Ground connection of a particular PS .... where ???

[kagliostro]

I'm near to finish the 3 different versions of the layout  for a 6AF11 tube guitar amp

The PS I want to use is this (following Merlin's council a 56R resistor was placed on the negative path)



The preamp ground connections are planned to be at the input jack

but I'm not sure where to connect to ground the PS and the Power Section of the amp

if the PT has a CT I think the right place to connect the PS and Power Section is there

but here the PT has not a CT and the Rectifier Bridge is "floating" because of the use of the 56R resistor on the negative path

I'm confused 

Someone can help me ?

Thanks

Franco

[sluckey]

Connect to the point where the ground symbol is drawn.

What's the purpose of the 56Ω resistor? Will there be a requirement to use the negative voltage that is across the 56Ω? Or is this just to reduce the B+ a bit?

[pdf64]

if the PT has a CT I think the right place to connect the PS and Power Section is there...but here the PT has not a CT

Whatever type of rectifier, the rectified + and - outputs should always be connected directly to the reservoir cap's + and - terminals.
So as to retain the rectified current pulses confined within that circuit, don't want them to contaminate other circuits.

[kagliostro]

Ciao Steve & pdf64

I'm sure I didn't explained well which is my doubt

my question is:

Where to place, on the layout, the ground connection of the PS capacitors

The negative of the bridge and the negative of the first capacitor isn't to be connected to ground because of the use of the 56R resistor on the negative path

I added that resistor following a Merlin's council, you can see here how Merlin motivate it



from this file

http://www.valvewizard.co.uk/Grounding.pdf

--

I didn't yet revised the 3 Layouts I've draw, but I post here one as to be more clare about what I'm asking for (Preamp ground to the input jack, the other ground ..... where ??) (schematic on the bottom)



Many Thanks

Franco


p.s.: I forgot .... this is the schematic

[sluckey]

Power ground connects to chassis near the PT. Preamp ground connects to chassis near the input jack.

[kagliostro]

Many Thanks Steve

Power ground connects to chassis near the PT.

This is also if there isn't a PT CT, right ?

(I was thinking something like it was to be connected to the bolt of the green/yellow wire of the 3 wire of the line income if no CT on PT)

Thanks again

Franco

[shooter]

here's my thought;

the "chassis" ground (looks like garden rake) I call dirty or high current ground
the signal ground (pre-amp section) is as you say, at the input jack

[kagliostro]

Ciao Shooter

Thanks

Yes, your mod to the schem respect what I've draw in my layout and what Steve told

My big doubt was where to connect, on the layout, the power section ground

Steve replied suggesting near the PT

Franco

[vampwizzard]

A lot of people will take the power circuit ground, put a crimp ring on it, then attach it to the PT mounting screw. This can eventually rattle loose. The better way is to do the same with a dedicated lug/screw, mounted near the PT. Sluckey's builds show these pretty regularly.

[kagliostro]

Ciao vampwizzard

Thanks for your contribute

I understand what you are saying, only remember that  Steve, that is a fantastic builder and planner

on his jobs almost always he use PT with CT (I examined more than 15 of his jobs and no one used a PT without a CT) and in that case is a must to connect the PS capacitors ground to the bolt used to connect the PT CT to the chassis (and  Steve uses to do it near the PT but not to the PT bolts)

my case is a bit different as my PT has not a CT, so, as far as I can know, there isn't an "official" place where to place that connection (of course I'll follow  Steve's council, he is really a skilled builder)

Thanks again

Franco

[sluckey]

It doesn't matter if the PT has a CT. My grounding scheme is the same for both. The power ground will be located near the PT (and power components. The preamp ground will be located near the input jack.

In this pic of my revibe which used a PT with no CT, you can see my power ground lug mounted between the cap cans and the board. And the preamp ground lug is located near the input jack.

     http://sluckeyamps.com/revibe/revibe_02_big.jpg

[kagliostro]

Thanks Steve

Franco

[tubeswell]

Elsewhere in Merlin’s grounding chapter, The power amp ground is not split from the preamp ground. Rather, it is joined to the main signal ground buss, and the other end of the buss is attached to the chassis at the input jack sleeve. That’s how I’d do it YMMV

[kagliostro]

Ciao Tubeswell

Due to translation I don't want to interprete incorrectly what you mean

Are you saying to connect all the circuit grounds to a single bus and to connect the bus to the chassis at the input jack ?

Franco

[tubeswell]

Yes look at the diagrams in Merlin’s grounding chapter

[labb]

Elsewhere in Merlin’s grounding chapter, The power amp ground is not split from the preamp ground. Rather, it is joined to the main signal ground buss, and the other end of the buss is attached to the chassis at the input jack sleeve. That’s how I’d do it YMMV

If you use this grounding scheme you need to be sure that you get the order of the grounds connection to the bus correct. It works for sure and it is hard to argue with Merlin, but I have had a lot better luck with Steve's type of grounding. I would guess that most builders have their favorite type of grounding. Heck, take a look in some of the old vintage amps...Multiple ground points and they may be anywhere.

[vampwizzard]

Elsewhere in Merlin’s grounding chapter, The power amp ground is not split from the preamp ground. Rather, it is joined to the main signal ground buss, and the other end of the buss is attached to the chassis at the input jack sleeve. That’s how I’d do it YMMV

If you use this grounding scheme you need to be sure that you get the order of the grounds connection to the bus correct. It works for sure and it is hard to argue with Merlin, but I have had a lot better luck with Steve's type of grounding. I would guess that most builders have their favorite type of grounding. Heck, take a look in some of the old vintage amps...Multiple ground points and they may be anywhere.

Im 3 for 3 so far on quiet amps utilizing Steve's method.

[kagliostro]

Heck, take a look in some of the old vintage amps...Multiple ground points and they may be anywhere.

Oh, yesss, you are correct, I've a GEM Super Deluxe 50 (old italian guitar amp), the circuit is PTP and ....

which a mess, ground connections everywhere

Franco

[SnickSound]

Yes, a lot of old amps got away with dubious grounding practice. Doesn't make it best practice.

If you're using an known layout you can probably get away with it. But it's worth learning best practice.

I've built a few amps with Dual Rec level of gain so far where the circuit is only grounded at one end (near the input), with each node bunched together along the ground bus on the board, as per that Merlin paper, and they are dead silent without resorting to DC heaters (NB: heaters ARE elevated). Using old approaches like having separate grounding points for the preamp and power amp, there was always a but of residual hum. Until about JCM800 levels of gain (3 stages) you can get away with it though and many have.

I used to think that having to switch to the clean channel between songs was normal, now there is no need. My 4 stage builds can stay on the dirty channel all night long and no one can tell.

[silverfox]

Yes, a lot of old amps got away with dubious grounding practice. Doesn't make it best practice.

Perhaps the two wire ac system had something to do with the noise levels. In a positive fashion.