You are here

Rockruepel Comp Two

Vari-mu Compressor
Published December 2013
By Hannes Bieger

Rockruepel Comp TwoPhotos: Hannes Bieger

This all-valve dynamics processor offers amazing versatility, with uses ranging from sublime transient control to brutal compression.

One might infer from the Rockruepel name — 'Ruepel' translates into English as 'bully' or 'rogue' — that the Düsseldorf-based boutique manufacturer's latest product is an aggressive-sounding device. Yet, the CompTwo has actually been designed with much broader appeal in mind. Don't get me wrong, it's certainly capable of extremely fast compression, and it can also be driven into distorted mayhem, but its signal path has been optimised for transparency and clarity.

History & Lineage

The Comp Two has evolved impressively from the company's first 2U rackmount prototype, which I tried a few years ago. Following this, Rockruepel's mastermind Oliver Gregor teamed up with German studio specialist Guido Apke to create the Comp One, a 3U dynamics processor which was essentially a proof of concept, created with a no-expense-spared approach — it even employed featured silver/gold wire by Mundorff throughout the entire signal path — and was limited to a production run of just 50 units. The Comp Two has been developed with the same ambitions of quality, but in this design Gregor has judiciously chosen a few corners to cut in order to reduce manufacturing costs. The result can by no means be called a cheap device, but Rockruepel have been able to manufacture it in slightly larger quantities.

The right channel uses two Sowter transformers, two valves and two WIMA coupling capacitors. The right channel uses two Sowter transformers, two valves and two WIMA coupling capacitors.


The Comp Two is an all-valve variable-mu design: apart from the VU meter drivers, which have absolutely no sonic relevance, there are no transistor stages. Its signal path adheres to audiophile principles — it has been kept as short as possible — and the device boasts many special features (and, not least, extremely wide parameter ranges), which make the compressor suitable for a wide range of applications. The Comp Two can be employed as a tone shaper during tracking, it serves as a versatile mixing tool, and it also delivers great results in a mastering chain. Even amongst the high-end competition, this degree of flexibility stands out.

Each of the time-constant rotary switches offers 10 positions. The attack and release values are slightly interactive, they vary to some degree depending on the setting of the otherparameter. Thus it is difficult to provide exact values for every combination. Both parameter ranges cover a lot of ground, though. The release is specified between 200ms and 4s at a medium attack, whereas the attack can be set between 3.5 and 70 ms at a medium release. But with faster release values the attack becomes faster, too. The shortest possible attack time is around 600 microseconds, which already places the Comp Two in the realm of ultra-fast 'limiting amplifiers', such as the Universal Audio 1176LN. To put that another way, the time constants of the Rockruepel compressor allow for brutal, aggressive limiting as well as the slow, thundering transient shaping, which might be more ideal for mastering applications.

This flexibility extends to the gain-staging possibilities, too. By way of using the input and output potentiometers, the levels inside the unit's circuitry can be set to extreme values without overloading the next processor in the chain. At higher input settings the Comp Two can be driven into a meaty saturation, thanks to its maximum gain reserve — a hefty 32dB, which might be enough to serve as a mic preamp in some circumstances! The Comp Two boasts a threshold knob in addition to the input/output pots. This way, the amount of gain reduction can be set almost fully independently from the tone and output level of its valve-driven line stages.

Flexible side-chain control: the Comp Two offers three side-chain low-cut filter frequencies and an additional 'amp only' mode.Flexible side-chain control: the Comp Two offers three side-chain low-cut filter frequencies and an additional 'amp only' mode.

Finally, the side-chain offers a few interesting controls. There's a 'flat' setting, but the Comp Two also offers a side-chain high-pass filter, with three selectable corner frequencies: 54, 74 and 110 Hz. The amp-only mode deactivates the compression, but the entire circuitry remains in the signal path. This way, the Rockruepel compressor may also be used as a saturation device, and the dynamic reduction which can be achieved by rounding off the transients through soft clipping provides an interesting alternative to the actual compression.

