Roland’s lightweight monosynth from the 1980’s.

Roland’s SH series are undoubtedly among the finest synthsizers ever made. Their sonic character has stood the test of time and they are sought after to this day despite the large number of new offerings in the mono-synth arena. It’s hard to think of a more reliable and potently useable synth than the little SH-2, a true dark horse of monophonic synthesizers and an instrument that people who own them usually put on their “never sell” list. The larger SH-5 and SH-7 flagships from the 1970’s are imposing and capable instruments that are a huge amount of fun to use. There are 11 different synths in the original SH series. In the early 1980’s Roland came out with a very different member of the SH family. It was a small, 32 key speedster format bass/lead synth. It departed from Roland’s usual rugged steel chassis for a lightweight plasic case with a steel bottom cover. This low weight along with it’s ability to run on batteries allowed the SH-101 to double as a keytar – Attach the optional modulation grip and the strap mount and slip on a guitar strap and you can play the SH-101 while you walk around the stage under battery power. Remove them and the SH-101 sits neatly in your keyboard rig ready for a lead solo or a bass line.

A Blue SH-101 with factory accessories

The most common grey version of the SH-101

The SH-101 introduced another innovation – It had a micro-computer installed that gave the synth features that were uncommon at the time: An on-board arpeggiator, a simple sequencer with an external clock input jack, a button to hold the current note and the ability to transpose the keyboard by simply holding a button and tapping a key. It also provides a handy test mode to make calibration of the synth easier. It did not go so far as to use the micro for patch storage and recall and this may actually be part of the great sound of this little synth.

Once an analog synthesizer is designed with digital patch storage a fundamental change in the synth circuitry is inevitable. In an analog synth the faders and pots and foot pedals are an actual part of the synthesizer circuits. For example if you open up an SH-101 and remove the resonance slider the filter resonance feedback path is broken and it will no longer work. In an analog synth that has digital patch storage you can go in there and remove the pots and the synth will still play stored patches perfectly, you just wont be able to edit those sounds. This difference gives an immediate response and a cleaner circuit than a synth that has it’s parameters adjusted by a control voltage from a digital-analog converter. The SH-101’s keyboard CV is generated by a DAC but the top panel controls are direct. The 101 also has CV and gate inputs and outputs on mini-jacks so it can be interfaced with other synths and sequencers.

A tour inside the SH-101

The main circuit board

The SH-101’s internal layout is quite simple. A keyboard action, a board containing the front panel controls and the circuit that generates the sub oscillator waveform, a main board with most of the 101’s circuitry laid out pretty much in order of signal flow, a couple of small jack boards and a board for the pitch bender panel. Servicing is quite straighforward. Unlike the other SH-series instruments the case is somewhat fragile and it is essential to ensure that when screws are installed that they are inserted gently so that they follow the original thread to avoid damaging the plastic posts that mount the boards and bottom panel onto the shell. It’s definitely a synth to re-assemble carefully by hand, don’t be tempted to use that battery powered screw driver. Most of the electronic components are common and easily obtained, there are some uncommon chips and transistors that are rare.

The power supply section

End view of the power supply section

Lets take a look at how it all works, starting with the LHS of the main board where the power supply can be found. The SH-101’s power supply is an unusual design largely due to the need to be able to run the synth on batteries. The 6 x “C” size cells provide 9V which isn’t enough to power the synth. For example the Curtis 3340 oscillator IC which is the 101’s VCO requires a dual positive/negative supply and the range of the positive rail is 10-18V, the negative rail is -4.5 to -18V. This means that the very minimum voltage range that the VCO needs to function at all is 14.5 Volts. The SH-101 needs several different internal voltage rails so the Roland engineers designed a small step-up transformer circuit where the 9V DC from the battery (or the 9-12V DC from the mains adaptor) is first turned into AC and boosted through a tiny transformer that you can see in the above photos which generates a higher AC voltage that is then rectified back to DC, regulated and fed into the synth and the computer circuits. The transformer is the component with the silver sticker on the top in the photo. Around it are the transistors that create the oscillator that feeds the transformer and the rectifier diodes and smoothing capacitors that create the final correct DC voltages that run the machine. The power supply must be stable as the VCO is very sensitive to supply voltage as is the DAC.

