So many threads about the QSD-1000, it's hard to know the best place to post my listening impressions.
If this site had a better search function it would not matter.
I could start a new thread but that would make matters worse. I often think that there are far too many threads about the same topic. Rant over!
First as a QS decoder I have never heard anything better. I won't dwell on that now, I have so much more material to listen to first.
Now what I would consider a decoders primary function is the enhancement of stereo. For years previous I've mainly used the S&IC for that function. I would still consider it the best, however QS has the advantage of better filling the front corner speaker location than SQ type enhancement. I've talked about that before visa vie my Photolume decoder. The Photolume decoder always sounded cleaner to me than the tri-band QSD-1. I attributed that to that decoder not using the output all-pass phase shift circuit. Likely the sound difference is caused more by the tri-band frequency filters. Capacitor replacement and careful adjustment of my QSD-1 greatly improved its sound. As expected the (stock) QSD-1000 is very clean sounding indeed. It passes full bass as well, other decoders except the S&IC all sound bass shy.
Looking at the schematic the input and outputs employ what you might refer to as a discrete op-amp. It reminds me of the pre-amp circuits designed by Erno Borbely published in "Audio Amatuer". He designed some excellent Mosfet power amps as well, I'm still using his 60 watt Mosfet as my bass amplifier. Notably the design includes a dual FET as part of the differential input. The FETs in the dual package will be better matched than using individual units. Sansui could have simply used regular op-amps in thier circuit, but I guess that this was intended as a purely "Audiophile" product so no skimping anywhere! Looking inside all the pots are all those high quality blue coloured ones from Alps.
From what I can tell the "Protection Circuit" simply mutes the outputs at turn on. I really need to print out copies of the schematic to better understand the inner workings. These old eyes have trouble focusing on the fine details of the rather complex circuit, it is difficult reading off the computer screen or from a small printout.
I have never liked stereo played through a QS decoder, surround mode on the other hand pulls the mix farther apart. The side effect of that is a slight reduction in centre vocal level. Often that level reduction goes unnoticed. In the case of "Pop" recordings the lowering of the vocal level is often welcome. Listening to this decoder, I found that I prefered straight QS enhancement of stereo about half the time. I think that there is a bit too much blend applied in its surround mode. Next I'll have to try out Scott's variable pre-synth with the QSD-1000!
I've long said that I've never noticed any anomalies with vario-matrix decoding, however I was listening to Jimi Hendrix "Smash Hits" in surround mode. On one or more tracks the guitar is panned back and forth. Well as it moved to the left back the sound from the right back seemed to soften, returning to normal as the guitar moved back. Would tri-banding prevent that?
I don't know.
