Topics

I ran across this piece in my travels--
http://daily.redbullmusicacademy.com/2017/11/instrumental-instruments-fender-rhodes

It's got some of its facts wrong, but, all in all, a pleasant history of the instrument.

I've been a fan of the stage piano for a long time, having owned both a suitcase piano and 2 stage pianos.  I think that Fender made some unfortunate choices in the suitcase amp that caused it to be much heavier than it needed to be as well as to have a tone quality that was not to my liking.  The great advantage of the stage piano are the wide variety of amps and speakers that are available, allowing a much greater range of tone, volume range and size.   

Because of the variety of available amps and pedals, I've been a bit surprised at how much interest there is in preamps for the stage piano.   Why build a special preamp that may require irreversible modifications to one's piano when one can pick an amp and pedal to get the desired tone?

The Dyno-My-Piano preamp is a good example.  It creates a large hole in the frequency response centered around 500Hz.  That's fine if you like that sound, but for less money and fuss, one can by an equalizer that can not only create that tone quality, but many others as well.  Tube preamps also seem to enjoy some cache.  But, why not just buy a tube amplifier if one finds tubes to be advantageous?

People often think the soft clipping provided by tubes will be a boon to the Rhodes' sound, but that idea is largely a siren song.  If one is playing moderate to complex chords, any audible distortion will sound really awful.  If one wants to play single-note leads and power chords like guitarists do when using distortion, then full-blown distortion such as provided by distortion pedals will work well.  Also, tubes, specifically triodes, provide soft clipping over a relatively narrow range of volume that doesn't work well if one is playing using both single notes and chords together.

After thinking about all of us, I decided that there was one type of preamp that would make sense.  The output of the Rhodes harp is pretty low—lower than most guitars.  Also, the sound of the harp changes when loaded by the control in the stage piano.  So, I thought if one could design a preamp that would deal with these issues, and, at the same time, require no modifications to the piano and no external power supply, it would be worthwhile.  So, that's what I did.

My preamp is very small and mounts by its ¼" phone jack, using the preexisting hole in the name rail.  A phono input jack connects between the harp and the preamp, and the output of the preamp connects to a 2nd phono jack using the preexisting phone plug for the piano's name rail. The preamp is turned off unless a guitar cord is plugged into the piano.  Given the preamp's tiny load current, a 9-volt battery will last more than 400 hours—that's a lot of playing..  So, if you play your piano 10 hours a week, the battery will last at least 40 weeks—pretty close to a year.   If the preamp or its battery should fail, in about 2 minutes one can unplug the preamp from the harp, and plug the front-panel controls back into the harp.  Here are the specs, which were derived from direct measurements or SPICE simulation.  BTW, the preamp is a totally discrete design, with no ICs.  With its high impedance, and the short cord between the harp and preamp, none of the harp's signal is lost or suppressed.

All specs were measured with a 2V P-P input signal and an output load of 10 kohms
Distortion              approx. 0.25%, largely 2nd harmonic
Input impedance   2 megohm
Output impedance   500 ohms—set by series resistor
Freq response      6 Hz to 110 kHz 3db down, flat in between
Max input              3 V P-P
Slew rate              0.3 v/usec
Gain                    5.5 dB
Output noise      2.8 uV (50 Hz to 10 kHz)
Power supply      9V battery
Current drain      1 mA

This 1st pic shows the preamp itself.  If I relayed it out, I could make it much smaller—I purposely left lots of room between the components for this initial trial in case I needed to make some modifications.

The 2nd pic shows how the preamp is mounted on the name rail.  The ¼ phone jack is removed, and the preamp installed in its place.  The green and yellow wires were previously soldered to the removed phone jack.  The little battery box is attached to the name rail by double-stick foam tape.  This stuff holds ferociously, but can be easily removed by slicing through the foam with a single-edge razor blade.

The final pic shows what the installation looks like with the name rail in place.

I have not been fully satisfied with the sound of my '78 stage piano.  With the piano's so-called bass boost knob turned up, the left half of the piano sounded dull and boomy.  With the bass-boost knob turned down, the sound quality of the lower notes was fine, but then their volume was too low.  BTW, I should mention, as many on this forum no doubt already know, that the bass-boost knob is actually a bass-cut knob; turned fully clockwise, all the signal from the harp is applied to the volume pot.  As the knob is turned counterclockwise, more and more bass signal is filtered out.  Also, the volume potentiometer on these pianos is 10k ohms, which definitely removes some brilliance from the sound, and also cuts the volume to some extent.

