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In addition to their efficient power/weightratio, these amps also feature sophisticatedcircuitry that requires some in-depth ex-amination. For many years now the Wen-den-based company Camco from the sou-thern part of the German „Sauerland“ regi-on has made an excellent name for itself bymarketing its own high-quality products, inaddition to various other distribution ac-tivities. The Camco program includes dim-mer packs of all sizes as well as Camco po-wer amps, which are currently marketed un-der the names DL and DX. Both series enjoya reputation as high-grade and indestruc-

tible workhorses, which are, however, notparticularly light-weight and employ con-ventional power supply circuitry. At thisyear’s Music Fair in Frankfurt Camco pre-sented the first model of the new Vortex Se-ries, the Vortex 6, which is a completely newdesign and follows the trend of the time. Itwas the first time that designer CarstenWegner employed switched mode powersupplies, without which a power amp fromthis performance category will hardly haveany future. The goal was to get into the6,000-watt range of total power, which ma-kes quite stringent demands on the peri-

pheral circuitry and protective devices used;after all, „normal wall outlets“ can deliver along-term maximum of 3,600 watts only.

M o d e l d e s c r i p t i o nFrom its outward appearance you couldhardly tell that the Vortex provides so muchpower capacity, because it weighs in at amere 12.4 kg packed in a 2U enclosure. Thefront panel is dominated by a well designedventilation grille and plastic cover that ma-ke it possible to distinguish your Vortexfrom other amps even at a distance; yet, the

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Camco Vortex 6 and Vortex 4With their Vortex models the renowned power amp designers Camco from

Germany are launching a newly designed power amp series based on switched

mode power supplies and bipolar Class H amps.

Special print from the german magazin:

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Fig. 1: Gain vs. frequency (CH1, CH2) Fig. 2: Phase response vs. frequency (CH1, CH2)

Fig. 3: Crosstalk attenuation (CH1→CH2, CH2→CH1) Fig. 4: Damping factor into 4-ohm load vs. frequency (CH1, CH2)

Fig. 5: Common mode rejection (CH1, CH2) Fig. 6: Interference spectrum at output (CH1, CH2)

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design is not too showy. In addition to asmall power switch, which is of course notthe main power switch, the front panel alsofeatures two level controls and one opera-ting LED, one signal-present LED and one clipLED per channel. Three additional LEDS ser-ve as status indicators informing the userabout remote control activities and opera-ting modes. Unfortunately, all front panelcontrol elements are so densely packed inthe lower left corner that you need plenty oflight and have to get very close to the unitto be able to adjust them. Both conditionsare less likely to be fulfilled in a power amp’s„natural habitat“, which is usually a darkcorner somewhere behind large speakerstacks or underneath the stage. It may bementioned already here, however, that thiswas the Vortex 6’s only drawback we couldfind.Just as the front panel, about 2/3 of the rearpanel, too, are necessarily covered by venti-lation slots. Located to the left of the slots arethe RJ45 (Western Telecom jack) connectorsfor the remote control network and thespeaker outputs, which are on two Speakonconnectors. For safety reasons, there are noother connecting options available here, be-cause the outputs can deliver voltage levelsthat may well be in the order of the mainsvoltage; thus, contact protection is a top-pri-ority issue. Both channels are cross-connec-ted and routed to both outputs, so that active systems can be directly connectedto the power amp, using a 4-cond. Speakoncable.The right-hand side of the rear panel ac-commodates the mounting slot for the E.U.I.(Extended User Interface), whose standardversion is equipped with two balanced XLRinputs and two XLR link connectors. Above,there is a row of 4 slide switches, which al-low you to set the ground lift, operating mo-de, limiter function and power amp gain.Available operating modes are: conventional2-channel mode, mono-bridge mode andmono-parallel mode. It should be noted thatthe Vortex provides a real parallel mode,which has the outputs, too, connected in par-allel, so as to enable the amp to deliver twi-ce the current as in normal operating mode.The Gain switch allows you to set gain levelsof 26 dB and 32 dB, which is standard onmost professional amps today, and to adjustan input sensitivity of 1.4 Veff (nominal po-wer), which corresponds to 37.7 dB of gain.

