Audacity Forum

http://www.thatcorp.com/press34.html

Koz

Very similar indeed.

From the product page:

The ICs are available in a variety of packages and pin configurations, making them pin compatible with the Analog Devices SSM2019 and SSM2017 (discontinued), and the Texas Instruments INA217 and INA163.

May I'll just get both and do a head-to-head comparison?

From the specs looks like SSM2019 has more distortion, but that might also give it a warmer sound... hard to guess which one would sound better... THAT chip is slightly more expensive, but not a big difference...

I used to work in the manufacture of semi-conductors for the MOD - they have extremely tight specifications, but that did not mean that the components were necessarily any better than lower spec. "off-the-shelf" equivalents. It just meant that the specifications were higher and in the case of MOD products it meant that the specifications were guaranteed. The specifications are so close here as to be within natural variability and the marginal differences could easily be accounted for by how the measurements are made and the degree of certainty. Having said that, there is little doubt that both of these chips (assuming that they are not identical) are high quality devices.

<<<that might also give it a warmer sound.>>>

Dream on. Semiconductor Distortion, unless specifically tailored to the purpose, always sounds terrible. Vacuum tubes have that graceful, non-linear characteristic and internationally famous overload sound. Semiconductors have crossover distortion, transient intermodulation distortion, and surgical clipping which sound like somebody poking your ears repeatedly with ice picks.

If you get far enough down into the theory books, most microphone transformers are in the circuit to electrically match the microphone to the amplifier. This latest generation of chips match the microphone without going through coils. It's an impressive feat, although I will say that making something with these chips is a challenge. In order to get the stunning noise specs, they leave out all the stuff you need to make an unconditionally stable amplifier, and at 60dB gain (1000) any electronic errors at all are immediately fatal.

Koz

HI!!!
I have a Shure SM57 and I want to connetct it to the amplifier, which configuration figure in datasheet should I use???
Single-Ended, Pseudo-Differential or True Differential???

Thank you very much!

True differential is the only configuration that will reject electrical interference on the microphone cable. Noise arrives single ended and the microphone signal arrives differential. If both the microphone and the noise are single ended, that's the end of the show -- there's no way to get rid of the noise.

If you have a very short microphone cable in an electrically quiet room, it's not going to make any difference.

Koz

True differential.
The input impedance on the two inputs should be matched as closely as possible for maximum CMR (common-mode rejection).
The SM57 is designed to be used with a low impedance load, so the overall input impedance (across the two inputs) should be somewhere around 500 to 600 Ohms.
If you are building a microphone pre-amp from scratch, it may be worth considering including switchable high/low input impedance as many condenser microphones benefit from a substantially higher load impedance (2.5 to 10 kOhm)

<<<The input impedance on the two inputs should be matched as closely as possible for maximum CMR (common-mode rejection).>>>

I don't know that I agree. Common Mode Rejection is a function of the current match between the two sides of the balanced line. Impedances are irrelivant, but they are required to match. See: unshielded copper telephone lines.

Noise is a completely different matter. There, impedances are critical, and they don't necessarily have to match. Mic-In on commercial sound desks is 1200 ohms and they're expecting a 150 ohm microphone for best performance.

Koz

Let me hit that again. Interference Rejection depends on the two sides of the balanced line to be actually balanced. The start and stop impedances don't matter, although I attended a lecture by the Jensen Transformer people who make a good case for maximum trash rejection when the destination is high impedance. No current, no signal.

There are actually companies wired like that, NBC Washington being one.

Koz