A couple of days ago, I decided to revoice the piano with the bass-cut knob fully clockwise, and then to be sure I was hearing the full sound from the pickups, I decided to bypass the piano's bass and volume controls altogether and connect the harp output directly to my amp.  In preparation for the revoicing, I set my amp's tone control for a flat frequency response.  The result was very gratifying--the bass end of the piano sounds punchier, and, in fact, with the bass-cut knob all the way up, the sound is almost just right, needing only a slight adjustment from my graphic equalizer.  This result got me to wondering what ideas other contributors to this forum have about voicing the Rhodes.  Do you have a procedure that works well?

BTW, while we're talking about the stage piano's controls, I made some simple changes to my piano to eliminate almost all the reduction in brilliance caused by the low impedance of the stock components.  I replaced the volume pot with a 50k audio taper, replaced the bass pot with a 250k reverse audio taper, and replaced the .047u tone capacitor with a .010u tone capacitor.  This leaves the bass pot's frequency adjustment as it was.

A while ago, there was a discussion about adding a tweeter to complement the typical 10" or 12" guitar speakers used with Rhodes pianos.  The desirability of doing so depends on a number of factors including the speakers used, the type of cabinet they're in,  the amplifier, and the hammer tips used, just to name a few.  In my case, I decided, by comparing what I heard from the speaker verses what I heard from headphones, that I could use a bit more highs from my speaker cab.  After some searching, I found the Eminence APT-80 tweeter, which has the required sensitivity to combine with a guitar speaker, as well as a more than sufficient power rating, combined with a relatively low cost.  I crossed it over at 3500 Hz, using a 2nd-order crossover, to keep unwanted lower frequencies out of the tweeter.  I used only what could be called a half crossover--a high-pass filter for the tweeter, without the customary low-pass filter for the speaker.  The rational is that the guitar speaker starts rolling off at about that frequency, and by 3500 Hz, most 12" guitar speakers have an impedance of around 12 ohms or higher.  Thus, putting the speaker and tweeter in parallel would not excessively load the amplifier. 

One might look at the frequency response of a typical guitar speaker, which usually has a big bump in its response near the crossover frequency, and wonder if it's a good spot at which to cross over to the tweeter.  Well, much of that big bump has to do with beaming.   A 10" or 12" speaker becomes quite directional at those frequencies, so a good amount of the bump is caused by much of the speaker's output to be aimed right at the measuring microphone, whereas off axis, there will not be so much sound.  The net result is that the total power put out into the room is flatter than the response curves suggest.

Below is the diagram for the crossover.  It is important to note that the tweeter is connected at opposite polarity to the guitar speaker because of phase shifts in the crossover and in the guitar speaker itself.   I used an L-pad to adjust the tweeter-- the particular one I used came from Parts Express, and I put their part number in the diagram.  Suitable capacitors and inductors can also be bought from Parts Express, and any number of other sources.  I found a fairly large range of prices for the tweeter, so shopping around may well be in order.  Finally, I should mention that the resulting sound is very good--the L-pad allows the highs to be adjusted to one's taste, and the extra highs gave my piano more clarity, which I like quite a bit.

Has anyone tried a Digitech Luxe with their Rhodes?  I was thinking of ordering one instead of a chorus pedal.

For some reason, Rhodes pianos seem more sensitive than guitars to uneven frequency response.  Closed-box cabinets can suffer from various resonances unless they are stuffed.  Ordinary polyester fiber fill is an excellent stuffing material, and it is cheap and easily available.  A stuffing ratio of about 1 lb of fiberfill to 1 cubic foot of cabinet volume is a good place to start.  I have been having some difficulty adjusting my Rhodes for optimum sound, even with the use of an equalizer.  Playing the piano through headphones showed that the issues were not the piano, but the speaker.  I already was using a good quality 12" speaker, so I opened the cabinet, and found it had little stuffing.  For a princely sum of $6.99, I bought 24 ounces of fiber fill at a local fabric store, distributed it carefully in the cabinet, and voila, problem solved. 

Polyester fiber fill does two good things in a speaker cabinet.  At low, i.e., bass, frequencies it makes the cabinet look bigger to the speaker by slowing down the speed of sound.  Given that many manufacturers like to make the cabinet smaller than it should for both cost and sales appeal, this effect is usually desirable.  At higher frequencies, i.e., midrange and treble, the fiber fill acts as damping, and prevents standing waves from occurring in the cabinet.  If you're dissatisfied with the sound of your amp, before spending lots of money on new equipment, stuffing a closed-box speaker cabinet is a cheap and quick experiment to try.

