Avion Studios

Premium Parts & Service for Rhodes, Wurlitzer, Hammond and more

Retro Flyer - Long Flight Edition

Morgen SharpComment

Designing the Retroflyer took place over hundreds of hours. Involved working with several American manufacturers for custom parts and consists of over 100 components - all carefully assembled in our workshop. The end result is a truly high quality preamp and effect for the Fender Rhodes. With so many considerations and details to cover we thought it would be best to make a long form article to go into depth on some of the design hurdles, engineering considerations, manufacturing techniques and ultimately the sound of the Retroflyer.

First you Retro-fit…then you Retro-fly!

A hilarious tagline to be sure, but also the fundamental challenge in designing the Retroflyer was getting whatever we made to fit within the existing architecture. That left us with only 3 holes, one of which was immediately used by the output. To maximize the functionality we took the long journey of finding a good dual-concentric potentiometer. This allowed us to utilize 4 controls (plus two switches). Very few potentiometer fit the bill. And by very few, I mean basically none. Custom pots started reaching the range of $20/piece and we didn’t want our retail price point to be ruined before we even started. So instead, we found a slightly smaller pot by bourns and had some custom neoprene rings fashioned to fit these pots into the existing holes. To our shock, no one made knobs for these potentiometers! So we had those custom made as well.

Bourns PTH series potentiometers with our custom USA made knobs thanks to our friends at Rogan. Special shoutout to Carole.

Bourns PTH series potentiometers with our custom USA made knobs thanks to our friends at Rogan. Special shoutout to Carole.

Now that the controls had been sorted, pcb design, power and signal inputs needed attention. The most awkward aspect, even on the final version has been power entrance. There is no other access available to get under the lid. This was also an issue with the dyno-my-piano (active 1970-80’s preamp predecessor to the Retroflyer). So without a custom cheek block (which may come later as an add-on) we decided to give the customer a choice. One, drill a small hole in the fiberglass lid and install a socket. Two, file a small grove at the corner of the lid. Or three, simply sneak the cord along the rail. None being ideal but choosing one a simple necessity. To avoid possible strain on the pcb we opted to use a clip-mounted terminal on the pcb. So in the event the power cord is accidentally pulled the pcb won’t be damaged and the cord is also easily replaceable.

High-flying features (components and design)

In our opinion it’s never worth it for a company doing small-batch hand-made products to skimp on components. The labor is much higher than something that is mass produced and thus component cost is a much smaller factor. Plus, somewhat obviously, we wanted the Retroflyer to sound excellent! So no surprise that top-brow name-brand components are found throughout. Kemet, Nichicon, Panasonic, Bourns, Vishay, TexasInstruments and AnalogDevices, etc. But of course, components are worthless without proper design.

Power: We expect a noisy power supply. Cheap, noisy power supplies are everywhere and quality power supplies are now extraordinarily expensive. So we added several power filtering features onboard including a mechanical relay, large capacitors, several stages of inductors and low-pass filters. We provide decent power supplies, but if you lose yours, you can feel confident in buying one off eBay for $10 and the Retroflyer still performing very well.

Preamp: The Rhodes puts out an enormously dynamic signal, sometimes over 1 volt! Because of this we needed something with low-noise, and a very high headroom. The venerable TLE2072 is used, the modern version of the 072 you might find in much high-end studio gear from the 70s,80’s and 90’s. (and some cost-saving stuff made today) This is a nice JFET op amp with great noise, bandwidth and slew rates. But for those of you who are extremely discerning, all the op amps are socketed. So (with proper knowledge) swapping op amps is possible.

Here’s one of our prototype boards looking pretty. Note the opamp sockets, clip-style connectors, kemet 5% film caps and dual VCAs

Here’s one of our prototype boards looking pretty. Note the opamp sockets, clip-style connectors, kemet 5% film caps and dual VCAs

High Pass Filter: Before we get too far along we should mention the high pass filter as well. The low end of the Rhodes can be very powerful. And whether you’re playing with a full band, recording in the studio, or just playing through a guitar amp - the amount of energy in a strong bass note can be too much. So while it’s not accessible on the front panel there’s one more way you can control your sound with the Retroflyer. An on board high pass filter with 3 settings. 20hz, 60hz and 130hz. It does wonders for cleaning up rumble and giving cleaner and clearer notes.

