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Exclusive Kenwood with dc-kopplade monosteg

L-07M and L-07C

  This initiative from Japanese Kenwood meant lanserandet of an exclusive combination in a high price range.

  L-serien meant an amount both original, sophisticated and framåtblickande features. The took permanent on a high degree of control over the signal during all stage (with among other thing specialkablage etc and comprizes stem a stage and different dc-kopplade mono-effektdelar.

  This thorough test with quantities of measurements and practical tests show on high aspirations from the producer and an advanced circuit technical mastering.

  Some clearly unnecessary misses must however be noted, and the price like the whole concept can be discussed then the applies Hifi-bruk — near defends these elitgrejorna your position in a proffsinstallation.

  Bengt Olwig and Ulf B strict deepened itself in Kenwood-finesserna during almost a half-year.

Here years their report.

  Little of a metamorfos has happened with the Japanese Hi fi-firman Kenwood, that in the native country not at all is particularlily well-known during this name without where is called Trio (Kenwood is a “made up” names for certain big export markets, in front USA. In England, one may not however cold itself Kenwood, since the product that name is registered of hushållsma-, shining producing clean K. in Sweden farms Hi fi-materie-len hot Kenwood during the that hf-kommunika-tionsapparatur and measuring instruments carry Trio-namnet.). The is small than 10 years since RT in a test utrönte that those days' Kenwood-namn stood for a particularly wretched quality… Today has the compared with a row domestic competitors in Japanese the small factory with its only approximately 2 000 employees on Hi fi-sidan clear big aspirations, as our current test quite clear shows.

During these years has the namely happened a lot of. As we earlier concerned in other contexts revolterade the plural concerned in Japanese on your time against that the then in force family business so narrow-minded invested on a huge uppdriven production technology but so awkward low. quality on the products. The then in force company was divided up. and among other thing took place the utbrytning that might to results Kenso-nic-märket in Yokohama. The as became left of Kenwood was reconstructed in entirely other direction than earlier, and that way of present of cheap debris as not undeserved vidlådde the name was cleaned away. That is history now — the fast development is reflected goodliest of facts, that then one today gästar Japan's most prestigetyngda audiofirmor and will carry out the always mandatory mättekniska the comparisons between toppgrejorna in “the stereo battalion's” labb exists steadily one or more Kenwood with among the competitor devices.

Kenwood has in Japanese consulted to the precursors with dc-kopplade units, a trend that one now may to see accepted of almost the whole sector. In beginning, one went for all part on certain s k mines (acoustic?) and in Japanese had Kenwood some years at the start of dc-epoken a certain rumor in order to be delicate p g a dc-stegens känslighet for the miscellaneous miss destiny as temperature operation and equal excitement occurrence on the ends like t ex strömrusning in the end transistors. Etc. Today, one knows these risks and has långtgående k ' allowed to protect the apparatus against a lot of of them. and since long lies a long row of interesting and delicate konstruktioner with Kenwood-namnet on bästsäljarlistorna the world around. The willed probably to be sufficient with reminding about t ex all big receivers, record playing clean 550 with your dc-styrda servomotor and the in the studio's used variant with stone deck flat and the tip combination 600-serien; an interesting experiment that to relative fashion taking prices create an inbrytning in the luxe-klassens audio. Förf:a to this provningen also at several occasions has had the entertainment strike Kenwoods structure staff with engineer Ohara in the point and can vittna about that one in Kenwood-fabriken accommodates surely based expectations on the future as a result of both high aspirations and implemented, lyckosamma investments, as been received well of the audience in both east and vest. That design one invested on with that common on the amplifiers' front panel middle facing big volume the thumbwheel has also hit an. An of ourselves consulted once a well-known American Hi fi-skribent to commend Kenwood on the basis that the company's amplifiers obehindrat goes to use of also vänsterhänta persons…! That type's ergonomi believes we however has not lain behind the thumbwheel location. But clear has Kenwood gone a gyllene (silver glittering?) compromise in your way of present and avoided extreme fashion features in the design. One has invested on a massive solid look and big increased panels, osv. The resemblance with Pioneer in a part cases perhaps is more than a chance — but the both brands did not will probably nevertheless to have same categories consumer.

With this assessed, the new and sophisticated series L-07 has Kenwood taken the stage in full and offers an equipment in some as has big similarity with the very topmost, the heavy class's Hi fi. The way of present is the on certain holds highlily paid tax s k professional, but praiseworthy enough not thought for the Japanese 17-tumsstandarden (=18.89 inch. in order to last exactlily) without actual for 19 inch's tripod paste-up. Greppbyglar has fö since long consulted to Kenwoods prop details (where the not been standard). L-seriens units are gloomy olivgrågröna on la Military Look and constitutes a conscientious contrast to the metal brilliant. the common devices. The is admittedly tvivelaktigt about so bad many yr-kesanvända (or militära grejor) sees out so here. but clear will the audience be may to believe the. “reverse imponatorverkan”, willed one can to say.

