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
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
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
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.
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
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
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
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
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.
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
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
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
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
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
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
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
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
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'
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
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.
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 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
Lay temperature operation important
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
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
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
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:
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
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
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
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
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.