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-   -   Doug Self Preamp from Linear Audio #5 (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a.html)

Carl_Huff 15th May 2018 07:53 PM

Quote:

Originally Posted by fvzeppelin (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post5434495.html#post5434495)
Just finished my boards: Very easy to build up, great quality and very good first listening experience :) Thank you, Carl and Douglas, for this project!


You are welcome! Jan Didden had a hand in this too. Please enjoy.

hadihf 19th May 2018 04:50 AM

Happy builders, Trying to understand grounding for this preamplifier.

Please correct me if wrong.

The ground plane on main board is connected to ground plane on the I/O board through 20 pin header. The XLR(pin 1) and phono connecter ground pins are connected to I/O ground plane. The Power supply 0v is connected to 0v on main board. this is the signal ground.

The XLR outer shell shield is not connected to above signal ground but is connected to metal chassis when connectors are fixed to chassis.

The signal ground should be connected to chassis with single wire from I/O ground. There should not be any other ground connection.

Best Regards
Farooq

Carl_Huff 21st May 2018 04:23 PM

Farooq,

Your description is mostly right. The exception are the XLRs. The XLRs by default are grounded to the backplane in same fashion as are the phono connectors. This grounding scheme works well for most people in the consumer use space.

However if you have a need to separate the XLR ground as is the standard for pro audio gear, simply use XLRs that have wired connections on their backsides and not the thru PCB XLR connectors that are specified in the BOM. Using 'non-PCB' XLRS allows you to change up the grounding scheme to suit your need.

If all of this seems a bit confusing to you, I would suggest sticking with the thru PCB XLRs. Most builders have done that and have been very happy with the results.

hadihf 21st May 2018 05:15 PM

Thanks Carl,

However bit still confused..

The XLR footprint used for your pre has four pin footprint. Pin 1, 2, 3 and mating connector shell pin.

Pin1 is signal ground and is connected to ground plane. pins 2&3 are L or R pin 2&3.

I was referring to mating connector shell pin which I believe should not be connected to ground plane. In the type of XLR connectors being listed in parts list, when one fixes the connector to chassis through a bolt, then this pin is automatically connected to chassis due to presence of small clips in the mounting hole.

Now the mating connector outer shell of inserted plug is automatically connected to chassis when one inserts an XLR plug connector wire.

For a star ground to work properly, a single ground wire from I/O board ground plane (connected preferably very near the input being used) and connected to a chassis base common bolt to which the mains earth should also be connected.

What do you think?

Best Regards
Farooq

heijnsva 21st May 2018 05:25 PM

Hi Farooq,

I used Neutrik sockets and wired pin 2 and 3. Take care that there is good contact between the socket's housing and your chassis. And between all the chassis panels for that matter. I used a ground loop isolator between power ground and chassis ground.

Best wishes, Vincent

Carl_Huff 21st May 2018 05:38 PM

Quote:

Originally Posted by hadihf (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post5440470.html#post5440470)
... For a star ground to work properly, a single ground wire from I/O board ground plane (connected preferably very near the input being used) and connected to a chassis base common bolt to which the mains earth should also be connected.

What do you think?

Yes, you make a valid point. However I have built a couple dozen of these for myself and others. They have all went into metal enclosures. A few are in pro/ commercial use and I know at least one is in a portable system. In every case I built them using the thru PCB XLRs specified in the BOM. I run a 16 gauge ground from the back of the IEC power connector bolted thru the chassis. So far grounding has not been a problem.

I invite others to comment.

hadihf 22nd May 2018 05:36 AM

pin1 problem
 
This is a good article. Though sure most have already read it.

Pin 1 Revisited

Farooq

hadihf 23rd May 2018 04:40 AM

In my opinion...

Pin1 and pin4 (shell) of XLRs should be connected to ground plane at the I/O board PCB.
When XLRs are bolted to metal chassis both pin1 and shield are connected to chassis (due to small projecting pins in the mounting hole).

No need to make any other ground connection on the preamp except for the mains earth which should preferably be through a loop isolator.

I do not have the I/O boards but suppose XLR pin4(shield) in unconnected. connection to pin1, which is already connected to ground plane, can be made via small wire links.

Please comment and correct me if wrong.

Best Regards
Farooq

Carl_Huff 23rd May 2018 04:38 PM

Quote:

Originally Posted by hadihf (https://www.diyaudio.com/forums/analog-line-level/280458-doug-self-preamp-linear-audio-5-a-post5441927.html#post5441927)
... Please comment and correct me if wrong.

Best Regards
Farooq

I see nothing wrong with what you have written. As an aside, I use a filtered IEC power entry module on my projects.

Of late I have been using Schaffner #FN9264B-2-06 Mouser ... FN9264B-2-06 Schaffner | Mouser

There are many good products out there. I just happened to buy a box of these very cheaply a couple of years ago.

hadihf 23rd May 2018 06:08 PM

Thanks Carl. I have exactly the same but w/o switch. will definitely use it in pre.

Best Regards
Farooq


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