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Kenwood KA-7X

Stereo Integrated Amplifier (1982-83)

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Kenwood KA-7X


Power output: 100 watts per channel into 8Ω (stereo)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 0.008%

Damping factor: 1000

Input sensitivity: 0.2mV (MC), 2.5mV (MM), 150mV (line)

Signal to noise ratio: 69dB (MC), 86dB (MM), 107dB (line)

Output: 150mV (line), 30mV (DIN)

Dimensions: 440 x 109 x 340mm

Weight: 9.5kg

Year: 1982


service manual   English -

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Reviewed Jul 26th, 2014 by PZ IX

This device is a Basic M1 with tone control added to the feedback of power amplifier, phono pre-amp and obviously some switches and knobs. Great amplifier with advanced designed circuit (dual output stages, which second turns on at higher output signal levels). Good sound, heating not too much for that power. Quality of components also good.
My vote is 8/10 because of fault which occurs sometimes in K-7x's - damaged transistors on higher power output stage and some in previous stages, but after many years - I think this is reliable amplifier. Excepting this, my rate is 10/10.



PZ IX's picture


Another interesting thing in this device is design - class G which is almost not found in another home amplifiers. My error in review - some little transistors in the input driver stage get hot every time even in low levels on output and it causes to scratch sound which teels user to quick replace of these components (very cheap), otherwise it causes a very serious and expensive fault. I worked in mine KA-7X with it, after replacement of these little semiconductors I gave extra heatsinks to all transistors which get hot in idle including driver stage of outputs - now all it's good.

re: KA-7X


I have just acquired an old KA-7x with a blown channel and I am trying to replace the damaged parts. Could You please clarify which are the small driver transistors to replace ( according to the SM) ?

Thank You.

PZ IX's picture

re: KA-7X


As far as I remember they were Q19, Q21 and Q23. You can recognize them accurately from similiar to TO-92 packages and little "cooked" PCB under these elements. Replacing driver pair Q25 and Q27 is strongly recommended - heating so much all the time without heatsink is very bad idea.
Add heatsinks for all the five transistors per channel and put on working side too.
Remember to check whole transistors to prevent from serious damage of new or remained old transistors. If you had blown primary side fuse I'm almost 100% sure that you have burned out some or all outputs.
Also temporarily replace primary side fuse with circa 70-100W bulb with rated voltage according to your electricity in your region - it saved higher power (usually expensive too) elements for me, even in this KA-7X too.
I think repairing this is not easy and not cheap (if you have blown more than few cheap as a bread components) but worth it. While mouting another, simplier DIY seems to be ok for more popular design circuits, for unusuall and innovating like this - no.

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