With these stereoapparaterna is a circle closed: Ty how began stereofonin at the end of 1950-talet unless with that one to a preamp docked two big monosteg (touchs. of course) on la Dynaco and Quad and lived happy with them. remote from each thought on such as receivers and other that come willed. And double, independences net divide had one!

i-grejorna from Kenwood is an outermost consequence of those many years' discussions as been pursued about unidirectional net units, osymmetri etc and likewise is reminded one about a concept that t ex J B Lansing and others tried to launch on 1960-talet in the form of the in the the speaker's veiling integrated amplifier, the s k energizern. With Kenwoods double monosteg and well thought-out solutions for shortliest possible stem ties between signal part and sound source has an old idea become new again. updated of the intensive endeavors to good sound quality as become 1970-talets signatures. The as most each a practical thing earlier, or a generous solution, has now been promoted to a serious experiment to reach control over several stages in the signal distribution.

The preamp is as said little obestämbart gray green, and the does that the in certain room illustration becomes a lot of poor contrast between the front's gravyr and the sheet metal's nuance. Then thumbwheels and bolting give is black becomes the visual impression literally weak of L-07C!

Reglagen is. fr v t h. net breaking clean (big and considerable) long out against the gable. In operation situation shines a small red diode upptill. Därnäst sits the key for utspänningen to end the stage and the is followed of the key for activation of the at 18 Hz relocated subsoniska the filter that cuts with 12 dB/oktav.

The first thumbwheel that meets becomes förstärkningsdämpsatsen. a double thumbwheel that is graded from 0 to — 30 dB in 2 dB stages. The is not question about a gängad control, without the internal and the extraneous thumbwheel goes to twist independently of each other but the locks against each other then one so wants to. This strengthening regulation is described to your practical function further forward. Here will only be established, that the detail is relativelily exceptional and that in Europe t ex Braun earlier been provided with the.

Fig in. here is seen Japanese Kenwoods tyngsta programmes in sound electronics: L the three series's units. --. standing of the new preamp L-07C and the two dc-kopplade monostegen L-07M. The speakers are the big systems LS-990, which however not been tried in this. On the picture, included the extensive is not specialkablage that is little of core a point in this specialanläggningen.

Fig 2. Of the photo shows on the other hand little of a carrying idea behind Kenwoods L series: The in sammanhör, the electrical important stem disposition of effekldelen near next to the speaker, where a specialkabel links förstärkare—ljudkälla. Marks the cable's formulation. with a build up of an entire amount evil in common hölje. Sees the text.

Fig 3. The preamp L-07C is a spartanskt simple formulated, low and flat unit, as konstrutivt seen is a paragraph “heavy “electronics with quite big kretsförtätning and in certain respects new solutions for Hifi-sektorn (and some one recognizes from other of today's conductive Japan-märken).


The thumbwheels for bas- och the mist edge impact is found in the middle of the panel. Both is divided up in dB markings with “flat” - or the neutral situation upptill and excellent with letters.

Next, a group follows about three big thumbwheels — in all is first goat provided with three differently big productions to twist to bolt to give, which gives a little fragmented impressions. — the first of the three big is the head volume thumbwheel. Masts Volume. In conformity with the other thumbwheels has this not only degree ring without also snäpplägen. The the following big thumbwheel is the operation situation selector for tape with an amount divided functions, among other thing double band duplication. In the situation Recording Offäi the production circuits blocked and the signal goes “straight”, some as we portrayed in connection with the test of Yamaha-steget C 2. In situation Recording exits input swallowing clean signal on the band ends. So exists normal Tape monitor, here called Play A/B. two situations are left — the is band duplication A — B respective B—A. In situation A — B goes Play A to Record B (band end) and vice versa. Ingångsväljaren functions in those situations that common to central end.

The row of thumbwheels is completed with input swallow clean with two pica shade inputs. MM respective MC. and mound level two inputs. Aux and Tuner. The preamp permits therefore directlily connection of a pick up of elektrodynamisk type (“movable bobbin”). Our provning has also largely been aimed on lyssning with pick up of such type socketed.

Some utstyrningsinstrument of for the Japanese devices common type searchs one in vain after here. the is f island hardly worthwhile neither, then the is suitable to be relocated on the floor far too next to those speakers which will be run. — the exception is 300-wattsversionen. sees picture

The backpanel to L-07C has the now on good Japanese Hifi-apparater not the exceptional coarse connector, and in fallen Kenwood L-07C exists moreover some so sophisticated as guldpläterade hylsor to the connections for optimum flame kontaktresistanser. some as shown itself last quite importantlily.

Försteget is well-balanced and steady performed. A glance on shows on a likewise solid work with an ideal paste-up, strict cable draw and väldisponerade printed circuit board. That the device been done during leverage of professional equipment shows among other thing the big jordningsskenan that travels in the centers, a heritage from the trade technology's mixer's etc The rough, crowd the braided cable strains run on the underside in disciplined knippen.


The components as been used seems common to hold high class. Thumbwheels and omkopplare proves to have the now in Japanese, högklassiga devices likewise common, the coarse arbors and considerable genom-föringarna. The internal skärmningen is effective and done with understanding about each problem can to arise if one omits that correct printed circuit board layout and links after logical requirements. — no risk for brumslingor here.

Slutstegen in your monochassier sets itself difficult to compare with some Hi fi-förebilder of today.

Here exists instead almost only trade equipments to compare with. t ex German Klein & Hummels Monobloc and others. These ascended to finns in several variants from Kenwood, and an a lot of considerable — the gives. 300 W in 8 ohms — is therefore also provided with ut-styrningsinstrument. despite intended the stem the disposition far too next to the speaker. Term: L09M. Sees the change!

