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Incorrect adapter bought, can I modify it?


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#1 Mustey

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Posted 18 September 2017 - 10:59 AM

I've recently bought a Marantz CP430. It is currently running on 3x1.5 batteries.
The manual says the adapter is 4.5v with the + on the outside and - on inside.

I bought an adapter as recommended here but it is not working. 
The plug fits well but the adapter is 5v and reverse polarity.

I can rewire the polarity but wouldn't 5v be too much for the 4.5v that the Marantz expects?

Thanks.



#2 caution

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Posted 18 September 2017 - 11:41 AM

A 5V supply will work just fine. Fresh alkaline batteries are about 1.65V, so three of those would be 4.95V anyway.



#3 Superduper

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Posted 18 September 2017 - 12:03 PM

I bought an adapter as recommended here but it is not working
The plug fits well but the adapter is 5v and reverse polarity.

 

So, are you saying that you've already bought, connected, and tried the adapter in the reverse polarity configuration, and that it did not power up?



#4 Mustey

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Posted 19 September 2017 - 02:58 AM

The polarity is reverse to what the Marantz expects and I need to reverse the reverse in order for it to be not reverse :)
I hope it's a simple wire, not those bundles of thin wire, coated with lacquer (like in headphones).
I think I can manage that.

I am more worried about the voltage



#5 Superduper

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Posted 19 September 2017 - 12:46 PM

Like Caution says, it's most likely OK.  Those wall wart adapters are not regulated anyway and I would not be the least bit surprised if you check the voltage with a meter and find that it is actually something more....  like 6 or even 7 volts!  That's because with no load, voltage will be high.  With a load, voltage will drop.  However, if you are concerned, you can install a diode in series and it will drop the voltage probably right around where you need it.  That is due to the nature of the diode which typically has a forward voltage drop of about 0.6 volts.  Shottkey diodes have slightly lower voltage drops ranging from 0.15v to 0.46v.  Using a standard diode of sufficient amp carrying capacity, your 5v adapter should theoretically then output 4.4v to the device.  However, once again, since these adapters are non regulated, pin pointing down the exact voltage to your device will be difficult.

 

Here is another bit for you to chew on....  most devices use a power adapter specifically designed for that particular device based on it's expected current consumption.  Since they are almost always non-regulated on older devices, the voltage rating is "average" based on the expected current consumption of the device in normal use.  Like mentioned above, once there is a load, the voltage will sag.  If you get a weaker PS adapter, then the voltage may sag MORE than expected and would result in a lower than normal "average" voltage from that adapter and inversely, if you get a larger very robust PS adapter that can output gobs of current, your marantz might not draw enough current to cause the voltage to sag to the "average" value and therefore, it will get a steady stream of higher than normal voltage.  How can you check?  Simple...  just monitor voltage with adapter connected and device operating.

 

Now, with all that being said...  if you are concerned with your Marantz and really don't wish to damage it....  you can simply build your own power adapter using batteries.  Yep, get a standard 3-D cell battery holder, wire up the output pigtails to the correct plug and if your marantz uses 3 AA batteries internally, you'll find that with external D cells, you will get at least 5 times the life you did with the AA batteries.  Plus you can be assured that you have provided the proper voltage to your device.  Although D cells doesn't last forever like a plug in adapter would, on a small portable like that marantz, it will last an obscenely long time.  



#6 Mustey

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Posted 20 September 2017 - 02:59 AM

Wow thanks! I thought about a diode or resistor but wasn't sure I ain't just hillbilly engineering it :)
Anyway, I have a 4.5 adapter of quite good quality coming over and I'll just wire in the existing plug.



#7 Superduper

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Posted 20 September 2017 - 11:46 AM

The voltage drop of a diode is a very specific amount & only affects voltage, not current.

If you used a resistor, it limits current. Although by association (ohms law), it can also drop voltage, the amount varies with the amount of current consumed. Therefore, it's only practical to use in a circuit with static current demands (like a lightbulb) and not a dynamic circuit like an audio amplifier where current demands can drift from very low to very high.

#8 Mustey

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Posted 24 September 2017 - 05:37 AM

yeah I know this :P