Vintage Kenwood KA-2000 (vintage Audio Rules)

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2[H]4U
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Jun 12, 2001
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I just found a kenwood KA-2000 in the dumpster at my apartment and I rescued it just before the rain and I have to say at only 13WPC it sounds better than my "New" Onkyo receiver (For Stereo Music that is since it is not a Surround receiver). The only ting that was wrong with it was it was missing the speaker terminal block there was just two wires sticking out of the back (Blue and a yellow and I figured out that the Chassis was the audio ground

I will be set now only if I could find a proper speaker block as the one I got from R$ fits but is not long enough to fully screw down to both screws. I got it working for now just need to clean the dials (With what?) because I get crackling when I move then and the switches are doing the same thing.

Also I hope I rewired the speaker plate right please tell me if I am wrong

Yellow = right
Blue = Left
I used a short piece of 18 AWG jumper wire to jump the two Negative termininals to a point on the chassis (I just crimped a ring terminal to the wire and then when I put the cover on. (I put it through that screw on the inside of the chassis)

Oh and if anyone has any old audio equipment be very and I emphasize VERY careful when messing around the inside
epically while plugged in to a live outlet (No Polarized plug) and I think there is a way the chassis could become
electrically hot Don't know how though but I do remember that old TV's had what was called a hot chassis I don't know if Vintage amps are the same way

Two questions OK Three
1. why do the two channels share the same audio ground?
2. How do I fix the crackling/poping when I turn the volume/Bass knobs
3. How to I fix the stereo/Mono Switch I can tap the switch and I hear crackling and one side gets louder (Right

now I have it set to stereo and I have it so it is working ok for now but if I move it at all it will do that again)

Thanks for reading my post and thanks in advance for any reply's
 
You might want to join the forums at audiokarma.org as they are more suited for this sort of thing.
 
Old amplifiers rock. The reason they sound so "good" is because they actually sound like crap - they're built to be put together as cheaply as possible, and they distort and color the music that goes through them. Which depending on your ears, can actually make music sound better.

To answer your notes...

(1) Two channels sharing the same ground is common on lots of amps. It's really only newer HT amps which don't have a negative power supply (cost savings) that tend to use BTL, single-chip amplifiers. These "chip-amps" really only started coming out in the late 80's/90s.

(2) Crackling/popping when you turn knobs: replace the potentiometers. You can take them apart and clean them with contact cleaner, but chances are they'll go crackly again. I highly recommend the Bourns conductive plastic ones since they're super reliable.

(3) Stereo/mono switch: dissasemble them and try contact cleaner, or find new switches. Finding an equivalent switch might be difficult, so you could always permanently wire the amplifier so it's in stereo mode regardless of switch position.

I'd spend some quality time with the Digikey catalog for potentiometers/switches. There might also be a speaker terminal block which fits this amplifier, though I'd sooner modify your RS one so it fits.

Some other notes on your post: using a 2-wire power cord is fine provided that some basic rules are followed regarding insulation and internal wiring, and if this thing is CSA/UL/CEwhatever certified then you're OK. For audio equipment, it's actually a bit beneficial since it avoids a ground loop through the AC ground.

TVs are another story, however - using a floating chassis in TV sets avoids the need for an isolated AC/DC power supply for the horizontal voltage. However in an older TV set there's really only one input (RF, easy to isolate) and every control surface/button/etc can be made of insulating plastic. But in the case of audio amplifiers, there's lots of IO connectors which aren't easily isolated, and there's really no application for direct-rectified AC.
 
I am actually using it right now with a pair of Insignia Speakers from Best Buy and even with the cheap speakers it sound awesome (To me as I am not a Audiophile) I was just wondering why the power cord is so thin (SPT-1 20AWG,) it only draws about 60 - 120 Watts and has a 1A fuse protecting it. I only say 120 Watts because that is the maximum allowed only if you plug something into the 60 Watt switched outlet (Which is also non polarized so nothing new will fit into it) I know it has a fuse protecting it
I always thought the Minimum wire gauge was 18AWG so the OCPD (Over Current Protection Device) would be able to trip a breaker or blow a fuse with out making the wire THE fuse and possibly causing a fire (Provided back in the day there was not all greenies in the fuse box or worse a penny behind the fuse) I know I am safe but I was just wondering why (I Live in a newer APT Complex with breakers and GFCI/AFCI Protection so I am not woried about using this)
Oh and I meant to post this in the Home Theater area
 
