Hohner Combo Pianet

Electric / Electromechanical Piano

There was once a time when Hohner, the brand most famous for their accordions and harmonicas, was quite a prominent manufacturer of electromechanical keyboards. Specifically, they had a pretty good run from around the late 50s to the early 80s. Most famously, Hohner manufactured the Clavinet (which remained a unique Hohner product for a long time until Vintage Vibe released their "Vibanet"), but they also made a number of other equally excellent products, including their Pianet series.

The first Pianet was introduced in 1961. Using ground stainless steel reeds plucked by leather-faced pads with an "active" electrostatic pickup system, it was quite similar to the Cembalet (introduced in the late 50s), the main difference being that Cembalets use plectrums with dampers instead of sticky pads, and with a range from C to C instead of F to F. Both were sold simultaneously until the early 70s. This type of unit, the Combo Pianet, had an apparent manufacturing run from around 1972 to 1976. Around 1976-7, production of the electrostatic Pianets stopped, and the Pianet T, M, and Clavinet-Pianet Duo (basically a Clavinet integrated with a Pianet T) were introduced, which utilized electromagnetic pickups, rolled spring-steel reeds, and solid silicone pads, and thus had a different, mellower sound. These were produced until the end of Hohner's keyboard production in 1982.

Features

  • 61 full-sized semi-velocity-sensitive keys (F1 to F6 / 5 octaves + semitone)
  • ground stainless steel reeds with electrostatic pickups for tone generation
  • sticky pads (silicone or multi-layered) which pluck the reeds
  • one knob, which acts as both an on/off switch and volume control
  • 1/4" jack for output
  • 1/8" jack for 9V DC power supply (tip positive)

Trivialities

  • One very simple PCB using all through-hole components
  • 2 transistors; the manual specifies BC239CR, but mine has a BC413C and 2SC1317, which may not be original

Repairs

As compared to many other keyboards I've received, not a whole lot had to be done to this unit to get it playing to my satisfaction, since it was already in fairly good condition to begin with.

It should be mentioned that this keyboard was shipped from Ontario to Alberta, since I could not find a Pianet locally. One small issue that may have been caused during shipping was that the plastic retaining front on one of the keys had broken off. This was repaired easily using "Super T" cyanoacrylate glue during the process of vacuuming the keybed and cleaning the keys (with moist paper towels), when all keys were removed. The keys are injection moulded plastic, with metal rods for holding the sticky pads glued into the plastic pieces.

The rest of the inside was also somewhat dusty, so that was vacuumed and in some cases wiped with a damp paper towel. As well, I removed and cleaned the sticky pads that it came with (which were Clavinet.com replacement pads) using soapy water, and cleaned the reeds using 99.9% isopropyl alcohol on cotton swabs.

Once everything was cleaned, I adjusted the reed tongues for an even response across the board. When received, the bass section in particular was quite weak and in need of attention. Cleaning the sticky pads and reeds, as well as moving the pickup tongues closer to the reeds in many cases, resulted in a much louder bass section particularly.

Now, a few things concerning the pads that it came with, those originally from Clavinet.com. These are solid silicone, rather than the original 3-layered form (plastic, foam, and silicone-oil-soaked leather). The particular pads that came in my unit are between 4 and 13 years old, since they were installed at some point between when production started (about 13 years ago in 2002), and when the previous owner received the unit (4 years ago).

I found that with these pads, even after cleaning them, the middle-high keys had very pronounced clicking noises at the beginning and end of a keypress, louder than on any other Pianet with Clavinet.com pads that I could find. While cleaning, I noticed many of the pads had slight (between 0-1mm) indents where contacting the reeds, which I determined to be the most significant source of the loud clicks. Swapping very indented pads with pads without so much indenting (i.e. from the bass section) resulted in reduced clicking. This wasn't a great solution though, since indented pads would not work well on reeds of greater width than what they were indented by.

I found as well that this physical deformation was not reversible. Even after sitting for months outside of the unit, the pads did not completely regain their original shape. Will this happen to all Clavinet.com pads within a decade or so? Who knows; the original owners may have had poor storage conditions, or perhaps there was something else that could have started or sped up the process. I'm also not sure whether any chemical degradation has taken place. It's possible, and one thing that might suggest it is that the pads are slightly yellow, whereas in all images that I've seen online they appear completely white.

Now, I did end up replacing these pads, but here are two solutions that might work if you find yourself with this same issue. One fellow informed me that a common way to reduce clicking of Clavinet.com pads in general is to apply a thin layer of dielectric grease to the pads, presumably to reduce triboelectric charging between the pads and the reeds. Another possible solution would be to slice off a thin section of the end, so that the pad would once again have a flat surface. Again, I did not have a chance to try either of these before...

I decided after a while to order the replacement pads of Ken Rich Sound Services (see Links section), which are essentially reproductions of the original pad design. This does mean that perhaps they carry the same inherent flaw of the original in that the foam will decompose after a while, but I decided that what I desired most was the sound that the Pianet would have originally produced. Here's what the pads looked like once arrived:

Note that it says Pianet N specifically on the package, but these will work on any electrostatic Pianet (i.e. any one except the T, M, and Clavinet-Pianet Duo). Also, some of the pads didn't have the leather between them cut all the way through, but this was easily resolved with some scissors. Once installed:

As you may be able to see in the very close-up image, the pads when first installed do tend to leave little blobs of silicone oil on either side of the pad. This is no big deal on the low notes, but I noticed that on the high octave particularly, the oil caused the reeds to become considerably flat (due to increased mass). Cleaning the oil off a few times, particularly near the tip of the reed, solved the problem.

