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DIY line level schematic... noob here
DIY line level schematic... noob here
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Old 3rd February 2006, 06:44 AM   #1
benhart007 is offline benhart007  United States
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Join Date: Feb 2006
Location: Ole Miss
Default DIY line level schematic... noob here

Hey all, new guy here. First off I apologize if Im posting this in the wrong forums...never been here before. Anyway I have been searching for a simple line level converter schematic for the past few days.. possibly with a LP x-over as this converter will only be applied to a sub amp. I've got a decent amount of electronics skills, but when it comes to design I just draw a blank. I have a good old school electronics tech that I work with if a bit of design does come into play. But anyway if anyones got anything that I might be able to use please reply.

Thanks!!!
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Old 3rd February 2006, 07:37 PM   #2
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
You'll have to determine what type of signal source you have. Some are biased to 1/2 B+. Others have no DC bias. A transformer type line output converter can deal with either. If you are going to use some sort of resistor divider to cut the voltage, you may have a significant turn on/off pop depending on the muting circuit of your amplifier.

A transformer type LOC will also help break ground loops.

Most 'hi-power' LOCs have transformers. I don't think I've seen one wthout a transformer recently. If it has 6 input wires (2 for each channel and 2 for shield ground) it's a transformer type isolator.

A typical isolator has a 20 ohm resistor across the speaker level inputs (parallel to the input of the transformer). The output of the transformer goes to the RCA output jacks. The ground wires are connected to the RCA shields. On some amplifiers the ground wires must be grounded. For others, they make no difference.
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Old 4th February 2006, 08:08 AM   #3
benhart007 is offline benhart007  United States
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Join Date: Feb 2006
Location: Ole Miss
Thanks for the info...how would I measure the outputs to determine if their bias? Should I just go buy a LOC or are they easy enough for a slightly skilled solderer?
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Old 4th February 2006, 05:33 PM   #4
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
You can use a multimeter set to DC volts to see if there is DC biasing. Black lead on chassis ground. Red lead to each of the signal leads. Although the volume level shouldn't make a difference, set it to zero.

I would buy one instead of making one. They're inexpensive and readily available.
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