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-   -   Grounding for an external power supply (http://www.diyaudio.com/forums/chip-amps/210728-grounding-external-power-supply.html)

JVDM 14th April 2012 02:42 AM

Grounding for an external power supply
 
Hi all,

I'm embarking on my first gainclone attempt, using the chipamp.com kits. I have assembled the two LM3886 amp modules, and the power supply PCB.. The plan is for an external power supply unit, using a 300VA toroidal with dual 25V secondaries.

My current concern is with the grounding of the unit, given I'll be using an external PS.

At the moment, I'm thinking of using a 5 conductor umbilical, carrying P+ve, PG+ P-, PG-, and a ground connection between the amp chassis and the power supply chassis and the amp boards grounded in the amp chassis.

An alternative would be a 6 core umbilical, allowing the P+, PG+, P-, PG-, CHG and the amp chassis ground point. With this method, I could star-ground everything back in the power supply chassis, without having to ground the CHG in the amp unit.

Does this make sense? Which would be the best strategy?

Cheers,
JD

danielwritesbac 14th April 2012 09:17 AM

That investment and the wiring makes more sense as a dual-mono or monoblocs.

JVDM 14th April 2012 10:07 AM

I had originally intended to build a pair of monoblocks, each with external PS's, and bought 2 amp modules and 2 PS modules. However, I switched to a stereo with a shared external power supply to simplify things. I could quite easily run a separate power supply for each channel, but that would mean running 2 umbilicals, or one with more conductors. I could probably manage dual monoblocks with external power supplies (like the original gain card) if I spring for another enclosure. Would the improvements be noticeable?

All of these options would still leave me with the grounding issue though. Do I ground the amp pcb in the amp chassis, or run a ground for both the chassis and the pcb separately back to the safety ground in the PSU via the umbilical?

AndrewT 14th April 2012 12:08 PM

Do not put the Main Audio Ground in the PSU or that vicinity.

Bring the PSU Zero Volts to the amplifier's Main Audio Ground.

danielwritesbac 14th April 2012 02:37 PM

It is a good time to review Star Grounding and power supplies at Decibel Dungeon:
Building a Gainclone chip amp power supply.
If the server is not responding well enough to display photos, you can use the PDF backup file.

AlexQS 14th April 2012 04:31 PM

Quote:

Originally Posted by JVDM (Post 2984570)


At the moment, I'm thinking of using a 5 conductor umbilical, carrying P+ve, PG+ P-, PG-, and a ground connection between the amp chassis and the power supply chassis and the amp boards grounded in the amp chassis.

An alternative would be a 6 core umbilical, allowing the P+, PG+, P-, PG-, CHG and the amp chassis ground point. With this method, I could star-ground everything back in the power supply chassis, without having to ground the CHG in the amp unit.

I am trying something simular with an Audio Sector kit.

What AndrewT says makes the most sense to me, and I have also come accross agreement to this in other reading.

I made an umbellical, but haven't had a chance to try it yet. I have been focused on other areas recently, volume-pots and whatnot.

I am new to chip-amps, but the theorie lines up with other things I have learned in my years. When I was a kid, my friends and I became pretty darn good at installing car-audio stuff. If you put an audio amplifier in the trunk of a car, you must make sure that the ground wire from the amp is of at least equal guage wire (or larger) than the voltage power input wire, and also that the ground wire is as short as possible between the ground of the amp, and the chassis of the vehicle. Make it too long (like running a line all the way back to the ground of your fuse block under the bonnet) and you'll hear the cars engine in your speakers. Ideal way is to screw the ground line to the metal of the car as close to the amp as possible.

I realize I'm comparing apples and oranges here, but I think the theorie is the same in both places, "keep the line between the amplifier and chassis ground as short as possible".

So, use 5 conductors, not 6. Using 6, and running earth to your amp chassis, and then running CHG from the star of the board all the way back to the PSU, seems to me that this would create a big loop inside your umbelical.

Do a google search for something like, "Patek Grounding Audio Sector Peter Daniels" Keep in mind that the amp boards are different. The star point of the audio sector board is OG, where as I believe it may be CHG on the chipamp board. I think the photo might be helpful to you, even though they are different kits.


p.s. Remember to twist the pairs.

AlexQS 14th April 2012 04:56 PM

Quote:

Originally Posted by AlexQS (Post 2985129)
So, use 5 conductors, not 6. Using 6, and running earth to your amp chassis, and then running CHG from the star of the board all the way back to the PSU, seems to me that this would create a big loop inside your umbelical.

Do a google search for something like, "Patek Grounding Audio Sector Peter Daniels" Keep in mind that the amp boards are different. The star point of the audio sector board is OG, where as I believe it may be CHG on the chipamp board. I think the photo might be helpful to you, even though they are different kits.

On seccond thought, don't pay too much attention to me.... I just confused myself.

Here's photo I meant to point you to: http://www.diyaudio.com/forums/audio...tml#post787778

I can't see where the "5th" conductor is to connect amp-chassis back to earth in the mains plug. Maybe it's another line outside the umbelical???

danielwritesbac 15th April 2012 02:41 AM

1 Attachment(s)
The confusion is because those kits are specifically designed to make compact monobloc amplifiers. I will try adapt them for you. Please check other references for comparison and safety.

You can make a first start by equipping both chassis with earth ground cable. It may be good to complete most testing prior to installing the kits into the chassis.

To simplify your wiring and avoid loops with stereo builds, solder a jumper from PG+ to PG- at your power boards. This will reduce the confusion. You now have a Zero Volt ("CG") cable and therefore wiring standards for stereo amplifiers can work as expected.

And, see CarlosFM attachment for umbilical cable wiring.
The audiosector power board needs 3300uF caps added. The chipamp.com power board needs the 10,000uF changed for 3300uF. The chipamp.com amplifier boards need 470uF to 1500uF (same as the audiosector amp board) caps on the power rails of the amplifier boards instead of that 100uF mistake.
BOTH amplifiers need a pair of 10,000uF caps inside the amplifier enclosure (equally VERY close to the amplifier boards) and it is this (zero volt, "CG") Star Ground point where speaker negative (speaker return) and earth ground meet up with the zero volt cable. See attachment. See National Semiconductor datasheets for your chips. See also star grounding.
Note that the 100nF caps below are lossy polyster dip caps (internally a snubber), and do buy an extra pair of this type 100nF to use for your output zobel caps.


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