Help with grounding scheme in 18 watt clone

[Silvio55]

Hello! I´m building my first amp, an 18 watt lite from scratch and I´m using this layout:

I don´t know if this grounding scheme is OK, I´ve seen many other grounding schemes in other 18 watt layouts, I have read many articles on grounding but I can´t really figure what scheme should use.
Should I follow this layout or are better ways for gorunding in this amp?
Thanks in advance!

[soundguruman]

It's better to ground all the power supply stuff to one side of the chassis. Close to the power transformer.
Then ground the audio signals to the other side of the chassis. Far away from the power supply filter grounding.
Otherwise you wind up with power supply hum in the signal path.
The chassis acts as a resistor, so there is a couple ohms between the power supply ground and the signal ground. Less noise that way.
In the past, people have used "star" grounding, connect ALL the grounds to one point. BUT there is more hum and noise if you do that.
As the demand for lower noise increases, you will see manufacturers splitting the grounds into separate areas, and NOT connecting them together.

The FIRST ground is the safety earth, the green wire. This is attached to the chassis to make sure the chassis remains at 0 volts. This ground comes from your electrical receptacle.
The second is the ground from the Power transformer (center tap) or the ground from the rectifier or power supply filter capacitors. This is the ground that you will keep away from the signal path ground. You are usually staking this to the chassis at the power transformer side, not the preamp side of the chassis...
The third, your signal path ground (from the preamp) should be grounded on the other side, the preamp side of the chassis, away from the power supply grounds.

On your schematic, the power supply ground from the filter capacitors IS your preamp ground, (the green line), which is the worst way to do it, results in the most hum.

The input jack should be LIFTED off the chassis ground, using a plastic jack, or insulated washers. The input jack should be grounded to the (above mentioned) preamp grounding point, along with the preamp circuitry.

[big_teee]

I agree with keeping the power grounding away from the preamp grounding.
Not real fond of grounding all the pots together.
I like the ground bus on the board, with a large bus wire.
Here is a real good example of the bus wire, and separated grounds.
Look at the layout on page 3.
This is not your plan, but you can get ideas from it.
http://site.tubedepot.com/pdf/british18w_v14b.pdf
Be careful not to have to many area grounds tied together, you end up with ground loops.
Good Luck,
Terry

[Silvio55]

Thanks!

On your schematic, the power supply ground from the filter capacitors IS your preamp ground, (the green line), which is the worst way to do it, results in the most hum.

That´s was what I thougt it wasn´t right, it goes against everything I have read about grounding, but being my first build I´m not so confident to go without asking first!
Big_Teee, that layou is cool, I will use it as a guide to do the grounding in my amp, it´s basically the same, just less grounding wires in my amp.
Just one more thing... I have the metal non isolated type input and output jacks, should isolate them or use them straight to the chassis without isolation?

[Silvio55]

Thanks!

On your schematic, the power supply ground from the filter capacitors IS your preamp ground, (the green line), which is the worst way to do it, results in the most hum.

That´s was what I thougt it wasn´t right, it goes against everything I have read about grounding, but being my first build I´m not so confident to go without asking first!
Big_Teee, that layou is cool, I will use it as a guide to do the grounding in my amp, it´s basically the same, just less grounding wires in my amp.
Just one more thing... I have the metal non isolated type input and output jacks, should isolate them or use them straight to the chassis without isolation?

[big_teee]

Thanks!

That´s was what I thougt it wasn´t right, it goes against everything I have read about grounding, but being my first build I´m not so confident to go without asking first!
Big_Teee, that layou is cool, I will use it as a guide to do the grounding in my amp, it´s basically the same, just less grounding wires in my amp.
Just one more thing... I have the metal non isolated type input and output jacks, should isolate them or use them straight to the chassis without isolation?

If you want to be Marshall Like!
Marshall always uses insulated cliff jacks.
Either should work, but with the insulated jack, you can put the ground where you want it.
T

[Silvio55]

OK! I couldn´t get the insulated jacks around here, and the metal jacks seem more robust, I will use them but insulating them with some plastic or fiber bushing and some teflon tape.

[big_teee]

I would just go ahead and let it ground to the chassis.
Your going to ground the preamp Ground bus on that end of the chassis anyway.
I think that will work ok.
Or, you may try it both ways.
Good Luck,
Terry

[Silvio55]

Yeah, but I have two inputs, I can just put one jack grounded to the chassis, no both I think (that would be a ground loop, wouldn´t it?), and the speaker jacks must also be insulated from the chassis, or I can also ground them to the chassis?

[big_teee]

Yeah, but I have two inputs, I can just put one jack grounded to the chassis, no both I think (that would be a ground loop, wouldn´t it?), and the speaker jacks must also be insulated from the chassis, or I can also ground them to the chassis?

That's not the best layout.
Don't even see the OT and the output jacks on that diagram.
This is a fairly basic amp, and not a real high gain amp.
I think you will be fine to chassis ground the Output and input jacks.
Since you are going to separate the Preamp and power grounds, I would try that first.
Good Luck,
T

[Silvio55]

Yes, that layout kinda sucks, but it was the only one I could find for an 18 watt lite, not the liteIIb version (my idea is to make a single channel version of the 18 watt with no changes or tweeks, just like the original). I found this one, I think it´s a lot better:

It´s a liteIIb but it´s almost the same after all, just changing some values and that´s it.
By the way, this layout shows uninsolated output jacks, don´t know if it´s just the drawings or that means that you have to (or can) use those kind of jacks.

[olddawg]

If the Ceritone layouts are still up they work well. Also, a tightly twisted filament dress run along the back edge of the chassis helps a lot for hum reduction. You might want to see if 18watt.com is accepting members. They have a lot of archive stuff specific to 18 watt builds.

[big_teee]

If the Ceritone layouts are still up they work well. Also, a tightly twisted filament dress run along the back edge of the chassis helps a lot for hum reduction. You might want to see if 18watt.com is accepting members. They have a lot of archive stuff specific to 18 watt builds.

Here we go again!
T

[olddawg]

Here we go again!
T

Here's the Ceritone TMB Layout:
http://ceriatone.com/images/layoutPi...Bceriatone.jpg
It is tried and true. You can lead a horse to water but you can't make them drink. Do not use Switchcraft style jacks.

[big_teee]

Here's the Ceritone TMB Layout:
http://ceriatone.com/images/layoutPi...Bceriatone.jpg
It is tried and true. You can lead a horse to water but you can't make them drink. Do not use Switchcraft style jacks.

I was referring to the 18watt.com and the new members.
If you remember I never could get my coronation, or blessed by 18watt with a membership.
Which isn't a big deal cause I always build 50 Watt Amps with EL34s.
Back to the Thread, the Brown Note Liteiib looks good, but I don't see any shielded inputs with 68 k resistors.
T