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ELTIM Volume modules
A preamplifier is basically a bunch of connectors, volume control and sometimes a buffercircuit. Mostly this is done by a lot of electronics where the sound depends on the volume level (different impedances, etc.). The volume control is the basic part of it, which can be done in many ways. In most cases a €2,00 (logarithmic with bad L/R symmetry) potentiometer is used. In some cases the best available blue ALPS potmeter is used. All have an attenuation range from around -60 / 0dB. There are also "digital" versions, some with relais, some with an IC ladder network. All of them are made suitable to obtain a reasonable L/R symmetrical and more or less simulated logarithmic performance. Mostly the audio signal has to "travel" a long way over the PCB, influencing the sound quality.
We provide volume control circuits with built in Voltage Controlled Amplifier (VCA) IC's from the in high-performance analog IC circuits specialised THAT Corp. You can find their products in the very most expensive equipment. Their specialised VCA IC's show an exceptional wide control range and with way lower (range and balance) tolerance than a regular potentiometer can do. They are current driven IC's and not just some modified opamp circuits and simply are the best volume control devices available!
The audio signal always "sees" the same electronics, so unlike as with potentiometers a constant impedance > no difference in sound. We made our modules in a way that their attenuation/gain can be set over an extremely wide range by a LINEAR 0 - 4,8Vdc voltage (f.e. via a LINEAR potentiometer ). The IC itself is transferring from linear to exponential range. You could mount an SPI/I2C controlled dual DAC IC (not provided), resulting in a digital control in 4096/1024/256 steps, depending the IC type.
The VCA is inverting the signal, which is corrected by a socket mounted opamp lilke NE5532 or OPA2134. There is space to mount the BURSON hybrid versions. As shown below in the picture there is space to mount significant sized input capacitors. Instead of mounting those, headers can be placed, which connect to a same sized capacitor module, fitting a pair of about any serious and large High-End capacitors.
By connecting a cheap 200mV DVM display module (or uP system), the attn/gain can be read within 0,1dB as well from -90,0dB to +12,0dB.
Our volume control "feels" way more pleasant than common ones. Regular ones give signal right away from turning from left to right; ours do too, but from -90 instead of -60dB. Unlike many similar devices 0dB is not around 12.00 o'clock position already, but around 3.00. While turning more right, others circuits start to distort, ours even gains the signal up to 12db actually (could be +30dB after modification). With a centre positioned 20 turn trimmer you could adjust the L/R balance a bit.
Most versions are available with IC's which only differ in distortion level (A/B/C types) which is laser trimmed to a mimimum possible at the factory. The VCA-2181 versions can even be trimmed to a lower, record breaking distortion by use of suitable test equipment.
All boards listed below are pin and size compatible and are all byuilt in an independent two channel design.
VCA-2162, cost effective version VCA-2180 high-end quality versions VCA2181 Reference quality versions
These modules work "stand-alone" but can also be mounted on our Preamp modules. While doing so, these preamp modules change from passive to active preamps where the signal paths are shortest possible.