Input Impedance: Much is made of meeting the Rhodes with a high input impedance. Perhaps because factory Rhodes so utterly failed in this respect. The importance and qualities of proper input impedance is a subject lengthier than even this article should approach. But in quick: typically input impedance is recommended around 10-20x the output impedance of any instrument. Our input impedance (exactly like the dyno-my-piano) is 330K. This is well beyond the standard protocol and more than enough to recover the missing tonal character lost to early passive and active circuits. For people claiming they need in excess of 1M input impedance there is likely more involved in whatever circuit they are using than this simple specification.

EQ: The mid boost/cut offers a wide but very useable tone shaping circuit. With a Q of around 0.7 and 7db +/- the EQ gets a lot out of a single knob. When boosting, it allows the Rhodes best quality (its midrange) to shine through. This is great for cutting through during a solo or to help focus the sound away from where other instruments may conflict.

The cut function gives a big, heightened full range sound. The Rhodes perceived volume follows very closely along the Fletcher-Munson curve of human hearing. This is generally a result of the Rhodes being mechanically linear…which is perhaps a silly way of saying the tone bars and tines are made in a linear fashion which then produces a (mostly) even amount of energy across the frequency spectrum. The human ear of course hears this quite differently and the mid-range appears pronounced. But cutting the mid-range you are essentially doing what a sonic maximizer or any “hype” style EQ does - which is compensating for the natural curve of human hearing but increasing these deficient frequencies and lessening the mid-range.

Tremolo: Many people, thanks primarily to Fender, often confuse this for vibrato. Tremolos vary the amplitude, while vibratos vary the pitch. Many people highly regard the Peterson tremolo circuit of the early CBS and Fender model Rhodes. Others of course revile it. What it does is essentially make a sort of rounded off sine wave tremolo (many people refer to this as the cat’s eye tremolo) with the second channel being 180 degrees opposite, for a sort of ping-pong effect in stereo. Many people believe this style of tremolo was used to emulate the whirling of the then popular Leslie speakers. In fact Fender re-branded a rotating speaker design at one point in the early 70’s. Nevertheless, the tremolo effect combined with the Rhodes became it’s own classic sound. The Retroflyer uses two VCA (voltage controlled amplifier) chips in tandem to create a modern version of this stereo tremolo. With a rate of around 2-12Hz and depth from very subtle to complete chop. We round off the peak of the sine wave to achieve a similar overall shape to the cat’s eye while avoiding high-maintenance and/or inconsistent parts. Another major benefit with this VCA circuit is that it utilizes a full sine wave. Whereas more rudimentary circuits are reductive and simply use half of the whole wave. This is the main reason the Janus preamp will appear to drop in volume when the tremolo is engaged and also loses some dynamic range. Regardless, the Retroflyer contains a stable, low-noise, low-distortion, high-dynamic tremolo that just sounds great.

The famous cat’s eye tremolo from the Peterson preamp. Note the opposite peaks and valleys.

The famous cat’s eye tremolo from the Peterson preamp. Note the opposite peaks and valleys.

Sound & Use

The best thing one can do for a Rhodes is, in our opinion, let the real sound shine through. This requires enormous headroom, proper impedance throughout the circuit and a preampfification stage capable of highly-detailed representation. Unfortunately the passive controls that came standard on hundreds of thousands of Rhodes have water-logged its sound and given the Rhodes perhaps an undue reputation for being tubby and flat sounding. The passive controls certainly lend a sound that excites very few people today. Even in regards to active preamps - the Janus design is nearly 50 years old and in many ways sounds the part. (although if you have one please don’t toss it, recap and upgrade the opamps and you’ll at least be a couple decades farther along!) In contrast, when listening to the Retroflyer you hear everything. Big full bass notes, complex harmonic overtones, a clear middle and the sparkle comes back to the high end. We’ve been recording Rhodes for years (straight harp, through various amps and with sundry preamps) and we were honestly shocked to hear how good the Rhodes can sound just running through the Retroflyer.

Pricing with Pride

We know there were cheaper ways to make the Retroflyer. And we know if we followed standard pricing formulas it should rightfully cost 50% more than it does. But a big part of this project was to make an active preamp that’s accessible and affordable for everyone. While providing a top-notch sound that belongs anywhere. So we cut cost where we could - if it didn’t hurt the sound or functionality. And we paid more for some things to have them made in America or simply made to a higher standard. Because we believe in doing that. And we believe our company can reflect our values down to each component.