These monoförstärkare is delivered in an execution with “opens” chill parts over the chassis the whole plate in a rectangular hölje, but the exists also a variant as may a överdimensionerad chill body round höljet and with a putting off, profilerat grill on the centers: effective but not decided beautiful. The normal L-07 M is on the other hand discreet in your mould and välgörande dainty and simple. The only as skvallrar if operation conditions are a small red diode on the gable.

In practice seen is the easy stem endowed in the plant, but mild powers what cable the is required! Test our room belamrades with regular skeins to ends.

The chassis are considerable and with good chill air circulation due to the genombrutna höljesplåten. How the symmetriska and the exceptional chill elements are arranged is clear from fig 10. The has got the mould of bin agencies or “footwear pc unites” that between themselves carries the electronics. The strongly increased the net part lies in the front part of the amplifier and here exists also the big, double 18 000/iF elektrolytkondensato-rerna. Nätdelen has your own printed circuit board while the circuits in other respect has their. The Japanese kiseltransisto-rerna for the symmetriska the stages (entire complement honors) is thickset three on chill each body. The chill the whole packet is. as been mentioned, the central in starching clean. Förstär-kardelen is the rear, and on so ways have one the achieved advantage of can to draw a lot of short managements from the inputs. Also here has Kenwood used guldpläterade kontakthylsor.

Really performed printed circuit board layout gives high kanalseparation

An in many transfer system often overlooked parameter is kanalseparationen and those different mechanisms that influences the. Of special interest, the occurrence is of s k power loops in printed circuit board, since these as well reduces kanalseparationen that basis puts conditions to instabilitet and thereby cohesive distorsion in förstärkarsystemet.

Fig 4. a) Försteget seen from the top. Marks that common land the rail that divides left and the right channel to, a construction way as been retrieved from pro sound the electronics's domains, particularly mixer table even. One can also take into consideration the good component the dissemination.

Fig 4. b) Förförslärkaren seen underifrån. Here should clearlily show the specialbyggda omkopplarsek tionerna with surely separate “decks “for minimum överhörning or coverage between the channels. Labels also the small number cable stem ties that exists — almost stem all ties are relocated to the duplex circuit the card.

Through a circuit technical logical distribution of the components over printed circuit board the surface in control amplifiers L-07C has Trio-Kenwoods konstruktörer on an apparent way decreased conditions to power loops in signal the roads. Härigenom has the stability become good. Further has one at printed circuit board the layout tillsett that omkopplare, volume control, tonne controls osv become channel song surely separate through good component dissemination and using of an earlier mentioned special land rail, that parts right and left förstärkarkanal to (fig 4). These measures combined with careful performed cable a draw within L-07C has resulted in the a little fantastic kanalseparationen — 100 dB within 20-20 000 Hz!

Double grammofonsteg with capacitor loose input

Kontrollförstärkare L-07C has been equipped with two separated and entirely complete Ä//4/4-korrektionsför strong, suitable for givare according to the principle movable bobbin respective inducerad and movable magnet. One has thus valt to relinquish the conventional build up with a for pica shade all types common Ä/^4^-korrektionsförstärkare. preceded of linear flame noise an amplifier for pickuper with movable bobbin.

The reason to that one among konstruktörerna at Trio-Kenwood select to abandon the classic circuit the solution on grammofoningångarna is. that one so far possible worked for a reduction of the number contact transitions between in- och ends on control strengthening clean. Through to thus use two. entirely complete korrektionsförstärkare avoids one changing over a point between ended on the flame noise amplifier for movable bobbin and the common pica shade the input. In order to additional contribute to low kontaktresistans along korrektionsförstärkarnas signal roads have one equipped the two grammofoningångarna on L-07C with guldpläterade phonokontakter.

Kretstekniskt is the two RIAA - the stages a lot of equal each other. The has both among other thing differentiellt BOLD input stage, which made possible capacitor loose pick up-ingång. Further means JFET-bestyckningen that the input impedance at korrektionsförstärkaren in the near can be held constantlily within big frequency an area.

fig 5 principle schedule over input pc own for pickupen of type movable bobbin. Observe the use of in pair double BOLD input transistors in the simple kaskodkopplade differentialsteget. QI — Q4. with dynamic load. Sees text.

fig 6. Corresponding circuit but concerning input the stage magnetodynamisk pick up. The stage proves to have big similarities with mc input pc own. Sees the text.

fig 7a Baskontrollens, suitable regleromrade according to the producer, jfr mätdata.

 fig 7. b) corresponding a) Jfr the mist edge control. Sees the text.


Both RIAA-stegett works with the whole ±47 volts matningsspänning. This has made possible abundant överstyrningsgränser on the two grammofoningångarna (sees mätvärden). For normal insignalnivåer comes and korrektionsförstärkare to work entirely within linear work your area, why distorsionen in these stages becomes a lot of low.

Mc-ingången. i e that input that is suitable for connection to a pick up with movable bobbin, is on the input side to equipped with a simple kaskod-kopplad differentialförstärkare and s k dynamic load (fig 5). The late is received m h a a s k power mirror (Q7 g). whose information is to take part to high excitement a strengthening in differentialsteget. Härigenom comes RJAA - the stage's noise factor to mainly to be determined of the actual differentialtransisto-rernäs noise mechanisms (sees article about lågbrusför-stärkare in 1977 noes 9). Through that further choose field effect transistors with in particular low drain-resistan-ser. and, that is clear from simplified the principle the schedule, parallel links a number transistors (Q, 4). has one achieved acceptable noise number stem mc-steget. Considerable lowly noises can however be achieved about one instead of JFET uses bee polar lågbrusiga prap-transistorer.

Kaskodtransistorerna Q5 6 is used in order to give a so constant drain-ström through fälteffekttransisto-rerna as possible. Stable drain-ström means namely lowly distorsionsalstring in differentialsteget, concurrent as this measure improves the stage's mound frequency properties. The late depends on that the s k MiV/the era effect is counteracted (i e mvn avoids kapacitansförstoring of among other thing the transistor's egenkapa-citanser). product through the differentiella ingångska-pacitansen in input the stage is reduced highliest appreciablily. Yet another positive property at kaskod-förspänning of differentialtransistorerna is that the likfasiga störsignalundertryckningen (CMRR) is increased.

The subsequent 2:a differentialsteget is conventionallily edified with power generator (Qu) and bee polar two transistors (Q, 10). Since this stage lacks local motkoppling is its excitement strengthening rather big. The exact value on the strengthening depends of the used transistors' branthet and the carbon senior master obstruction's values.

The ultimate end the stage is mainly a conventional, complement pea emitterföljarsteg, preceded of a normal GK-kopplat excitement strengthening stages (Q12). Through choosing this type of end stage has konstruktörerna on Trio Kenwood can dimension era the circuit for low out time impedance, which in turn has made possible an turning of lågimpedivt RIAA korrektionsnät.

The advantage with such a lågimpedivt nets are. ati the to RIAA - the amplifier's input side added noise the signal, brought forth in RIAA the net, becomes a lot of low the is in this context important that end pc goat's power capacity is sufficientlily big in order to clear of fast report changes in återkopplings the net, about RIAA - the stage's transient properties will become good.

Mm-steget reproduced in fig 6, d v s RIAA - understands the vats suitable for högimpediva pick up-element does not prove to have some big circuit technical olikhetei compared with mc-steget. The only important difference is. that mc-stegets 2:a differentialsteg hai been replaced with an emitterföljare. The reason to this äi among other thing that one in mm-steget does not need equal mound råförstärkning as in mc-förstärkaren.

What one lacks on a control amplifier off L 07C:s kaliber is possibility to eligible pica shade charge on mm-ingången. Since the big majority pica shade systems according to the work principle movable or inducerad magnet proves to have a more or less pronounced trend to frequency variation wide t ex capacitive charge, had the been motivated with a control function on L-07C, where the just pica shade adaptation on mm-ingången could be optimized. On this way willed the last possibleily to compensate for t ex different grammofoners kabelkapacitanser o dyl.

Fig 8. Effect of activated subsoniskt filters for two tonarmsresonansfall, according to Kenwood


Fig 9. Blockschema and level diagram over the preamp. Puts among other thing brand to that one divided up the level adjustment in volume control a thumbwheel respective a passive dämpsats, sees the text. Dämpsatsen is facing signalmässigt framfor the combined utgångs- och filter pc own.


From Trio-Kenwood has one regarding pick up-anpassning clearly declared that, according to the company's view, “mechanical ofullkomligheter as t ex nålrörsresonanser in pick up-systemet should not comes penseras with electrical methods, since such measures have negative impact on pick upens tran-sientåtergivningsförmåga”.

This in and for itself correct assertion is afternoon electricity smiles time a small comfort for that consumer that with his in other respects högklassiga pick up got interfered reason seeing to phenomenon, depending only on miss adaptation between pick up and grammofonförstärkaringång. As long as the big plural pick up-tillverkare around in the world does not succeed with doing entirelily belastningsokänsliga pick up-system. sheep we enough find us in that with electrical manipulationer “straightens” the plural pick upers frequency curve if we want to few them to let as fabrikanten thought itself.

Tonkontrollenheten: distributes and deficiencies

In order to one will can to change tonne curves and thereby good to adapt the acoustic sound the depiction to current properties in the depiction chain has control amplifiers L-07C been equipped with active tonne two controls. Their intended varia tionsområde shows avfig 7.

The active tonne the control is built around a 20 dB bufferförstärkare. circuit technical similar mm the stage. Through that one introduced a with the signal frequency varying, negative återkoppling over bufferför-stärkaren, can differently increases and reductions of tonne the curve be received. Variationsområdet at 10 kilohertz respective 100 Hz is+7,5 dB, inställbart in stages about vartdera 1,5 dB. That one works with omkopplare instead of t ex a normal potentiometer depends on, that one härigenom good can check and op-timera respective stage song change of tonne huddling used to.

So long all well. but since the only is a few persons stem allowed to may an acoustic entire symmetriskt lyssningsrum. is the a clear miss that konstruktörerna of L-07C has not made possible ka nalvis individual adjustment of the tonne controls.

When the tonne controls are set in O-läge, is linked all reaktiva elements away in motkopplingsslingan and only a normal linear 20 dB bufferförstärkning remains. On this way, one can at attitude of straight tonne curve achieve low fasvridning within the consults only the frequency area. Through that one further feeds the tonne control stage with ±47 volts can over 20 Vrms is achieved on ended before klippning! With normal insignalnivåer on control strengthening clean different inputs can full increase of bas- och mist edge the register be permitted without minimal risk for överstyrning of tonne the stage.

Special bufferförstärkare is required travelled matning of long signal conductors

Since L the 07 system builds on that effect lute the stages to be placed in immediate vicinity of högtalarsystemen, becomes in normal cases signal boredom clean between control amplifiers and effect amplifier rather long. Common skärmade cables have as a rule an egenkapacitans between conductors and display on 100 — 200 pF/meters. Trio-Kenwoods own “targeted” cable has t ex 180 pF/meters egenkapacitans. For 10 meters long connection cable becomes thus that capacitive load as control strengthening clean “sees” on ended 1,8 nF. In order to can to transfer the the audible frequency the whole size 20 — 20 000 Hz without interfered mist edge loss must the end impedance at utgångsbuffern assume small values. Further is the important that one tries to counteract interruptions in återkopplingsslingan at transient signal forms and big capacitive loads.

In order to come tillrätta with the described problems has konstruktörerna taken forward special end a circuit with small than 0,1 ohms' end impedance. This low worth is achieved through introducing of 100% - ig återkoppling. In order to concurrent prevent damagedlily highlily power levying wide possible short slutning on the end has power restriction an obstruction pickled in series with ended from buffer-förstärkaren. Motkopplingen has since been fitted via two different roads in order to one in this way will avoid interruptions in återkopplingen then the end t ex is hard capacitivelily lasta. Härigenom is prevented the effective origin of internal block ring.

Only subsonicfilter enters in the circuits

In connection with buffersteget has a s k subsonicfilter engaged. This is concurrent that only filters that one from tillverkarhåll has considered last requisite in a high-quality depiction system off the described kind. So has that is to say all shapes of mist edge - and loudnessfilter been eliminated in the structure.

The intention with the current subsonicfiltret is to efficiently to can to reduce possible reason seeing to phenomena in the system combination tonne wretched — pick up. Moreover undertrycker the filter modulationsdistor-sion that arises p g a läckning between pick up-elementets winds at allusion of irregular records. Yet another advantage with this subsonicfilter (actually a 2:a the order's mound passport filters) lies in the possibility to counteract flame frequent acoustic återkoppling between högtalarsystem and record players. In Jig 8 shows curve forms and reduction ability wide resonans in pick uper with different fjädrings-mjukhet.

Newly designed volume control complemented with dämpsats of constant impedance type

In order to counteract unnecessary distorsionsalstring in the control amplifier has a special type of volume control framtagits. As well lyssningsprov as laboratoriemätningar has namely shown, that normal types of volume controls with carbon chute and though runners can, despite that the in themselves is entirelily passive units, brings forth a certain measure of distorsion. The underlying reason is, that the around the contact surface between carbon chute and runner poking arises power loops and potential differences. On shallow of this is brought forth distorsionsprodukter.

In order to decrease the risk for the described distorsionsformen has one in control strengthening clean L 07C an used special developed potentiometer with s k 20 - point runners. Through that on this way “broadens” the contact surface between carbon banana and the runner can one more or less short possible power loops in kolskiktet and thereby to eliminate distorsionsalstring.

Apart from the special volume the control, one has introduced a passive dämpsats of constant impedance type in .systemet. The total moderation of the signal is in stage suspending bar between — 30 and 0 dB. Then one has placed this dämpsats so near been paid on the preamp that possible (sees block schedule in Jig 9), can the noise on been paid be reduced to a minimum.

In order to further eliminate the need of a separate balance control has dämpsatsen been done individuallily to suspend bar for respective channel. Följsamheten at equally suspended value on the moderation be stated to last goodly than 0,3 dB.

Abundant chill bodies distinguish the effect part

As a whole, effect lute the stage is L-07M solid and steady edified. As carrying frame is used two in particular developed considerable chill sections. These has the mould of a four sektioners “footwear stone” (fig 10). The total chill the surface becomes on this way a lot of big. why the thermal resistansen at the chill elements becomes low. This gives along with a välordnad air throughout a mound värmeavled-ning. why end pc own temperature becomes relatively low also at big effect levying. The risk for överhettning may härigenom is considered as small at normally using of the unit.

On each chill section exists place for three of the total the effect six transistors in L-07M. Infästningen takes place on an against “the footwear stone” perpendicular basis plaque. Apart from function that transistor attached service does the basis plaque also as sammanfogningsstycke for two the chill the sections.

Considerable and väldimensionerade net divides in the amplifier

In conformity with earlier effect amplifier acrimonious Trio-Kenwood has one attached big weight at the dimension ring of monitor strengthening clean net part. Used the net the transformer can t ex give more than 7 ampere continuous power, i e entirely sufficient for 200 watts' ineffekt at 4 ohms. The used equal rich tarbryggan numbers big shock powers ocn more an 25 ampere mean power levying with only 1.05 volts' frainspänningsfall.

For glättning of the equal targeted that excitement has one used an in particular produced elektrolytkon-densator pa 18 000 out. From tillverkarhåll has one in particular winning endowed itself about the just choice of glätt-ningskondensatorer. since one considers itself na proofs in order to the capacitors' properties influence the final sound the quality. The ostabiliserade matningsspänningen that one father out over the two glätt-ningskondensatorerna (±66 volts) is used in order to drift effect strengthening clean end stage. Other divides of the amplifier father its force maintenance acrimonious a to see paired net part. comprizing double excitement a balancer with high brumsignalundertryckning and placed load depending.

