80hinhiding
Well-known member
- Joined
- Sep 27, 2016
- Messages
- 97
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80hinhiding said:Thanks for the suggestions though, and taking time to sketch something out.
80hinhiding said:edit: As far as I know, having a high impedance on an input, like a tube, isn't only reserved for instruments. I'm not being smart here, I'm asking the experts more than telling, of course.
Monte McGuire said:If the common mode performance of your balanced line input stage is good, you can simply plug in an unbalanced signal to the balanced input and skip the switching and summing stuff. With some balanced line inputs, the resistive imbalance that happens when you stuff a single ended signal into one side of the balanced input and ground the other side can screw up the CMRR, but this depends on how the line input circuit is designed - not all circuits will do this, and it might not matter that much either.
It's at least worth a try using a 1/4" to XLR adapter or an adapter cable.
80hinhiding said:Edit:
Here's a line receiver made from a NE5532 and external components. This circuit is described as having 40-50dB CMRR.
https://m.eet.com/media/1177907/audio_line_receiver_fig3.jpg
That dB figure seems like it'd be noisey, but is it acceptable or even pleasing contribution in sound? A mystery to me
Newmarket said:The 40-50dB CMRR figure ? - it's no different to a conventional stage (lose the inverting amp and the 10K from the non inv inout to 0V).
The accuracy comes from the tolerance of the resistors shown and the value and tolerance of the source impedances feeding it.
40 - 50dB probably representative of using 1% parts. Improve by using tighter tolerance eg 0.1% and / or trimming.
See Douglas Self - Small Signal...p509 . Note lowering of resistors around the inverting amp stage.
80hinhiding said:Is 40dB of CMRR on a line input receiver acceptably low in realistic application, or should I be aiming for much lower? I was surprised to see a TL071 circuit here: http://sound.whsites.net/project51.htm that was described as having 40dB CMRR unless trimmed with a variable resistor. Going from 40dB to 80dB.. he also used an NE5532. I see SSL uses two NE5534 chips on line input.
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