An off-center prototype from Detroit Etching. The same company that made the original Rhodes face plates over 40 years ago.

An off-center prototype from Detroit Etching. The same company that made the original Rhodes face plates over 40 years ago.

History & Future

Despite its flaws, Fender brought the Rhodes to thousands upon thousands of people. And while not perfect, this electromechanical keyboard continues to be relevant, desired and played. Back in the 1970’s Chuck Monte introduced the dyno-my-piano as a way to get the most out of your Rhodes. While not selling massively it was used in countless recordings and brought the Rhodes farther into relevance and renown. But the Rhodes, sometimes beyond belief, is still here and still being played today. We believe it needs a modern preamp. A preamp to help people get excited and stayed excited about their Rhodes again. To make it more usable, more recordable and more musical. I think we’ve done that and we thank anyone interested enough to read this all-too-long flight edition.


Team Avion Studios

Hammer Tips - The Extra Long Version

Morgen SharpComment

Rubber...well specifically neoprene hammer tips came about as a result of the major redesign that Fender undertook from 1969-1970. The original CBS/Rhodes design used felt hammer tips which were one of many expensive aspects to production Fender hoped to change. (The other notables being MUCH lighter tone bars and slimmer tines. As well as cheaper damper felt.) I often complain about Fender's cost-cutting - but the fact is that Fender managed to make the Rhodes cheap enough that they sold around 250,000 in total and that's why so many people can still play them today.

So the engineers at Fender came up with some small neoprene tips. Neoprene is basically a chlorinated polyolefin which was first synthesized in 1930. The cool thing about chlorinating is that the chlorine molecules "fill the gaps" per se in the carbon structure of the polyolefin making it denser, more impact resistant and more resistant to ozone/atmosphere. To imitate the hardness of the original felt hammers (which became progressively harder as the felt was reduced from around the wooden core) they manufactured these new neoprene tips in a 4 (well sort of 5) hardnesses. At first Fender had colorants added to the tips to make them easy to identify. However it turned out that the dye made the tips degrade very quickly so they switched to spraying the extruded strips of neoprene before they were cut.

Foreground original decaying red-dyed hammer tip.  Background are some square tips from an original Fender Parts Set. This set features short and tall red tips and large thinner wrapped wooden core tips. The original set also came with tines, grommets, springs and bridal straps. 

Foreground original decaying red-dyed hammer tip.  Background are some square tips from an original Fender Parts Set. This set features short and tall red tips and large thinner wrapped wooden core tips. The original set also came with tines, grommets, springs and bridal straps. 

Shape: Fender tried a number of shapes for these hammer tips. The first generation were sort of rounded like the felt hammers they were replacing. Then Fender switched to these square-type tips. They ultimately settled on a modified tear-drop style which was a little more precise about the striking surface and angle of attack. The neoprene tips, opposite of felt hammer, get slightly taller as they approach the treble section. The main concern being a clean let-off. The new thinner bass tines in particular move a great deal and a shorter hammer tip made it so they were less likely to touch the hammer tip after a strike. Whereas the treble end has very limited space where a sharper, taller triangle was necessary.

Hardness: We talk with a lot of techs and it's rare that I've talked to anyone that's perfectly happy with the voicing across a board. In an ideal world we would have twenty or thirty sizes and hardnesses of hammer tip, closer replicating the gradual attack of the original felt. But this is the real world people! So Fender decided 5 hardness levels was enough and extruded the softer 4 in long strips and then had them cut on an auto-feeder. The 5th, the wooden core will get it's own paragraph.

Hard-core: Because of the constraints of both space and hardness neoprene couldn't quite fit the bill for the highest treble end. However wood alone could damage the tines and also sound too different from the rest of the hammer tips. So a hybrid tip was born. Originally wrapped in the 3 layers of neoprene heat shrink, the design and materials also evolved along with the rest of the hammer tips. The size of the wooden core, the number of layers and the thickness of those layers has changed over the generations and re-designs. Fender had the advantage of large scale production but today these tips are made quite slowly by a handful of makers like Avion Studios. We lose a little less than 1/4 of the raw material during production - making these tips about 5X more expensive to produce than the others.

