No comment, except that Dan is of course right saying that there should be a
100 ohm resistor, not 200. The mail should not have been sent, I was working
on it.
200 Ohms between 2 and 3 is the standard floating way.
The idea with a resistor loading the phantom power is probably right, as
some power devices give ripple when used.
Klas.
At 13:03 2004-02-16 +0100, you wrote:
>> DAN
>> > >The way to listen to -just- preamp noise is to solder a 200-ohm
>> >>resistor across pins 2 and 3 of an xlr, and plug that in as a "dummy
>> >>mic." You can make valid comparisons of the noise of different
>> > >preamps this way, assuming a method for setting them at the same gain.
>>
>> KLAS
>> >Hmmmm. 2 * 200 Ohms in series with a condensor from pins 2 and 3 to
>> ground!
>>
>> Assuming big enough capacitors, that network would simulate a 400-ohm
>> source, rising to infinity at DC, center tapped, not floating.
>
>DAN
>> If the mic's output is transformer coupled, the simple 2-to-3
>> resistor will be a closer simulation, I think, besides being simpler
>> and an industry-standard way of testing. One might argue for a lower
>> value like 150 ohms or even 50, or a parallel capacitor-resistor to
>> lower the impedance at low frequencies. But I'd rather keep it
>> simple. Big value caps that can take 48V aren't going to fit in an
>> XLR shell, either.
>>
>> I only have schematics of a couple of mikes; I see the Sennheiser K-6
>> preamp is transformer coupled. The Schoeps preamp is direct-coupled,
>> no coupling caps. Explains why their low-low frequency response is so
>> good!
>>
>> I see that your network might be a better simulation of
>> capacitor-coupled condensor mikes, but isn't the 400-ohm impedance
>> too high? As a mic manufacturer, you're probably more familiar with
>> mic electronics than I am.
>
>
>In phantom-powered setups, I would add two additional 22 kohm resistors
>between pin 2 / pin 1 and pin 3 / pin 1. These additional resistors would
emulate
>a phantom power current of about 3 mA. This may reveal addional noise caused
>by the phantom power circuit (that circuit may behave differently under
>load).
>
>Regards,
>Raimund Specht
>
>--
>GMX ProMail (250 MB Mailbox, 50 FreeSMS, Virenschutz, 2,99 EUR/Monat...)
>jetzt 3 Monate GRATIS + 3x DER SPIEGEL +++ http://www.gmx.net/derspiegel +++
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
________________________________________________________________________
________________________________________________________________________
|