Neumann too hot for AKAI?

[jonathan2008]

Ever the sucker for a silly name, I bought the AKAI EIEIO - the Pro version - and tried it out on a friend who came around with acoustic guitar and some songs. I put a Rode NT4 (stereo mic) into two of the inputs and my trusty Neumann TLM103 into another. The Rode was fine but the Neumann gave a whine, clearly audible in any silences, at around 2.5kHz. It no longer whines but now gives a hum like a bad earth.

I have swapped inputs, cables and cleaned contacts to no avail. The Neumann is fine going into my desk, into a Zoom H4 and into an old Roland 1680. I've tried to replicate the hum with the Rode and with an SE2200a but they both work fine with the AKAI. A technician friend thinks the Neumann signal is too hot for the EIE Pro. Is he right? Is there anything I can do to fix this?

[Jeraldo]

Try measuring the Akai's phantom power voltage with the 3 ( Rode X2) mic's connected, and making sure the Rode is using phantom power from the Akai. Perhaps you could remove the battery from the Rode mic if one is installed, just to reduce variables.

[jonathan2008]

Thanks. The phantom power measures 51.4v at the unit and 51.v3 at the mic (inputs 1&2) and 50.4v at both the unit and the mic (inputs 3&4). Plugging in the Rode had no effect on my measurements. I've previously been using the TLM103 with an Allen&Heath desk (48.6v at the unit) and a Roland VS1680 (45.1) at the unit. Might the voltage from the AKAI be too high for the mic?

[Jeraldo]

Assuming you made the measurements with mic's plugged in, the voltage is within spec.

The symptoms don't seem to be consistent with a mic that is too hot for an input.

Perhaps someone will be by with a good answer. Until then, I think it's a matter of careful elimination of variables to determine the cause. But I don't think the output level of the mic is the problem.

[jonathan2008]

Thank you, Jeraldo.

(I should also have mentioned the current - 6.86mA at the mic.) But is it possible to measure the voltage with the mic plugged in? I unplugged the mic in order to get to the female XLR plug with my multimeter.

As you say, it doesn't appear to be a voltage problem and the mic checks out fine elsewhere. I shall ask Neumann too, and post their response. Meanwhile I remain open suggestions from the room.

[Hugh Robjohns]

The Rode was fine but the Neumann gave a whine, clearly audible in any silences, at around 2.5kHz. It no longer whines but now gives a hum like a bad earth.

Whines and whistles are usually caused by some form on interference getting into the mic through bad cables etc, or by noise from a DC-DC converter getting into the power rails.

A technician friend thinks the Neumann signal is too hot for the EIE Pro.

Not likely -- that would cause distortion, not whistles. The TLM103 is more sensitive than the Rode, but only by 5dB. It also takes almost half the phantom current, so I would have expected the Rode to cause DC-DC problems rather than the Neumann!

hugh

[Hugh Robjohns]

The phantom power measures 51.4v at the unit and 51.v3 at the mic (inputs 1&2) and 50.4v at both the unit and the mic (inputs 3&4).

This is slightly high but well within tolerances. There shouldn't be able voltage drop across a short-ish cable -- if there is it suggests the cable has significant resitance which isn't a good thing!

The phantom voltage at thge mic will be lower when a load (mic) is connected because the current flow through the output resistors with generate a voltage loss. It should be between about 32 and 38V for the Rode and Neumann, respectively.

Might the voltage from the AKAI be too high for the mic?

No, the phantom spec is 48 +/-4V -- meaning 44-52V is the tolerance range and your system is easily within that.

Your current measurement (presumably shorting between pins 2/3 and 1) of 7mA indicates a healthy supply too.

Hugh

[jonathan2008]

Thanks, Hugh.

It's reassuring to know that both items appear to be functioning properly. But I'm left with two good pieces of kit that work fine with everything else but not with each other.

The only thing I can add is that when I scratch the mic grill with my fingernails I get a clean sound with the mixer etc, but a distorted sound with the AKAI EIE.

[jonathan2008]

I thought I'd better finish the story. After conversations with Neumann, AKAI and Digital Village (who supplied the EIEPro), much scratching of heads, testing of voltages and an XLR cable upgrade to one with Neutrik plugs I still couldn't use the mic with the interface.

But yesterday Digital Village replaced the unit and today microphone and interface are working together very happily. So it was probably a fault with the AKAI all along. I'd still recommend the EIEPro though and am very pleased to report a happy ending.

[Jeraldo]

Thanks very much for posting what happened! I had wondered about this one. Glad you have it sorted. It would be interesting to know exactly what the fault was, but I doubt there's a chance of that.