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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Doug Self Preamp from Linear Audio #5
Doug Self Preamp from Linear Audio #5
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Old 17th December 2017, 07:55 PM   #911
scottjoplin is offline scottjoplin  Wales
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Have you decided that mains voltage could get into the preamp chassis?
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Old 17th December 2017, 08:25 PM   #912
heijnsva is offline heijnsva  Netherlands
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Quote:
Originally Posted by scottjoplin View Post
Have you decided that mains voltage could get into the preamp chassis?
Well I'm no longer sure two boxes have real benefits beside transformer noise. So I think it's going to be a one chassis preamp with mains in it. Except that I'm overlooking other advantages of a separate psu chassis.
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Old 17th December 2017, 09:20 PM   #913
scottjoplin is offline scottjoplin  Wales
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The only benefit might be less transformer noise but that transformer is small enough to keep far enough away from the boards to not be an issue
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Old 18th December 2017, 07:17 AM   #914
AndrewT is offline AndrewT  Scotland
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Originally Posted by heijnsva View Post
..................
This leaves me wondering though why devices with wall warts don't require a safety earth connection and consequently why there are no symmetrical wall wart power supplies.
some/many wallwart power supplies are ClassII = double insulated and guaranteed by design and construction to be safe without any connection to Protective Earth. All these ClassII have the concentric squares symbol printed on the labelling.
Quote:

I do notice on many build photo's in this thread extra parts ie from rca chassis to ground or from power ground to safety earth. Is there a recommendation in this particular situation?

Also, how is the pin1 connection made? As i can tell from the photo's pin1 is routed to power ground through the main pcb. Is there something extra to be done around the XLR connectors to follow the recommendation to take the shortest path? Hope you guys don't mind my rambling or asking what should be obvious.
Pin1 is the connector for the screen of a cable.
That screen is an extension of the enclosure. The screen goes direct to the enclosure via pin1.
Pin1 does not get connected to the audio.
Attached Images
File Type: jpg The right way to use Pin1.jpg (56.3 KB, 364 views)
Attached Files
File Type: pdf Grounding.pdf (602.5 KB, 59 views)
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Last edited by AndrewT; 18th December 2017 at 07:21 AM.
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Old 18th December 2017, 07:52 AM   #915
heijnsva is offline heijnsva  Netherlands
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Originally Posted by AndrewT View Post
some/many wallwart power supplies are ClassII = double insulated and guaranteed by design and construction to be safe without any connection to Protective Earth. All these ClassII have the concentric squares symbol printed on the labelling.Pin1 is the connector for the screen of a cable.
That screen is an extension of the enclosure. The screen goes direct to the enclosure via pin1.
Pin1 does not get connected to the audio.
Thanks Andrew I thought the same only the connector in the BOM are made of plastic so I wondered how it contacts the chassis.
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Old 18th December 2017, 08:06 AM   #916
AndrewT is offline AndrewT  Scotland
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A short wide wire made from many fine strands to connect Pin1 to enclosure. If there are two screws/bolts fixing the XLR socket then a lead to each screw would be slightly lower impedance.
A bit like a tiny version of the Earth strap from engine to car chassis.
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Old 18th December 2017, 08:36 AM   #917
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by reedcat View Post
Thanks to Doug Self for the design. Thanks Carl Huff for prompt PCB shipment and quick email replies.

Front Panel Express have done a very quality job with these panels. I highly recommend the company.

Thank you everyone for your help at the forums! I couldn't have done it without your help.
Beautiful, well done!

Jan
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Old 18th December 2017, 03:26 PM   #918
heijnsva is offline heijnsva  Netherlands
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Quote:
Originally Posted by AndrewT View Post
A short wide wire made from many fine strands to connect Pin1 to enclosure. If there are two screws/bolts fixing the XLR socket then a lead to each screw would be slightly lower impedance.
A bit like a tiny version of the Earth strap from engine to car chassis.
A closer look revealed a small sharp contact to touch the chassis. It goes inside the connector where it contact the XLR plug's shell. On the pcb this contact is on an isolated island. The pin 1 is on the ground plane. So if one uses cables with the shield connected to the plugs shell and pin 1 everything should be OK right?
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Old 19th December 2017, 07:57 AM   #919
AndrewT is offline AndrewT  Scotland
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The "ground plane" is probably carrying audio signals.
That is NOT where pin1 connects to.

Pin1 connects the screen to the enclosure, because the screen is an extension of the enclosure.
See diagram post914

some reading:
Pin 1 Problem
Pin 1 Revisited

a Test procedure:
http://pin1problem.com/as032.pdf
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Last edited by AndrewT; 19th December 2017 at 08:03 AM.
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Old 19th December 2017, 08:21 AM   #920
heijnsva is offline heijnsva  Netherlands
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You're right Andrew. The diagram and the pcb seen different to me. I would very much appreciate an explication how everything should be wired up because I'm really confused now.
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