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The New Celviano Grand Hybrid, with C.Bechstein Grand Piano Action, touch and feel! Independent Review.

Posted by Hans Heshusuis on 6th Jan 2017

Wednesday, June 1, 2016

Tim Praskins, AZ Piano News

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsUPDATED REVIEW - December 7, 2016 - New Casio GP500, GP400, GP300 Celviano Grand Hybrid Digital Pianos - Recommended - I try to play every new digital piano that comes out on the market regardless of whether I already like that brand or not. There are some brands known for poorly designed digital pianos, others are known for cheap price digital pianos, and still other brands are known for being pro quality instruments that top pianists, music teachers, and other advanced players (like me) enjoy playing. So when it came to trying out and playing the new Casio Grand Hybrid series, especially the GP500BP with a retail price of $5999US (the BP stands for polished ebony), I was very skeptical that it really could be a good piano, and in reality I thought there was no way the GP series, in particular the GP500, could be taken seriously, especially at its $5999US price. Casio? $5999? I figured there is just no way those two things could possibly work together, especially given the huge competition in quality digital pianos from big well known names like Kawai, Roland, and Yamaha The name Casio has had a reputation for producing low priced but high quality consumer digital pianos as opposed to the much higher price Grand Hybrid pro series pianos. I like the consumer Casio piano products very much such as Privia and the lower price Celviano pianos and have done many reviews on those models under $2000 and they're a leader in that price range. But a Casio well over $3000?...and upwards to $6000?...there is just no way I thought...but wow, was I ever wrong.

The new Grand Hybrid GP500, GP400, and GP300 are called "Hybrid" for mainly one reason...the key/hammer action. These days it seems as if all the major digital piano companies want to do whatever it takes in getting as close as possible to reproducing a real acoustic "grand" piano. So the GP series key action and piano sound chip is Casio's way of doing this, especially in replicating the touch action of a real grand piano. The question is...did they do it? Actually, I believe they did a remarkable job and the result is a fairly life-like key movement and weight unlike other digital piano brands, but it was not Casio who designed and built this Grand Hybrid key actions, it was the C. Bechstein grand piano company in Berlin, Germany. The C. Bechstein piano factory was founded in October of 1853 by Carl Bechstein in Berlin, Germany. Carl Bechstein wanted to manufacture an acoustic piano able to withstand the great demands put on the instrument by the virtuosos of the time, such as Franz Liszt. List was a phenomenal pianist and was very hard on pianos (he played like a monster) when it came to key action. In 1857, Hans von Bülow (Liszt's son-in-law) gave the first public performance on a Bechstein grand piano by performing Liszt's Piano Sonata in B minor in Berlin. By 1870, with endorsements from Franz Liszt and Hans von Bülow, Bechstein pianos had become the norm in many concert halls and private mansions.

By that time three piano makers, all of which were founded in 1853, became established as the industry leaders across the world and they were Bechstein, Blüthner and Steinway & Sons. So the Bechstein brand was in very good company:). In 1881 Bechstein began supplying pianos to Queen Victoria and a gilded art-case piano was delivered to Buckingham Palace followed by several more Bechstein pianos to Windsor Castle and other royal residences. By January 1886 they were among the piano manufacturers holding was called "a Royal Warrant" as a supplier to the Queen. Several British embassies across the world acquired Bechstein pianos and they are still popular across the world today and used by professional pianists in concert. However, that brand is not as well known in America as they are in Europe and other parts of the world.

