Tonestar 8106, 8106 Filter & Slim O Review – Top-Notch Sonic Noodling

Continuing its quest for world domination in the filter market, Studio Electronics brings us a new flavour of Tonestar, and a separate filter and oscillator, drawing inspiration from Junos and Jupiters. Dave Gale visits the new Gods of Eurorack… Details Kit Tonestar 8106 synth voice, 8106 filter, Slim O oscillator modules Manufacturer Studio Electronics Price […]

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Continuing its quest for world domination in the filter market, Studio Electronics brings us a new flavour of Tonestar, and a separate filter and oscillator, drawing inspiration from Junos and Jupiters. Dave Gale visits the new Gods of Eurorack…


Kit Tonestar 8106 synth voice, 8106 filter, Slim O oscillator modules
Manufacturer Studio Electronics
Price £499/£249/£209
Contact MSL Professional
0207 118 0133



If there’s one thing they like at Studio Electronics, it’s a filter. Goodness knows, in both its Boomstar and Modular range, you can buy just about any filter you want, from Moog- and ARP-based designs, to something akin to the CS-80. It’s also possible to buy designs based on the Roland TB-303, but now SE bring us a new Roland-style flavour, in the shape of the Tonestar/Filter 8106, which offers a full synth voice and the 8106 Filter on its own, in Eurorack form. As if that wasn’t enough, you can also now buy a small single oscillator to add fatness to your Tonestar. So, plenty of options to choose from – let’s dive in with the new Tonestar first, and take a look.

Buy Jupiter

The ‘8106’ moniker is a nod to Roland filter designs which, according to SE, are all pretty much the same. The differences lie in the way things are tuned, so what we have here is a Filter/Tonestar design which is based firmly on the Jupiter-8/Juno-60 and 106. It’s very much a discrete, through-hole design, which has had a little bit of an upgrade in certain areas – most notably the operational amplifiers, which (as I was to discover) give an altogether more dynamic and lively sound and feel. There’s also been tweakage elsewhere; the Jupiter-8 filter wasn’t able to self-oscillate, and you’re going to want that, aren’t you? Good, because in tune with its Juno counterparts, it does indeed self-oscillate, but that’s just the beginning of the story.

The Tonestar 8106 shares many similarities with the Tonestar 2600 (reviewed in issue 161). It’s the same size and layout, with a few little tweaks here and there. Firstly, and almost by osmosis, the layout of the original Tonestar 2600 actually lends itself excellently to the original Juno design. The VCO section offers level/amplitude controls for Saw, Pulse/Square and the all-important sub-oscillator, which is completely in tune with the original Juno DCO architecture. Nestling at the bottom of the channel is a small pot to feed in some all-important white noise. The Tonestar also offers a very nifty little Triangle wave, which can be detached from the filter, meaning that you can always have an unfiltered fundamental to anchor the tonal centre.

Joy of joys, there’s an octave switch, which will quickly and easily jump across two full octaves (three positions). All the waves are available to separate output, as well as a summed mix output, and again, in tune with the old Roland DCO structure, the white-noise channel has its own independent volume control. So far, so good…let’s now move to the back end of the Tonestar and look at the envelopes.

Unlike some stripped-down modules of this kind, the Tonestars are very generous when it comes to envelopes. There are two: one a fully fledged ADSR strip, the other a simplistic, but useful, ARP design, allowing for a certain flexibility of routing. There is also a Hold play-through setting, if you just want to drone. Now, I’m reliably informed the envelopes differ between the original Tonestar 2600 and this new flavour.

Apparently, the older ARP envelopes used to bleed a little, so with outrageous attention to detail, that’s what SE engineered it to do. The new 8106 Tonestar, on the other hand, doesn’t bleed. In fact, in my direct comparisons, the envelopes feel much tighter and snappier, exactly like an old Juno or SH-10. Turn all those phases down and there’s plenty of clicking, always a great sign of a snappy envelope, but so easily backed off. The knock-on effect is that the overall decay time appears to be a little less, but it’s still generous enough to hold a long-held release, should you desire.

At the centre of the module and the filter, we see some changes over the original Tonestar, with the loss of the Modulation switch. This has been replaced on the 8106 by a fully sweepable High Pass Filter pot instead. This does mean you lose the ability to modulate the filter Resonance from the onboard LFO, but LFO modulation of the Cut Off remains hardwired and intact, so no harm done.

