Audio line DC offset

Status
Not open for further replies.
Jump to Latest
F

foryourdemons

Member
Joined 2010
#1
Hi, new to the forum (and dyi electronics generally, so bear with me for any stupidity).

I'm trying to build a crossover for use with a portable system.

This is the setup:
iPod line out - Crossover - Amplifier

The crossover is this one
An externally hosted image should be here but it was not working when we last tested it.

Linkwitz-Riley Electronic Crossover

and the amplifier is one of these class D amplifiers
An externally hosted image should be here but it was not working when we last tested it.

4*100 watt @ 4ohm, TK2050 D-class Audio Amplifier Board_Audio Amplifier Boards_Audio Amplifier and other Audio Boards_RF and Audio, Video Equipments_Sure Electronics' Webstore

Both the crossover and the amplifier are going to be powered by the same 12V battery. So to drive the opamps in the crossover I need one of these
An externally hosted image should be here but it was not working when we last tested it.

Project 43 - Simple DC Adapter Power Supply for example.

But if I use that circuit, the GND of the audio signal will be at +6V. Will there be a problem with the amplifier, since it is driven with GND=0V and +12V? Or does the amplifier only care about the difference between audio GND and audio SIGNAL?

/Daniel
 
#2
Very quickly... if you power both the crossover and the main amp from the same DC source then the GND line (your PSU) is at 6 volts with reference to the -VE line (which I assume is connected to the main amp and is "ground" on there.

All you have to do is AC couple the inputs and outputs of the crossover. Make the 100k input resistors 470 k and use a 0.47uf poly cap.
Depending on the input impedance of the power amps choose an appropriate value cap. An electroylitic is fine. I would (depending on the input arrangement of power amp) add a 100 k to GND to define the DC level at the output.
 
#3
Mooly said:
Very quickly... if you power both the crossover and the main amp from the same DC source then the GND line (your PSU) is at 6 volts with reference to the -VE line (which I assume is connected to the main amp and is "ground" on there.

All you have to do is AC couple the inputs and outputs of the crossover. Make the 100k input resistors 470 k and use a 0.47uf poly cap.
Depending on the input impedance of the power amps choose an appropriate value cap. An electroylitic is fine. I would (depending on the input arrangement of power amp) add a 100 k to GND to define the DC level at the output.
Click to expand...

Thank you. I googled around, and figured out why this method works. And also that it becomes a high-pass filter. Although the 100kOhm to GND I'm not really sure about yet. I'll just trust you on that.

I checked the documentation for the amplifier, which quoted the typical impedance (had to google that term too), at 22kOhm.

You chose a capacitor which gives 0.72 Hz as the cutoff frequency.
1/(2*pi*470 Kohm * 0.47 uF) - Wolfram|Alpha

So I tried something around that, with 22uF which gives a cutoff frequency off 0.33Hz
1/(2*pi*22 Kohm * 22 uF) - Wolfram|Alpha
 
Status
Not open for further replies.
Top Bottom