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Recapped and Upgraded Kenwood KA-4002

eizner23

eizner23

Super Member
I had a few KA-4002 solid-state amps laying around, I decided to modernize one of them. I started with the thumb screw speaker terminals, replaced with gold-plated banana jacks. Ground screw is now 24k gold. The main capacitor was upgraded from a 2200uf to a 4700uf Nichicon Super Through Type III KG Gold cap, the channel capacitors with Super Through Type Nichicon KG Gold 1000uf caps. Nichicon KZ or FG, a few Silmic II throughout the signal path and tone path. The higher value film caps I replaced with Sprague Orange Drops.

After testing it, I was pretty blown away with the crispness of the highs and
undistorted lows it reproduced, well worth the $300 in capacitors (with leftovers for the other ones). Cant beat that golden solid-state sound!
 

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Well, I do like my KA-4002, but I don't think I would put $300 into it.:D
But that's just me.

Mine is original and still going strong. I use it all the time for my computer sound.

It has a bunch of inputs, sounds great, and has a mono out that is perfect to run a sub.

Nice work.

Rob
 
Thank you gentleman. It is a resilient little amp. I definitely recommend giving this amplifier another look. As for burn in, I might assume the quality will get a little better after a little operation time.

After auditioning a little jazz music through the device, the highs roll off so nice and precisely. The old caps' tolerance were just all over the place. I can now clearly hear the dynamics of a cymbal crash and high hat.
 
hi OP eizner23 , looks nice. How is it working still?
I have two of these amplifiers (one is from a friend to clean the controls) and that one sounds less crisp than the other.
So I think it is time to follow your example..
Or rather follow lead because I'm actually not quite knowlegeable enough to find out where to put which capactor and which ESR value is optimal.
Do you still have a parts list that you would care to share with us?
Thanks!
 
Nice work. That is a lot of capacitor money but if it makes it sing to your satisfaction that is great.

Can you talk a little about the issues, good and bad about dealing with these earlier units with all that wiring going everywhere in the unit vs. the later designs with the wiring more tightly packed out of the way of the boards? I'm curious if it is easier to service or not.
 
Hello Loalaweiter,
Recapping isnt too difficult, just read the value and voltage rating on each cap and replace it with a replacement one at a time, noting the polarity. Take plenty of photos beforehand in case you lose track. I can look at my notes to see if i have a list of caps to share and note what the brand/type was. I might have spent a total of $80-$100 for all the top-end capacitors. This is a good beginner amp to experiment with.

The amp is still working and sounds better than new. After the recap i was starting to get popping sounds from some transistors. I also thought the mid range was a bit overwhelming and slightly distorted. I proceeded to replace 90% of the transistors in the unit. Made a big difference in fidelity but I still wasn't satisfied with midrange. I proceeded in replacing some of the diodes and all the Carbon or composite resistors with 1% metal film resistors. Popped in a HiFi-Tuning Gold fuse for good measure. A lot of work, but Bada Bing, what a beautiful, transparent and smooth sound up and down the octave band.

Blue Shadow: This is a very easy unit to work with, everything is basically on one board, aside from the tone board; all accessible by removing the bottom cover. I didnt have any issues with the amount of wiring or how it was packed.
 
I just received one of these pretty little KA-4002's today, it sounds wonderful, and I'll recap and replace the noisy transistors in a new BOM thread. Can't wait to hear the improvement you're talking about!

UPDATE: I did my KA-4002 restore and recap and documented in it in this thread: https://www.audiokarma.org/forums/i...ist-on-kenwood-ka-4002-integrated-amp.767861/

FYI: There are many Kenwood recap/restore threads cataloged in this stick thread: https://www.audiokarma.org/forums/i...epair-recapping-and-servicing-threads.789484/
 
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ZOOM said:
Now do a blind test with one of your original units. When you can't hear a difference, you will learn the lesson that you shouldn't waste your money on expensive capacitors.
Click to expand...

What is expensive, maybe we just want more headroom not to have to recap in 20 yrs from now when good parts are even more rare? I would always pick the 105 degrees C version if possible.

"I proceeded in replacing some of the diodes and all the Carbon or composite resistors with 1% metal film resistors.
Popped in a HiFi-Tuning Gold fuse for good measure. A lot of work, but Bada Bing, what a beautiful, transparent and smooth sound up and down the octave band."

Eizner23, thanks for the followup: The resistors do work, I did the blind test with two late sixties Sony STR of one the resitors were replaced. Crispness!
 
freezecone said:
have recapped and upgraded around 10 of these amps.
Click to expand...
The Orange drops in there look familiar. Did sell a few of these units on ebay 5 years or so ago? If so seeing them inspired my first 4002 rebuild, I used orange drops and Muse in same positions.
 
eizner23 said:
I had a few KA-4002 solid-state amps laying around, I decided to modernize one of them. I started with the thumb screw speaker terminals, replaced with gold-plated banana jacks. Ground screw is now 24k gold. The main capacitor was upgraded from a 2200uf to a 4700uf Nichicon Super Through Type III KG Gold cap, the channel capacitors with Super Through Type Nichicon KG Gold 1000uf caps. Nichicon KZ or FG, a few Silmic II throughout the signal path and tone path. The higher value film caps I replaced with Sprague Orange Drops.

After testing it, I was pretty blown away with the crispness of the highs and
undistorted lows it reproduced, well worth the $300 in capacitors (with leftovers for the other ones). Cant beat that golden solid-state sound!
Click to expand...
Very very nice job. I have one of these and even though I also own some very high end gear I would never part with this amazing piece of audio technology. A couple of years ago I did a side by side comparison with this and a Rega Brio R and IMO its a better sounding kit. If you see one of these for sale under $200-$300 grab it!
 
I highly recommend a recap, bump the value of the main power filter capacitor to 3300-4700uf and replace the Hitachi 2sc 458 transistors (6 or 8) with modern equivalents.
 
taineasy said:
Very very nice job. I have one of these and even though I also own some very high end gear I would never part with this amazing piece of audio technology. A couple of years ago I did a side by side comparison with this and a Rega Brio R and IMO its a better sounding kit. If you see one of these for sale under $200-$300 grab it!
Click to expand...
Its size and weight is convenient, lift it with pair of fingers. But yeah once you thoughtfully gave it a good work over it is something to hang on to. I have a bag of Toshiba C2240 used in my units for those Hitachi’s, always sounded better to me than the Fairchilds in Kenwoods.
 
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