Brown Deluxe/Constellation build...help please...

[Structo]

Yes, it was my understanding that the AC ground can also have the have the power supply grounds at the same place.

I have done this several times without much noise.

[Phil_S]

Regarding mixing the mains ground with the PT grounds...I've seen this done many times, and those amps have always been very quiet and hum-free. I think I'm going to give it a shot and see if it changes anything.

I don't care what you've seen. This is a foolish and dangerous thing to do. Ask a licensed electrician to explain it to you before you try it.

[Structo]

How so?

To correct what I said, my AC ground goes straight to the chassis below the IEC and the PT Center taps connect to the transformer bolt just an inch or two away.

[Phil_S]

I posted elsewhere for reply from a licensed master electrician who is also a guitar amp guy. We'll see if I get a reply and I'll post what I'm told, right or wrong. He stops by almost every day, so I think a little patience is in order in the interest of safety.

[dehughes]

Regarding mixing the mains ground with the PT grounds...I've seen this done many times, and those amps have always been very quiet and hum-free. I think I'm going to give it a shot and see if it changes anything.

I don't care what you've seen. This is a foolish and dangerous thing to do. Ask a licensed electrician to explain it to you before you try it.

Interesting....then many professional amp builders would be in the wrong. I don't really see how it would be a bad thing...feel free to elucidate....

[M Fowler]

I couldn't help but notice this thread about not puting the AC ground with the other AC grounded parts to the lug for tranny mounting. I was always told to do that.

I had to go back through a few books I had and they all say the green wire is grounded to the chasis pick a point usually a terminal under a power transformer bolt for AC ground. All the AC parts will be grounded to this point such as the center tap.

Then pick another convient spot to locate a star ground for filter caps and tone circuit. All the audio circuit will be attached to this one ground point.

Now in my own builds and they are quiet I use several ground schemes and have not had any problems.

Mark

[Structo]

Yeah I'd like to get a definitive answer to this too.

The only thing I can think of is if somehow the AC ground got lifted or broke then you would have some AC current on the chassis.

But if the AC ground and the center tap and power supply grounds are separated by too much chassis between them, couldn't that cause a ground loop?

This is what Aiken says:

The AC mains input ground (the third, or green, wire) should not be connected to either star point. It should be connected to the chassis right at the point where the AC comes in, with a short wire. It should also be well bonded to the chassis, preferably soldered, so there is no chance of it coming loose.

[M Fowler]

Well as you can see in the Trainwreck layouts a ground lug is bolted to the chassis right near the IEC plug and the green wire is soldered to the lug and the center taps are also soldered to this AC lug.

I also watched Gaby do one of his amps on his video and he also uses a tansformer bolt with lug for his AC grounding scheme.

Mark

[Phil_S]

I'm still waiting for my electrician "friend" to respond.

Meanwhile, while URL posted below is a bit verbose, it makes it pretty clear that the signal ground and the chassis ground cannot be mixed under the NEC. It's in there. You have to ferret it out. There are a number of references to the effect, "it is a mistake to mix the signal ground and the chassis ground".

Read here: http://www.scribd.com/doc/7270710/Groun ... -Reduction

[Phil_S]

I've got a partial answer. Here's what a licensed master electrician says without having actually checked his "book", note the second paragraph:

Hmmm. I'd have to look it up, but I believe the safety ground bonding point is a sacred place in a piece of equipment that no other piddly little conductor should share. It's quite possible that I won't find it in the NEC, but someone well-versed in UL standards would be able to say for sure.

Damn near every factory-wired amp with a 3-wire supply I've ever been in (probably all of them) has the safety ground point separate from the signal grounds.

Tangent: that ground wire from the cord should be the longest of the three. That way, if the cord gets pulled out it'll be the last to be ripped loose, so that if the hot wire contacts the still-grounded chassis, the OCD (over-current device; CB or fuse) will trip.

The book is in the van. I'll see if I can find the article and get back to you.

[dehughes]

Interesting. Thanks.

BTW, I found that pushing on the ground solder joints for the two volume pots caused hum and noise to increase dramatically. I've re-wired and re-soldered them and moved the tone cap off of the tone pot and grounded it to the buss wire. We'll see how it goes when I plug it back in.

This amp sounds great, IMHO, so I'm dying to get it hum-free...

[dehughes]

Update: Sooo, it hums, albeit a bit less...BUT, when I rotate the volume pot to or near zero, the volume jumps WAY up...like it just got turned up halfway. The noise and hum goes up as well, so I'm wondering if the pot is bad??? Something isn't right...but I've never had a bad pot so I don't know. It is a 1M CTS pot...

[M Fowler]

Phil,

First off I didn't see anywhere any one of us said we were mixing our signal grounds with the IEC ground. We said we may or may not in certain cases use the IEC grounding lug with our other AC grounds. Such as center taps. No one is using this ground for anyother purpose but AC grounding point.

In fact the main reason you put ground lugs in certain parts of the chassis (which is ground/earth) is to shorten the path to ground. For such parts as the pots and tone stack components. If you took a continuity light and clipped it to the chassis and the probe to the transformer it will light. To the 4, 8, 16 taps it will light. To the filament wiring string, it will light and to each ground lug it will light. Looks like it is all grounded showing continuity.

Mark

[Phil_S]

Phil, First off I didn't see anywhere any one of us said we were mixing our signal grounds with the IEC ground.... Mark

This is what the original poster said:

One thing I've considered is grounding the AC input to the same point as the PT grounds (heater and recto center taps) which is the same ground for the filtering caps.

I see now that I misunderstood "grounding the AC input" which I took as the mains ground. It seems time to admit that I made a flap about nothing. Sorry, it happens.

Yes, when I build, I use a floating ground buss and run a wire from the high potential end to the single chassis ground where I tie the buss, power tube cathodes, OT, PT CT, filter caps, etc.

Phil

[M Fowler]

All is good Phil.

As for people worrying about shocks if a wire came off, this is why you use a fuse. All should know that the black power wire is hot, the white wire is neurtal and the green we call ground. The fact is white is grounded at the grid in all USA electrical power household distributions. The extra added green wire came about as an extra precaution to provide and extra means of grounding the recepticle boxes and lighting boxes. If you opened a 200 amp service panel the white (neutral) and bare wires of your 14/2 romex wire goes to the same buss bar. The black (hot) goes to the breaker.

Building guitar amps has a theory and application all of its own and my electrician brother does understand one thing I am doing inside that little tiny box I call an amp.

Mark