V2 filter I/V board up and running

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Richard DudleyRichard Dudley 06/11/2018 at 10:590 Comments

Since the new DAC board reduced the number of DAC chips to two, a new filter-I/V board was called for which was able to run on half the signal current. Here it is - there are a few significant changes :

  1. Filter inductors are increased in value as now the filter has a higher characteristic impedance (about 50ohms)
  2. Capacitors which were X7R have been replaced by NP0 - increasing the filter impedance has made this practical. The main advantage of using NP0s is their closer tolerance and much better stability, meaning the filter build no longer needs a long time fiddling to get the right cap values.
  3. This board runs on 9V which means it can now deliver the industry standard 2VRMS DAC output signal, if desired. Although the supply voltage has gone up 50%, the current draw has gone down so this board consumes less power.
  4. The I/V stage is a bit more complex but the new circuit has better compatibility with alternative DAC chips. I plan to try this with the TDA1387 but powered from 3V (rather than 6V as at present) which wasn't practical with the first generation board.
  5. It sounds a little bit better too - there's slightly more detachment of the images from the speakers.
  6. The BOM cost has gone up (NP0s being dearer than X7Rs) but OTOH the build time has gone down markedly.