Fig 10. a) here shows end pc own (L-07M) footwear stone similar double chill bodies in the form of considerable 'sections “. Through a väldisponerad air circulation may one good värmeavledning. Sees the text.

In order to sa far possible minimize the end impedance at the balancer circuit has its dc-återkoppling been fitted on such way. that excitement case arisen in the circuit card's copper foil partial is eliminated. The method is in principle the same that is used in certain net units during the name “remote tendon see”.

Fig 10. b) on photo can we see the whole end pc own innandöme.


Kretstekniska finesses in L-07M-stegen

Effektförstärkare L-07M comprizes circuit technicallily drift stages. a discreet edified. Darlingtonkopplat end ascended and protection circuits.

Drivsteget is equipped with three different differentialsteg, each and a with high CMRR. L-07C the first stage is in its build up similar input the stage in control to strengthen clean. Thus, one uses double field effect a transistor with teams temperature operation and endowed own noises. typical 10 nV/Hzå (Ups= 10 volts. lps= 1 mA. t= 10Hz). The occurrence of BOLD in input the stage has made possible full dc-koppling between effect strengthening clean in- och ends.

Pa similar way that in t ex L-07C:s RIAA stages use one drain-strömstabilisering and transistorbestyckad power generator in first differentialsteget (flg Ii). The other stage is conventionallily edified with bee polar transistors, while the third differentialsteget works as a konstant-strömdrivning with high strengthening. Since all stages before the actual end the stage works in class A. is feed these with a special, välstabiliserad matningsspänning, as mentioned above. Pa this way nar the been possible to avoid modulationseffekter depending on excitement variations arisen at considerable effect levying.

Ingångssidans strömbuffer proves to have interesting circuit a solution. Konstruktörerna pa Trio-Kenwood has when select to work with a 3-stegs discreet Darlingtontransistor. Travelled that one will take out big power capacity in the effect transistors nar one parallel cup lazy end three transistors pa vardera the half of the kompl * nentära utgangssteget. Only most the linear strengthening the area at the discreet implemented Darlingtontransistorn is used, which among other thing resulted in good råförstärkningsegenskaper as t ex teams distorsion at high signal frequencies.

All transistors in Darlingtonarrangemang-et works in class's Ltd. Through a careful attitude of idle running the power has the been possible to optimize the amplifier on such way. that övergångs- och switchdistorsion been eliminated. The late distorsionstypen depends most often on instabilitet in för-stärkarelektroniken: mänga times compel to of t ex dahg cable draw within the unit. In order to avoid distorsionstillskott, caused of instabilitet and kabelläckning. has one in L-07M therefore consistent retreated all matningskablar as genomflytes of big amperages acrimonious sensitive excitement stem strengthening all stages. The final result of taken caution all measures is a förstärkarsystem with only 0.002 — 0.004% distorsion.

fig 11. Slutstegets förstärkarsektion — here is the principle schedule. Here, the build up with drift stage respective stem stage is seen. Marks particularlily the discreet edified, Darlingtonkopplade end pc own.

Fig 12. Kopplingsskiss over the two mättekniska the cases. A plant is conventional uppkopplad, the other according to Kenwoods recipes with cards speakerkabel and special, signalmässigt targeted \ f-kabel between for- och end ascended.

Low end impedance characterizes L-07M

L-07M has been designed in view of low end impedance. Therefore, one has deliberately eliminated all unnecessary kontaktresistanser along the signal roads. Further has one undergoing used rough cables for internal stem tie in L-07M.

Apart from conventional methods introduces Trio-Kenwood here a new motkopplingsteknik. s k Multi-£oop i-eedback (MLF) in monitor strengthening clean. Through that pa this way fit motkoppling as well before that after effect strengthening clean protection relay has one among other thing can to compensate for kontaktresistansen at skyddsreläets brytare. The result has become a total team end impedance in the magnitude 75 mohm.

Lay temperature operation important structure objectives

An of the important properties to take considerations to in an entire dc-kopplad amplifiers that L-07M is dimension small for a sa stable work point that possible, temperature variations can. about the is not counteracted, gives origins to significant operation. The consequences become offsetspänningar on strengthening square past. osymmetrisk klippning and in certain case also increased distorsion.

In a väldimensionerad amplifiers are the mainly the very first amplifier tea goat's temperature properties that decides how big temperature operation the entire system will beast. In order to effective counteract the possibility to undesirable excitement operation in monitor amplifiers L-07M has input pc eget therefore bestyckats with an a lot of temperature stable double MOSFET. Through that one further tillsett that end the stage works with constant bias powers exists the conditions tor good temperature stability. In L-07M has one therefore to placed down big toil on counteracting thermal operation in the effect transistors. Among other thing, one uses s k varistorer as avkänningselement at bias-stabiliseringen.

Due to these different types of temperaturstabiliseringar and good cooling properties in the amplifier total the variation of the end transistors' idle running power to only 20 “o between idle running and 100 watts uteffekt over 8 ohms.

Summary and evaluation:

Endeavor after simplicity is enough good. but for L-07C has we found, as been implied, that a part things can to become good than the now given. The appropriation of the front and panel its terms. t ex. The is lie to scan these, unless the light falls directlily on the front panel!

About the function of the controls can be said, that the volume thumbwheel has reasonableily select, though mechanically little odistinkta stages that give a good-looking toning da one gradual decreases down and a sufficiently fast increase da one goups in intensity. The volume is complemented with a stegad dämpsats for level determination. and in practice gives this arrangement good possibilities to optimering of the noise level. since this dämpsats of course is facing in before the very the last stage in the preamp. Moreover, one can with the control carry out level balance a ring. Good!

Tonkontrollerna: The stages the is divided up in is in and for themselves surely select and as such without objections. But bottom can one with a glance in measured test computer establish, that the the whole is rightly error the kind, da encroachment the points lies mis-. Lyssningsmässigt has our misgivings been confirmed on this point. One cannot influence the balance in the registers that are naturallily.

We can also intend ourselves. that a lot of users consider that a plant in this class proves to have an awkward deficiency through lacking individual opportunities of influencing for each channel, therefore double bolting corporal punishment pursues basis/mist edge. Here is t ex Technics 9600 exemplary.

The expanded band function the selector can of course show itself to last of value that tillgå da one diligent uses band two devices of some kind and wants to pursue over signal between them etc But the is an open question how mänga that thinks that this is some pluspost and moreover can use the facilities fully. OKAY. in an AV-central ETC is the valuable.

Ingångsväljaren proves to have no distinctive features at all without is fully conventional.

That only type of control one possibly lacks is a combined monostereo and stereo fasreverseringsomkopplare. special interestinglily as one lyssningsmässigt can consult differences in the sound da a stereosignal fasreverseras. On the other hand can the be intended that mänga is fond to get away details that fysiologisk volume control (loudness). flame passport filters osv:

The is meagreliest plausible that one plays 78-varva-. re and race maid or poor records on an apparatus that this!

But! To irritation for anxious gene shows the itself that some hörtelefonuttag on this preamp does not exist, despite sweets about scope on the panel and its reverse. Now, one is strict referred to trying to dock your naps on högtalarklämmorna. which causes problems, since each individual amplifier of course been placed next to your speaker! Further is sabotaged the whole thought behind Kenwoods philosophy with short, rough cables about one before changing over boxes in the signal roads. Like in fallen Yamaha C 2 wants to one to say: Comes out from designatelje and mätlabb and strides in in the user's everyday existence!

Subsonic-filtret exists and does literally no väsen of itself. The down precise what the will.

This endeavor to the hard look has done that certain of Kenwoods earlier successful grips on the bolting corporal punishment area — takes t ex the volume thumbwheel on mock-up 600 — not can be pursued. These thumbwheels think we both is for klena, and the is to reply that few some substantial grip about. The mechanical is general not correct in class with the electrical, and the appropriation of the front finds we to be directly tempting to confusions. All is certainly habit a thing, but here had one enough away to cost pa little more than as taken place. The bursts little in “feeling” and gedigenhet for a genuine knappofil…

The guldpläterade the contacts one finds on the rear panel gives without doubt good conditions for high contact ability and thereby goodliest attainable sound quality. The constitutes a clear positive phenomenon on the device.

The cables: As connection cable between the units has Kenwood bee packed a special, targeted cable with guldpläterade. screw catch takes contacts. This is clearlily praiseworthy. What as additional facilitates is that different cable lengths exists that tillgå, which is praiseworthy, da one always should rough after having sa short stem ties that possible. About this will we type in a late RT-nr.

P g a Semco-bestämmelser can for Swedish market not ifrågakomma some fjärrstart of end pc own. This means, that we sheep to accustom us at the thought that irra around in lyssnings-rummet and to hit of and on our units separate in the plant. This type's private member ' s bill consults however to the more umbärliga — the should have gone that few exemption, and how that entire pc should at Semko happen a serious överprövning of the provisions for use of these electrical functions, that more or less always is found on good equipments from USA and Japanese and may be thrown away in Sweden. The is quite questionable.

In operation, both stages retain its thermal properties and develops only modestlily with heat, despite the effect resources.

Likströmskopplingen has not given some as entire pc problems during the extensive provningarna.

And how becomes da sound related the the impressions, if we submit the electrical mechanical the complex?

On swim grammofoningångarna travels one a transient fast. distinct and ogrumlat sounds with Kenwood L-serien. In particular good seems mist edge and average registers. Where wants to we to denote the depiction that exemplary surely balanced in the registers. General applies about L-enheterna. that the överlag gives a small amount own boosts to the sound, which in itself means that the is not easy to describe how this neutral amplifiers “actually” lets.

Ljudbilden presents a not insignificant breadth and shows prominent tendencies to giving a depth in the productions. Probably, one willed can few still more “deep” in panoramat if the number ascended in the preamp could is eliminated some against now.

Effektresurserna at L-07M is sufficient for all normal needs more than sufficient, which was reflected in the presence of high. undisturbed dynamics and want of all klippningstendenser. also with to wa on fire dynamic programme materials. Special noticeableily became the; takes da we did not use the acrimonious charge view entire okomplicerade the speaker Dahlquist DQ-10. That this just speaker was chosen for the majority lyssning depended mainly on its analytical capacity and intrinsic good fas- och lokaliseringsegenskaper. When it comes to physical of amplifiers is the of course the electronics one searchs to listen to. the strict while, why the is important part's that referensljudkällan—högtalaren is surely well-known. part's that the allocates so little contributions in the form of koloration as possible. On that point, we are both agreed about that DQ-10 is a good choice. and we have both big experience of the.

