Re: Narration, part ?

On 23 Okt., 22:27, Mike Rivers <mriv...@xxxxxxxxxxx> wrote:
On Oct 23, 3:45 pm, "Igor (t4a)" <t...@xxxxxxx> wrote:

Hm. The frequency analysis with the connected mike looks different
from the resistor.

That's to be expected. With the mic you have acoustic plus electrical
noise while with the resistor instead of the mic, you have only the
electrical noise.

While the distortions from the mains frequency are
obvious I am really bothered with that noise above 2 kHz. Where might
that come from? I thought the microphone had just that noise pattern.

That's "hiss" and it's electrical, in the preamp. All preamps do that
when running near full gain. Just for comparison, this Mackie 1200F
mic preamp with A/D converter and Firewire interface gives me a noise
level of around -72 dBFS with the gain up full. It's not likely that
anything other than a much more sophisticated design would give you
more than about 3 dB less noise. When you take the gain into account,
that's pretty close to the theoretical limit.

That is what we had worked out during comparison measurements also.
Epecially when comparing different pre-amps a subjective advantage
dissappeared after the gains were equalized. There are great
differences in the low frequency region though.

The mains hum problem in my pre-amp was much less prominent during
former measurements. I have to check were that might come from. I
looks as if it comes via the microphone because when a resistor
replaces the mic is is less prominent. It could be caused by the
heating.

(same link that I posted as a reply to Arny)
quiet room* - 150 Ohms** - sc**
*RE-20
*microphone cable attached

http://download.yousendit.com/7612ABA228BA66D3

I've had better figures but this is from today. According to my
software I get for the
RE-20 -68.6 dB
150 Ohms: -74.3 dB
short circuit: -77.9 dB

Thanks again.

Best wishes,
Igor

.

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