The signal path of each channel employs only a handful of parts, which, from an audiophile point of view, is a great thing: there's a pair of Sowter input and output transformers, two WIMA coupling capacitors and two input and output valves — and that's it! Each channel boasts a 6CG7 dual-triode for the make-up gain. This valve is less common than the ubiquitous 12AX7, but it has played an important role in the circuits of some coveted vintage compressors, including various Altec compressors (and, thus, also in the legendary EMI RS124 units). For the input valve, which is responsible for the gain reduction, Gregor has chosen the more exotic 6N3 — a Russian Heptode valve, which, to the best of my knowledge, has never before been employed in a compressor circuit.

The Comp Two boasts quality components outside the signal path, too. There are ALPS potentiometers and ELMA rotary switches, and the PSU delivers fully independent supply voltages for both channels, making the Rockruepel a true dual-mono design. The gain reduction of both channels can be linked at the flick of a switch, and the Comp Two offers relay-buffered bypass switches for each channel. The two Hoyt VU meters are mounted on the chunky 6mm aluminium face plate, which, together with the other parts of the enclosure, offers a safe environment for the circuitry.

One obvious question remains: which of the Comp One's corners have been cut? Actually, surprisingly few aspects have been changed. The Comp Two employs internal Sommer Cable wiring instead of the expensive and difficult-to-handle braided Mundorff wires, and the Mundorff Silver/Gold capacitors of the Comp One have been replaced with the WIMA Polypropylene film caps. The side-chain of the Comp One is rectified by means of vintage NOS Telefunken diode valves, while the Comp Two employs semiconductor diodes. Finally, the visual appearance of the Comp One is even more lavish. The only truly functional difference between the two units is the 'Ruepel mode' of the Comp One. In a similar fashion to the all-button mode of the 1176LN, this offers an extremely aggressive compression that sounds almost like a gating effectwhen set to shorter time constants. This is a characterful addition, but it can make the operation of the unit less stable and it could also reduce the life span of the 6N3 valves. It's one of the most unique features of the original Rockruepel design, but it's debatable how useful it is in the trenches of daily studio work. Bearing in mind the purchase price, I suspect most users will probably employ the compressor in a mastering environment, and thus rely more on the transparent and clear-sounding side of the compressor's tonal spectrum, in which case it's not a huge loss. The fact that the Comp Two's predecessor offers even more, then, doesn't take anything away from this processor: it's a brilliant, original design, which employs high-quality components throughout.

In Use

Because of the plentiful features and wide parameter ranges, the Comp Two is well equipped for many applications. So much so that the best way I can think to demonstrate what the unit can do is to explore a few very specific scenarios. Normally, it seems to be good practice to start with the input, output and threshold controls at their 12 o'clock settings. This way, the compressor sounds pretty clean to begin with, and then the saturation can be brought into play gradually, by turning up the input and backing off the output level.

In most mastering applications, one would wish to employ a slower attack and medium to fast release settings. Such a setup brings out the transients and the low-end punch that so many engineers seek today. I'd suggest a 30ms attack (position 8) and a 300ms release (position 4) as a good starting point for mix-bus and mastering duties, but you will, of course, need to adjust these settings according to the material. My next idea was to try the Rockruepel as a 'limiting amplifier', which simply required that I set the time constants to their fastest settings to see what happened.

The third starting point is the amp-only mode, which I recommend you do not overlook! With the copious amounts of internal gain at hand, the Comp Two may very well serve as a line, or even, in some scenarios, a microphone amplifier. Also, the soft-clipping that occurs when the circuitry is driven into non-linear behaviour can be a good alternative to actual compression. Saturation, by definition, limits the dynamic range of the signal, and the way the Comp Two breaks up can do wonders to some material. In some cases, it's possible to gain a few decibels of average level when pushing a drum bus into saturation, without ruining the sound at all. In fact, as in this case, the results often sound slightly mid-forward, which can make the source seem somehow 'sweeter'. Saturation works instantaneously, without applying time constants to the signal. This way, some transients can be rounded off without the pumping artifacts which might occur using regular compression.

