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moshik
Copper Member
Israel
13 Posts |
 Posted - 04/16/2006 : 23:11:28
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Hi there,
I have few Boss pedals that when I power them with external PS the led is light up in a low light and when I power it with battery, the led light up in strong light. (The PS is 9v)
I open one of those effects (LM-2) and found that to the external PS ground (GND) a series resistor + diode are connected to the battery GND (which is the effect GND).
This cause a voltage drop of 0.6v (on the diode) + 10mA* 220 Ohm (the series resistor)=2.8v
Now if the external PS is 9v to the effect remains only 9-2.8=6.2v
by shorting the resistor there is only 0.6v drop and the effect works fine.
Can someone explain the logic behind this design (yes, to protect from reverse external voltage, but what about the drop voltage)?
And how come on other effects this mechanism is working?
Thanks |
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stinkfoot
Silver Member
Sweden
181 Posts |
Posted - 04/16/2006 : 23:20:14
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Some of the older Boss pedals were designed to work with an unregulated 12vDC supply (known as the ACA adapter), and the diode+resistor from adapter jack negative to ground helped bring the voltage down to the 9-ish volts the circuit wants to see. In 1997 Boss had a re-think, and the remaining ACA designs (SD-1, DS-1, GE-7 and a couple more) were modified to work with a regulated 9vDC supply, and at the same time the unregulated ACA adapter was redesigned to 9vDC.
The full story can be found [url=http://www.stinkfoot.se/andreas/diy/articles/bossadapt.htm]here[/url], btw.
/Andreas |
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moshik
Copper Member
Israel
13 Posts |
Posted - 04/17/2006 : 08:48:32
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Thanks,
This is explain the difference between the strength of the led on the different pedals.
I looked at my pedals and indead see on the old one that they need an ACA power aduptor, and on the new ones they need a PSA.
Is there a published cuircuit that I can modified the old ones to the PSA version? |
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lightburst
Silver Member
Germany
158 Posts |
Posted - 04/17/2006 : 09:45:57
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Just short out the diode and the resistor that�s all. I did this mod with all my ACA dedicated pedals.
I just desoldered the wire that comes from the dc input (-) and goes to the diode/resistor pair and connected it with the one that comes from that pair and goes to the input jack direct on the pcb. So I don�t need to replace the diode/resistor with jumpers.
And the mod can easy rewired to original specs in case of selling that pedal. |
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Topic |
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Technical question