Here is an image of my find in its new home as my computer amp

Kenwood_KA-2000.jpg


Here is an image of what the original speaker terminal post looked like I wish I could find one but I don't know the correct terms to search for
I don't get why the person that trashed the thing took the speaker terminal post

KA-2000_Rear_120.jpg
 
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1. why do the two channels share the same audio ground?
why not... ground is ground and all goes to the same place.... this is fairly common practice in older electronics and is a fine art that seems to have been lost in modern electronics....

2. How do I fix the crackling/poping when I turn the volume/Bass knobs
i suspect its the pots (variable resistors attached to said knobs) that probably are worn out.... replacement should eliminate the static during knob operation....

3. How do I fix the stereo/Mono Switch I can tap the switch and I hear crackling and one side gets louder (Right now I have it set to stereo and I have it so it is working ok for now but if I move it at all it will do that again)

its time for a new switch.... depending on what you have you should be able to find a suitable replacement......
 
You might also try some tuner cleaner on the pots.

Also, can't you verify the signals yourself?

1) Hook your speakers up
2) Apply a signal to only the right channel of an input
3) If you hear sound from the right speaker, you've got the wiring right
4) If you hear sound from the left speaker, you need to switch the yellow and blue wires around.

You don't have a hot chassis. The ground screw on the back panel is a dead giveaway.

You can find the service docs for this unit online for about $15.
 
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I found a service Manual (Caution!!! Big 666KB PNG file so be prepared to DL it or wait for it to DL to your browser)

Any way I did exactly what you said although more dangerously :D
1. Alligator clip to chassis other end to Negative speaker terminal (Only used one speaker for the test the left one and I only hooked up the left channel)
2. both wires bare and not covered but not touching anything or each other
3. Touched the positive wire to each of the colored wires and when I got sound I knew that was the left channel. Whew! :eek: I though for sure I was going to fry myself or the amp

that is done with for now but now I have an annoying buzzing problem that only plagues the left channel and I hear it no matter what is connected to the amp, As long as the power is on and the speakers/headphones are connected I can hear it even if no source is on or even connected to it.
I asked the AK forums and they said recap it (They said recap with emphasis to the big Grey power caps the ones that are near the power transformer) but that raises a couple of other questions/concerns for me

1. I suck at soldering
2. I suck at soldering
3. did I mention I suck at soldering :D OK enough of that
4. I have a friend that will do the work for me provided I buy the right parts (Which I found and cost more then it is worth as-is) so I have a "Moral" dilemma trash the old amp or pay more then it is worth to replace the caps and hopefully have years of trouble free service (Which I can not say of "Newer" stuff)

anyway for pics of my fix and more pics of the "Suspect" Go Here
 
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I asked the AK forums and they said recap it (They said recap with emphasis to the big Grey power caps the ones that are near the power transformer) but that raises a couple of other questions/concerns for me...

4. I have a friend that will do the work for me provided I buy the right parts (Which I found and cost more then it is worth as-is) so I have a "Moral" dilemma trash the old amp or pay more then it is worth to replace the caps and hopefully have years of trouble free service (Which I can not say of "Newer" stuff)
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And this is why switchmode power supplies rock. They're a lot more complex, but give much smoother power.
 
Mohonri said:
And this is why switchmode power supplies rock. They're a lot more complex, but give much smoother power.
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A 1967 Amp has a switch mode Power Supply??, what are you getting at? I thought it had a linear supply hence the big caps and power transformer? I suck at soldering and electronics I can do basic soldering (Basically I can solder wires together or to widely spaced terminals) I think I did a fine job on that speaker terminal block:D the second time around the first time was horrible and I thought that was my problem so I got another block and did it again this time I heat shrinked and taped the ends off so no loose strands would touch the chassis or each other but the buzzing problem is still there :mad: and I used stuff I had around the house to secure the second part of the block as the screw holes did not line up with the factory holes
So should I toss it or just replace the two power caps and see what happens as the power caps are easy to find and are cheap $$$ wise or does the problem lie deep with in this beast of an amp :D I say that sarcastically as it only puts out 13WPC but the sound is much bigger , brighter and louder then my 5.1 Receiver (And it is also really heavy for its size)
 
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A 1967 Amp has a switch mode Power Supply??, what are you getting at? I thought it had a linear supply hence the big caps and power transformer?
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Sorry, I should have been clearer. You are entirely correct--you have an old-school power supply, and I was speaking in generalities.

