hifi preamp


my plan is to use a volumio powered board (am not decided yet) as a controller and digital music streamer for a input selector/mastervolume controlling preamp to feed my dsp amps inside of my speakers.

Inputs would be a phono preamp and two aux devices.

I see two options:
First is to use a simple board like a raspberry b+ with dac as just another analogue source into an all analogue signal channel and its GPIO pins for controlling digital potentiometers (master volume) and some relays for changing channels.

Second is to use a more powerfull board and feed it with digitized analogue sources and use volumios software volume control as mastervolume and have spdif outputs, which would be better for connecting my amps.
I have an TA ADC module with up to 24bit/96kHz i2s output already working well with an minidsp ministreamer and my pc. The ministreamers chip seems to be working well as an ALSA device:
alsa-project.org/main/index. … Vendor-ESI
Tenor TE7022L is the chip
Is there a software mixer in voumio where i could enable/disable the ministreamers input and stream it live to spdif output via ministreamer again with software controlled volume?

i hope my question is clear, since i have no board where i can install volumio and test this myself. I need to decide between boards first, either a raspberry b+ or some cubieboard :slight_smile:


Personally I don’t see the attraction of having an analog source, digitizing it, then changing the volume in the digital domain and converting it to analog again. You would get much better fidelity if you kept your analog signal analog, and changed your volume in the preamp stage.

Not necessarily, since the analog amplification is often done with a circuit like this one:

and that opamp has itself a more or less constant noise, therefore, just like changing volume in digitial, also the analog way has decreasing s/n ratio for decreasing volume.

The analog way can be better, but only if the circuit is very well done and anyway as soon as somewhere in the circuit you find a not-so-perfect component, there you go again.

Summary: if you are very lucky, changing volume in analog is better, otherwise equivalent. But is the small difference worth the trouble?

Modern op-amp ICs (even the old TL072 or NE5532) are so vanishingly quiet that their noise floor is well below the noise level of DACs. The best option (in this instance) is to build a simple preamplifier in the analogue domain, treating the output of the DAC as just another source. If you want to get really pedantic about your routing, the best option is to use hermetically-sealed gold-contact relays, operated from a separate supply (so that no switching noise can get on to the audio paths). If anyone needs circuit schematics or layouts, ask here and I’ll draw something up. :ugeek: