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Back in 2010 I bought this handyman's special 1967 "sparkletop" Rhodes in a store for peanuts. "Sparkletop" was the unofficial name given to these 1960s pianos with their attractive fiberglass shell with a silver base coated with shellac mixed with metal reflective flakes (a boat company made them for Rhodes). It was missing the original electronics but still had the 1960s era tonebars pickups and tines. A previous owner had done a lot of monkeying with the piano - the original felt hammerset had been replaced with the wood/plastic hammerset from the early 1970s (they are interchangeable). These pianos with its original 1960s-era square tonebars has a unique sound. The 1960s-era pickups also contribute to the sound, their tone is dynamic depending on how hard you play, gets everything from that bell tone to fusion bark, very controllable. The key action feels great.

I never liked the sound of Rhodes with the felt hammers, but this mutt with mixed era components has an awesome tone. With two exceptions all the original Raymac tines were intact (two Torrington tines from the 1970s had replaced the broken ones but they don't sound any different). I saw no point in restoring it to "vintage original" as I never liked the tone of the 1960s Jordan preamp and power amp or the felt hammers. I used to own a newer 1976 stage piano - despite duplicating the sound chain I could never duplicate the dynamic tone of that sparkletop. The pickups make a huge difference.

Eventually I fitted the bottom cabinet with four Celestion 75w speakers (same ones used in guitar amps) and drove them with a Tubeworks MosValve stereo power amp. Rhodes used to stuff these things with crap sounding speakers. Since I take the signal right off the harp, I experimented with outboard preamps and effects between the piano and the amp.

Two years ago I acquired the Tines-N-Reeds RhodeStar preamp (now rebranded TineMachine) which sounds great and is very flexible. Here I am demonstrating the chorus effect with a Supertramp song. I would never had guessed that I could get a Wurlitzer electric piano sound out of a Rhodes! No the song ain't perfect, I was just monkeying around with the camera running.

Might be loose screw on the tine post, might be dried/hardened rubber washers on resonator mounting screws, might be pickup too close to the tine.

Phasors that used OTAs for the phase shifting network:
Mutron Phasor II (not BiPhase)
Oberheim Phaser
Moog rack mount 12-stage phaser
Moogerfooger MF-103 6/12 stage phaser
many more...

...those are actually more common than opto-based phasers.

I have a strong suspicion that Herbie's Suitcase 88 was fitted with pickups from late 1960s sparkletop pianos.

I bought a 1967 sparkletop piano back in 2010 that was missing the original electronics.  No loss as I never liked the sound of the Jordan preamp/power amp, so I was forced to use the output right off the harp.

While playing with pickup adjustment I discovered an interesting trick of the late 1960s green coil wire pickups - if you place them too close to the tines, the pickup coils saturate causing a squaring of the sinusoidal timbre of the Rhodes sound.  But if you back them off just right, you get a brief pleasant "thunk" on attack transients with hard playing, which sounds like a limiter.  When I heard that I recognized the Herbie Hancock sound.

Herbie's first use of Rhodes piano was with a sparkletop piano provided by Miles Davis, so Herbie may had exploited that trick.  I tried that trick with pickups on 1970s Rhodes and they will not produce that effect.  It only seems to work with the green coil wire pickups of the sparkletop era pianos.

Since the original electronics on my piano were gone I was forced to experiment with external amps, preamps, and DIs.  Turns out that the Jordan preamp was hiding a wonderful tone.  The green coil wire pickups are very sensitive to loading - if the impedance of the receiving device is too low, you get tone suck and the pickups get very noisy.  I had read that recording engineers would record the Rhodes signal right off the harp using a DI with minimum one mega ohm input impedance.  I have several DIs and the varying input impedance of each did impact the tone and noise.  None were optimal so I acquired a Countryman Type 10 DI that has an input impedance of 10 mega ohm.  When I used that, the noise disappeared and I got this wonderful tone from my sparkletop, which ranged between a beautiful bell tone and the "fusion bark" of early 1970s pianos with dynamic playing.  Later pianos would not reproduce this trick.

During the 1960s there were no active devices with 10 mega ohm input impedance, the technology didn't exist.  The Jordan preamp wasn't optimal so it was designed to drastically reduce the treble to cut the noise from the pickups.  Using the harp signal you could use a Fender amplifier - such as a Twin Reverb which had a one mega ohm input impedance, that was the best there was at the time.

One of my favorite amps with my sparkletop piano is my old Selmer Truvoice Zodiac Twin Thirty, a UK amplifier from the early 1960s that is not common in the US.  I play guitar through it as it resembles the sound of a Fender Twin Reverb, so why not try it with the Rhodes.  It sounds great with the sparkletop piano but it still a little noisy.  So I recorded the sparkletop direct using the Countryman DI, then reamp'd it back to the Selmer using a Radial JCR Reamp box - same great tone but no more noise.

So my strong suspicion is that the "Herbie Hancock" Rhodes sound was achieved using sparkletop era green coil wire pickups adjusted for that "thunk" attack transient, recorded direct off the harp using a high input impedance DI, then reamp'd back to an amplifier of choice and mic'd for the final sound.

Not impossible.

Mark V pianos were only in production from 1984 to 1985.  Mark II pianos were still made in 1983.  Someone on the production line probably didn't bother to look twice at the stamp.  "5383" could be the 1st week of 1984.

Fender put crap sounding speakers in those suitcase cabinets.  When I bought my sparkletop piano it was missing the original electronics and speakers.  I play guitar as a 2nd instrument and own various speaker cabinets with various guitar speakers.  After experimenting with the various guitar speakers, I fitted the suitcase cabinet with four Celestion 75w speakers.  Much better tone and they aren't expensive.  I don't bother with the original Peterson preamp (great stereo tremolo but dull tone), I bought the RhodeStar preamp and use a Tubeworks MosValve amplifier (another guitar gear) to drive the suitcase cabinet.

Why should guitar players have all the fun?

They both come from eras of different pickups, which is the major contributor to tone.  Therefore preference is highly subjective, there is no "correct" Rhodes.

Yes a dummy load is likely needed. Although the amplifier is solid state, some were designed for a specific load impedance.

15" speakers will not fit in the bottom cabinet.  I tried.

I play guitar as a 3rd instrument and have a variety of cabinets with different speakers that I mix with different guitar amps.  Lot of variety there.

I bought a sparkletop piano that was missing the original electronics and speakers.  So I experimented with playing the piano through the guitar cabinets.  I settled on Celestion 75w ceramics which are common in guitar amps/cabinets, so I loaded the bottom cabinet of the sparkletop piano with two on front two on back.  That's 300w of speakers which is a comfortable margin, and the piano has a nice tone.

The only speaker that was better was the Celestion alnico "blue" speaker, but it is only 15 watt and they are more expensive.  Four of those in a Rhodes cabinet would have a power handling of only 60w (not enough) and the cost would had been three times as much.  Weber makes alnico speakers with higher power handling but the cost isn't much better.

Why should guitar players have all the fun?

I have the same issue with the longer bass tines too close to the pickups.  The magnets are pretty strong on those 1960s pickups.

You are correct it is not a piano bass.  I checked my pictures of 49 key piano basses and the low C is the lowest C of a piano.

But it is also not a Celeste.  The highest pitch is two octaves above middle C, which is too low for a real Celeste (think "Dance of the Sugarplum Fairy" from The Nutcracker).

I have a chart from Rhodes expert Olivier Grall that confirms the ranges of 49 key Celeste vs 49 key Piano bass.

And your specimen has the preamp with the suitcase amp cabinet, and the pitch ranges places it between the Celeste and Piano Bass.  I think what you have is a very custom 49 key piano similar to the newer Rhodes 54, where the pitch range is suitable for comping but neither for bass or for solo playing.

That's a 49 key piano bass not a Celeste.  Custom order product but still rare, that is the second one I have seen.  Late 60s with the plastic hammer shanks, good era.

I owned three Rhodes since 1978 - a stage piano from 1973, stage piano from 1977, suitcase sparkletop from 1967.

The piano from 1977 was my least favorite.  Had the felt on the hammer cams which made it hard to play.  No amount of tine adjustment would get any good tone, it was always dull.  No better straight off the harp.  If you want the tone of the 1974/75 pianos, then pass on the 1977 piano.

Naphtha, but use it outside or in well ventilated area.

Each oscillator board has a bias trimpot.  These trimpots are open frame that exposes them to airborne debris and they tend to fail.  The bias may need to be set (I don't know the procedure) or the trimpot is bad.

Never buy NOS power cords.  The insulation on the wires crack with age, posing a fire hazard.  I have had to throw out power cords that were 20 years old.

I agree with Sean - replace the AC inlet.

The Line 6 box is a guitar amp modeler.

Guitar amps distort way too easily with electric pianos.  That includes modelers.  So yes, as you bring up the volume on the piano the Line 6 is going to get fuzzy.  Exactly what it supposed to do.

The pickups on Rhodes pianos are very sensitive to loading.  If the input impedance of anything you plug a Rhodes into is not high enough, the pickups become noisy.  That's likely the case with the Line 6.

Years ago I tried my Rhodes into my Vox Tonelab SE amp modeler and found the same problem.  Not a good pairing.

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Over the years I have owned Rhodes from 1972, 1976, and 1967.

As a piano player, Rhodes from the years 1972 to 1978 have the worst action and no matter what you will want the pedestal mod.

The pianos from 76-78 have the dullest tones.  Forget about any bell tone, they are all mids.  My 1976 model was muddy and nothing would get any bell tone. 

Go for the 1974-75 era pianos, they're a brighter piano and you can always use a processor to tame the bell tone.

My 1967 sparkletop Rhodes is a keeper with great action and great tone, but they are not good for gigging as they lose their tuning when moved.

I haven't even had a chance for basic voicing or regulation.

Do your regulation and voicing BEFORE you tune the piano.

The pickups on these old 1960s piano sound great but their magnetic polepieces are a little strong.  They can pull on the vibrating tine and throw it out of tune.  I found out the hard way when I voiced the piano by adjusting the tine position relative to the pickup, and the tine went out of tune.

With the longer tines in the bass end, the magnetic pull is worse.

A '67 Sparkletop, complete with all original tonebars, came up for sale near me at a reasonable price.

That's the magic year.  I also own a '67 sparkletop piano, used to own a 1972 stage many years ago.

Which should you own?  That depends...

Will the neoprene hammers really sound THAT different from the early teardrop style? I know most of the sauce is in the raymac tines and larger tonebars.

Like you, a former owner of my sparkletop piano had swapped out the felt hammers for the neoprene tip hammerset.  I played other pianos with the felt hammers and was not a fan of the sound, but I really love the combination of the neoprene tips with the raymac tines and large tonebars.  Listen to my piano.

I miss having a suitcase amp

My piano was missing the original preamp/power amp/speakers so I am using it as a stage piano (the empty suitcase speaker cabinet is a keyboard stand), I am taking the signal right off the harp.

Also the original sparkletop power amp is a poor design and they fail.

Do not use a newer suitcase amp with a sparkletop piano, they are not compatible.

The only thing keeping this from being 100% original is that someone swapped out the felt hammers for neoprene at some point.

I would not get so hung up on 100% original with the displaced felt hammers.  One of the main issues with felt hammers is premature wear of the hammer tips and warping of the wood shanks.  The former requires a piano tech to refresh the felt on the hammers, the latter can't be fixed.

1967 was the era of the old Jordan preamp/power amp, not the classic Peterson electronics of 1970s suitcase pianos.  Jordan electronics do not have stereo tremolo, they distort too easy, and they actually hurt the tone of the pickups due to impedance mismatch.  There's a magic tone hiding in the pickups of a 1967 piano.

Is this an idiot move? I know how special the Mark 1A is, but man, sparkletop...

I used to gig a 1972 Mark 1A, they stay in tune when they are moved.  My sparkletop went out of tune every time I gigged it.  Do not gig a sparkletop piano, keep them in the studio and do not move it.  Today I would gig with a plugin or ROMpler, Rhodes are just too bulky to cart around.

However - my 1967 sparkletop has the factory pedestal bump which has a MUCH better feel than my Mark 1A did.

One trick I love with my '67 is with a Countryman Type 10 DI straight off the harp, the tone varies between bell tone and fusion bark with dynamic playing.  With proper adjustment, I can get that fusion bark without hard playing, thus reducing the possibility of breaking a tine.  You can't do that with the old Jordan electronics.  I owned three other 1970s Rhodes and no amount of adjustment would duplicate that trick, even with the same signal chain.

Make sure you have mounted the harp correctly.

Not sure about the era of your Rhodes, but my piano has two holes for mounting screws on the treble end.  Only one is used and it's not hard to place the screw through the wrong one.

The holes in the harp frame are large enough that you can loosen the screw and move the harp a little.  That may fix the strike problem.

Make sure there is nothing between the harp frame and the frame support.  Any debris in there will raise the harp and change the strike point.

I must admit I prefer the look of "all wood" keys but if there isn't any mismatch on my piano keyboard it's a good news anyway ! 

I prefer the feel of wood keys.  I had a Rhodes with the hollow keys and I bought a set of surplus wood keys to replace them with.  Unfortunately the guide pins are not in the same locations and they would not fit.  They were made by different vendors and are not interchangeable, and the vendors changed over the years.

The Fender Rhodes story website seems to have suffered bit rot.  Some of the links take you to a page with no association with Rhodes pianos and in a different language.

Any active DI with minimum 1Mohm input impedance.  Plug the DI directly into the harp.  Rhodes pickups are sensitive to loading and if the input impedance of a DI is too low then the tone will change and/or noise will be louder.

My personal preference is the Countryman Type 10 DI, next best one is Radial J48.

Tines-And-Reeds is introducing the new "Rhodestar" preamp.  I've been waiting a long time for a device like this, it's like a channel strip for Rhodes pianos.

Scroll down the website (there's an English option) for the audio demonstration.  While it's a "work in progress", I love the tone of this box.  It's rack-mountable and rack ears will be available later.  Three band EQ with sweepable mid and low pass filter, mono or stereo tremolo with sine or square LFO waveshape, various DSP effects with adjustable parameters (3rd control is reverb and always live), headphone output.  You plug your Rhodes into the rear panel input using the harp RCA jack.

A very welcome feature is the rear panel effects loop with stereo returns, meaning you can use your favorite processor with this box.  Nice touch!  I'm very glad I can still use my ADA STD-1 Tapped Delay with this.

The image below is a rendered image of the final product, due for release by May 2024.  There's an "early bird special" price in the shop if you order now.  I already ordered one.

Do not gig the 1960s Rhodes pianos.  They are not rugged and they go out of tune.

I gigged my '67 sparkletop pianos maybe three times before I grounded it in my studio.  Every time I moved it the piano went out of tune.

Just wondering: Have you also played the Vintage Vibe Tine Piano? If so, discounting the electronics built into some of the Mark 8s, did you prefer one over the other?

No I haven't, and I always wanted to.

From what I heard on VV's YouTube demos, their piano sounds like my sparkletop with the felt hammers replaced with wood/plastic with neoprene tips.  Which sounds great but isn't the atypical Rhodes sound.

The Mk8 sounds more like the atypical Rhodes.

Both are great sounding pianos, can't really say I have a preference.  I would definitely prefer them over the vintage deal, because so many of them are crap!

Played the Rhodes Mk8 at NAMM 2023 in April.

As a Rhodes player since 1978 who has gone through four pianos looking for "the one", the new Rhodes is excellent.

Dan was maniacal about making a quality piano with the best traits of pianos from each era, and he succeeded.  They have great action, the pickups sound excellent and can get anything from that bell tone to fusion bark with playing dynamics.  That is a feature I love with my '67 silvertop and was never able to duplicate with the later Rhodes.  Dan was aware of the superiority of the early pickups from '65 to '72.  I played the basic model and the one with FX, both had the same feel and raw sound.  Finally someone is making a Rhodes that is consistent from unit to unit, which Fender could never do.  The new Rhodes is almost half the weight.

Yes there are thousands of used Rhodes at a fraction of the price, but they varied all the map due to CBS/Fender ruining the product through corporate bean counting, inferior parts through poor substitution (which drove Rhodes engineers nuts), and stopwatches to monitor production rates that resulted in forced inferior product out the door.  Many of the deficiencies of the older pianos aren't easily fixed.  Frankly my experience with buying used Rhodes was a crapshoot until I found my silvertop.

Cyril Lance designed the preamp and effects and I know Cyril from his days at Moog Music.  I asked him some engineering questions regarding his design, and I liked what I heard.