Using a method known in the guitar-pickup industry, I measured the frequency response of the harp in my 1978 Stage 73 piano.  The technique employs a coil that is used to couple to a pickup via mutual inductance.  The coil is driven by a constant-current amplifier, and the output of the harp is sent to a high-impedance preamp followed by an integrator.  I used my oscilloscope with a 10X probe for the preamp, and did the integration mathematically in Excel.  The 10X probe provides a 10 megohm impedance with a very small amount of capacitance.  I connected various resistors across the output of the harp to see how they affected the response, and I also connected a 220pF capacitor, which would represent about 8 feet of coax cable connected directly to the harp.  The graph below shows my results.  The curve labeled "Pete" shows the simulated response of the Peterson preamp combined with the 42.2k resistor.  The Peterson preamp had a 33k input resistor, but the 42.2k was the closest value I tested.  I should note that putting resistors across the harp reduced the output, but I normalized all graphs to have a 0 dB output at 400 Hz so their frequency responses could be more easily compared.  I would estimate the accuracy of my measurements to be about +/- 1 dB.

After doing this test, I also did a listening test.  This test used a solid-state amp whose tone controls were set to a flat response, combined with a hifi speaker with a 40 Hz to 20 kHz bandwidth.  The amp had a 1meg input resistance.  Using the same resistance values as in the previous test I listened as hard as I could to detect any changes in tone.  Even though the graphs show response differences up to the highest impedance, I could not detect aural differences for any resistance between 50 kohms and 1 megohms.  I believe this result is caused by the fact that the Rhodes has little response beyond about 8 kHz, and even at this frequency, the only response is the sound of the hammer hitting the tine, which damps out very quickly indeed.  Except for the initial sound, the Rhodes produces little output over 3 kHz.

The stage models used a 10k pot for the volume control, and it is clear both from the graphs and my listening tests that this value reduced the initial ping or tinkle associated with the Rhodes.  Whether or not that's a good thing depends on your personal taste.  The Peterson preamp was designed to eliminate this initial attack sound as it substantially reduces response above 3 kHz.

Based on the response and listening tests, my conclusion is that any input impedance higher than 50 kohms to 100kohms will capture the full Rhodes sound.

The 3 highest notes in the '78 Stage 73 that I've been restoring had awfully short sustain--especially the high E.  I noticed that the tuning springs in these notes were not particularly close to the ends of the tines.  They weren't far away, but the tines are so short that I wondered if moving the springs closer to the end could affect sustain.  So, I took out the high-end tonebar assembly and, using a Dremel tool, removed 1/2 turn from one end of the tuning spring  to make it lighter.  That didn't do much, so I next removed 1/2 turn from the other end.  I was making some progress, and at that point, took a little off the end of the tine with my bench grinder.  I was proceeding cautiously, lest I make the tine too short.  Well, after this, the high E had dramatically more sustain, so I used the same procedure with the D and D#.  Their sustain increased dramatically as well.  I didn't attempt to measure the before and after sustain, but my impression is that the sustain increased by at least 3 times.  When I was through, the springs were probably between about 1.5 and 2.5 mm from the ends of the tines.

Is this a well-known technique?  If so, I hadn't run across it.  If it isn't, I'd be interested to see if anyone else might have similar success.

I ran across a guy on youtube who posts under the name of "Uncle Doug,"  and perhaps many of you have seen some of his videos.  I though his 2 videos on applying Tolex were well done, and so started this thread just to post the links.

https://www.youtube.com/watch?v=cxcLri3yn8Q

https://www.youtube.com/watch?v=qI8PTa4FieM

This topic has been discussed in the past, and some posters have disagreed with the general approach I am proposing, but nevertheless, I think my methodology is sound, and I have successfully implemented it on my own piano (an early 1978 stage 73), which I am currently restoring.

The Rhodes is unique among all pianos, to the best of my knowledge, in that the downward key motion is not limited by some kind of stop under the key.  For example, in acoustic pianos this stop is a thick felt washer--a so-called front-rail felt punching.  Instead, the downward motion of a Rhodes key is limited by the hammer going to the stop-lock position.  In fact, if one attempted to limit key dip before the key was in stop-lock, the hammer would tend to bobble and double strike. Once in stop-lock, all force on the key is transferred to the hammer pivot via the lever ratio of the key.  Thus, a heavy blow can transmit quite a bit of force to the plastic hammer pivot.  Although hammer pivots don't break all that often, this excessive force must surely cause wear, and therefore sloppiness in the bearings.