C i r c u i t d e s i g nThe fundamental design of the Vortex is ba-sed on conventional bipolar Class H circuitrywith a 3-stage supply voltage, as this is theonly way to achieve such high power capa-cities without having to wire tons of powersemiconductors in parallel. The operatingvoltage of the power amp is adapted to thecurrent demand by means of 3 stages, whichallows drastically reducing the power dissipation at the semiconductors. WithoutClass H circuitry the worst-case power dis-sipation of such a power amp would be ashigh as that of a powerful radiator, in whichcase even massive heat sinks and fans wouldbe of no avail. The Vortex is equipped withan unregulated switched mode power sup-ply, which first rectifies the mains voltage tosubsequently chop it at a much higher fre-quency. Then follows the mains transformerwhich can be much smaller and lighter con-sidering the higher AC voltage frequencythan it could be at 50 Hz mains voltage. Thebalanced 3-stage supply voltage for the po-wer amp is finally produced by means of 6secondary voltages. The actual filtering andenergy storage is done after the mains rec-tifier at high voltage, because the energystored in the electrolytic capacitors equals1/2CU2. However, the capacitor size is mere-ly proportional to CU. Owing to the squareand the fact that the transformer transformscapacities to the power also in square, thedesign works well with relatively small fil-ter capacities compared to conventional po-wer supplies.On the secondary side, there are a few filtercapacitors, which can be dimensioned muchsmaller owing to the now considerably shor-ter recharging cycles. Compared to a con-ventional design the switched mode power

supply of the Vortex is not only less heavy,its HF mains transformer also has a much lo-wer internal resistance, which allows forvery large reserves as long as the mains vol-tage is of appropriate stability. The poweramp can draw currents of up to 57 A from themains, without overloading the circuitry. Ofcourse, this would be too much for the pro-tective devices. More on this in the safetycutout simulation chapter (see below).In the actual power amp circuit fast analogcomputers monitor the output voltages andcurrents and ensure the safe operating ran-ge of the power amp transistors. In criticalsituations they simply block the steppingup of the supply voltage or force the amp tostep down. In extreme cases, e.g. overhea-ting of the amp or short circuits at the out-put, the supply voltage and hence the enti-re channel affected is switched off comple-tely. The Vortex 6 allows for a maximumoutput current of approximately 66 A.

L i m i t e rThe limiter switch provides three positions:Off, SpP and Clip SpP. The clip limiter is of aconventional design; in case of permanentclipping it reduces the input level so that on-ly signal peaks are slightly cut back. The SpPlimiter (Speaker Protect Limiter) is some-thing very special in that it protects thespeakers in case the power amp is overloa-ded. Power amps with multi-stage supplyvoltages (Class H) are protected internallyagainst excess currents and/or power dissi-pation into low-resistance loads by steppingdown the supply voltage. Thus, the outputsignal may contain square-wave surges thatcould reach and damage the speakers, inparticular the tweeters, in the form of high-

^EN61000-3-2

In this context it may be interesting to know that the European Standard EN61000-3-2 hasbeen ratified recently and will become effective early in 2001. This standard regulates the po-wer and current consumption of electrical consumers, but does not stipulate a limitation ofthe harmonics contained in the mains current for consumers for professional uses, with mo-re than 1 kW of power consumption under nominal conditions, i.e. for power amps loaded withbandwidth-limited pink noise and an averaged output power of 1/8 of their sine power. Forsmaller audio devices the existing limits shall be preserved. In the case of switched mode po-wer supplies, this will usually mean the use of PFC (Power Factor Correction), which is, howe-ver, not mandatory according to the standard, as long as the limit values are achieved other-wise. This regulation does not apply to the Vortex, because under the given conditions it al-ready draws more than 1 kW of nominal power from the mains. A standard for this devicecategory is currently being discussed.

