Modding phase 2
My last attempt to post got eaten by my PC, so here's another try.
I've had a closer look at the PSU in the Superdac and it uses two voltage doublers to create +/-18V from the single 9V input (and a seperate half-wave rec to produce the raw feed for the +5V).
The input from the transformer is AC coupled into the doubler, via the two 470u caps next to the DC input socket.
The output caps, which are the input caps for the +/-15V analouge reg's are also 470u, and are the two caps directly to the left of each reg (looking from the front of the DAC).
Raising the value of these (I'm curently using 1000u Panasonics, since they're in my parts bin and fit) reduces the ripple into the reg's and is beneficial. Since we are drawing little current from these supplies (a few mA) lowering the input coupling caps (I've used 220 Rubycon ZA's, same reason as above) seems beenficial, as it reduces the peak currents flowing from the transformer and around the doubler circuit. The raw supply V will drop a little, but not enough to cause problems.
These little mods were quite effective in my case, adding better bass quality and punch to the sound.
Secondly, as mentioned before, I've modified the loop filter components. If you follow pin 20 of the CS8414 you'll find a 1K followed by a 47n capacitor - these two components with the receiver internals form a second-order loop filter for the PLL clock recovery circuit.
In this form they only attenuate jitter above about 10-20kHz, so an attempt to reduce this seemed in order.
Currently I have 0.47u + 200R in place of the existing components. With care you can do this from above, removing the old components and fit the new.
Additionally I changed the loop filter to a 3rd order, to do this you need to add a capacitor directly between pins 20 (loop filter) and pin 21 (AGND). I'm currently using a 6800pF cap here, you may be able to go to 0.1u, but I didn't have a suitable cap in the bin, with long enough legs!.
Soldering this is tricky if you're not into SMD, but can be done with care - double check all soldering afterwards to ensure there are no shorts. I laid the cap on top of the chip and bent the legs down, cropping them to length before soldering.
This latter mod is effective, but in the same way a better clock sounds, i.e. no change to the basic character, but an improvement in the music, tighter punchier bass, more detail, better treble etc.
The unit still locks on to a 44.1 signal well, I've not checked a 96k signal yet, although the previous modified loop filter to this one (not described) locked on fine.
Give the new components a while to run in, the Superdac seems to take about an hour to really come on song, even after a relatively short downtime.
It's sounding rather good now, I'm shocked!
Andy.
Wm
my DAB tuner as well as my CD player.
