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Zaxcom Deva II crazy phantom power


Christian Shaw
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Having worked out how to extract the Deva II files from the DVD-RAM using a modern PC, and having had the phantom power supply on mic input 4 fixed, I now have the four track up and running. Tests on the phantom power voltage reveal a strange issue that I'm hoping someone can chime in on. With the 12v external supply connected, we have around 55v dc phantom power at the inputs. This is obviously slightly over spec for most mics. I then tested with a full li-ion NP1 and was disturbed to get a reading of 72v at the inputs! This drops off progressively as the battery drains. Testing with a variable PSU seems to indicate that 10.5 to 11v give closest to 48v at the inputs. I have tested the unit with inexpensive mics which seem to have taken no evident harm; I wouldn't want to be plugging in anything by Schoeps or Sennheiser though! With phantom power needing to be constant, I'm guessing there must be an issue with the power supply in the unit that the tech didn't address (I've gone back to him about this), but was wondering if anyone here might be able to offer some insight. If it is another fault, it may be a case of just using the unit with a linear PSU of 10.5-11v (if I can find one), because there is no point sinking any extra cash in I feel. Could it also be that the unit was designed to work with NiCad instead of li-ion? 

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35 minutes ago, jpb2 said:

You have to test phantom under load. (mic pluged in)

In this case, no.

The 48 Volts at the mic (under load) is not regulated in the usual sense since it configured as a supply with a high internal resistance (6.8k). What is regulated (spec'd) is the no load voltage, i.e., the 48 Volts. Under load, the voltage can fall to many possible values.Since the 48 Volt supply has a 6.8k resistor in each leg, a 1 mA load on each leg would give 41.2 Volts, 2 mA would give 34.4 Volts, a 7 mA load would give 0 Volts. And yes, there are some high current mics that will pull it down to 12 Volts or so. Measuring the no load voltage is the correct measurement.

Best Regards,

Larry Fisher

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23 minutes ago, LarryF said:

In this case, no.

The 48 Volts at the mic (under load) is not regulated in the usual sense since it configured as a supply with a high internal resistance (6.8k). What is regulated (spec'd) is the no load voltage, i.e., the 48 Volts. Under load, the voltage can fall to many possible values.Since the 48 Volt supply has a 6.8k resistor in each leg, a 1 mA load on each leg would give 41.2 Volts, 2 mA would give 34.4 Volts, a 7 mA load would give 0 Volts. And yes, there are some high current mics that will pull it down to 12 Volts or so. Measuring the no load voltage is the correct measurement.

Best Regards,

Larry Fisher

I thought this was the case. Certainly I will not be using the li-ion NP1s in the unit. The 12v NiMH should be better. I did notice the current output was a relatively low 5.2mA on each input rather than around 13.5mA for the MixPre. Perhaps this is to balance the slightly higher voltage?

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The voltage should never go to 72 Volts and should have little variance with the battery voltage. I assume something is wrong with that particular unit and that it is not a design fault.

Best Regards,

Larry Fisher

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When The Deva II was new 1997 there were no Li batteries. So this condition was not anticipated. All current Zaxcom recorders are very exactly regulated no matter the voltage of the battery or external power source.

 

Glenn

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37 minutes ago, glenn said:

When The Deva II was new 1997 there were no Li batteries. So this condition was not anticipated. All current Zaxcom recorders are very exactly regulated no matter the voltage of the battery or external power source.

 

Glenn

Thanks for your response Glenn. So can I assume this is normal behaviour for the unit? I'll stick to 12v NiMH or NiCad batteries in that case and stop worrying!

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6 hours ago, glenn said:

When The Deva II was new 1997 there were no Li batteries. So this condition was not anticipated. All current Zaxcom recorders are very exactly regulated no matter the voltage of the battery or external power source.

 


A DEVA IV would be fine?

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