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Fig. 7: Total harmonic distortion (THD) at 1 kHz and into 2x4-ohm lo-ad (CH1, CH2)

Fig. 8: Distortion spectrum at 1 kHz and into 2x4-ohm load (CH1,CH2),3dB under full load (basic oscillation at 1 kHz attenuated by 40 dB)

Fig. 9: Total harmonic distortion (THD) vs. frequency, 3dB under fullload and into 2 × 4-ohm load (CH1, CH2)

Fig. 10: Intermodulation distortion DIM 100 (3.15 kHz and 15 kHz) into2 × 4-ohm load (CH1, CH2)

Fig. 11: Modulation distortion according to SMPTE (60 Hz and 7 kHz)into 2 × 4-ohm load (CH1, CH2)

Fig. 12: Difference tone distortion (10.5kHz and 11.5kHz) into 2 × 4-ohmload (CH1, CH2)

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frequency distortion. Such problems are qui-te natural in any Class H design like the Vor-tex. The more the stages are spaced apart, i.e.the lower the number of stages, the morecrucial such problems become. Now, the SpPlimiter detects this condition and reducesthe signal level accordingly, if the poweramp steps down repeatedly into a rising sig-nal edge to protect itself against overloa-ding.

O t h e r p r o t e c t i o n sThe heart of all protective circuits in the Vor-tex is a microprocessor, which controls allparameters from the mains voltage adapta-tion via the gain setting to the limiter. Afterpower-up, the entire peripheral circuitry isactivated from a small-voltage mains supp-ly. The microprocessor checks the mains vol-tage to select an operating range of 115 or230 V and then activates the power supplyand the amp itself in a controlled manner.Once all components of the power amp ha-ve reached their proper operating states, andneither internal nor external malfunctionshave been detected, the microprocessorturns up the volume level to the adjustedvalue.The gain potentiometers are not directly wi-red as part of the signal path, but only pro-vide the control voltage, which is then eva-luated and passed on to a DCA (DigitallyControlled Attenuator) in the form of a 12-bitcontrol variable. In this way, the input sig-nal can also be controlled by the power-updelay, limiter and remote control functions.Other control variables are sent to the micro-

processor from thermal sensors on the heatsinks and the transformer, DC detectors atthe output and from a fast analog computerwhich monitors the safe operating range ofthe power transistors. If the power amp isoverloaded, the microprocessor can use thelimiter function (if activated) to cut back theoutput power. If the limiters are off, only thepower amp itself can limit the output po-wer by stepping down the supply voltage toprotect itself. An exception to this rule is themain current limiter, which is always on and

also uses the limiter to control the outputpower. More on this below. In extreme si-tuations the microprocessor can also switchoff the entire power supply, for instance, ifthe mains voltage permanently exceeds 260V or if the unit suffers from an internal mal-function.

L i ve t e s tAs a kind of acid test, two Vortex 6 had toprove their quality during 16 hours of conti-

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Fig. 13: Two-channel cont. power at 1% THD into 2 (red), 4 (blue), 8 (green) and 16(light blue) ohms (left: Vortex 6; right: Vortex 4)

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Fig. 14: Peak reserves, 2-channel, into 4-ohm load (left: Vortex 6; right: Vortex 4)

Fig. 15: Performance diagram for one channel with simultaneous load applied to all channels (left: Vortex 6; right: Vortex 4)

Fig. 16: 1 kHz basic oscillation and distortion components (50 dB en-larged)

Fig. 17: Vortex 6 response when connected to stable power supply(red), and via 50-m cable (blue)

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nuous operation at this year’s Mayday event,which took place in the Dortmund Westfa-lenhallen. In hall 1, both amps were used todrive one of the towers comprising 8 EAWSB750 subwoofers, so that all channels hadto process music material with lots of bassfrequencies in tough 2-ohm mode and witha low crest factor. Despite high ambienttemperatures, both amps were fully stableand showed no signs of weakness. To be fair,it must be said that none of the other poweramps used showed any signs of weaknesseither, just as none of the speakers got da-maged.

S a fe t y c u t o u t s i m u l a t i o nAs already mentioned, the Vortex 6 is di-mensioned internally in such a way that itdraws 57 A of current with 2-ohm loadsconnected to both channels and a maximumoutput current of approximately 66 A perchannel (which corresponds to an outputpower of 4.3 kW). Naturally, such an amountof current would not take long to trigger any16-A safety cutout and also blow the inter-nal 25-A fuse. Still, the amp is capable ofhandling this extreme current at least tem-porarily. The thermal time constant of a sa-fety cutout is so high that 24-A currents arepermitted for 1 to 1.5 hours. The Vortex the-refore includes another small analog com-puter, which evaluates the mains currentand uses appropriate time constants to si-mulate the behavior of fuse and safety cut-out. If a critical condition ‘just-below-thres-hold’ is detected, the analog computer usesa control variable instructing the micropro-cessor to activate the limiter. This is the on-ly limiter function that cannot be disabled,which does make sense though, becauseotherwise the amp would trigger its safetycutout or blow the internal fuse.