The effects include compressor, chorus, phaser, and delay.  Nothing fancy but they fit the Rhodes well.  Compressor is nice for getting that Herbie Hancock vibe.  The other effects are stereo.  Chorus is effective, phaser sounds like the EH Small Stone.  Delay is stereo and I found it most effective at short delays combined with chorus.  The FX model has a headphone amp with the jack in the left side cheek.  I neglected to check for MIDI ports.  There are buttons right at the name rail for toggling the effects in/out and are easily accessible while playing.

The preamp in both models feature volume, envelope, drive (overdrive), three band EQ with sweepable mid, and stereo tremolo with selectable modulation waveshapes.  One thing they missed is that the classic Peterson stereo tremolo is modulated with a trapezoid waveshape LFO.  The new Rhodes offers square, curved ramp, triangle, and sine - no trapezoid.  The closest to trapezoid to my ears is sine; I mentioned this to Dan, apparently there is a feature to remedy this in firmware but I haven't played with it.

Complain all you want about the price - you're getting quality that Fender could never have dreamed of.

I passed the Rhodes booth multiple times at NAMM and the booth was busy every time.

I crossed paths with Chuck today at NAMM in front of the Rhodes booth.  Had an interesting chat with him.  I asked while they are not the Dyno My Piano, did he approve of the new Rhodes?  He did.

Hammond organ also had a non-sequential serial number system.  They did this to hide the production capacity from competitors.

The early sparkletop pianos had untapered tines which are less durable.  My 1967 sparkletop has tapered tines.

Those pickups with green coil wire are hiding a wonderful tone.  My piano was missing all the original electronics so I had to take the signal direct off the harp.  Those pickups can be noisy and the preamps intentionally filtered the piano signal to eliminate the noise, and the piano bell tone with it.  I started experimenting with my DI boxes and found that the piano tone improved and the noise was lowered as the input impedance of the DI box went higher.  So I bought a Countryman Type 10 DI box (10Mohm input impedance) and not only was the noise gone, but the piano tone was excellent.  I had a 1976 stage piano with different pickups (red coil wire) and when I tried that DI trick it did not sound as good.  The sparkletop piano pickups are really sensitive to loading.

Another trick I learned with the green coil wire pickups is saturation.  As the pickups are placed closer to the tines, the coils saturate from the hot level.  As I backed the pickup away, I found that saturation to be a pleasant "thump" compression effect on the attack transient when you play hard.  You'll hear this on early Fusion songs especially Herbie Hancock.  Again, no such trick with the 1976 stage piano.

But don't place the pickups too close to the bass tines, the pickup magnetism is strong enough to "pull" on the vibrating tine and change the pitch.  Not a pleasant effect.

Here's my webpage on my piano:

1967 Sparkletop Piano

Answer: Impedance.

The higher the impedance, the more sensitive pickups are to interference and hum.

Guitar pickups are high impedance.  Rhodes pickups are much lower impedance.

Rhodes pickups aren't completely impervious to interference - if you stack anything with a power transformer on top of a Rhodes, the pickups WILL hum.

Rhodes pickups are sensitive to loading.  "Loading" meaning the input impedance of the preamp or amp it is plugged into.  The pickups on my Rhodes were very noisy when I tried to take the signal directly off the harp.  If the input impedance is too low on the preamp or amp, the loading causes noise and the piano tone sucks.  But when I tried a Countryman type 10 DI with input impedance of 10Mohms, the noise stopped and I got a great sound from the piano.

The pickups make a difference.  Rhodes changed them over the years.  I found a great sounding 1967 sparkletop Rhodes, with the right signal chain it gets everything from mellow bell tone to fusion bark, with the pickups adjusted right I could get a wonderful attack transient THUNK just with hard playing.  Very dynamic, very controllable.  I tried the same signal chain with my 1976 Stage 73, it sounded too dull and no amount of pickup adjustment would get close to the 1967 piano.  Both signal chains are straight off the harp.

Where is the "resonator bar"? I don't see this on any diagram I've come across. The hammer strikes the tine/spring, which is attached to a post that connects to the tone bar. Is the resonator bar part of the tone bar?

The tone bar is the resonator bar.  It is designed to resonate at a particular frequency.  Every solid mass has a resonant frequency, all the resonator bars in the piano are different lengths set to the pitches of the keys.  When the tine is set in motion, the resonator bar resonates by way of sympathetic vibration.  Same principle of sympathetic resonation in a string instrument.