Special note - some customers have brought to our attention that some makers have used oak instead of maple. Oak is about 2/3 as hard as maple and also harder to mill properly.

In the front you can see our lovely maple-core hammer tips which are double wrapped. In the rear are some very poor looking hammer tips we received from a different supplier which helped inspire us to make something better.

In the front you can see our lovely maple-core hammer tips which are double wrapped. In the rear are some very poor looking hammer tips we received from a different supplier which helped inspire us to make something better.

Conclusion: I hope this has been at least a bit useful or interesting. Mechanical keyboards often live in a really fun junction between engineering and imagination. These odd little hammer tips represent a creative solution to a unique problem. Like a lot of what Fender did, they aren't perfect but they are functional and relatively inexpensive. It was fun for us to get into the engineering and production aspect of this small piece to the Fender Rhodes puzzle. Please let us know if you have any questions. We're here to help!

Making a top/lid for your Fender Rhodes - DIY

Morgen SharpComment

We just finished building our dozenth top enclosure so I figured it was time to disseminate some of the tips and tricks we've picked up along the way.

New over old. Rounded corners, screws mostly covered and routed for heavy duty butterfly fasteners.

New over old. Rounded corners, screws mostly covered and routed for heavy duty butterfly fasteners.

Warning: to do this project you will need some basic woodworking tools and general knowledge of how to use them.

For some reason, most likely either due to weight or faulty hardware, there seem to be a ton of Fender Rhodes out there missing their lids.

There are several styles of cases used throughout the years and we'll talk about a few of the differences but we are not going to go into any actual dimensions. The reason for this is because there is enough variation box to box that it's better to precisely measure your enclosure rather than rely on any figures we might give you. That said...

Step 1: Measurement

I'm omitting a common first step because it isn't totally necessary but we often disassemble the Rhodes, removing the feet and pulling the action from the base enclosure because more often than not we're doing a re-wrap. The advantage of this is you get a clean slate which is easier to measure and you can take the opportunity to repair any dings or gouges on the base.

Either way it's time to measure. The easiest way to mess up is using the rounded edges to get your measurements which can leave them short all the way around by anywhere from 1/32"-1/8". If you need a measurement from these dimensions it's often best to tack a flat piece sticking up over the edge so instead of hooking your measuring tape you can butt it up against the overhanging piece. Make sure the piece you tack on is tight against the side. Clamps will also work well.

If the corners are rounded you're measuring the bottom of the base, which is generally a good idea, but beware because often the manufacturing at the Fender factory was not that precise and the open sides may have slightly different dimensions than the bottom. Suffice to say it's best to get as many measurements as you can before you make any cuts.

Also note the angle of the various pieces. Typically around 15 degrees. Some cases level off in front of the keys giving a flat surface for the case in front of the keys while later models slant the key rail and back rail. This change makes for a less conventional key rail but an easier build. If you end up building both top and bottom this is an easier way to go.

Step 2: Materials

We typically use 3/4" project 5-ply and find that a single sheet is plenty. Project ply will have one sanded better quality side and one rougher side. Since you're most likely wrapping the case it isn't super important which side ends up facing where, we just find this plywood the most well suited that is commonly available. Wait to fill in any voids or knots until after assembly so you can address any chips or cracks from cutting and construction. 

We use the project ply for the sides, but for the long rails we use clear or fine quality 1x boards because they cut easier with fewer voids and in the case of the front rail can be shaved down well with a hand plane.

I've seen people only use glue on their joints but we glue and screw because you never know when your drummer is going to get a call on his cell phone while you're carrying your board up a flight of stairs. Drummers amiright!? Anyway, you'll need wood glue and screws #8 or #10 1 1/2 to 2 1/2 inches. And some wood filler for later.

And of course, don't forget the tolex and spray adhesive. Or shag carpeting, we're not here to judge.


Routed for the new butterfly latches. These don't need to be super precise so were done freehand - but be careful!

Routed for the new butterfly latches. These don't need to be super precise so were done freehand - but be careful!