To see how the filter on the new Tonestar compared, I powered up my trusted SH-101 and Juno 60, got squelchy and made direct comparisons. The 8106 seems a little harsher and crisper than my Juno, but that may have more to do with the fact that it has more of the flavour of a 106, rather than a 60; I found the filter was more akin to my SH-101; crisp, nice and bright in the top end, with plenty of wispy fizziness, and with a lovely hint of harshness that made the 101 such a favourite. In fact, to quote Lord Flashheart, it’s pretty “firm and fruity” in the bottom end, too. The resonance is great; it whistles like you want it to and can be easily backed off or exceeded as you see fit, and with all that great Tonestar architecture on the front and back ends, it’s a dream to listen to and work with.

SE told me it has looked at the original circuit designs, and due to an upgrade to contemporary components, and improvements in the Op-Amp circuitry, confirmed that the overall effect should be more punchy, lively and dynamic. It might be based on a Juno, but it’s definitely got some 101 gnarliness about it which, as it’s a mono machine, you have to appreciate.

The previously mentioned HPF can also come into play here, as a separate entity. There’s the usual loss of bottom end, when the resonance is applied to the extreme, but as with the previous Tonestar, there’s a Drive pot right on the filter to help bring some bottom end back into play. However, I found the backend overdrive even better at reinstating the the lower frequencies. There’s LFO or envelope modulation on the filter Cut Off, and the LFO Rate and Amount controls are below this section.

This might be a synth voice, but it’s also semi-modular, and there are plenty of jack points to interface with the rest of your Eurorack. You have everything you could possibly need, from wave outputs and white noise up to envelope outputs and options for modulation input and even external audio input, too. It’s comprehensive, if you want or need it to be, or use it as is.

I love this new take on an old classic. It’s full of character with plenty of charm, too, and can be subtly sweet or suitably harsh, according to how you feel; but in line with the rest of the SE lineup, it’s also possible to buy the filter as a module, in its own right…

The filter option

As I said before, SE loves a filter, and offers an amazing amount of choice. This new design fits into a 12HP panel, but dispenses with the Juno-106 grey colours of the Tonestar, in favour of a more vintage-looking black panel, with a striking red stripe across the top. It looks really classy, but does the sound match up?

As is traditional with these settings, SE have again tweaked the filter-only offering to give additional options to the Tonestar version of the Filter. There are the obvious pots for frequency Cut Off and Resonance, but we also have CV control of both of these parameters, with onboard positive and negative attenuation. The High Pass Filter also has its own large pot, with amplitude control for both input and output. But here, and in common with other SE filters, ramping these phases to the extremities will induce overdrive. With an SE Oscillations patched into the ‘from’ end, there was an amazing amount of frequency depth. It really does sound fantastic, and has all of those Roland calling cards from the classic 80s era.

We’re not quite done yet, as the filter module also offers a rather desirable 6dB and 24dB option. This can be deployed via a switch, from the main output; or there’s a dedicated 6dB output, meaning you can take both filter types out simultaneously, if so desired. The 24dB filter sounds amazingly crisp and clean, but when switching to the 6dB, a wonderful fuzziness surrounds the tonal centre. It’s almost like the fundamental had eaten some Ready Brek, and a wonderful fuzzy warmth was illuminating from its tonal centre. Dial in some resonance and further patch in an envelope to the Cut Off and you’ll get the distinctive sound we all love. The 6dB offering certainly has some grit to it, and contrasts really nicely with the purity of the 24dB option.

In common with the Tonestar, the 8106 Filter will self-oscillate and as you’d expect from a module of that era, it’s perfect for everything from those screechy sequencer lines, right through to some excellent Hi-Q-type sounds. In fact, in the case of the latter, it started to sound very ARP-like. The LPF is fully trackable, and I had the Resonance happily playing lines without the need for any inputted oscillator. Perfect for those drum ’n’ bass low tones.

In my A/B tests against the filter section on the Tonestar, it’s fair to say the filter module felt slightly more weighty. The Tonestar packs a hell of a punch, in a single-voice unit, where the filter-only option feels like it’s even more of a class act, particularly with the addition of the 6dB output. Apparently, the filter designs are identical on both units (with the Tonestar missing the 6dB option), so my guess is that it has more to do with the placement of the Input/Output pots on the filter-only module and the inducement of a small degree of overdrive. This isn’t a bad thing; it just means that on the Tonestar, you might have to induce some overdrive yourself, but frankly, why wouldn’t you? If you also factor in the feedback on the Tonestar’s back-end VCA, I think the choice will largely be dictated by budget and whether you feel you need a complete voice channel in your Eurorack.

Oscillator on a diet

The Tonestar offers a very substantial oscillator, with plenty of character, and a sub-oscillator built in. But as we all know, it’s often an idea to have a second oscillator sitting alongside, allowing for detuning or even a variance of pitch altogether, and that’s where SE has introduced the Slim O.