The exchange of energy between the tine and the resonator bar is what gives the tone a longer decay.  Otherwise the decay would be very short.

Another option is a tube preamp.  I used to put my Rhodes through a Tubeworks Blue Tube.  It is a 1U rack mount bass preamp, no speakers.  Cheaper than most tube guitar amps.  Bass preamps are designed not to overdrive as heavy as guitar amps.

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anyway, let me share with you all what I believe to be the ultimate E-Piano home set-up:

the dear sparkle-top active deluxe with two freakin' Ampeg M-15 Amps ( second one came via UPS from Italy today ... )

build in 1959, 20 Watts from two 6L6, 15" Alnico Speakers  - these two Amps are upgraded with Altec Lansing 418B's. 

Octal pre-amp tubes for all that warmth, shimmer and dynamics one can think of.

these are octal amps that stay clean once turned up in volume, there is nothing like them out there.

non compressed vintage tone, true magical 3D sound. 

I play guitar as a 2nd instrument and have a variety of cabinets with different speakers.  I experimented with my sparkletop Rhodes through different speakers.  My favorite for tone are the Celestion alnico "blues" speakers; they're only 15w each, OK for studio recording but you need at least four of them to get enough volume in an ensemble setting.

Passing along some words of wisdom I got from one of the nation's best vintage keys techs:  Don't replace anything on a Rhodes without having a good reason for doing so.  This isn't just to save you time and money.  There are a lot of bad replacement parts on the market that will change the character of the instrument.  (And for the record, this guy actually manufactures and sells replacement Rhodes parts, so he's speaking against his own financial interests.) 

Alan

Truth.  Years ago I bought a remote power supply from CAE Sound for a Peterson preamp.  It caused 60hz hum in the preamp when I used it.  When I opened the power supply, I found out that it was unregulated - useless.  A proper regulated power supply will not cause 60hz hum.

I restored two MM+.  There's a LOT to go wrong in these things, especially after sitting in a case for 25 years.  Some things can't be fixed over the internet.  This thing should be in the hands of a competent tech.

Yes the top lifts off, that's how maintenance is done.  You can take pictures there.

Other than the grill cloth, that's the cleanest silver top piano I have seen.

Restore or sell as is?  I'd say sell as is.  The clean condition will attract buyers.  There's a strong possibility that the felt hammers have worn grooves and will need re-shaving, which is a labor intensive $$$ repair.  Instead of re-shaving, the hammer set can be swapped out for the next generation hammerset with wood/plastic hammers.  They are interchangeable.  Reshave hammers or swap out - leave that option to the buyer, sell the piano as is.

I have a Vox Tonelab SE.  When I tried it with my Rhodes it distorted way too easily.

Tube amps are great with Rhodes as long as they don't distort easy.  That rules out most guitar amps.  Bass tube amps are specifically designed not to distort as quickly and are better for Rhodes pianos.  Usually anything with a 12AU7 or 12AT7 in the first tube stage of the preamp - 12AX7 tubes overdrive too easily.

Another good preamp for Rhodes is the Tubeworks Blue Tube.  It is a 1U rack mount preamp designed for bass.

If you're aiming for a bass combo amp, consider experimenting with different speakers.  I got a lot of mileage swapping different guitar speakers IE Celestion Weber.  If your combo amp has a 12" speaker that opens ups many options for different speakers.  If you don't want loud, my favorite speaker for Rhodes is the Celestion "alnico blue" that was popular in Vox amplifiers - only 15w but fine for low volume.

The pickups on the Rhodes are very sensitive to loading.  The input impedance of any preamp is crucial to noise and tone.

When I got my sparkletop Rhodes, none of the electronics were intact - no preamp, no power amp in the suitcase bottom.  So I experimented with DIs plugged right into the harp.  I had read that a 1Mohm impedance was ideal for that signal chain. 

What I found was that the noise and piano tone varied with different input impedances.  As input impedance goes lower the noise is louder and the tone is negatively affected.  Even my DI with 1Mohm input impedance was not free of noise.

But when I tried a Countryman Type 10 DI with 10Mohm input impedance, the noise was completely gone and I could get a nice full frequency tone.  I got both the fusion bark and bell tone.

