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In Reply to: RE: rca to xlr posted by backendloaded on September 10, 2014 at 05:44:43
Thank you all for your help! I need to clarify. I am building a tube phono amplifier. I would like to make it XLR out to connect to my pre amp. From what I have read I only need to use a female XLR connector and hook it with pin 1 chassis ground, pin 2 +, pin 3 -? I also have the chassis grounded to house and circuit. Would this be the best way? Also I have a dumb question that will help me tie this all together. Is a balanced signal just a single ended signal with the chassis grounded? I am confused as I thought that a balanced signal was different. Thanks you.
Follow Ups:
You have several choices:1) you could use some sort of transformer to do the job. This is really not a bad idea. There are a number of ways to do this, for example you could have a transformer made that can be the plate load for the final stage of gain (which means that the transformer has to be designed to have the DC current go through it).
2) Or you could have the conventional coupling cap, which then drives the transformer.
In either of these cases the secondary of the transformer is tied to pins 2 and 3 of the XLR; pin 1 is circuit ground and not connected to the transformer at all (unless there is a center tap, but if you were to use that the Common Mode Rejection Ratio would suffer, so don't do it).
3) you could create some sort of phase splitter circuit at the output of the preamp, and use the outputs of the phase splitter to drive pins 2 and 3.
To do this right you will have to do one of the scenarios above. The phase splitter is cheaper, and if done right will perform very well as long as you don't load the output too low. The transformers have the advantage of circuit simplicity and often have the ability to driver lower impedances that are common when you run balanced lines (for that you will need more gain from the phono as voltage will be lost during the step-down of the transformer).
Edits: 09/10/14
I have done more research and things are making sense. I understand the differential signal and how it works. I am always in favor of less manipulation of a signal. Would using a transformer or op amp to convert the signal degrade the sound? Wiring as I described earlier seems like a more simple solution.
The purpose of a balanced connection is to reject hum (usually in long runs).
If you don't have a hum problem (and you shouldn't between the output of a phono pre and the input of a line stage) then un-balancing one balanced input on your line stage should work just fine.
This is how you do that, connect the output of single ended phono preamp stage to pin 2, circuit ground to pin 3 and pin 1. Done!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I'd go with the transformer before an opamp, but that's me- I avoid semiconductors! Why have a solid state artifact smeared all over your vacuum-tube efforts? :)
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