LM48100 - Connection of imputs?

jashua · 24th October 2012, 02:49 PM

Hi Everybody,

i wann use LM48100 in my design. But i am not sure with connection of imputs.

May I connect a operational amplifier with differential Output direkt to IN1 and IN2. (via 100nF). (my schematic in Attach).

When I then connect the Speaker direkt to the Output of LM48100 (between Out1 and Out2), do I get then a right sound from speaker?

LM48100 can have following settings:
IN1 - On; IN2 - Off
IN1 - Off; IN2 - On
IN1 - On; IN2 - On

so I would try both inputs getting "on" with differential signal on inputs.

Will it play?

macboy · 24th October 2012, 03:27 PM

No, you can't do this.
The LM48100 is designed for single-ended inputs. It can mix IN1 and IN2, but since you are sending a reverse-polarity signal to IN2, it will cancel IN1, and you will get no sound. Why do you want to do this? Your DAC output is single-ended in the first place.

jashua · 29th October 2012, 11:45 AM

thank you for your answer,

I thought that the inputs must be differential.

so I connect only one Input direkt with DAC Output of my CPU and in Settings i choose only one Input, right?

i try it and i let you know.

R.

AndrewT · 29th October 2012, 07:58 PM

you can convert the opamp to operate as a differential, or balanced input, to an unbalanced or single ended output.
These are shown in most of the balanced papers. See Jung and Self and Whitlock.

macboy · 30th October 2012, 04:15 PM

[QUOTE=AndrewT;3220055]you can convert the opamp to operate as a differential, or balanced input, to an unbalanced or single ended output.
[QUOTE]
Which opamp?
LM48100 is not an opamp, it has no inverting input.

jashua · 31st October 2012, 02:52 PM

hi guys,

thank you for your answers.

I connected my DAC Output direct with Input from LM48100 and it works pretty fine.

I had another Problem, that the communication with LM48100 is not standard I2C (Start, slave address, command, data, stop) but only (start, slave address, registr, stop).

so, thank you again for your support.

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24th October 2012, 03:27 PM	#2
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	No, you can't do this. The LM48100 is designed for single-ended inputs. It can mix IN1 and IN2, but since you are sending a reverse-polarity signal to IN2, it will cancel IN1, and you will get no sound. Why do you want to do this? Your DAC output is single-ended in the first place.

29th October 2012, 11:45 AM	#3
jashua diyAudio Member Join Date: Jun 2011	thank you for your answer, I thought that the inputs must be differential. so I connect only one Input direkt with DAC Output of my CPU and in Settings i choose only one Input, right? i try it and i let you know. R.

29th October 2012, 07:58 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	you can convert the opamp to operate as a differential, or balanced input, to an unbalanced or single ended output. These are shown in most of the balanced papers. See Jung and Self and Whitlock.

30th October 2012, 04:15 PM	#5
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	[QUOTE=AndrewT;3220055]you can convert the opamp to operate as a differential, or balanced input, to an unbalanced or single ended output. [QUOTE] Which opamp? LM48100 is not an opamp, it has no inverting input.

31st October 2012, 02:52 PM	#6
jashua diyAudio Member Join Date: Jun 2011	hi guys, thank you for your answers. I connected my DAC Output direct with Input from LM48100 and it works pretty fine. I had another Problem, that the communication with LM48100 is not standard I2C (Start, slave address, command, data, stop) but only (start, slave address, registr, stop). so, thank you again for your support.