I can't guarantee this will work with a '75 Rhodes.  They varied the pickup design over the years.  When I got my sparkletop I also had a '76 stage piano.  I tried the "magic chain" on the '76, and could not get it to sound as good as the sparkletop.  The pickups on the '76 are different than the ones on sparkletop pianos.

The Peterson preamp has a FET input for high input impedance, but to my ears the Peterson (I have a surplus one) is not as effective as the Countryman DI.  I have no idea of the topology of the Countryman as the components are potted in epoxy.  The built in LPF of the Peterson serves to cut noise but at the expense of the bell tone.

Also consider that Rhodes put really crappy speakers on the suitcase bottom.  Since my piano did not have any speakers in the suitcase bottom I experimented with others.  You can get a big improvement in tone using guitar speakers like Celestion 75w like those used in Marshall cabinets (why should guitar players have all the fun?).  That's what I installed in my suitcase cabinet.  I got awesome tone with Celestion alnico speakers like the G12s or "alnico blues" but they weren't hefty enough to handle the wattage.  Weber makes higher wattage alnico speakers but I haven't tried them.

You gotta experiment... your mileage will vary.

Interesting how the tone bar twist is reversed for the 54. I doubt this would make a difference, though does this imply a different manufacturer? is there any other differences between them. Might be interesting the swap the tonebars to see if they have an affect.

Pretty safe bet that Fender changed vendors for the resonators.  The engineers complained that the bean counters were always looking for cheaper vendors but at the expense of quality.  Often the original vendor had something unique about their process that didn't get passed onto the cheaper vendor.

The resonator is supposed to be the same frequency of the tine.  If they're out of tolerance then this causes sustain issues.  The new vendor may had neglected this.

Primary culprit is wiring of the pickups.  54 is different from 73.  The pickups are very sensitive to loading, and the different wiring is going to result in a different sound. 

The preamp is going to sound different compared to the passive Rhodes (54 or stage piano).

If you want a true A/B comparison, use the harp output (the RCA jack).

Tine sustain problems are usually due to worn/degraded rubber gromlets on the mounting screws for the tonebar/tine assembly.

does anybody know what kinds of changes there were in design and parts during that era (1983)? What changed besides the plastic keys and smaller hammer throw from earlier Mark II's and Mark I's?

Pickups.  Different coil wire, different magnet poles.  Yes they do sound different.

The OEM of the tines changed over the years.  Raymacs were used until about 1971.  Then Torringtons.  Schagler tines were the last and most durable, and are more bell tone with less bark.

Resonators.  First generation were square resonators, replaced in 1969 with the cold rolled flat resonators to reduce weight.  They are not interchangeable.

Fender was ALWAYS changing suppliers, for two reasons.  One, they wanted a second source as a back up in case the first ran into supply or quality issues.  Two, the CBS beancounters were aggressively looking for cheaper and cheaper suppliers which drove the engineering department nuts when a new source did not make the new parts correctly or with inferior quality.

This is why it is futile to nail "the best year" for Rhodes pianos.

After listening to your audio sample, I think the piano sounds good.  You could really benefit from a different amp.  Tube amps work really well with Rhodes pianos.

The Mark II does not have the dreaded white tape pickups, but if that piano has the fiberglass keyset (white or black color plastic key shanks instead of wood) with plastic key guides, run away from it.  That keyset is prone to breaking.

The major tone difference between the pianos is the Mark II is more bell tone while the Mark I is more of the fusion style "bark".

If the Mark II has the integral pedestal bump, the action will play really good.  The Mark I is likely to have soggy action and harder to play.

As for market value, I haven't kept up with recent prices.  Ebay is a poor indicator.

Prepare to be disappointed.

Those pre-CBS piano basses used an integrated one piece resonator/tine assembly that had short life.  You will have a very very hard time replacing any broken ones.

And they did not sound very good.

I think someone needs to design a modular synth in the form of a Rhodes name rail.

This would be close - Moog Polymoog.  IMO the best synth interface ever invented, yet was never duplicated.

But a modular in that format?  The patch cords would drape over the keyboard.

The reason was economics not technical.  A sanding procedure would had added to the production expense, and we're talking about a company whose bean counters were searching everywhere to cut production costs.  Fender was changing vendors all the time which frustrated the designers because the new vendor could not make the components with the same quality as the previous one.  It was not a good situation for quality product.