Kenwood KA-907

Kenwood KA-9900

October   1 9 7 8 october 1978
1 9 8 0

Extra-rare and last iteration of Kenwood's "monster" period.

There is much shared with the the Model 600 from which the KA-907 took most of its layout - inside and outside.

High-Speed is of course the word to lower THD, TIM, dynamic crosstalk and improve damping factor, rise time and slew rate.
This here is done with two massive transformers, four 18,000µF caps and all-DC / FET / Class A pre and driver circuits.

Output stage is four pairs of parallel-connected high-speed 2SA165 / 2SC2489 50MHz output devices with cascode bootstrap, current mirror and constant current drivers - sounds very much like a Model 600 :)

Only the heatsinks were entirely reshaped with far more dissipating area : 20mV make the idling current... but 1kW is reached for at full power !

Still center of the show, the MC stage is a three-stage symmetrical complementary circuit with low-noise transistors in the first stage, a common emitter circuit in the second stage and an emitter follower circuit is used in the final stage ; an NFb loop links the first and third stage emitters while a suplementary NFb from the second stage emitter is applied to the first stage base.
Low impedance, low distortion, higher output voltage.

The MM stage has a DC FET-input circuitry similar to that of the power stage. Low distortion, high overload capability and S/N ratio.

The attenuator is a conductive plastic 4-gang from ALPS most likely, with two gangs either side of the buffer amplifier to gain linearity and reduce distortion at low levels.

- read the TECH I and TECH II for the rest and/or Zeljko's review of the Model 600.

Design-wise, the KA-907 inaugurated Kenwood's "frosted" period : all aluminium with semi-matte texturing and a much more angular design of the knobs and switches. But it nevertheless remains a renewed Model 600, just like the accompanying tuner, the KT-917, was a renewed Model 600T.

The last measurements for both components were done on august 21, 1978 by Mr H. Agatsuma.

The KA-9900 original japanese version is identical, looks-wise and specs-wise.

The KA-907 saw in Europe a limited edition with gold trims and knobs : 100 pieces, seemingly delivered only in Germany.
The serial numbers for these are "regular" ones - only the looks and specific numbered certificates identify them.

A complete dismounting of a KA-907 for caps replacement here and many large nudies froma complete restoration at Curt June's.
Indeed - "they" don't make like that anymore.

Kenwood KA-907, image 1 Kenwood KA-907, image 2 Kenwood KA-907, image 3
Kenwood KA-907 specifications
Title Value
Power : 2x 150W RMS, 8 Ohm, 20Hz...20Khz, 0,01% THD
2x 150W (8 Ohm, 1Khz)
2x 180W (4 Ohm, 1Khz)
Aux. IN to SP out THD : 0,01% (rated power, 20Hz...20Khz, 8 Ohm)
0,006 % (1/2 rated power, 20Hz...20Khz, 8 Ohm)
Phono IN to SP out : 0,01% (rated power, volume at -20dB)
IMD : 0,0045% (rated power, 8 Ohm)
Damping factor : 100 (DC...20Khz, 8 Ohm)
Rise time : 0,8µs
Slew rate : ± 230V/µs
Power bandwidth : 5Hz...100Khz (0,03% THD)
-70dB (DIN 45500)
Frequency response : DC...400Khz (+0 / -3dB, DC ON)
1Hz...400Khz (+0 / -3dB, DC OFF)
20Hz...20Khz (RIAA, ±0,2dB)
Speaker impedance : 4...16 Ohm
Power IN sensitivity : 1V / 50kOhm
Inputs : 2,5mV / 33 - 47 - 100kOhm (Phono 1 MM)
2,5mV / 47kOhm (Phono 2 MC)
0,1mV / 100Ohm (Phono 1 MC)
150mV / 50kOhm (tuner, aux, tape 1 & 2)
S/N ratio : 90dB for 2,5mV input (phono 1 & 2, MM)
96dB for 5,0mV input (phono 1 & 2, MM)
102dB for 10mV input (phono 1 & 2, MM)
70dB for 0,1mV input (phono 1, MC)
76dB for 0,2mV input (phono 1, MC)
105dB for 150mV input (line level)
Max. phono input : 230mV RMS (1Khz, 0,01% THD, phono 1 & 2, MM)
9mV RMS (1Khz, 0,01% THD, phono 1, MC)
Outputs : 150mV / 180 Ohm (TAPE rec)
30mV / 80 Ohm (TAPE rec, DIN)
9V max. / 750 Ohm (PRE output)
Bass controls : ±7,5dB at 75Hz or ±10dB at 25Hz (turnover 150Hz)
±7,5dB at 155Hz or ±10dB at 50Hz (turnover 400Hz)
Treble controls : ±7,5dB at 10Khz or ±10dB at 20Khz (turnover 3Khz)
±7,5dB at 20Khz or ±10dB at 40Khz (turnover 6Khz)
Loudness controls : +3 / +6 / +9dB at 30Hz or 100Hz
Subsonic filter : 6dB/oct. below 18Hz
High filter : 12dB/oct. above 8Khz
PC : 1kW at full power
Dimensions : 46 x 16,1 x 46,3cm
Weight : 25,8kg.
Accessories : D-90 rack handles
Kenwood KA-907 : 0 topic
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page online since : march 2006
page updated : september 2010
page type : LGT / KNB
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