Grounding 101

earthsled · Dec 1, 2011

Hi All!

Before I build another project, I need to get straightened out on my grounding implementation. I figure there are probably some DIYers out there who could benefit from this discussion as well.

First question: I'm building a power supply, but I'm not sure how best to return the ground (or 0V) of the circuit it's powering. From the attached diagram, which scheme is better? Are there other factors to consider?

Thanks in advance!

ruffrecords · Dec 1, 2011

Neither - LOL.

The filter caps and regulation need to be very tightly coupled to the transformer centre tap. A big lump of copper is best. This is not ground it is zero volts, a completely different thing. Zero volts should be connected to ground (safety earth), at one point only, usually by a thick wire from the transformer CT to a big bolt on the chassis. The mains safety earth from the mains connector is also connected to this big bolt. +V and oV for the audio should go straight from the regulator to the audio circuits. No other connections to the chassis should be made aart from pin1 of XLRs.

Cheers

Ian

abbey road d enfer · Dec 1, 2011

None. Use hierarchical ground; input stage gnd to second stage gnd to third stage gnd and so on.
The final stage ground should return to a single gnd of the PSU, typically the ground that serves as a reference for the regulators (for tube gear to the ground of the last cap in the chain of smoothing caps).
Star ground is a safety notion, not good for audio; the only place where there's some kind of star ground is when the audio gnd is tied to the chassis ground.

abbey road d enfer · Dec 1, 2011

I promise: we didn't consult ;D

earthsled · Dec 1, 2011

I'm so happy to have your comments! ;D I should have posted this a long time ago.

Let's see if I'm interpreting ruffrecords correctly...

abbey road d enfer · Dec 1, 2011

earthsled said:
I'm so happy to have your comments! ;D I should have posted this a long time ago.

Let's see if I'm interpreting ruffrecords correctly...

I wouldn't do exactly that. I would have a short and sturdy connection between "regulation" and "filter caps", regulation should go to chassis , transformer and rectification should be left floating, it's the dirtiest "gnd" here, you don't want that to interfere.

ruffrecords · Dec 1, 2011

abbey road d enfer said:
earthsled said:

I'm so happy to have your comments! ;D I should have posted this a long time ago.

Let's see if I'm interpreting ruffrecords correctly...

Click to expand...

I wouldn't do exactly that. I would have a short and sturdy connection between "regulation" and "filter caps", regulation should go to chassis , transformer and rectification should be left floating, it's the dirtiest "gnd" here, you don't want that to interfere.

Yes, I you are right. That's what I generally do. Forget what I said about the CT.

One thing I would like to add is that you should think of the chassis (if there is one) as a screen and NOT as ground, earth or zero volts. It's purpose is screen the electronics from outside interference and to route interference currents (including those caused by so called 'ground loops') to safety earth without going anywhere near zero volts - it's interference currents going down zero volts that causes hum. So if you have a separate power supply then you should connect its chassis to the chassis of the rest of the electronics. Generally this means the PSU is connected to the main electronics by a cable. This cable should have a sceen connected to chassis at each end - this effectively extends the screening properties of the chassis around the whole of the electronics.

Cheers

Ian

ruffrecords · Dec 1, 2011

Rane do a very nice paper on this subject:

http://www.rane.com/note151.html

Cheers

Ian

earthsled · Dec 1, 2011

I probably should have mentioned earlier that my rectifier is a two-diode full-wave config (from the P2P REDD.47 thread) -- Would this mean the CT would have to connect to somewhere, rather than float?

Thanks so much for your help!

earthsled · Dec 1, 2011

Here's a revision...

abbey road d enfer · Dec 1, 2011

earthsled said:
I probably should have mentioned earlier that my rectifier is a two-diode full-wave config (from the P2P REDD.47 thread) -- Would this mean the CT would have to connect to somewhere, rather than float?

Thanks so much for your help!

You have to connect it to the gnd of the smoothing caps, but not anywhere else. that's what I meant by "float".

earthsled · Dec 1, 2011

Okay -- that makes total sense now. Attached is an updated diagram.

Next question: If I'm using the bias tap of this same transformer for my 48V PSU, what is the best way to handle the phantom power's return path?

On another post, letterbeacon and ruffrecords discussed this issue, with ruffrecord recommending to "connect the (common) HT and Phantom zero volts to the chassis right near the the mic input XLR. From this same (star) point, take a lead and connect it direct to the mains earth pin on your mains input connector."

What if I'm building two channels in one chassis, with the input XLRs on either side of the box? Where should this "star point" be located or is there a better way to implement the return path?

Thanks!

ruffrecords · Dec 1, 2011

earthsled said:
I probably should have mentioned earlier that my rectifier is a two-diode full-wave config (from the P2P REDD.47 thread) -- Would this mean the CT would have to connect to somewhere, rather than float?

Thanks so much for your help!

It connects to the filter caps by way of a short and sturdy connection. The filter rectifiers, filter caps and regulator should be really close together.

Cheers

Ian

ruffrecords · Dec 1, 2011

Scheme E is good.

Cheers

Ian

earthsled · Dec 2, 2011

Great!

Could I get your opinions on how best to implement phantom power to a 2CH preamp when the CT of the transformer is also serving as 0V for the 48V supply?

Thanks!

CJ · Dec 2, 2011

green pwr wire gets grounded as close to entry hole of pwr chord as possible

CT grounded with filter cap grounds,

audio grounds should be star grounded but if two channel box, use different star grounds for each channel.

wire the amp so that the input jack is next to the output jack.
do not run input jack on front of chassis and output jack on back of chassis

use a big soldering iron to weld a blob of solder to the chassis, then immerse the wires into the blob and reheat.
no nuts or bolts holding your grounds down.

make sure your pots have a good ground, some folks use a brass plate for all the controls, like you see on the fender amps.

there are a ton of grounding articles in the AES papers, but even if you read everything and follow every rule, you still might have som problems,

so grounding is an art, not a science. you might have to make a few changes, or you might get zero hum from the get go.

i built a 2 channel guitar amp one time and one channel had less hum than the other, even though each circuit was identical. the channel with the most hum was further away from the power trans, so why it had a tad more hum is still a mystery. :

abbey road d enfer · Dec 2, 2011

earthsled said:
Great!

Could I get your opinions on how best to implement phantom power to a 2CH preamp when the CT of the transformer is also serving as 0V for the 48V supply?

Thanks!

CJ · Dec 2, 2011

he said he had a bias tap, sounds like he is using a git transformer,

the same ct ground would probably be fine for the phantom.
ground the phantom caps there also.

abbey road d enfer · Dec 2, 2011

CJ said:
he said he had a bias tap, sounds like he is using a git transformer,

Correct. You're good at reading the fine details.

earthsled · Dec 2, 2011

It's true, I am trying to use a guitar amp transformer.

On this post http://www.groupdiy.com/index.php?topic=42745.40 ruffrecords raises concerns about having the CT of the HT transformer connected to the chassis at one point while pin 1 of the XLR connects to the chassis at a different point.

Is it acceptable to run wires from pin 1 on the XLRs to the "big bolt" rather than connecting them to the chassis right near the connectors?

Thanks!

Grounding 101

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