In addition to the hammer pivot, force on the front of the key is also transmitted to the balance-rail punchings, and if you look at a key with the name rail off the piano, you can see how the balance-rail felt squishes down as increasing force is applied to the key front.  The squishing of the balance-rail felt can be used to advantage to protect the hammer pivot.  The general approach is to used a balance-rail felt with as much resilience as possible, i.e., a soft punching, combined with a stiff front-rail punching, adjusted so there is a slight gap between it and the key bottom when the key is in stop-lock.  In practice, although Fender provides front-rail punchings, they are pathetic little things, without the size or firmness to provide any help.  Additionally, the pianos usually have no paper punchings under these front-rail felts, and they are too far away from the key bottom to be of any use.  In my piano, they were anywhere between about 0.080" [2mm] to 0.180" [4.5 mm] below the key bottom.

I noticed that in my piano the balance-rail punchings were thin, requiring a fair stack of paper punchings to bring the key to the proper position.  By measuring the combined height of felt and paper punchings I determined how thick a felt punching I could use and ordered a set--a thicker punching provides more resilience, other things being equal.  Standard front-rail punchings are really too soft to help with this project, but for a few years, a new type of front-rail felt has been used in some high-end European pianos--they are sold as Wurzen felt punchings.  These punchings look quite different front the standard punchings, as they are just felt, not felted cloth, and are quite a bit firmer than the standard punchings.

After the new balance-rail punchings were installed and keys leveled, I installed the Wurzen felt punchings so that with the keys in the stop-lock position there was about 0.010" [0.25 mm] between the bottom of the keys and the top of the felt.  The action functions normally with this setting, and as you continue to press on the key while it is in stop lock, instead of the balance-rail punching continuing to squish, the downward motion of the key is largely stopped by the Wurzen-felt punching, thereby showing that the felt punching and not the hammer pivot is absorbing a good proportion of the force applied to the key.

We all use the word Tolex to refer to almost any flexible, fabric-backed vinyl covering used with amps and musical instruments, but Tolex is a trademark that goes back to 1945.  Go to http://tmsearch.uspto.gov/bin/gate.exe?f=searchss&state=4807:rp10al.1.1  and enter tolex as the search term.  There's even a wiki page on it, https://en.wikipedia.org/wiki/Tolex

For years, silicone spray has been considered to be the lube of choice for pedestal felts, but is it still the best?  To test this idea, I compared it to McLube Sail-Kote, microfine Teflon powder, and Protek CLP.  The test setup is shown in the picture.  A piece of piano felt is slid over a scrupulously cleaned piece of acrylic, while weighted down with a 500 gm weight.  A piece of string attached to the felt is directed over a ball-bearing race to an adjustable weight that hangs down out of sight of the picture.  The weight was adjusted until the felt just slowly started to slide over the acrylic.  I used acrylic because I had a piece, and the possibility of getting a piece of Cycolac of the same type used in the Rhodes' hammers was pretty remote.  Given that we're only interested in comparative results, the use of acrylic seemed justifiable.  Here are the results. 

Plain felt-- 190gm  The plain felt was tested as a control.

Microfine Teflon powder--200 gm.  I was not surprised that the powder made friction worse.  Every time I have tested it, no matter what the application, I have gotten the same result.  Instead of resulting in a slick, smooth feel, it creates a greasy, almost gummy feel.  Additionally, I wonder how safe it is to use.  The powder really is exceptionally fine, and some always gets in the air.  Should anyone be breathing it?  Well, I'm going to throw out my remaining supply.

McLube Sail-Kote--140 gm.  I had high hopes for this substance.  It works exceptionally well when sprayed on metals, but I guess felt is not its strong point.

Protek CLP--110 gm  Not bad at all, but I noticed that when slid over the acrylic, a thin oily layer was deposited.  It seems like this could attract dust and dirt, so I'm not inclined to use it.

Silicone spray--90 gm.  Silicone is still the winner.  I noticed that when initially slid over the acrylic, it didn't do so well, but after sliding it back and forth a few times, the friction decreased dramatically.  Clearly, some silicone was being transferred from the felt to the acrylic.  One has to wonder if both surfaces having the silicone made the difference or if it was mostly the plastic being coated that made the difference, and the felt was principally acting as a reservoir for the silicone.