Something worth noting: The SH-101’s power switch is a little 3 pole push button and it often can cause problems with tuning. You can see this on many SH-101’s if you hold a note and gently touch or tap the power button – if the button is dirty or tarnished inside the 101’s pitch will wobble. If your synth is having pitch stability issues this would be the first place to check.

The tiny transformer

Power button removed to show switch

The micro computer and peripherals

Moving along the circuit board to the right of the power supply we find a few chips and components that handle the trigger generation circuitry and the LFO oscillator section (IC 3, 4 & 5 in the photo below). Beside them we see the large micro-computer chip (IC 6) and the DAC section (IC 7, 9, 10 & 11). The Toshiba CPU chip reads the keyboard and buttons, feeds the DAC the correct data to produce the VCO and filter pitch CV, runs the sequencer and arpeggiator, monitors the hold button and runs the test mode feature. It scans around the keys and buttons every 1.5-3.5 milliseconds. It also handles the range and transpose switches by adding an appropriate voltage offset to the final CV that the DAC produces for the VCO and filter. It’s similar to the Sequential Circuits Pro-One in this respect, both need the DAC in the keyboard circuit in order to be able to provide the sequencer and the arpeggiator feature. to the right of the photo is IC 8, this chip decodes the data to light up the LED’s on the top panel.

The LFO circuit to the left, the Toshiba Micro at the centre and the DAC circuitry below it

Closeup of the Toshiba TMP80C49 micro

The Toshiba TMP80C49P IC was chosen by Roland as a compact way to put a micro-computer into a small synth. The TMP80C49P is an “all in one” micro-computer that can replace several IC’s that are usually found as separate parts in most other microprocessor controlled synths. It has CMOS architecture and includes an 8 bit CPU, 128 x 8 RAM, 2k x 8 ROM to store the operating system, an 8 bit timer/counter and 27 I/O lines. The chip is more limited than using separate IC’s for memory and counters but for a tiny machine like this it covers every need and saves power when used with batteries. It only has a few functions to handle and so it can get by with it’s tiny amount of RAM and ROM. It was designed as a dedicated controller and it works very well in this application.

If you are into the Maker scene then this might be a fun chip to experiment with replacing with a tiny custom programmed micro controller, potentially you could really boost the sequencer of the 101 to new levels and features.

The synth circuits

The filter and VCA section

The IR3019 VCF IC 

The SH-101 uses some famous IC’s including the Curtis Electro-music CEM3340 oscillator IC which we have already met in some of our other posts. The 3340 is found in some of the most important analog synths of all time. The VCF is a custom Roland IC called the IR3109 which is a chip containing a set of 4 buffered transconductance op-amps and an exponential converter arranged specifically for use as a music filter. It is found in many other Roland synths such as the Jupiter 8 and Jupiter 6, some Jupiter 4’s, the Juno 6 and Juno-60 and the MC-202 and it produces one of the most recognisable classic Roland filter sounds. With the oscillator from the Prophet 5 and the filter from the Jupiter 8 it’s no wonder that the SH-101 has such a big sound.

In the image above you can see the filter and VCA section. The VCA is the vertical chip on the RHS with the light blue paint mark, it is another Roland custom IC, the BA662 which is found in just about every Roland vintage synth from the TB-303 right up to all of the Jupiters, often in large numbers doing different duties within the synths. The IR3109 and a couple of BA662’s comprise the infamous Juno-106 “voice chip” however the standard IC’s don’t share the reliability problems of the Juno-106 module.

