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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 9th August 2019, 05:47 AM   #1451
tcpip is offline tcpip  India
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Originally Posted by Carl_Huff View Post
If you wire each RCA the way that it is shown in the schematic page 1 it should work. This assumes of course that you do not have different sources plugged into a common input.
Thanks a lot. I'm now beginning to plan a new I/O board, generic, where each analog input will have both RCA and XLR (assuming of course that the board feeds a preamp with balanced input.)

Is the PCB footprint of the Lorlin 12-way switch you're using available as a Kicad library, do you know? Do you use Kicad?
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Old 9th August 2019, 06:06 AM   #1452
Carl_Huff is offline Carl_Huff  United States
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Originally Posted by tcpip View Post
... Is the PCB footprint of the Lorlin 12-way switch you're using available as a Kicad library, do you know? Do you use Kicad?
I don't know much about Kicad. I use Sprint Layout for these projects. I have a collection of library objects that I would be glad to share.

Sprint Layout is inexpensive to buy and works really well. Sprint Layout 6.0, ELECTRONIC-SOFTWARE-SHOP
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Old 9th August 2019, 07:16 AM   #1453
tcpip is offline tcpip  India
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Originally Posted by Carl_Huff View Post

Sprint Layout is inexpensive to buy and works really well. Sprint Layout 6.0, ELECTRONIC-SOFTWARE-SHOP
For me, it's KiCAD, because it's "pretty good", open source, and runs on Linux. Hard to find an eCAD package which runs on Linux.
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Old 13th August 2019, 03:16 PM   #1454
tcpip is offline tcpip  India
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Originally Posted by still4given View Post
I believe if you use a balanced input with an unbalanced source you must short to ground the -ve. Maybe better to just use a RCA to XLR adapter.
I finally managed to find Doug Self's comment about this in his Audio Power Amplifier Design Handbook:
Click the image to open in full size.

And this is the circuit:
Click the image to open in full size.

Looking at all this, will this schematic work?
Click the image to open in full size.

Doug Self talks about putting resistors of appropriate value in the input signal paths. If I have to put identical series resistors, they will have to be on the input selector board, before the unbalanced and balanced wires join into a common set of wires.

My schematic is just a small part of the final board -- it just shows two inputs, and XLR+RCA for each. The rotary switch which will drive the relays is not shown here.

Against each input "way", I've put a switch, to draw the -ve signal line to ground, in case you are choosing unbalanced input and dislike the idea of leaving the -ve signal input hanging. (Doug Self says it's ok, but I wanted to put the switch here to show that it can be done.) SW1 does something similar with the output -- if you want balanced output, leave the switch off. If you want unbalanced out, you can choose to turn the switch on, and the -ve signal pin will be joined to signal ground.

Last edited by tcpip; 13th August 2019 at 03:44 PM.
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Old 13th August 2019, 10:11 PM   #1455
235 is offline 235
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If it's any help, Diptrace has the footprint for the Lorlin switch.

This is a good idea however you should check the original schematic as it deals with your design through placing the unbalanced input across pins one and two of the xlr and leaving pin 3 open.
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Old 21st August 2019, 07:56 AM   #1456
vasillis is offline vasillis  Greece
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Carl i send you pm.
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Old 21st August 2019, 06:05 PM   #1457
Carl_Huff is offline Carl_Huff  United States
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Originally Posted by vasillis View Post
Carl i send you pm.
Sorry but your message has not shown up. Could you please send it again?
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Old 21st August 2019, 06:09 PM   #1458
vasillis is offline vasillis  Greece
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Carl PM send again
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Old 28th August 2019, 06:01 AM   #1459
vasillis is offline vasillis  Greece
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Carl have you any update?
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Old 30th August 2019, 09:47 PM   #1460
fvzeppelin is offline fvzeppelin  Germany
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Originally Posted by Hicoco View Post
This is the Front panel..
Hello Hicoco,
I really like your design
Would it be ok for you to provide front and rear panel fpd files?
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