What this all means is that the wood key action movement in the Casio Grand Hybrid pianos is directly from the Bechstein piano company and built for the new Casio GP piano series and the keys themselves are authentic full size grand piano keys made from real sprucewood from individual spruce trees in Austria (wow, that's pretty cool!). From what I have learned, the natural wood is precision cut and aged slowly over the time so that the keys in the key action can remain solid, aligned, and playable over years of practice and performance. Attached to the wood key action inside these Grand Hybrid models is a moving hammer mechanism designed to imitate real hammers in an acoustic grand piano. This moving hammer mechanism is made from resin and synthetic compounds, etc that can withstand weather and humidity changes so that the hammers will last almost indefinitely without the need for adjustment or maintenance as you would otherwise have in a real acoustic piano. When the hammers move as you are pressing a key, you can actually feel the weight of those keys under your fingers and direct connection of the moving hammer mechanism inside the piano to the keys which gives the player a feeling of natural expression and being directly connected to the music in a way that digital pianos without moving full length hammers cannot really do. The hammers in the Grand Hybrid pianos don't actually strike any strings in the piano because there are no strings...and that's one of the positive points of a digital piano...no strings to tune and maintain.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsWhen I played the GP500 for long periods of time, it was like I was actually playing a real grand piano in many ways and the feeling was pretty amazing for a digital piano. The weight of the keys are also unique in that they are like no other top name brand digital piano that I have ever played in this price range in the way the keys move and feel under your fingers. Although the key action is a bit firmer in my opinion when pressing the keys down than the some of the other higher price digital brands, the touch-weight (amount of finger pressure/force your fingers need to push the keys) is still relatively smooth, easy, and quick so that the overall experience playing the keys is more like playing a natural Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsCasio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsgrand piano than many of the other digital piano brands in this price range, and I have had other piano players tell me that as well. The GP key action does not have the escapement/letoff feel that you would normally experience playing a real grand piano but there is a reason for this. I was told that the Bechstein company wanted the fastest responding acoustic piano style action that was possible to get in a digital piano. To make this happen Bechstein's only recourse was to leave out the escapement "simulation" because otherwise that feature would have prevented a faster key movement for those players who perform at very high skill levels. In reality for most pianists, the escapement function on digital pianos is somewhat irrelevant because it's not the near same thing as in a real grand piano and is only simulated in a small way. With this in mind, the importance of key movement and faster triggering of the piano sound took priority over having a "simulated" escapement feature. I believe that Casio/Bechstein made the right choice because this Grand key action is lightning fast when it comes to playing authentic piano pieces and if giving up a simulated escapement/let-off function allows for a better moving, better responding action and sound then I am all for it. As I mentioned earlier, the key weight when pressing down on the keys is firmer and a bit heavier than other digital piano key actions I have played but the movement is still smooth, responsive, with excellent touch-weight and if you are looking for piano playing authenticity that is not available on other digital pianos, then I believe you will be impressed with this GP key action. As far as the material used to produce the key tops, the white key-tops are made from the latest technology in plastics and are identical to the keytops of the Bechstein European concert grand pianos. Many of the new name brand digital pianos are using synthetic ivory feel white key tops with the purpose of trying to recreate the feel of older grand pianos from the 1960's and earlier years when real ivory was the material used to create the key tops. However, for many years now, real acoustic grand pianos have not had real or synthetic ivory on their keys so the key feel of the new Casio GP500 is identical to what current day acoustic grand pianos feel like. In this way you can transition from a real acoustic grand or upright piano to a Casio/Bechstein Celviano Hybrid GP500 digital piano (or vice-versa) with no differences at all in the key "feel" and materials used on the keys. The black keys are a natural satin finish made of phenol so that feel will also be the same as an acoustic grand piano. *Take a look at the video at the bottom of the page showing the key action hammer movement. It's pretty cool:)

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsAs a reference and comparison, the only other top name pianos with actual moving piano hammers in a digital piano is the Yamaha Avant Grand series of digital pianos including the NU1, N1, N2, and N3. However, these pianos all use wood hammers, wood hammer shanks, and organic connective parts which are very good and just like an acoustic piano but will likely require more maintenance over time. The Yamaha NU1 (left pic - see-through front is for display purposes only) upright style piano sells for approximately $5000US at local store discount price and it has an upright console hammer key action but not a grand piano key action, and there is a Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsvery big difference between the two types. Beyond that, the NU1 has very few sounds and very few digital options and features so it's a very, basic digital piano in that way, although the cabinet is attractive in its polished ebony finish. The higher priced Yamaha N1 ($10,000US retail price) has a grand piano style action with all wood parts, but would likely require more maintenance over time as I mentioned earlier. The Yamaha N1 AvantGrand is an exceptionally nice digital piano, but even at discount price it sells for approx $8000US in Yamaha piano stores and the functionality and features are also very basic, The N2 and N3 go up in price quite a bit from the N1 and all have the same key actions as the N1 and pretty much the same basic features with a few exceptions. So when it comes to a key action mechanism in a digital piano, this new Casio Celviano Grand Hybrid GP500 (above left pic) in my opinion is years ahead of the lower priced Yamaha upright NU1 and very competitive to the higher priced Yamaha Avant Grand N1, N2, and N3 pianos, especially when it comes to all of the additional digital features and user display screen.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsCasio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsThe GP500, 400, and 300 have the industry standard 256-note polyphony processing power which is important in helping to give the player enough power to play more complex pieces of music without the loss of notes or damper sustain. As far as piano sound authenticity goes, all of the major digital piano companies would claim to have the best piano sound in their digital pianos and certainly Casio is no exception. What else would you expect them to say?! Casio wants you to believe they have the best piano sound found in these new hybrid digital pianos and overall I believe they have done a very good job and I was impressed. Casio has developed a new proprietary piano sound chip and electronics key sensing system not found in some of the other digital pianos and I thought these new acoustic piano sound samples to be very impressive in the GP series, especially the GP500. All of the digital piano companies use fancy words and phrases to describe how they get their piano sound along with the natural organic nuances they try to capture from real acoustic grand pianos to enhance the piano sound of their digital pianos. I won't bore you with all the terminology except to say that Casio records/samples 3 distinct well known European acoustic grand pianos which includes the Bechstein (Berlin) German Concert Grand, the Steinway (Hamburg) German Concert Grand, and the Bosendorfer (Vienna) Viennese Concert Grand. These three famous piano brands are the standard by which all other Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsacoustic and digital piano companies try to emulate. Since the Casio GP series is designed in cooperation with the Bechstein piano company of Germany, it is easy to understand why the three main piano sounds in the GP series are so good. I found each piano sound sample to be unique with their own qualities of tone and dynamic range, but yet they were all enjoyable to play. What did impress me Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsmost about the piano sounds were their dynamic range of tone and the ability to really express yourself across all tonal ranges depending on your touch and finger movement. The Viennese Bosendorfer sound was also impressive to me and much more natural and realistic than the Bosendorfer sound sample offered on the new Yamaha Clavinova CLP models. With 256-note polyphony processing power along with good pedal sustain and dynamic expression, even advanced classical music can be played well including the layering of two instrument sounds together.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsPedaling is always important to the piano playing experience and the Grand Hybrids will likely not disappoint you since it is done the traditional way with damper pedal including continuous detection pedaling along with adjustable half-damper control, sostenuto pedal, and soft pedal. The pedals seem to move naturally and they have a type of grand feel movement to the pedals unlike some other digital pianos I have played that have lightweight movement or no half-damper pedal control. Casio also added pedal resonance and damper noise to simulate what real acoustic pianos do when using the damper pedal for sustaining the piano tones. So the pedaling portion of this model is convincing, at least it is to me and I played it quite a bit.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsCasio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsAs far as the operating system goes, Casio incorporated a side panel control unit with LCD display which is very similar to what Kawai and Yamaha are currently using in their digital pianos. Although this is a simple and elegant design created to reduce the "digital look" of the buttons and controls of the piano and make it more minimalistic, I would prefer an attached lid or cover on that panel so you wouldn't see it at all when the piano is not in use or you just don't want to change controls while playing and don't want to see the panel. Kawai offers this design on its top of the line digital piano called the CS11, but that model retails for more than $8000. The Samick piano company offers a beautiful upright style digital piano called the NEO with a side control panel and it has an attached cover that closes up over the buttons and display screen, and that piano is less than $4500US retail price. Regardless, the control panel still looks good, is minimal in design, and I found that using the controls was fairly easy to do (although there is still a small learning curve) and the display screen was, overall, easy to read and buttons were easy to use. However, in additional to the LCD control panel, I would also like an iPad/Android app to connect wirelessly or with Bluetooth to the piano which could display all internal controls and features on an app so that you could access all functions that way. There still is no top name digital piano that can do that yet although some of them are trying and do have a few features accessible with an app for iPad/Android use, but it is all still quite basic yet. The GP's are designed primarily for a person to play piano with a few other extra features added along with some basic but good instrument sounds, MIDI & audio recording, and some editing features, so the display screen & navigation is generally satisfactory for those purposes.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsThe feature set and sound library in the GP500 & 400 pianos include 35 instrument sounds (the GP300 has 28 sounds) which include acoustic pianos, strings, choirs, organs, harpsichords, etc. Theses sounds can be layered 2 at a time, split with 2 different instruments one on the left side and one on the right side, duet piano mode for 2-person simultaneous play, registration preset "scene" mode for saving your own setups or using preset factory Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewssetups for instant play, lots of different hall/reverb settings which really adds to the realism of the piano sound along with adjustable touch sensitivity, brilliance, and DSP which helps the user/player create a customizable piano sound and action response. There are a number of specific organic piano sound elements which Casio/Bechstein incorporates into the GP500 & GP400 which allows the pianoCasio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNews sounds to be even more natural and organic. This feature is called the "Acoustic Simulator" and would include things like adjustable Hammer Response, Damper Resonance, String Resonance, Aliquot Resonance (this feature is found in fine grand pianos and adds to the harmonic richness of the piano sound), Open String Resonance, Lid Simulator, Key Off Simulator, Damper Noise, Key On ActionCasio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNews Noise, and Key Off Action Noise all of which are adjustable so that you can micro -customize the piano tones the way it would sound best to you. The GP's also have a variety of tuning temperaments as well as a variety of piano stretch tunings including being able to shut off the stretch tuning depending on what sounds best to you. But for many people the factory default preset acoustic piano sounds may likely be enough to give you an outstanding piano playing experience.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsWhen it comes to adding some "fun" to this model, Casio has a new feature called "Concert Play" which means that you can select from up to 15 songs that are full orchestral CD quality renditions of famous classical music that you can listen to and play along with. You can even slow down the concert song while you try to learn it as well as rewind, fast forward, and loop a set of measures together for Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsrepeat play. You can also download new Concert Play songs from a Casio internet site, save them on a USB flashdrive, and then play them on the Grand Hybrid's. The Concert Play songs sound absolutely authentic just like listening to a full, live orchestra right in your home coming through the internal piano speakers. You can also play MIDI piano performances along with education piano song lessons by downloading those files on the internet and saving them to a USB flashdrive for playback on the piano.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsSpeaking of speakers, the internal speaker system is unique in that the top of the piano has a movable lid which can be propped up to allow more sound to come out towards the player which gives you the feeling of a grand piano sound experience with the lid open. You can even see the hammers move by looking through the inside top of the piano while you or someone else is playing. The only other digital piano that has a lid that opens in this general price range is the Roland LX17 but that piano retails for $1000 more at $6999 and has no moving hammers like the Grand Hybrid's. These new pianos have 6 speakers, 4 amplifiers, and 100 watts of power each which is actually plenty for these models, but they pull only 38 watts of power from your electricity, so the amplifiers are fairly energy efficient. The 2 main, larger speakers of the piano are housed in separate acoustic boxes mounted underneath the piano with the speakers facing downward rather than forward as on some other digital pianos, so that the GP piano sound is coming both towards the player on the top and the bigger speakers towards the floor like a grand piano soundboard would do. In my opinion this makes for a more natural piano sound experience and I did like it very much.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsThe piano also has 2 headphone jacks for private play along with USB output to device for iPad and computer connectivity and USB flashdrive input for song play and recording, and also two regular MIDI connectors for those people who have MIDI music gear that they want to connect to the piano. Casio included 1/4" input and output audio jacks for connecting external devices to enhance the piano sound even further through external speakers or use the internal speaker system to amplify other sound devices such as computers, tablets, MP3 players, etc.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsCasio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsThere are other functions and features on the GP500, GP400, and GP300 but those are secondary things as compared with what I believe it this digital piano's primary purpose and goal...to offer an impressive grand piano playing experience in a beautiful polished ebony cabinet with folding key cover, full size music rack, opening lid and matching bench along with a complete 5 year factory warranty on manufacturer defects if they should ever occur. The GP500 is only available in polished ebony finish, so if you want a non-polished ebony coloe, the GP300 & GP400 come in satin black. Based on what I have seen for many years on all of the other digital pianos that Casio has produced and the overall quality and "bang for the buck" they have brought to the table, I believe Casio has a great future in this premium category for higher priced digital pianos with the advent of their new Grand Hybrid series in cooperation with the Bechstein Piano Company. For some people the Casio name has a negative connotation because over the years people have wrongly equated the Casio name with low price and low expectations simply because Casio has focused on the lower price range with many of its electronic products. But nothing could really be further from the truth as in reality all that means is that they offer a lot of product and features for less money than you would otherwise expect and the same seems to be true for the GP300, GP400, and GP500 pianos.

Casio has not, in the past, had the prestige or gravitas of a digital piano name like Yamaha, Kawai, or Roland. I know that, they know that, and many shoppers know that. But a name means less these days considering how much great technology is being developed by Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewscompanies who were not as well known before with having higher priced technology products, such as these Grand Hybrid pianos. There are many examples of these kinds of consumer electronics companies in the computer, cell phone, and TV industries, and even though Casio is very well known in the lower priced digital piano keyboard world, they are definitely not known for having digital pianos which compete with the highest price Kawai, Yamaha, or Roland digital pianos...but now they do. With the help of the Bechstein acoustic piano company along with new piano sound technology developed by Casio, I believe this is just the beginning of their successful partnership and they should be able to continue to develop even more impressive digital pianos in the future. I would not be surprised if they came out with a mini-grand piano shaped product in the future as that would be a logical next step for these two companies working together. But for now in my opinion the GP series certainly is up there with the best digital upright style pianos that Yamaha, Kawai, and Roland have to offer in this price range, and in fact the GP400 & GP500 is even more realistic than the competition in a few different ways, as I have already talked about, such as its special all-sprucewood European hammer action key movement and tonal dynamic range of expressiveness.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNews
GP300 satin black
As for the other Casio-Bechstein models like the GP300 ($3999US retail price), the piano sound is not quite as realistic as the GP500 although it is still very competitive with other digital pianos in its price range. In addition to this, Casio is just coming out with the new GP400 which has the same features of the GP500 but with a new cabinet design available in a lower priced satin black simulated woodgrain finish priced at $4999US retail. After putting the GP's through their paces, I agree that these models would make an excellent addition to anyone's home, church, school, or studio as long as they understand that the Grand Hybrid digital pianos are primarily designed to be purchased in place of an acoustic grand piano and are not heavy on additional features such as wireless, Bluetooth, lots of extra instrument sounds, has no drum patterns, no automatic interactive chords, no General MIDI recording or playback, no multitrack sequencer, and no proprietary iPad apps like some other digital pianos do. However, with USB to device connectivity you can plug in a USB cable and use many MIDI iPad apps with full MIDI/USB interaction from a Grand Hybrid to the iPad along with Bluetooth audio connectivity using a 3rd party Bluetooth adapter plugged into the piano audio input so that music from your iPad/Android device can stream directly through the GP500 speaker system. Also, it has been my experience that direct connectivity using a USB cable is more stable than with internal Bluetooth or WiFi connectivity.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNews
GP500 polished ebony
As far as I am concerned, at 170 lbs in weight with cabinet dimensions of approximately 56" x 19"x 38", the very attractive polished ebony GP500 is a piano I would definitely own if I wanted to focus squarely on the best possible grand piano playing experience that Casio-Bechstein has to offer along with being a more minimalistic looking instrument which adds to the overall elegance of this piano. The Bechstein key action hammer system is not available in any brand of digital piano and you won't get a moving grand piano hammer mechanism until you get to the Yamaha Avantgrand N1 which has a retail price of $9999US. The appearance of the GP500 is also impressive in that when you prop open the lid of the piano to let the sound come out more, you see an attractive red material covering the inside piano top and you can actually see the moving piano hammers through two long rectangular windows in the top of the piano while you are playing the keys. It's a very cool visual experience along with having a beautiful piece of furniture. The GP300 and GP400 have this feature as well.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsThere is one thing I find to be a bit odd when it comes to the GP500 and that is the height adjustable black bench included with the piano does not match the high gloss black piano finish. The bench is a single size satin black (non-gloss) finish and even though an adjustable height bench is very nice to have, I am a bit baffled by the lack of a matching high gloss finish on the bench. Is this an oversight on the part of Casio or what? I just don't understand the reason for this but it's something which can be easily corrected if Casio chooses to do that which I recommend that they do. The satin black bench is fine for their satin black pianos, but not for the Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewspolished ebony finishes in my opinion. It's also important to note that some very nice high gloss polished ebony benches are available on-line at Amazon.com for low prices anywhere from about $50-$75, and some of those benches look to be as nice or nicer than the Casio bench included with the GP500. So the bench is a solvable problem and the extra cost for a polished ebony bench is a small price to pay, but it still should not be the responsibility of the owner to do that in my opinion. The bench issue is definitely not a deal breaker and is a very small thing as compared with all of the great things this piano can do. Another thing I noticed about these pianos is that when you plug in headphones, the output volume of the headphone jack is a bit weak, at least it is for my ears. For many people it will be just fine, but for others, like me, I like the piano volume in my ears to be louder when I want it to be and the maximum headphone volume could be better. Along the same lines, the maximum volume output through the internal speakers could also be a bit louder just like in the headphones, I prefer to get a big volume because I like to be able to play loud when I want to and the GP series could be better in this way in my opinion. Since the GP500 costs more money than the other GP models, I was hoping that the GP500 speaker system would also have an upgraded internal sound system, but it is identical to the lower priced GP models. I would prefer to spend a bit more money on the GP500 to get a more powerful internal sound system, but for many people it will be more than adequate the way it is.

Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewsBased on my personal experience I am pretty sure that the $6000US retail price of the GP500 and the retail prices of the other two models will be discounted a bit in US piano stores that carry this model as most stores do discount their piano prices. The GP pianos cannot be purchased on-line from a US shopping cart piano dealer, and the Hybrid Grand models are not yet available everywhere in the US at local dealers, so you may have a difficult time finding one at this point. However it is definitely worth the effort and if you want more info on where these models are located or what their competitive pricing would be, please email me and I can give you more info and advice. This is Casio's first attempt to enter this Casio Grand Hybrid GP300, GP400, GP500 Review - AZPianoNewspremium digital piano category and I am sure we will see even more models come out in the future having their continued partnership with Bechstein piano company of Germany. As for the the lower priced satin black GP300 and GP400 models, if the GP500 seems to be out of your price range and/or you want a satin black finish, then you should consider those lower priced Grand Hybrid pianos instead of the GP500. You can still be quite happy with the GP300 and GP400 and they stacks up extremely well against their competition. Be aware that the new GP400 probably won't be available at stores until near end of August. Below is a comparison chart of the 3 models so that you can visually see and know the primary differences among them.

