Laptop AC/DC adapter to bipolar supply for Marchand XM1 - diyAudio
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Old 17th February 2010, 09:35 PM   #1
dooper is offline dooper  Canada
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Default Laptop AC/DC adapter to bipolar supply for Marchand XM1

I sent these questions to Phil as well, but while I wait I will ask here.

The manual for the XM1 includes diagrams for using the crossover in a car. From the manual:

The XM1 can also be used with the sound system of a car. The problem here is that most cars have a single 12 volt battery as a power source, and the XM1 requires positive and negative supply voltages. Figure 9 shows a simple solution where the 12 volt supply is used directly to drive the crossover; the ground reference is derived from the battery voltage through a simple voltage divider. This circuit works well if AC coupling of the signals is allowed and the signal levels do not exceed 2.5 volt RMS (4 volts peak).Resistors R1, R2 and capacitors C2, C3 remove noise signals from the power supply to avoid alternator whine to be passed on to the output signals. R3, R4 and C4 define the ground reference for the crossover. The input signal is AC coupled with C1, and the output signals are AC coupled with C5 and C6. Using film capacitors for C5 and C6 should be considered with high performance systems.

If the power source is a 20 VDC laptop AC adapter:

1. Would the AC coupling capacitors (C1, C5, and C6) be required?
2. Would R1, R2, C2, and C3 be required?
3. What voltages would be available at P2 pins 1 and 3?

I would like to house the XM1 module and the voltage divider circuit (R3, R4, and C4) in a small project box and use the laptop AC adapter as an external power supply. Would this configuration perform well in a bass guitar amplification system with nominal 1 volt line-level inputs and outputs?

Thanks
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Old 18th February 2010, 01:10 AM   #2
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1. Yes.
2. Maybe, maybe not. Better safe than sorry.
3. +9ish volts and -9ish volts DC, assuming the power supply is actually 19V, which is very common. This sort of virtual ground isn't the most accurate in the world, but it's good enough for a lot of applications.

I assume it would work just fine with 1V line-level signals...
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Old 18th February 2010, 02:42 AM   #3
dooper is offline dooper  Canada
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Thank you for the reply Nemo.

The supply reads 20.0 VDC with no load other than my meter. It is an adapter from an IBM / Lenovo ThinkPad.

I will give this a try and report my findings. Thanks again!
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Old 18th February 2010, 07:43 PM   #4
dooper is offline dooper  Canada
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Update: I received this reply from Phil today:

Indeed, you can do without parts in 1,2.
Be sure NOT to attach ground to pin 1.
You would get +10V on pin 3, and -10V on pin 1.
Hope this helps
Phil Marchand
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Old 4th March 2010, 04:07 AM   #5
dooper is offline dooper  Canada
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Still waiting for the xover board to be delivered but the enclosure and power supply are ready.
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Old 10th March 2010, 01:40 AM   #6
dooper is offline dooper  Canada
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The board arrived today and it works great with the 20 VDC supply. Nice when a plan comes together
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