The Noise generator, VCO, VCF and VCA section

The image above shows the noise generator circuit on the top left (the two transistors and the IR9022 IC), the oscillator section is towards the centre (the CEM3340 IC with the blue dot and the silver timing capacitor beside it). In the centre you can see the two blue trimmers that are used to scale and tune the VCO if it drifts out due to age or if the ambient temperature changes significantly, they are marked as “VCO width” and “VCO tune”. These are the two trimmers that you need to adjust for a quick fix of the synth’s scaling if an octave on the keyboard doesn’t result in an exact octave of pitch change. To do so you will need a tuner connected to the 101’s output, the procedure is in the 101 service manual and it can be done quite easily. The metal “VCF width” trimmer above them allows the filter to be roughly scaled so that at full resonance it can be used as sine wave oscillator that can theoretically play a chromatic scale. The two trimmers on the left side of the image set the VCO pulse width and the DAC scaling.

The ADSR envelope generator circuit

There is a gap in the circuit board with no components and then all alone at the far right hand end of the circuit board is the little cluster of parts that make up the ADSR envelope generator circuit. Nothing special here, it uses mostly common parts rather than a custom ADSR chip such as those found in the Jupiter 8 and Juno-6 and 60 which are rare IC’s indeed. as mentioned above the ADSR sliders are an integral part of the circuitry, they are located in the top panel board which is connected to the main circuit board via white ribbon connectors, one of which is visible at the top of the image above.

Circuit board identifier

The 101’s envelope section

Buying guide, servicing and reliability

The most common faults in the SH-101 are caused by worn or damaged sliders. Fortunately this is not a show stopper as new replacement sliders are readily available. Pitch issues can be caused by the power switch, it’s a good idea to occasionally disconnect the 101 from power and exercise the switch rapidly a few dozen times in order to keep the contact surfaces from tarnishing too much.

The big killer of the SH-101 is corrosion damage from leaking batteries. If you use your 101 with batteries or keep them installed to hold your sequencer memory then make certain to replace them regularly and to remove them if the synth is to be left stored or unused for a long period.

As far as servicing goes the 101 is quite simple and straightforward to repair and calibrate, one thing that can cause a problem if it fails is the sub oscillator: It uses a 4013 dual flip flop IC which it is a very common chip that is still manufactured to this day. The problem is that for some reason Roland synths can be very picky about the brand and vintage of 4013 that will work properly. Sometimes you often need to experiment with the brand and batch to find a chip that will work, some just won’t operate in the 101. The same issue appears in the System 100M phaser/delay module. It likes a Toshiba TC4013BP IC in it’s delay chip clock circuit and not much else. Replacing it with another brand, either buffered or unbuffered will often not work. It’s not just Roland that can be choosy about 4000 series IC’s – If for example you replace the 4011 IC that handles the ring modulation on an ARP Odyssey with a brand that the synth doesn’t like you can finish up with the chip oscillating, VCO leakage throughout the synth and modulation on the power supply rails so it is always wise to be careful replacing certain 4000 series devices.

When buying an SH-101 you can readily tell the condition of the synth as testing every function does not take long. Check the battery compartment and make sure that it is clean and that the springs and contacts are not corroded. It would be worth taking a set of batteries along and loading them to ensure that the instrument runs using battery power. If the compartment has battey leakage damage then you will need to look more deeply to make sure that the leakage hasn’t gone further inside the machine.

Look for missing screws on the bottom panel which would usually indicate broken off plastic posts inside. Power up the synth and try every function, make sure that the bender is smooth and that the LFO works when you gently push the bend lever forward (and the LFO mod slider above it is up). Operate every slider and make sure that you hear the expected changes to the sound with no jumps or scratches, play some notes into the sequencer and check that it plays back and check that the hold, arpeggio and key transpose buttons work. Play up and down every key to make sure that all of the key contacts are good. Try the synth without batteries using a power adaptor.

And finally, the SH-101 is choosy about it’s power adaptor too, best to use an older regulated linear (transformer) unit, modern lightweight switch-mode power adaptors can often make the synth noisy, possibly due to high frequency switching noise from the adaptod interfering with the SH-101’s unusual power supply circuitry.

From there in it will depend on whether you want a particular colour, grey is the most common, you will pay a premium for red or blue and for the mod grip option if it’s available with the synth. Happy playing!

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