This is a stripped-down version of the SE Oscillations VCO. At a not-too-small 8HP, the Slim O offers full-sized pots for Frequency and Pulse Width control, along with +/- attenuators for both Frequency Modulation and Pulse Width control. There are separate outputs for Triangle, Sawtooth and Square waves so, in essence, you lose the summed output, Sub Oscillator and Sine Wave capability from the Oscillations, but save money along the way. This makes it the Tonestar’s perfect partner and will turn the synth-voice channel into something more akin to an old Roland SH-2, which was always such a wonderfully phat-sounding machine, thanks to the dual-oscillator architecture. The external input on the Tonestar will allow very easy integration of the Slim O, so it can almost be considered part of the same unit.

Sonically, there’s nothing to choose between the Slim O and the Oscillations. It sounds huge, even without the sub; and thanks to the addition of a three-position octave switch, it’s possible to jump up and down a two-octave range without the need to turn the frequency pot. So if you have a Tonestar, you’ll have a sub; pop the Slim O alongside and you’ll be churning out some serious detuned noises in seconds.

Do I really need this?

If you like that Roland sound, and have a smaller Eurorack system, the Tonestar 8106 represents excellent value for money, and offers an amazing amount of functionality with it. It is a synth voice, all in one, so it could be a useful way of starting out in Eurorack, or equally a way to get a lot into an existing system, within a reasonably small footprint, for sensible money. If, on the other hand, you have a larger rig, the filter is a class act that would be at home in just about any setting.

It’s the weight in the bottom end that particularly impressed me, but when coupled with the HPF and 6/24dB outputs, it’s very good value for money, and sounds suitably impressive. The Slim O is a sensible second oscillator, and the absolute perfect partner for the Tonestar modules. But if it’s your first oscillator, consider the Oscillations first, as you’ll appreciate having the sub built right in.


There’s no doubt that these products fit the bill in a number of settings. The Studio Electronics build quality has always been among the best in the market and all three of these modules are impressively sturdy in design. I’ve always loved the Tonestar 2600, but somehow, I find the 8106 Tonestar even more endearing – which is most likely thanks to my relationship with Roland products since the early 80s. It really does sound very punchy, but it’s nice to have options, if you feel that you don’t want a whole synth-voice channel.

With an existing system, you might feel that the allure of a separate filter is more up your street, and the Slim O would not be out of place as a standalone oscillator, either. My only concern here is that if you are considering the Slim O, it’s financially not a million miles away from the SE Oscillations which, with its added extras, might appeal.

For my money, the Oscillations is one of the absolute-best VCOs on the market, and the Slim O/Oscillations combo would make for an awesome pairing – as I discovered when I paired up the two in my own rack. Add a couple of SE filters into the equation, and you’ve got something very stunning. That’s also where I feel the 8106 Filter plays a major role. I absolutely adored using it; the rewards from sonic noodling are great, it’s wonderfully tight, and different to something more Moog Ladder like – after all, variety is what makes for a versatile Eurorack


Possibly the closest synth-voice channel to the Tonestar 8106 is the Intellijel Atlantis, which is modelled to offer similar characteristics to the Roland SH-101. This offers some impressive credentials, which the 101 never could in terms of patching, but some users report than it lacks the weight of the 101, which you couldn’t say of the new Tonestar. If you’d prefer just the filter section, then other Roland Jupe/Juno-style filters to consider include the new Jove filter from System 80, which is firmly modelled on the Jupiter-6, or the rather older and more established AMSynths JP8 filter, which is now discontinued, but can be found second-hand in all the usual places.


Key Features – Tonestar 8106

  • Juno-style voice structure
  • Semi-modular analogue architecture
  • Hard-wired or semi-modular, with plenty of patch points
  • Onboard Juno/Jupiter-style filter
  • Width: Tonestar 32HP
  • Current draw: +12:130mA; -12: 80mA
  • Depth: 35mm (including connectors); skiff-friendly

Key Features – 8106 Filter

  • Juno/Jupiter-style filter module
  • Comprehensive filter control
  • 24dB/6dB outputs
  • LPF is fully trackable
  • LPF and HPF onboard
  • Width: Tonestar 12HP
  • Current draw: +12: 130mA -12: 80mA
  • Depth: 38mm (including connectors); skiff-friendly

Key Features – Slim O oscillator

  • Small and compact VCO
  • Octave Range switch
  • Oscillator Sync input
  • CV control of Cut Off and Resonance
  • Width: Tonestar 8HP
  • Current draw : +12: 20mA -12: 39mA
  • Depth: 38mm (including connectors); skiff-friendly

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