Marsh headphone amp from Linear Audio

[Neutrality]

Originally Posted by RNMarsh

No. Thats fine. can also put a bypass cap across the 10 ohms so the ground is low at Hf and only affective at 'hum' frequencies.
Also can try using shunt caps, as shown on pcb, withOUT lowest esr for damping, if needed.

With the headphone ground return wire going into the SGD plane wouldn't that disturb the sensitive SGD plane?

Also if you add a 10 Ohm resistor parallel with a 100nF cap you do end up with a nice SGD plane isolated from the star point which is a good thing. However, since the headphone ground return wire goes into the SGD plane it has to go through that 10 Ohm resistor before it reaches the star point. Would that not have some sort of negative effect on the headphone amplifier performance?

[Neutrality]

Expanding on that would it be ok to have a separate audio gnd star point on a powersupply PCB where the Right and Left SGD as well as the headphone gnd return wire meet and then the audio
gnd star point is separated from the main/regulator gnd star by 10R parallel with 100nF

[Neutrality]

Something like this.

[sonidos]

I thought that was what he has been saying all along? No? I took it pretty much the way you just drew it up..that there is the separate signal ground plane area (sig in, sig out grounds) with the parallel C and R between sig ground , tied to main star ground. I wouldn't put the signal star point on the psu board, but that's just a hunch on my part.

[Neutrality]

Originally Posted by sonidos

I thought that was what he has been saying all along? No? I took it pretty much the way you just drew it up..that there is the separate signal ground plane area (sig in, sig out grounds) with the parallel C and R between sig ground , tied to main star ground. I wouldn't put the signal star point on the psu board, but that's just a hunch on my part.

Yes, that was what he was saying but I am a little worried that having signal ground and headphone ground return wire sharing the same audio ground would create some issues due to the currents through the headphone ground return wire.

Also having the headphone ground return wire going through a 10 Ohm resistor is something I am a little nervous about.

Attached is my supply.

The top left and right 3-pin Molex connectors are for supplying each amplifier board, Power ground from each board goes to the regulator/cap multiplier ground in the middle of the board.

The middle 3-pin Molex connector goes to my audio ground where SGD from each amplifer board as well as the headphone ground return wire meet. My idea was to separate this audio ground from the regulator/cap multiplier ground by 10R parallel with 100nF.

At the bottom I have my third ground, the rectifiers and first caps before the regulators are attached to this ground.

[Neutrality]

What you end up doing is having your headamp driving your headphones as well at the 10 Ohm resistor. You lose a little voltage across it for one and it might have a few other side effects, although I'm not certain what they could be.

Some clarification would be much appreciated.

[sonidos]

someone will come along and give a better and more thoughtful answer...but this is how I see it.

That 10 ohm resistor "lifts" the sig ground above the power ground. Noise, if given the opportunity, will go 'downhill'. So as I see it, any noise generated in the audio ground flows downhill to the main star point. And any noise in the psu ground will not flow 'up' into sig ground.

I ran a calc just the other day. A 1V signal with a 12dB gain comes out to 4V. To me, if you lose a volt or two, that is significant. What you're stating doesn't sound right to me. But again, a better statesman should hopefully come and clear things up.

[RNMarsh]

I use the ground 'planes' mostly as shields... not as convenient connections for picking up I/O signal commons and power grounds. The current loops will not pass thru any common signal between the input, output or power. Its harder to know if this is happening when using a ground plane to attach each of the seperate commons to it.... it can be done but carefully.
Does that make sense?

[jackinnj]

Originally Posted by RNMarsh

I use the ground 'planes' mostly as shields... not as convenient connections for picking up signal commons and power grounds. The current loops will not pass thru any common signal between the input, output or power. Its harder to know if this is happening when using a ground plane to attach each of the seperate commons to it.... it can be done but carefully.
Does that make sense?

On the boards I made, this was explicitly designed in -- with the option of connecting the "shield" nearer the input or output.

[sonidos]

Yes, makes sense. I made a head amp with a ground plane and... hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm