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Kenwood KM-209 Impressions

rickl

rickl

I'm just a bass player
Subscriber
In my quest in finding affordable high power Kenwoods, I’ve been curious on the late 80s KM/KC rack series.

I picked up a $20 KC-209 and updated it with the Basic C1 updates. You can read about it here. I was looking for a matching power amp.

I’ve read most of the posts of the KM-10X (125 w/c) and KM-20X (150 w/c) power amps on AK. Seem like cheap, reliable power. I think the major differences are the face plate and power meter to match the KC preamp. I think they are all basically the same.

Here are a few discussions i thought were interesting. I'm sure there are more.

@dognut posts this.
@himniok even talks about the KM-209 here.
@davidro post
@Roadrash wasn’t impressed
@theophile always has nice things to say about these power amps. These are almost like a “gateway drug’ amp to the Basic series and other Kenwoods up the food chain.

I finally picked up a $20 KM-209 on ebay as a parts unit.

Specs from HIFI Engine:
  • Power output: 150 watts per channel into 8Ω (stereo)
  • Frequency response: 5Hz to 200kHz
  • Total harmonic distortion: 0.015%
  • Damping factor: 35
  • Signal to noise ratio: 120dB
  • Dimensions: 440 x 133 x 269mm
  • Weight: 8.8kg
I wish the damping factor was like my L-07M monos but they where not $20.

Checking a few things before powering up the amp:
dirty
7amp fuse is good and correct size
corrosive glue on PS caps look like a problem (or going to be one in the future)
dirty
Sheet metal chassis and cover is very thin and bends easily. But works.
no one has been underneath. You need to cut away some tabs to access the bottom.

After a quick bath, I powered up on DBT and bulb dimmed and relay clicked
Display doesn’t work. LED power meter works. I replaced the display bulb from @dlucy HK 330B restore (I’m also working on a 330B) and now have a working KM-209 with working display. About 10 minutes of work.
Scope signal looks fine
Powered up on AC mains
DC offset is fine at 2.3mV/3.0mV

Hooked up a test setup (and KC-209) and played music
After an hour checked bias 21.0mV/23.1mV. Factory says 9-18mV so I’ll adjust that.

My $20 power amp seems to work. Going to remove some glue before critical listening.

Looking at the schematic, only an input coupling cap and a couple resistors in the signal path.

I updated a KM-208 for a customer with a pair of WIMAs. Might do the same here.

Here are a few pics since everyone likes nudes.

dirty-pcb.jpg front.jpg cap-glue.jpg

Not sure what I’ll use it for so stay tuned...
 
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a few crusty jumpers. At least none broke like in my 07m amps.
jumpers.jpg

pic of the cleaned board with the glue removed. this was a huge PITA. I feel this is kind of necessary.

no-glue.jpg
 
i did a comparison of this combo with my Basic C2 and M1. I threw in a Hafler pair for fun. You can read about it here. no surprises but I was curious how the pair would stand up to other combos.

Here are all three on my carpet and the preamp covering any amp venting :eek:. I didn't play them long and none got warm. Only a few tunes to see how they sounded.

Here are all three.
3-amigos+mac.jpg
 
Hi Rickl,

I've been hanging onto two KM-206's for future fun. Both are stock except for me having adjusted the bias and checking them over. I've always been a little fascinated by the KM series because of how dead simple they are. They're basically, "Let's throw in a decent transformer and crank some class A/B watts out of these," and then spent the rest of the development budget on meters.

I've contemplated several things, including output transistor replacements/upgrades, up to and including doubling the output transistor count. The low dampening factor also bothers me. Given their simple layout, overall cheap cost, and ready availability, I've pondered from time to time doing something with these to special them up a bit. Would love to kick around those ideas.

Going to read your shootout message....

Edit - and yeah, the entire KM series is basically the same design internally. I'd have to pick through one of each revision, but I'm pretty sure they're all the same, with the KM-10x series just being lower-power.
 
When I studied the schematic of the 209, only the input cap and a few resistors are in the signal path. Seemed very simple like you say. I had to replace the two input electrolytics with WIMAs.

I fixed a KM-208 and really didn't like power 'on' lights. Big and bright. I think I got my 209 so cheap was this light was burned out and the owner didn't think amp was working. Between this and the paper thin case that bends when you breathe on it are the only things I don't like about my 209. I really need to use it more. Or the M1, or the ...

I probably wouldn't have got the KM-209 but had the KC-209 and found the matching amp for $20. I was curious...
 
ajfink said:
the entire KM series is basically the same design internally. I'd have to pick through one of each revision, but I'm pretty sure they're all the same, with the KM-10x series just being lower-power.
Click to expand...

If I had a choice between the KMs I would just look at aesthetics. Since I picked up a KC209, I wanted the matching KM. I just waited until I found one in my price range.

I think some of the KCs and KMs look like BPC no matter how they sound. The bright red display bar of the KM-208/KM-209 drives me crazy. Probably helps keep the price low.
 
rickl said:
If I had a choice between the KMs I would just look at aesthetics. Since I picked up a KC209, I wanted the matching KM. I just waited until I found one in my price range.

I think some of the KCs and KMs look like BPC no matter how they sound. The bright red display bar of the KM-208/KM-209 drives me crazy. Probably helps keep the price low.
Click to expand...