Features
GP300GP400GP500
Polyphony256256256
Total sounds 26 incl strings, organs, harpsichord, etc35 incl strings, organs, harpsichord, etc35 incl strings, organs, harpsichord, etc
Main piano soundsBerlin, Hamburg, ViennaBerlin, Hamburg, ViennaBerlin, Hamburg, Vienna
Total grand pianos121414
Grand hammer actionYes – individual keysYes – individual keysYes – individual keys
Full length grand keysAcoustic grand keysAcoustic grand keysAcoustic grand keys
Graded-weighted keysYes, medium firmYes, medium firmYes, medium firm
Austrian wooden keysAged organic spruceAged organic SpruceAged organic Spruce
Grand fulcrum pointYesYesYes
Acrylic white keytopsYes - grand styleYes - grand styleYes - grand style
Phenol black keytopsYes - grand styleYes - grand styleYes - grand style
Key Center PinYes - grand styleYes - grand styleYes - grand style
Grand hammersResin - full movementResin - full movementResin - full movement
Hardware resonatorNoYes - affects each keyYes - affects each key
Triple key sensorYesYesYes
Key force detectionYesYesYes
Hammer responseYesYesYes
String resonanceYesYesYes
Lid simulator systemYesYesYes
Open string resonanceNoYesYes
Aliquot resonanceNoYesYes
Key on action noiseNoYesYes
Key off action noiseNoYesYes
Brilliance controlYesYesYes
Hall-reverb simulatorYes - 12 typesYes - 12 typesYes - 12 types
DSP & chorus effectsYesYesYes
Headphone ModeYes - surround soundYes - surround soundYes - surround sound
Touch responseYes - 5 levelsYes - 5 levelsYes - 5 levels
TuningYesYesYes
Stretch tuning effectsYes - 5 types, offYes - 5 types, offYes - 5 types, off
TemperamentsYes - 17 typesYes - 17 typesYes - 17 types
Grand pedal systemYes - weightedYes - weightedYes - weighted
PedalingContinuous detectionContinuous detectionContinuous detection
Adjustable half-dampYesYesYes
Damper resonanceYesYesYes
Damper noiseYesYesYes
TransposeYes - 2 octavesYes - 2 octavesYes - 2 octaves
Duet modeYes - adjust 2 octavesYes - adjust 2 octavesYes - adjust 2 octaves
Octave shiftYes - adjust 4 octaves Yes - adjust 4 octavesYes - adjust 4 octaves
Concert play modeYes - 15 songs + userYes - 15 songs + userYes - 15 songs + user
Music LibraryYes - 60 + 10 userYes - 60 + 10 userYes - 60 + 10 user
MIDI & audio recorderYes - 2 track, 1 trackYes - 2 track, 1 trackYes - 2 track, 1 track
Scene registrationsNoYes - 15 preset, 10 usrYes - 15 preset, 10 usr
MetronomeYesYesYes
Layer/Split 2 soundsYesYesYes
Backlit LCD displayYesYesYes
USB Flash drive inputYesYesYes
USB output to deviceYes - plug & playYes - plug & playYes - plug & play
MIDI input/outputYesYesYes
Dual audio ins/outsYesYesYes
Headphone jacks Yes - 2 Yes - 2 Yes - 2
Volume sync EQYes - 3 types, off Yes - 3 types, offYes - 3 types, off
Speakers2 x 6.3"+ 2 x 4" + 2 x 2" 2 x 6.3"+ 2 x 4" + 2 x 2" 2 x 6.3"+ 2 x 4" + 2 x 2"
Amplifiers 30w x 2 + 20w x 2 30w x 2 + 20w x 2 30w x 2 + 20w x 2
Cabinet dimensions 57" x 19" x 38" 58" x 19" x 39.5"57" x 19" x 38"
Cabinet weight171 lbs 188.5 lbs 171 lbs
Bench Yes - height adjustableYes - height adjustable Yes - height adjustable

*Please take a look at the video below of the Casio - Bechstein Hammer Action movement and watch how the moving hammers behave like a real Grand Piano. No other digital piano brand in this price range has anything like it. To me that's pretty impressive.