preamp noise floor specs question.

[Bob Olhsson]

I've never found a whole lot of correlation between a mike pre-amp's noise spec and its subjective noise level. The most important spec in my experience has been overall dynamic range which naturally is rarely advertised. Part of the story is how the pre-amp loads a particular mike. Transformers also can make a preamp that measures worse sound quieter because of where the noise spectrum lies.

I wish it were easy, you really need to listen and compare using the mikes and signal path you intend to use.

[littledoodler]

Thanks Bob.

that's pretty much what i thought.
gotta use your ears.

Heard the Chandler has an amazing dynamic range.

[Jim Williams]

Originally posted by littledoodler
Helllo,
i have a question regarding noise specs on preamps.

the chandler TG2 has a noise floor of -85dbu, while the Great River mp2nv has a noise floor of -126.
just wondering what these numbers mean and if they would make a difference?

also, i noticed that both these preamps have a lot of gain +70 db. does this make the great river much quieter than the chandler at +70 db or am i missing something here?

One is listing simple signal to noise ratio or s/n, the other is equivalent input noise or ein. S/n is measured at any gain setting, ein is a sum of the maximum gain + the s/n at maximum gain.

Most well designed transformer input mic pre's get an ein of about -127 db. Non-transformer pre's can best that typically getting to -129 with a 150 ohm source. Really well designed pre's are even quieter than that as long as the source impedance is lower. Theoretical limits or self noise of a 150 ohm resistor is about -130 db. Some pre's measure -132 at 50 ohms impedance. What's missing from the ein spec is real world noise at lower gains, some pre's are lower in noise at lower gains, getting equal in noise only at full tilt.

Jim Williams
Audio Upgrades

[littledoodler]

thanks jim

[Geoff_T]

Originally posted by littledoodler
Helllo,
i have a question regarding noise specs on preamps.

the chandler TG2 has a noise floor of -85dbu, while the Great River mp2nv has a noise floor of -126.
just wondering what these numbers mean and if they would make a difference?

also, i noticed that both these preamps have a lot of gain +70 db. does this make the great river much quieter than the chandler at +70 db or am i missing something here?

Hi

Unfortunately, IMHO, I don't think that some of the Neve cloners got around to swotting up on how Neve actually tested their units and measured noise.

For a start, a dB value for noise is pretty useless unless you reveal all the other aspects of the measurement. Like, what does -85dBu mean? Is this the noise when the unit is at 0dB gain or 70dB gain?

What filters were used? What termination was used on the input?

Neve measured noise by terminating the input with a 200 ohm resistor. The absolute electrons wobbling down a piece of wire type noise floor of a 200 ohm source at 20 degrees is -129dBu so this is minimum noise you could ever achieve.

They set the module to 80dB gain and measure the noise on the output with a 20Hz to 20KHz filter. It was generally better than -45dBu.

You add the measured noise to the gain of the amplifier and get a figure of -125dB and this is the EIN (Estimated Input Noise) which should strive to get near to the 129 figure.

In reality, the Neve modules were quieter than -45dB so it would appear that Dan (who obviously knows how to measure noise) makes modules that match (new) original Neve modules for quietness.

If the amplifier could only make 70dB gain, the noise would be around 10dB better (say -55dB) so adding this to the 70dB gain still gets us the -125dB EIN figure.

Until all mic pre manufacturers apply the same kind of measuring techniques there's little to be learned from the numbers.

What you need look out for are the termination value, module gain, and filter slopes and then you can work out the EIN for yourself.

[littledoodler]

thanks, Geoff!

yep that pretty much sets it straight.
numbers are useless to me

[Tim Farrant]

Geoff, slight error there, EIN = Equivalent Input Noise

Tim.

[Geoff_T]

Originally posted by The Buzz
Geoff, slight error there, EIN = Equivalent Input Noise

Tim.

Hi Tim

Gosh... did I really write "Estimated"?

Oh my gosh... senility is creeping up on me

What was my name again?