bgravato wrote:I see they use +18V/-18V for voltage supply... is this the standard supply voltage for this kind of audio amps?
"Standard"? What's that?
There is no standard voltage for this kind of chip - the "standard" is whatever it says on the data sheet.
A typical application for this chip might be for the inputs on a pro-level mixing desk. For such applications it does not matter too much what the specification is as the manufacturer can easily provide whatever voltage is required. Solid state devices will usually run well (though a little below optimum performance) at lower supply voltages - details are usually available in the data sheets. Care needs to be taken with some active filters though as filter frequencies may vary depending on the supply voltage.
A line level signal is in the order of 1volt and amplifiers typically need to have a higher supply voltage than the maximum output swing. Amplifiers will often become non-linear as they approach the rail voltages, so some degree of overhead is usually required. This chip, with +/- 18v, provides
a lot of overhead.
There are specialised chips designed for battery powered devices that use much lower supply voltages and low operating current. Surprisingly some are even able to produce output voltage swings that are greater than the supply voltage
Where low voltage/current requirements are not an issue, higher voltage/current devices can be used with the design focus firmly on sonic performance.
I think that the SSM2019 has been designed as an improved, but otherwise direct replacement for an older device (SSM2017?) This type of design practice is very common and has obvious advantages for manufacturers.
48v is a standard of sorts for phantom power. Just about everyone agrees that phantom power is 48v, but in practice you will find that the actual real-life voltage can vary widely. The specification of 48v should not really be exceeded as there is no guarantee that a higher voltage will not cause expensive damage to equipment. Many phantom powered devices will work happily down to 12v or even lower (the AKG C1000S may be run directly from a PP3 9v battery, but can also be used with a full 48v phantom supply). Again there is no guarantee that equipment will work at low voltage, and most mixing desks provide phantom somewhere in the range of 40-48v depending on design and load.
bgravato wrote:this sounds like a lot of different voltages in the same circuit
Even more with a valve condenser microphone - high and low voltage for the valve, another fairly high voltage for the condenser polarisation,in addition to whatever voltages are required by the solid state electronics. Valve mics will typically use a dedicated PSU with a multi-pin connector rather than running everything from 48v phantom (another reason why they are better suited to the studio than the stage).
DC regulators with floating outputs can be very useful for deriving multiple voltages from a single supply.
) Nonetheless I think I might order the components soon and start working on it before the enthusiasm starts to fade away...