No doubt about it, they're like Darth Vader's respirator, but better-sounding. They're closet amps, so to speak. But I think there's potential to tweak them upwards. :)
 
I got a KM-106 and KC-206 recently, haven't gotten them working yet. Burned out lamps on the KM-106, and I'll have to chase down some sort of remote to turn the mechanical volume control back on.

Electronically they seem to be pretty standard versions of Kenwood's amplifiers of the period. Not much in the power amp, just a PS and the transistors etc of the power amp section of a KR-950. Almost identical schematics, same input muting, etc.

I wonder why they are so under-rated other than being fairly light construction -- not really an issue in a rack system.
 
i was able to get a few remotes working with my kc-209. i posted it on the link above. i ended up with a kenwood rc-120 with a million buttons. it seems to control everything but is kind of complicated. my guess you can get a remote working with something you have laying around. I know I did.
 
I replaced the lamp in the KM-209 when I got it. I removed the red bulb cover and added a blue cover on the bulb. I wanted to better match the 'marantz blue' look of the pre. it came out more 'McIntosh green'. oh well.

it isn't 'yamaha red' any more!
209-pair.jpg
 
When I first got back into this hobby my first "audiophile like" system was a Kenwood Basic system that got started after finding a C1 preamp in a thrift store for $20. Liking the sound of my M1/C1 combo I made an effort to look for Kenwood gear and quickly found a lot of KM series amps out there often for $20-$25. As I recall from looking into it at the the time the Basic series were sold as separates while the KM series were sold as part of rack systems. I believe the rack systems went by the name Spectrum or Spectra. As the numbers in the series went up you usually gained about 25 watts per channel. It was difficult to get specs on them in part because they were part of rack systems. I do seem to recall that when compared with the Basic series amps the KM series power ratings were similar when running a 8 ohm load but there was a noticeable difference between them when looking at the power ratings for a 4 ohm load.

I may have things mixed up a bit since it has been some time and many amps since I had my Kenwood gear. I used the KM series amps to add power to the anemic HT receiver I had at the time and they were great in that role.
 
Hello everybody! My name is Frank and I live in Florida. Brand new to the site and I need some help. I have a Kenwood rack system that I probably bought between 1989 and 1992. Up until last week, the system still kicked ass! Now, it seems my amp (KM-209) is having issues. It will play for a bit (when it turns on at all) then I hear a "click" and I lose sound. I'd really love to fix this if possible even though my wife hates the tower speakers HAHA! I just don't feel like todays surround systems will provide me the house shaking sound this system does. Maybe I get a new amp? looking for some advice. If it's a component I can pop out and replace, I could try that but I'm not techie enough to solder circuits and stuff like that. I'd appreciate any advice!
THANKS IN ADVANCE!!
 
Frankieg021 said:
Hello everybody! My name is Frank and I live in Florida. Brand new to the site and I need some help. I have a Kenwood rack system that I probably bought between 1989 and 1992. Up until last week, the system still kicked ass! Now, it seems my amp (KM-209) is having issues. It will play for a bit (when it turns on at all) then I hear a "click" and I lose sound. I'd really love to fix this if possible even though my wife hates the tower speakers HAHA! I just don't feel like todays surround systems will provide me the house shaking sound this system does. Maybe I get a new amp? looking for some advice. If it's a component I can pop out and replace, I could try that but I'm not techie enough to solder circuits and stuff like that. I'd appreciate any advice!
THANKS IN ADVANCE!!
Click to expand...
Welcome to AK.

It sounds like a component is getting hot then failing. Does it act the same way every time?

The quickest way is to get some freeze spray. When the unit clicks off, spray a transistor, one at a time. Wait a few seconds, then try another. Start with the final transistors and work backward. I alternate channels.

How are your electronics skills and tools? Do you have a meter and know how to solder. Just asking because if it’s a bad device that needs to be replaced, you can do it or take it to a shop. Your interest in diy amplifier surgery’s will determine your path. Regardless, troubleshooting is a good skill to have.

Finally, you may want to start your own thread. Sometimes using an old thread for a new problem makes it hard for others to find in the future.
 
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Did the location and ventilation situation change? Has dust built up in it? It does sound like it's overheating. It's definitely fixable by a tech, likely easily, but it could also be as simple as blowing the dust out.
 
ajfink said:
It does sound like it's overheating. It's definitely fixable by a tech, likely easily, but it could also be as simple as blowing the dust out.
Click to expand...

I fixed a KM-208 in 2020 that had blown outputs. very easy to fix. bdent.com had outputs. Not sure if bdent.com still has them but like aj and semanon say it sounds more like a over heating issue since it initially works. if you are a tech (or know someone that can help), check the bias and dc offset to see if a component has drifted. service manual is available on hifiengine.

if you were closer, i'd ask you to bring it over. I have a marantz 250 on the bench but always make room for 'walk ins' :cool:
 
Picked up one of these in a van load of free audio gear the other day. Cleaned it out internally and when i powered it on it burned 3 resistors on the board before i could power it down. Guess its going in my repair pile for a rainy day. I like the look and specs and was planning on running it with my Optonica receiver as they look decent together.
 
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