I've made a video showing the tone differences between the original (cleaned, but otherwise unaltered) Clavinet.com and the Ken Rich sticky pads, to be found below:

The Hardware

On the outside, and really overall, the Combo Pianet is a particularly simple and elegant design. The rectangular casing is made of veneered particle board, which happens to very nicely match the wood of the Hammond S6 I've placed it on top of. This may not be a coincidence; it states in the service manual (available at the bottom of the page) that the Combo Pianet was specifically designed to be a "third manual" for an organ, and at the time, Hammonds with similar wood finish would have been popular.

Having a look at the very front and back, the front has a metal fascia with a golden hammertone finish that also bears lettering of the brand and model, and the back has similar lettering to the front. This particular one has unusual lettering; in fact, I've found only one image of another unit with the same style so far. On the front, instead of "Combo Pianet" on the far left and "HOHNER" on the far right, everything is towards the left (reading "HOHNER Combo Pianet®") and there is also a registered trademark symbol. Looking at the back, instead of a simple "HOHNER" on the right, there is a central "HOHNER" (much like on the Hohner International electronic piano), and "Combo Pianet®" to the right.

Below are images of what the typical Combo Pianet lettering looks like for comparison with the above (these are not my images).

On the left cheek block, there is the only control on the unit: a single knob, which functions as both a power switch and volume adjuster.

Removing two screws on the top allows you to carefully pull the covering piece out of its groove at the back, to have complete access to the internal workings. The inside of the case is lined with conductive shielding foil, which is grounded. On the back panel, there is a sticker warning users not to loosen the screws that fix the reed tongues, and judging by the presence of the red seal on all of the screws, it looks like no one has done so yet on this unit.

Shown below is a close image of some of the reeds and pickups towards the higher end. Each reed is a thin piece of ground stainless steel, fixed at one end, with the other allowed to vibrate freely. Geometrically, the reeds are simpler than those of Wurlitzer electric pianos, lacking any curvature or solder (although the lowest reeds have some brass weights). The metal "tongues" positioned with a thin gap at the free ends of each reed are the electrostatic pickups, which can be moved further from and closer to the reeds to respectively decrease or increase loudness and harmonic content. The reeds are held at ground potential, while the pickup tongues are brought up to approximately 300V DC, and this allows slight changes of capacitance between the reeds and pickups (and thereby the vibration of the reeds) to be amplified as an electric signal. What it also means is that any slight contamination between the reeds and pickups will be easily audible, typically as a "buzzy" noise. As well, triboelectric charging by solid silicone sticky pads can have an audible effect, whereas with electromagnetic pickups such as on the Pianet T, this is not an audible effect.

Because the electrostatic pickup necessitates active electronics, there is a circuit board, and it is quite simple; in fact, the simplest of all electrostatic Pianets. It lacks power supply circuitry due to using an external 9V DC supply, and it also lacks a tremolo circuit that is present in all other electrostatic Pianet models. It also lacks a power amplifier, since it has a single low-level output designed to be used with a standard instrument amplifier. All that it does contain is circuitry for providing the voltage required for the pickup, and circuitry for basic preamplification of the pickup's signal. There isn't even a power light.

Looking at the very back, on the left side are the only two jacks of the unit: a power jack which accepts 9V DC from a 1/8" center positive plug, and a 1/4" audio output jack. As well, the builder's plate is visible, with mine being #772835. Unfortunately, it seems even Hohner may not have a record of dates corresponding to serial numbers (I contacted them), so I'm currently unable to date it any more precisely than the overall production run of between 1972-76.

The Sounds

Probably the most similar sounding keyboard type would be the Wurlitzer electric pianos, but the differences are still quite considerable. When the amplifier is off, playing a key produces a faint reed sound that, especially in the middle section, has very noticeable overtones which exhibit a strange almost downwards-filter-sweep-like effect as the note rings out. Surprisingly, these overtones are not very audible in the output, but they still can be heard slightly. Some notes have sounds of beating/interference, or otherwise strange "inharmonicities", and I was at first curious as to if these were a result of aged reeds, but listening to recordings from "back in the day" indicated that this effect has likely been present from the start, and also contributes to the unique sound of the Pianet.

In the "features" section, I mentioned that this thing has some degree of velocity sensitivity to it. Of course, the design, with sticky pads plucking the reeds, is inherently not well-suited to very dynamic playing. Pushing a key down very slowly does produce a quiet note, particularly in the low end, but it takes a great amount of finesse to play so quietly in practice. Any keypress between a low-medium to hard produces around the same loudness; it's only in the very soft keypresses that dynamics become more apparent. Dynamic range is most possible towards the low end, due to the reeds being longest and with the widest range of travel, and thus there is simply more distance that the pads can exert influence over the reeds.

Another thing that distinguishes this keyboard from others is that is lacks a sustain mechanism. Since the sticky pads act as both pluckers and dampers, there is no practical way to add such a mechanism, at least mechanically. Some may consider this limiting, but I think it may be one of the keyboard's best "features", since it forces the player to play in such a way that they do not rely on a sustain mechanism.

If you notice any errors or have additional information that you would like to add, please contact me!


Last Updated: 7/21/2016