As long as we're talking about materials, we may as well talk about hardware. I personally prefer to do away with the Fender stuff and install things that are really road worthy. If this board is not going to leave your house for the next decade and you want that original look - by all means go for it. Most importantly have an idea of what hardware system you want to use before you begin...or even better have your hardware in hand. Oh and don't forget corners and handles.

Step 3: The first cut is the deepest.

It's tool time. So you need

  • circular saw or jigsaw
  • table saw
  • clamps
  • router and round over bit (3/8" i think)
  • drill/driver
  • straight edge/level and square
  • countersink

That's not such a crazy list for a DIYer so hopefully most people don't need more than one or two of these smaller things. 

General rule of thumb- big cuts first so get the big top piece out of the way. I sometimes free cut it a little oversized so it's easier to guide through the final passes on the table saw. 

Plenty left over for the sides even if you mess one up. Draw everything out first. Essentially you're mirroring the dimensions of the base....so if it's 3" tall on the front board and 9" high on the back the front of your top will be 9" high and the back will be 3". You can extend these dimensions taller as long as you do it proportionately. Double check the clearance with the fiberglass cover in place over the tone bars.

Finally, once you have your sides complete, start running your long boards through your tablesaw at the proper angle cut. We usually do several passes starting on a very cautious oversized cut and slowly decreasing until we have a very close fit. Make sure you temporarily clamp the boards to accurately check the fit. OR wait to get the proper fit once the sides are installed.

NOTE: Some people prefer doing a lap joint, which Fender did for quite some time. Any jointing is possible and can make a for a wonderfully built enclosure. The limitations being your time, skill and equipment. 

Once everything is cut and you're happy with the dimension it's time to assemble.

Step 4: Assembly

We have the luxury of many good clamps and workspaces and I hope you do too because these boxes are pretty unwieldy. One way or another you need to set your pieces, preferably with glue, and then screw them in place. We highly recommend countersinking fairly deeply. The reason being that after your box is assembled if you want to round the edges you don't want to run into any screws! On that note, we usually start our countersinking slightly away from the edge and angle outward just a bit. Making sure to not miss the piece above but giving a little extra margin for the router coming after.

Start with the sides. Make sure they are square (perpendicular) to the big top piece. Sometimes we wait for the sides to be installed before we finish milling the long boards. Either way, same deal, install the long boards. We use a screw about every 6 inches or so. We drive the screws down pretty far so the heads are about 1/8-1/4 below the surface - again because the of the round over. If you used lap joints this is not recommended because you risk splitting your thinner overlap.

NOTE: We've ignored the hinged storage section for this DIY, but adding a storage section can be really useful and not very difficult.

Step 5: Finishing

The hard work is mostly done. Now it's time to sand, putty fill, sand again. During this stage we sometimes route for specialized hardware, but if your hardware mounts on the finished lid then it's time to wrap.

Wrapping your board should take some time because while it's simple it also easy to mess up. Start with the ends of the enclosure cutting 45 degree slits at the corners and then bending /wrapping the tolex around the outside corner about a 1/2 inch beyond the inside corner. This is by far the hardest part but once your corners are set the best thing to do is use a single piece cut exactly to length. Start at the inside  corner and work your way all the way around the lid. Use plenty of spray adhesive and keep a rag handy for any drips or spots.

I would normally finish with some cheery saying or motivational platitude but it's late and I'm sleepy so good luck out there. Comment or question and we'll try to get back to you.

The first things to wear out on a Fender Rhodes

Restoration, Action / RegulationMorgen SharpComment

There were roughly a quarter-million Rhodes produced during the CBS and Fender production years. We like to think that most of them are still around and it's safe to assume that most of them are under-serviced. So if you've just bought a Rhodes or are finally getting around restoring that dusty thing in the basement here are few places to start.

Grommets: These degrade regardless of use. The reason is that, unlike the hammer tips, they are a rubber product and not neoprene. Also they are under constant stress from both the weight of the tone bars and the pressure from the springs underneath. Many rhodes are also poorly serviced over the years, one of the most common examples being over-tightened tone bars. The bars should be spaced about 3/8" from the plywood. However because they're the easiest part to access and adjust many people use these to address other problems such as weakening bridle straps or poorly adjusted damper felts.

The original grommets were already prone to being squished out (which causes them to become dry and brittle even quicker) but over-tightening really destroys the grommets quickly. It rarely effects the strength/resiliency of the springs but this can also be something to look out for.