... but the buzzing problem is still there :mad: and I used stuff I had around the house to secure the second part of the block as the screw holes did not line up with the factory holes
So should I toss it or just replace the two power caps and see what happens as the power caps are easy to find and are cheap $$$ wise or does the problem lie deep with in this beast of an amp :D I say that sarcastically as it only puts out 13WPC but the sound is much bigger , brighter and louder then my 5.1 Receiver (And it is also really heavy for its size)
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Considering the age of the amp, it would not surprise me at all to find that some of the caps on the amplifier board itself have dried out and are no longer effective. The fact that you get the buzzing sound only on one channel makes me think that the big grey caps are fine, but that something is wrong with the caps on the amplifier board itself.

(if you were willing to take the time to generate a schematic from what's on the board, I could probably take a good stab at what caps to test)
 
Where's the other end of this wire connected? I'm wondering if you're leaving the chassis floating, and that's allowing a buzz to be induced on the inputs.
 
One end is screwed to the chassis and the other end goes to both negative terminals on the speaker output block. Is there any specific point on the chassis for the audio ground? I just have it screwed down between one of the screws that hold the cover on but is there a better place for it? I know the chassis is the audio ground but is there a specific place for me to connect it to?
 
Rats, the manual is blocked from where I am. Any chance you could post it on your charter.net site?
 
There is no standard place to connect it. You need to trace the schematic and find a good spot that's grounded, if the lead is intended to be a ground for something on the back panel. A missing ground can readily induce a buzz or a hum in your amplifier.
 
I'll second mikeblas's comment--most likely, there's a ground connection missing. I took a look at the schematics, and there are a few caps that might be worth checking out. Specifically, I looked for caps that are tied between Vcc and GND, or are close to them (e.g. a resistor is between Vcc and the positive side of the cap), and that affect only one channel. C10 and C11 in the preamp are the only ones that jumped out at me. You might also check out C15 in the Main Amp, as well as the caps associated with the power supply (C9, C10, C11, which includes the big caps).

Incidentally, I took a look at the capacitor values in that power supply. On one schematic, the largest is 1000(uF, I presume) 50V, and the other is 2200(uF?) 50V. At mouser, you can get a 1000uF cap for $0.29 and a 2200uF cap for $1.18. Or, you could take two of the 1000uF caps and put them in parallel and save a few cents. Heck, go for broke, get a 10,000uF cap for $3.86 :).
 
The filter caps on the output of the power supply don't seem likely suspects. I think you identified, Mohori, the fact that noise in the power would most likely affect both channels.

I figure that the source of the noise is either induction (because of a floating ground, for instance) or oscillation because of a bad connection or damping capacitor in the feedback. Scoping along the affected channel would lead to the culprit pretty quickly. Detaching each stage from the next along that channel would help, too.

It's not clear to me if the buzz is on all selectable inputs or just one.
 
I think I fixed the problem W00T! I tied the left channel ground to the ground screw on the back of the chassis and no more buzzing! should I tie the right channel to the same place? as all I did was just take it off my speaker block for a test and I touched it to the ground screw and the buzz went away currently the wire is still there screwed down
 
Yes, both inputs should be grounded. Grounding them to the same place is fine.
 
gee said:
Old amplifiers rock. The reason they sound so "good" is because they actually sound like crap - they're built to be put together as cheaply as possible, and they distort and color the music that goes through them. Which depending on your ears, can actually make music sound better.
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I respectfully disagree. Old Kenwoods, Sansui and Marantz are high quality products that were built to high standards. My old 60 wpc Kenwood KA 7100 still sounds better to my ears than the majority of todays consumer crap. Personally, I don't think many kids today actually have a clue what quality audio sounds like.

As a tube guitar amp player, I will concede that certain distortions can result in 'better' sound, but I don't think that's the case here - if anything, it's today's products that are built as cheaply as possible. I highly doubt anything you buy today will still be working in 30+ years, let alone considered of any value.
 
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