it to the high side of the output stage cathode resistor. That will sometimes get rid of a small amount of 60Hz hum.

[mbratch]

Is the first tube a 12AX7 or 12AY7 ?

12AY7

Comparing your ground diagram to the Fender, I noticed the middle filter cap goes to the main filter on yours and the preamp filter on Leo's. Which one is right? The one that makes the quietest amp.

Good catch. The one I did is what the Fender Deluxe reissue uses. I can change it to the older, Leo method and see what happens. But I wasn't sure since the rest of my grounding isn't like Leo's either. It would be easy for me to flip it back around and see what happens.

The second thing I noticed was the virtual center tap going to ground. Try moving it to the high side of the output stage cathode resistor. That will sometimes get rid of a small amount of 60Hz hum.

OK, I'll give that a shot. I did see that on a one Deluxe layout somewhere (perhaps Mission?).

[tubeswell]

In your case then, instead of a buss, you are doing a star ground back to one input jack? Where do you run the grounds from the pots, to the same star location on the jack side?

yep + yep

Is it necessary that the CTs, filter cap grounds go to the same PT bolt? Should the AC ground go to a separate one or the same one?

yep + yep (in my system)

BTW the system I used fits one of the other members' scheme descriptions perfectly and theirs does not hum. :-/

Hum is different in each amp. All sorts of things affect it because it is caused by subtle differences, for example the type of metal alloy used in the chassis and in the wires has different resistances, creating different localised ground potential rises. We are talking about millivolts here. It is the millivolt differences in the ground potential in different parts of the ground return path that cause the 'bad grounding' hum. No two amps are the same - even when they are the same type of amp. So what might work perfectly in your mate's amp might not work (apparently) in yours.

The 'star' system I use, keeps all the ground return paths isolated until they get to the common ground reference point. This reduces the chance of picking up localised micro rises in ground potential.

[mbratch]

tubeswell, is that jack then grounded to the chassis directly near by, via soldering a ground wire?

[mbratch]

In the brass plate scheme, is the plate then soldered to the chassis? If so, at what point(s)?