By having a switch present the user can have active signals incoming from different sources on all inputs and simply switch between them. Not having a switch removes that flexibility. The balanced out and unbalanced out are both active (after a short turn on delay).
Does this answer your question?
Hi Carl.
Thanks, but that is not what I was asking. I was asking whether it would have been an equally high performance design if you had chosen to provide both XLR and RCA sockets for each of the 5 ways of your input. Today, I believe 2 of the inputs are XLR and the other three are RCA.Hi Carl.
Aah ...
To better answer your question, of equal quality but less flexible.
I was definitely not expecting this one.
How is it less flexible?I'm not trying to question or criticise what you've done, at all. I'm trying to understand the merits of different approaches for a board I want to design.
I was definitely not expecting this one.
I'm not trying to question or criticise what you've done, at all. I'm trying to understand the merits of different approaches for a board I want to design.
For the reason that I described previously. That being if they are wired together you cannot have active and different sources plugged in at the same time. The signals from the balanced would mix with the unbalanced input. One or the other must be unplugged if there is not a switch and relays in the path.
I am sorry Carl, but I am still getting the feeling that I am unable to explain what I'm asking. I never said I want to do away with the relays and rotary switch.
Let me try in a little more detail.
Think of your current I/O board. When I select Input 1 using the switch, a certain set of relays gets activated and the preamp gets connected, let us say, to a pair of XLR sockets. My question is entirely in the context of this state -- I have chosen Input 1.
In this position of the relays and switch, would there be any problem if I also wire up a pair of RCA sockets in parallel to the XLR sockets, keeping the switch and relays as they are? I'll connect the signal connector of each RCA socket to the +ve signal pin of the corresponding XLR socket, the shield connector of each RCA to the ground pin of the corresponding XLR, and leave the -ve signal pin of the XLR sockets unused.
Will this now become an input circuit which will let me plug in balanced XLR cables if I want or unbalanced RCA cables when I want?
I will never want to connect two different sources to the two sockets at the same time. I will connect only one source to Input 1, only a different source to Input 2, and so on. But I will get the flexibility of choosing balanced vs unbalanced cables for each input. Some people who live in a totally unbalanced world will get to use all inputs as unbalanced, while others may get to use lots of their inputs as balanced if they have lots of balanced-output sources. That was my objective.
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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.
This was what I had heard in another thread. But if you see the schematic of this preamp as it appears in the Linear Audio article, it seems Doug Self has drawn the two types of inputs as simply wired up as I had described.
Is he able to do this because his balanced-to-single-ended input circuit is in any way unusual?
Aah ...
Sorry for being so thick headed. 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?
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
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.I finally managed to find Doug Self's comment about this in his Audio Power Amplifier Design Handbook:
And this is the circuit:
Looking at all this, will this schematic work?
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.
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Hello Hicoco,
I really like your design
Would it be ok for you to provide front and rear panel fpd files?