M e a s u r e m e n t sThe measurements of the linear transmissi-on behavior (fig. 1 and 2) show that the Vor-tex is completely neutral over the entire au-dible spectrum. Its frequency response at20 Hz and 20 kHz deviates from the value at1 kHz by a mere 0.1 dB. The phase shift at20 kHz is about 40°, caused by the high-slo-pe 60-kHz low-pass filter (3rd order) at theinput of the power stage. The low-pass filteris particularly crucial in Class H power amps,because high-frequency or high-slope sig-

nal portions could overstrain the supply vol-tage change-over, which would lead to di-stortion. Yet, at 60 kHz the low-pass filterhas no audible effect whatsoever on the ac-tual audio signal.The Vortex achieved excellent results interms of crosstalk attenuation (fig. 3), com-mon mode rejection of the balanced inputs(fig. 5) and interference immunity (fig. 6).With an unweighted dynamic range of asmuch as 113 dB, interference noise won’t bemuch of a problem. Additionally, the gain canbe set to a maximum value of 26 dB, whichallows for adapting the power amp to the ou-tput voltage of most controllers and mixingconsoles, without major losses in terms ofdynamic range. The damping factor (fig. 4),measured at the Speakon connectors, is ashigh as 300-350, at 1 kHz and into 4 ohms,even though it drops considerably towardsthe high-frequency end (about 100 at 10 kHz);still, this is more than enough. The distorti-on measurements in fig. 7-12 also show verygood results, from which we can concludethat the design concept of the Vortex is con-vincing and logical throughout. The THD va-lues drop to -95 dB, even though the distorti-on spectrum shows that it mainly includesodd and high-frequency portions. The THDvs. frequency response (fig. 9) is approxima-tely -90 dB up to about 1 kHz, and then startsto rise by 6 dB/oct. or 20 dB/dec., which is qui-te typical. The hefty increase in distortionabove 25 kHz, which was 3 dB below clippingduring this series of measurement, could bedue to the switched supply voltage, whichtries to stay on its highest level, but is force-fully cut back every now and then by the cur-rent limiter. A similar effect can be seen fromthe intermodulation distortion diagram (fig.10), where there is no steep rise at the clip le-vel, but sporadically varying values causedby the current limiter, which is activated tem-porarily.

Pe r fo r m a n c e p r o f i l eAs with all power amps from this perfor-mance category, a sufficiently stable mainssupply had to be provided so as to be able tomeasure the performance profile of the Vor-tex 6. Although it has no regulation, theswitched mode power supply of the Vortexis extremely hard and hardly shows any in-ternal resistance blocking the current flowbetween wall outlet and power amp cir-cuitry. The only difference to a regulatedswitched mode power supply is the fact thatthe Vortex does not make up for a decreasein mains voltage by increasing its powerconsumption, so as to be able to maintain asteady level of power consumed. Certainly,such a behavior is a benefit in unstablemains networks, when the power amp doesnot respond to a mains voltage drop by anincrease in power consumption, which couldpossibly make things even worse and sooneror later trigger one of the safety devices.A preliminary sine burst measurement withthe Vortex connected to an ordinary wall ou-tlet yielded an output voltage response thatwas very similar to that of an amp with aconventional power supply (blue curve infig. 17). With the filter capacitors fully char-ged, the amp initially delivered a peak vol-tage of 150 volts at the output to subse-quently drop to an average value of appro-ximately 110 V. In a conventional power ampthis effect is primarily caused by the inter-nal resistance of the mains transformer ir-respective of the performance category. Ho-wever, the Vortex should actually show nosuch effect. During a second measurement,the mains voltage showing the response de-scribed above was measured in parallel.Thus, it was clear that the measurement sho-wing the response of the power amp to a si-ne burst did not reflect the behavior of theamp itself, but that of the mains power sup-ply. A second measurement, during which