• At the end. but especially, asks one itself sa of course: Is then this value for money. '

All is of course relative, and at least in your native country Japanese is certainly this exclusive and framåtblickande done Kenwood-apparaturen a clear good choice and an interesting alternative to a lot of other. Against that background is the with some regretting one finds, that the Swedish packet the price landed up sa high. approximately 13 000 sek. as the done for stem the stage plus two effect amplifiers.

• But of course finds always a so pass sophisticated and välljudande specialkonstruktion your audience than then. We are however prone to assume, that this both in pinch and technical execution högtstående the system in various respect, also economic, good does itself applying in an entirely professional and precise användarspecificerad application more than in a normal hem-Hi fi-miljö.

• Mänga enthusiasts etc. sound awareness even money willed without doubtly with blessing health the development of a — perhaps slimmed-down - “economy price mock-up '' of the delicate sound this system, that well also needs delicate polishing carcases in some details. The concept is both good and utvecklingsbart, and as tests on the new generation Kenwood-teknikers know-how and level of ambition weigh the heavy. ■

B O and U S

Stock, uses at provningen:

During the practical tests with Kenwood-förstärkeriet in operation during Hi fi-förhållanden used förf:a the following stock: Skivspelare: Thorén TD 160 B. microwave oven element muffled avfjädrad Tonarm: SME Mk Ii

Pick uper: Pickering XSV 3000. AKG P8 ES and Shure V-15 III. Ortofon MC 20 has constituted mc-pick up.

Speakers: Dahlquist DQ-10 Tuner: Kenwood L-07T

In addition to own productions in the form of original bands or other generation's copies of mastern has spelning of a number records been evaluated. These has among other thing covered these: Shefjields LAB-5, Discovered Again Direct dish, Rosie 0 ' Grady ' s Good Times jazz tied

Proprius 7770, Micaeli cam cursor in Bertil Al-vings upptagning

EMIHQS 1361, Garrick Ohlson plays Liszt European Monetary Institute C 066-130006, Theodorakis. Canto Ge-nerale (Pathé - Marconi - Columbia European Monetary Institute) DG 2530 467, LSO with Salvatore Accardo in Paganinis posthuma violinkonsert noes 6.


Comment to the measurements

Initiates we with utspänningsförmågan at Ken-woodförsteget, finds we that measured utspänning exceeds of the factory stated value with approximately 5 V.

Stated frequency size could not be may to exercize verge to agree with our measured values for stem the stage. Frekvensomfånget is in reality some low than stated.

Försteget was befinna cut osymmetriskt. The reason lies in amplifier tea direct build up. Since klippningen arises firstlily at 15 V is however osymmetrin of small importance.

Both RIAA the ladder's korrektionsanpassning proves to have actuallily remarkable discrepancies from the standard process. The input for mc-pick upen proves to have the whole 2 dB discrepancy in the basis area respective 0.75 dB in the mist edge. Corresponding relation exists also to see for mm-ingångens RIAA - curve. A so pronounced discrepancy from the standard is meagreliest acceptable in that class of amplifiers the applies, and one calls for a careful structure on this important point. In practice seen lacks perhaps these discrepancies crucial importance, then the performs in regions where only to dial or no information exists in the program material, but certain impact of the program material cannot omit.

Tonkontrollerna proves to have unfortunately the one to be tempted cold “the Japanese standard the error” 'with incorrect regulating area and with an encroachment point wide approximately 1 800 Hz in pcs f the of the producer the stated frequencies — sejig 7, a — b. That Japanese tonne controls so striking deviates acrimonious stated karakteristik amazes meagreliest longly, and the thing has been criticized in this newspaper at a number provningar. The is a strange uraktlåtenhet the Japaneses ådagalägger with error hit the these experiments to Baxandall-nät. Why will the last so difficult to achieve surely operational and correct tonne controls, then one clear is able to solve so many other and far difficult problems? Here may Kenwood companies in skamvrån with almost all competitors.

Uteffekten next. On that point, no complaints exist at all — our measurements agree agreed with or överträffar the producer's.

About effect pc own frequency time can be said, that the also överträffade tillverkardata important.

Signal/noise host unites: Required that the producer actually applied stated measurement method regarding S/N, i e IHF with vägning. sues measured values poor with computer specified. The differences amount actuallily to the whole 40 dB! This indicates undeniably olikheter regarding measuring technique. Lyssningsmässigt seems the noise level to lie satisfactorily placedly.

If we sees to klippningsbenägenheten in end the stage, proves to have this a fully acceptable symmetrisk klippning at 1 kilohertz with associated typical snip spectrum. At 10 kilohertz respective 1 dB överstyrning could no noticeable oscillationer be observed on the oscilloscope. On the other hand, the amplifier shows itself to have certain rest products of high övertonsordning.

On the area IM is below factory assuming even angivi value what our mätutrustning persuades detektera. D exists meager reason to doubt pa the of Kenwoc the stated figure here.

Differenstonanalyser shows, as common when d< applies tyngre Hi fi-produkter, no as entire pcs distorsionsformer. all mätresultat cannot ensure depending on intrinsic restrictions in mätutrustningen (— 90 dB).

No distorsionsprodukter each then visible. This is praiseworthy.

To sum up can be said, that Kenwood L-07-serie mätmässigt lies well to and is in class with the very the front device categories. The ä therefore the more regrettable to find a few entirely unnecessary structure misses that them. which been commented on above. This is however probably a thing that Kenwoods ambitious konstruktörer already works with improving to next whim of L-serien.




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