When applying punchy slower time-constants or faster attack and release settings to generate some 'squeeze' the Rockruepel impressed me with its results. Because of the soft knee of the compression curve (which is a typical feature of a vari-mu design) I didn't miss a dedicated ratio control; the soft knee results in a well-tempered gain reduction, even when applying more extreme settings. The Comp Two can definitely flex its muscles, and thus live up to the 'ruepel' part of its name, but it never exhibits any over-sharp edginess; the results always remain somewhat rounded. Nasty, almost surgical 'VCA pop' is not possible, of course, and it cannot deliver the most brutal colours of the 1176's all-buttons mode, either. Yet, while it can be set up pretty transparently, its character does shine through the more you push it. It's quite an open sound, with some accentuation of the higher mids — though its feet remain solidly grounded at all times.

A look inside the Rockruepel Comp Two reveals a clean layout and quality components. Clearly, the compressor has been manufactured to the highest of standards.A look inside the Rockruepel Comp Two reveals a clean layout and quality components. Clearly, the compressor has been manufactured to the highest of standards.

The time constants can be set pretty fast for a variable-mu design, and the fast attack settings, in particular, allow for explosive room-mic treatments and thick vocal tracks, with all those sharp consonants being kept at bay. The slight accentuation of the higher frequencies pushes signals forward in the mix, making them appear fresher and more alive, in a similar fashion, for instance, to the sonic behaviour of the Retro Instruments 176 I reviewed recently. Apart from its flexibility on individual tracks in the mix, the Comp Two can be used with great results on groups and buses. It can turn the drum bus into a mighty wall of sound, but it can also thicken up a program with a more transparent, less muscular attitude. Last but not least, by using longer attack values, the Comp Two can be employed as a punch-generator on the mix bus, especially when the side-chain filter is engaged. Even at lower gain-reduction settings (0.5 to 1.5 dB), which are not uncommon in mastering applications, the Rockruepel makes the sound picture thicker and more homogenous. Despite the longer attack settings, the program gets louder (both subjectively and measurably), and I suspect this is possible just because some transients are already being driven into saturation. This feature seems to me to be pretty up-to-date, as many mastering engineers are seeking more punch and more volume at the same time these days. Most compressors bring out one or other side, but with the right setting the Comp Two can hit both targets at thesame time! While this may seem a wonderful quality, it must be noted that these results can not be achieved with all kinds of program material. A slightly harsh-sounding mix will come out even harsher, due to the forward-sounding nature of the Rockruepel. It seems less suitable to 'slowing down' aggressive-sounding tracks, too, but it is quite capable of working the other way around, beefing up dull and boring-sounding mixes. One should be careful not to go too far, of course, but in most cases the flexible gain-staging inside the unit should make it possible to tame overly aggressive results.

Finally, the saturation that can be achieved when the input gain is turned up is far more then just an incidental feature. When you're looking for the harmonic sweetness that can be generated by way of employing quality valves and audio transformers, that pure, minimal, audiophile layout comes into its own. There's enough gain not only for a slight sizzle, but also for some meaty crunch, and, as stated before, this not only sounds good, it can also provide an interesting and useful soft-clipping effect.

Does the Comp Two sound less delicate than its predecessor? Really, the question is moot, since the Comp One is no longer available! However, having worked with all three versions of this compressor design — and bearing in mind that I own its immediate predecessor — I have to say that the Comp Two is more than worthy of the Rockruepel name. It transports all the key qualities that made me a fan of the Comp One, yet it costs a less and is more readily available.


The Comp Two is a genuinely original design with an unusual valve complement, and is far more than another repackaged vintage circuit. No audio processor will provide you with a sonic 'magic bullet' but this one does offer an amazing array of tonal options and possible applications. In most situations it will not be the perfect choice to make program material rounder and smoother, but if you're looking for something fresh, forward and exciting sounding the Comp Two might become a worthwhile addition to any setup. The concept, build quality, components and asking price position the Comp Two firmly in the high-end 'boutique' bracket — and it offers the range and quality of results that justify that position..


Other two-channel all-valve variable-mu compressors in this price bracket include the Manley Variable-Mu Limiter, which offers a similar feature set with slower time constants; Thermionic Culture's Phoenix, which is also equipped with a variable side-chain filter and Sowter transformers but slightly lower priced; the Tube-Tech LCA 2B, which boasts an additional limiter circuit in each channel; and the DW Fearn VT7, with its variable hard-knee/soft-knee control.

Audio Examples

Hannes has created a number of audio examples to demonstrate the capability and sonic qualities of the Comp Two. WAV files are available here.

Published December 2013