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the Vortex was directly connected to a 63-A sub-distributor confirmed this conclusi-on, as can be seen from the red curve in fig.17. So, the switched mode power supply andthe power amp circuitry are absolutely sta-ble, and once the initial peak is over the ou-tput voltage drops by a mere 2-3 volts.In practice, this will be of less significance,because we’re talking here of real sine con-tinuous power, which no power amp musthandle in real life, even with highly com-pressed music signals featuring crest fac-tors of approximately 9 dB.The performance survey of the Vortex 6 (fig.15), measured with the amp connected to astable mains supply, shows a response thatis largely independent of the signal shape

and/or crest factor, and is limited by themains current limiter (measured into 2- and4-ohm loads, continuous power, 6 dB crestfactor, 2-channel operation). In the case ofthe 2-ohm load the power amp’s own cur-rent limiter comes on and limits the conti-nuous power to approximately 3,300 wattsper channel.The performance bandwidth curves in fig.13 show an increasing power drop towardsthe low-frequency end, if decreasing loadimpedances are connected. This effect couldbe caused by mains harmonics that are su-perimposed on the output signal; however,the higher the measured frequency, the lessimportant this effect becomes.

A d d e n d u m Vo r t ex 4Shortly before the editorial deadline, theeditors were informed that the smaller Vor-tex 4 had been completed as well. Conse-quently, this test report was revised at shortnotice to include a few basic data of thisbrand-new model. From a technical pointof view, the Vortex 4 is identical to the big-ger Votex 6, but has a smaller power supp-ly that handles only 131 V instead of 155 V;as a result, the power semiconductors aredesigned for currents that are not as high asin the case of the Vortex 6. As regards themeasured values, it can be concluded thatthere are no significant differences to ex-pect in terms of frequency response, phaseshift, interference, damping factor, etc. TheTHD response should be similar, yet show aslightly lower clip limit. To avoid gettingdrowned in a sea of measured values, we

only included the performance diagrams ofthe Vortex 4 in this test report, as theseshow the substantial differences betweenboth amps. The Vortex 4 weighs 12.4 kg andhence features a performance/weight of 337 watts/kg; with a price of DM 6,020 itsprice/performance ratio is DM 1.44 per watt.

S u m m a r yCamco’s new Vortex Series delivers highestperformance in a compact and low-weightenclosure, which can ultimately be seenfrom the impressive performance/weightratio of 453 watts/kg. However, what makesthis result really exceptional are the excel-lent distortion values, the very good S/N ra-tio and the variety of sophisticated protec-tions. Actually, there is nothing negative tosay about this power amp, which has al-ready been confirmed by the impressive sa-les numbers in the most recent past. Thesecret of the Vortex is the successful com-bination of classic circuit designs with la-test switched mode power supply techno-logy and an ingeniously designed micro-processor controller that makes it possibleto get the most out of the circuitry and stillstay well below the limits of what is safe. So,you don’t have to be clairvoyant to predictthe Vortex Series a successful future.

Load 2 4 8 16Cont. 3300 2250 1365 6926 dB 4160 2450 1389 74012 dB 4290 2812 1482 75018 dB 4300 2960 1520 750Peak 4356 2964 1521 761

Output power in watts with 2-channel load,1% THD and signals with different crest factors.Mains voltage 228 V, measured with 3 dB crestfactor.

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^ Survey Vortex 6

Max. continuous power into 4 ohms,2-channel, 1% THD: 2259 WPeak reserves (4 ohms): 2964 WGain: 26/32/37,7 dBDynamic range (unweighted): 113 dBDynamic range (A-weighted): 115 dB(Dynamic range referenced to pulse outputpower at 18 dB crest factor)Remote control option: CAIWeight/HU: 12,4 kg / 2 HUPower/Weight: 453 W/kg(into 4 Ohm, both channels summed at 12 dBcrest factor)Price/Performance: DM 1,40 /W(into 4 Ohm, both channels summed at 12 dBcrest factor)Price: approx. DM 7.876 incl. 16% VATS.Nro.: 15092 (Vortex 6)

◊ Text and measurements:Anselm Goertz

Photos: Dieter Stork

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