One might ask why I used such a heavy weight on the felt (500 gm).  Well, especially if the piano has the bump mod, all the force of the pianist's finger is applied to a very small patch of felt, and therefore the pressure would be quite high.  In fact, come to think about it, I wonder if partial lubrication of the pedestal felt might be helpful.  The rear-most portion of the felt only touches the hammer at the end of the blow and acts as the stop lock, to prevent hammer bounce.  Maybe leaving the rear 1/2 of the felt unlubed would reduce hammer bounce.  I'm going to try it--it's always easy to add more silicone.

For reasons I don't understand, the Peterson Preamp, as used in older suitcase Rhodes, is often highly regarded.  My first Rhodes was a suitcase 73 with the Peterson circuitry and I did not find its tone desirable--if fact, it had a somewhat dull, muffled sound.  I ended up selling the suitcase Rhodes and getting a stage model, because I found that the Rhodes sounded better with many guitar amps than it did with its own suitcase amp.  Also, gigging with the Rhodes was bad enough, carrying around the large suitcase amp was the final insult.

To see if there was anything special about the Peterson circuitry in terms of its equalization, I simulated it in SPICE.  The graph is of its frequency response with the tone controls centered.   We can see that there's nothing special--its response is pretty flat, with a treble rolloff that may, in part, contribute to its somewhat dull sound.  The tone controls are standard Baxandall, centered around 500 Hz, which is common in guitar amps.  If anything, the slight bump in response in the 100 to 300 Hz range is exactly what a Rhodes doesn't need, though the bump is small enough that it's probably not particularly noticeable.

I'm also not a fan of the stereo tremolo as implemented.  First of all, the speakers in the suitcase camp are too close together to give a true stereo effect--especially in a performance situation in which the audience is much further away from the Rhodes than the spacing between its speakers.  If in the studio, then the preamp's 2 output channels, if fed to the mixing board separately, could create a true stereo effect.  However, my biggest gripe about the tremolo is its lack of smoothness.  The tremolo oscillator is a multivibrator, which creates an abrupt rather than smooth transition from speaker to speaker.  This lack of smoothness is readily heard, and not at all pleasant to me.

It seems that Rhodes pickups seem always to fail open.  That being the case, there is no need to cut or unsolder wires to find a bad one—all you need is an ohmmeter.  The newer Rhodes are wired with the pickups in parallel groups of 3, so each group has a resistance of 180/3 = 60 ohms.  Connect one lead of your ohmmeter to pickup ground, which is at the treble end of the harp, and touch the other lead consecutively to each group of 3.  You should see the resistance grow from 60 to 120 to 180, and so on.  A group of 3 with a bad pickup would have 90 ohms instead of 60, which is very easy to spot.  Older Rhodes had pickups wired in groups of 6, so for these pianos, each group of 6 would have a resistance of 30 ohms, and if there were a bad pickup, the resistance would measure 36 ohms—still easy to spot.  Note that the last group of pickups in the bass end in a 73-note Rhodes has 4 pickups for a newer Rhodes, and 7 pickups in an older Rhodes, for a group resistance of 45 ohms and 25.7 ohms, respectively.  Of course, the pickups aren't exactly 180 ohms, but that's not a problem.
If you find a bad group, tap the pole pieces of each pickup in the group with a steel-bladed screwdriver—a bad pickup will make much less sound.

Does anyone know what type of plastic Fender used to make the hammers?  Did it change over the years?  I seem to recall reading that it was ABS, but I have not been able to verify that.  It would be good to find out so we could definitively know which solvents and chemicals are safe to use around the hammers and which are not.  Please excuse me if this topic was already brought up.

Thanks

Hello everyone.  I'm new on this forum, and hope I'm not asking about things that have been already answered.
First, does anyone have any definitive knowledge as to when Rhodes switched to the 1/2 inch magnets?  I've found conflicting information.  For example, I had a 1972 or 1973 Mark I stage piano, and based on its pickups being wired in parallel groups of 6, and also based on the fact that decreasing the pickup-to-time gap to less than 1/16th inch caused detuning, I assume that it had the long magnets.  Nevertheless I ran across information that the shorter magnets were introduced with the mark I.  I believe the pianos with shorter magnets always had pickups wired in parallel groups of 3.  Is this correct?

Second, does anyone know which is lighter, the wood/plastic hammer or the all-plastic hammer?  I have never seen this discussed, but would expect that hammer weight would have an effect on tone.  Other things being equal, a lighter hammer will bounce off the tine more quickly, and this would favor the excitation of more harmonics, creating more of the ping when the hammer hits the time.

Thanks to all for any responses.