Worn grommets, particularly original grommets can also lead to a host of other minor problems beyond directly affecting the sound. Most importantly they can throw off the alignment of the tine in relation to the hammer tip, the felt and the magnet/pickup. For this reason and the tonal difference we illustrate in the following videos we recommend replacing the tone bar grommets before any other restoration is done.

Above are some old original grommets pulled off a 1978 Rhodes. Some of these actually crumbled when we removed them. You can see the "mushrooming" from the pressure of the springs and weight of the tone bars and also the uneven wear from side to side which will cause misalignment and make adjustment difficult. Our improved grommet is pictured also for comparison.

Below: as an experiment/demonstration we replaced every other tonebar with new grommets to show a side by side comparison of old versus new.

Next Up: Bridle Straps

Bridle straps are the key link between the hammer and the spring damper. They are simple cloth cords with reinforced tips. Used normally in the upright piano action they are put in a different situation in the fender rhodes. Most importantly they are under a constant and variable amount of stress whereas in upright pianos the bridle strap is normally slack except when involved in the key/hammer return. Because of this we recommend a "heavy duty" bridle strap with a very strong reinforced tip. But no matter what, the bridle strap is under an unusual amount of stress in the Rhodes design.

*Quick note: replacing bridle straps is not hard....but it is tedious. We usually use a new clean razor blade to first work the glue away then slowly work the braid out of the hammer slot. The most important thing is that you take your time to avoid breaking any of the clips. The blunt edge of the utility knife blade can be used to gently push/wiggle the new strap into the hammer clip.

So back to this unusual stress. The damper spring is constantly pulling on the bridle strap so even in barely used instruments the bridle straps are often degraded. This can be something subtle like a a slight stretching or tearing around the hole all the way to being full ripped which totally disables the release of the felt damper as the hammer comes up. We often tell people that replacing the bridle straps is by far the best "bang for the buck" as they're a pretty inexpensive part and the feel of the action is hugely dependent on them. Properly tensioned and intact bridle straps enable proper damper let-off and they also assist gravity with key return - making the keys feel "faster".

*Another installation note: stretch your bridle straps! Simply hold the tip and squeeze the cord while you pull away. Doing this will help give you a more consistent tension during installation and avoid any straps becoming slack as time passes.


Number Three: the Damper Felts

Some people think hammer tips should be on this list - but really they only degrade with wear. Felt dampers on the other hand (and in some cases foam dampers) do succumb to the ravages of time. And sometimes bugs. For that matter any of the felt on your Rhodes - like the key rail punchings or the name rail felt can become downright useless with little more than aging. (Moisture and temperature also play a big role.) But damper felts are often the first felt product to need swapping out.

Yikes. Here are some really poor quality notched felts. The tine has even carved a hole in one.

Yikes. Here are some really poor quality notched felts. The tine has even carved a hole in one.


The Rhodes has had a considerable amount of variation concerning felt dampers over the years. For the most part Fender used a square or rectangular felt damper of varying size but as I mentioned earlier they also experimented with notched foam, notched felt and angled pieces of dampening felt in order to affect the damper travel and maximize the release. The most substantial change coming with the Mark V where the hammer rail was rearranged and the placement of the damper springs changed.

Another alternating example. The original felts on this board aren't too bad but there is a lot of variation in how they have worn. You can see how the notched felts are taller overall but the dampening point is still about the same height.

Another alternating example. The original felts on this board aren't too bad but there is a lot of variation in how they have worn. You can see how the notched felts are taller overall but the dampening point is still about the same height.

Whichever style of felt they used in the factory most replacement damper felts will fit and function normally. There are some advantages to both the square and notched replacements. The square ones ensure a clean let-off and require less adjustment or fine tuning of the action. While notched felts dampen better, keep the tine centered and minimize vibration from other sources (playing other keys, sitting next to a drummer etc..)

Final Note: For a lot of people dead keys or sour notes are addressed one by one as they arise. But ultimately while some parts of the Rhodes should last a lifetime - others were never meant to last longer than a decade or two at most. If and when you're ready to start refurbishing your Rhodes look at these parts first to make the restoration go easier. Focusing on these parts first will make adjusting and doing further restoration go much more smoothly and help in identifying issues in other areas.