The Yamaha PSS580 is pretty much exactly the same as the 480 as far as I can tell apart from colouration. I had hold of a 480 first,and got the 580 because the rubber pads which control the LED display had worn out - which is a shame as it is the only thing preventing it from working properly. I tried putting pencil lead on the pads which worked for a while,but eventually had to hot wire the keypad of an old calculator to it - which is still working - a testimony to Yamaha that you can even do that and it carries on functioning!
[Note - I have recently found that you can glue tin foil to the pads to repair them - a cheap fix - but please let on if you use this when selling on Ebay - honesty is the best policy]
Both machines are described as "Music Station" which is pretty apt considering how Yamaha have laid out the MIDI filter - which is perhaps this model's greatest asset - as it can act almost as a signal router for a MIDI system - higher spec models I have found have never surpassed the flexibility of the MIDI filtering system on the PSS.
The machine also supports System Exclusive dumping - which means you never have to lose your voice settings as they can be saved to a PC - and also you get access to some parameters that are not on the front panel - the best thing to do is have an editor on your PC - which I was writing in Vbasic - but have all but given up the ghost (see members.lycos.co.uk/templarseries/pss480.html) - a free editor can be found on a link at members.lycos.co.uk/templarseries/synths.html.
I actually wrote my own editor on a VIC20 (and I am trying to make one for the DX100 on a C64!) and have moved the patches to PC,they are downloadable from the above site. The PSS model is a single operator FM system and as such is not as complex as say a DX100 or DX7,but it is quite amazing what a dual operator FM system can do - the front facia allows editing of the basic ADSR parameters and the manual suggests starting with a ROM voice and editing it into one of the 5 storage spaces.
There is no pitch bender - but it will respond to pitch bend in mode 99 - which is the multi voice/local control off mode - which is when it is a "music station". The pitch bend appears set at +/- one octave though which can be a pain when being controlled by a CASIO which is set at +/- 2 semitones,the result is two machines bending across different ranges - and short of intervening with a PC there is no remedy - perhaps short of using a Yamaha controller.
In mode 00 all the controls are for one voice plus accompaniment. Drums are on channel 16,which makes it a pain when connecting to modern channel 10 machines. It does drum synching though and the clock pulse is selectable in the filter - there is a filter each for mode 99 and 00 - enabling or disabling all 16 MIDI channels - something I have not seen on other systems for the home.
The MIDI data is passed to the OUT from the IN - so the filter acts on data passing thru the PSS which means you can toggle data on and off thru the keyboard and arrange which other keyboards respond to the signal it receives.
There is a 5 track sequencer - 5 tracks for melody and 5 for backing - which are re-writable with volume and tone after recording - and can be looped if you are quick on the stop button!
You can programme your own drum loops using the rather lacking number of drums,or play the drums from the keys by selecting the fill mode. The accompaniment sections can be turned off or on individually and the sequencer records those events too. The whole system can be tuned or transposed over 2 octaves,which is necessary when you realise that there are 15 frequencies for both carrier and modulator,meaning you may have to change octaves once the FM system has been set in motion.
The keyboard is mini-keys 4 octaves,the lower part being the accompaniment when it is switched on. There is only one output - which is a standard stereo jack,located at the rear.
Sustain, Reverb, Portamento (5 levels) and Vibrato can be introduced from the front panel - under SYSx we find that Sustain can be given a length and Vibrato a depth and delay - something you can't get from the front panel controls. The PSS also has level key scaling - which sounds fancy - but just means that the depth of the modulator changes up and down the keyboard - in an attempt to mimic the variation in timbre of real instruments - this is only editable under SYSx - and you can end up with some rather bizarre sounds once you start tinkering with the SYSx dump.
The keyboard can transmit on any channel and the unit will even indicate when there is an error in your SYSx dump and when you have overloaded a channel with MIDI data - the accompaniment plays on channels 11 to 16 - and the drums play by note as well as sync pulse - which makes it a tad more versatile than those that use channel 10 and don't sync.
FM synthesis is a story in itself - but luckily those clever bods at Yamaha explain it in layman's terms in the manual - which you can get from their website.
There are 100 voices and 100 rhythms - you can add your own 5 voices and one drum program.
The 680 and 780 are very similar models - sporting drum pads in front of the keyboard and adding pitch bend.
See: templarseries.atspace.com/pss680.html and templarseries.atspace.com/synths.html for SYX downloads.
Good points: The voices are not bad approximations of real instruments considering it is a one algorithm,2 operator system. SYSx is included - the MIDI filter is second to none that I have seen and makes connecting to everything but channel 10 drum machines (ie modern GM keyboards) a breeze. As an outboard add-on to a higher spec model it is an asset. MIDI out acts as THRU - so you don't miss the other socket.
Niggles: Fixed pitch bend range in Mode99 causes compatibility problems.You have to move to the 680/780 to get a pitch bender (with range setting).There is no LINE out connection. Drums are sparse and not super quality. The fact that the unit is stereo is not made much use of other than by the drum machine - the drums are spread across the stereo field. Those rubber pad controls tend to wear out and getting them repaired is either expensive,impossible or requires finding another model on Ebay that is broken or on a carboot sale - unless you can hotwire it with a calculator!