In researching the audio artifacts of spatial positioning, you'll find that sources a great distance away exhibit attenuated high frequencies in addition to the blurring of coherency typical of reverberation or short overlapping delay and a bit of low frequency distortion to induce rumble. This all makes sense, since a sound wave originating several miles away is going to travel over many folds in the surface of the earth, diffuse/reflect over objects moving and stationary, pass through variations in the air of temperature, density, suspended particles/humidity and mix with additional sound waves along the way.
These are Analog Devices 310J varactor bridge amplifiers, posed with a standard 8-DIP IC for scale. If the hand engraved four digit number is a date code, these hail from the 33rd week of 1973. Ever since laying my eyes on these I've known that I must one day integrate them into a build, exposed of course. My recent attention on the synthesizer project pulled these into the limelight, so I figured I should pull up product data and see what they are good for.
They claim a bandwidth of 2khz. The gain factor of this part starts taking a nose dive well into the subsonic, having tapered off to less than half the available gain once human hearing kicks in. It's like a mutant RIAA curve, that's hungry for woofers and human flesh.
Since these were obviously not aimed at the audio market they don't publish a frequency response graph. I realize that gain tapers to unity at 2khz, but that is not the same thing as a brick wall at 3khz, it will be interesting to hear how they sound. The generous low frequency amplification factor may work against me a bit, seeing as how these parts will be deployed in a modular synthesis environment through which direct current CV may be superimposed over signal paths at times. My initial plan is to feed the output of these into transformers to strip out the copious subsonics, It looks like the current delivery of these devices may not be enough to induce saturation of the transformer through application of DC and/or subsonics, so I might hide a small DC coupled amplifier stage within the module to open the possibility of CV driven transformer saturation.