Dual Power Amplfier KA-7010

[Ishmael]

Until I saw our recently purchased Kenwood KA-7010 I had never known that Kenwood made dual power amplifiers. While I was aware of the Harman Kardon dual power receivers, and the high regard they are held in by many, I had never come across dual power in Kenwood.

There’s not a lot on the web about this amplifier, but in looking for more information I found pictures of the KA-7020 twin transformer amplifier (the KA-7010’s sibling?). By comparison the KA-7010 has four capacitors (I assume two per channel) rated at, 71V7500uf, while the KA-7020 has two capacitor’s rated at 71V15000uf, all Elna.

Opening up the KA-7010 I found a light coating of dust, but again how lucky, no evidence of a smoker as the dust came right off in my wiping cloth and swabs (yes there’s still some dust under the more delicate parts, maybe an air blast will remove them from there while I run my shop vac over the area? Just don’t want to bend/break anything).

I then broadened my search for information about dual power Kenwood’s and learned more about these models including the gold standard Supreme and Model 500/600 amplifiers.

The history and specifications for the Kenwood 500 at the Vintage Knob impressed on me what a superb amplifier it is. Therein was noted:

RMS Power: 2x 100w (8 Ohm, 20hz-20,000hz, 0.08% THD
Dynamic Power: 520w (4 Ohm)
S/N ratio: 110dB short-circuited
IMD: 0.08% (rated output into 8 Ohm)
Damping Factor: 50 at 8 Ohm

However, after Aker fonon (thanks again fonon) provided the specification sheet for the KA-7010, I was quite surprised at the quality, at least by measured specifications, that went into this black box amplifier(and it’s sibling KA-7020 noted separately below), for example from the KA-7010 specifications:

RMS Power: 100 watts per channel minimum, RMS, both channels driven, at 8 Ohms from
20 HZ to 20,000 HZ with no more than 0.06% total harmonic distortion (same
for KA-7020 except with 0.008% total harmonic distortion)
Dynamic Power: 125 W per channel at 8 Ohm KA-7020 140 W per channel at 8 Ohm
200 W per channel at 4 Ohm KA-7020 240 W per channel at 4 Ohm
270 W per channel at 2 Ohm KA-7020 380 W per channel at 2 Ohm
S/N ratio: Tuner/Aux/Tape – (IHF-A) (IHF 66) 110dB for 150 mV input
IMD: (60 Hz:7 kHz = 4.1) at Rated Output Power 0.005%
Damping Factor: 160/50 Hz at 8 Ohm KA-7020 220/50Hz at 8 Ohm

So now comes the subjective part. I hooked the amplifier up to my garage Sony CD player and New Large Advent speakers. I first cued up the Titanic Sound Track and played “Hymn to the Sea”. While my restored vintage JVC receiver is very good, this was much better. The movement between the orchestra and the (Scottish/Irish) pipes as they sang this instrumental lament was effortless and textured. When the deep tones of the oceans abyss were played they literally pressurized the garage. Next was Elton John’s “Rocket Man” detail, much more detail in both his voice and the bands contribution. Finally, Fleetwood Mac and “You Make Loving Fun” Christine McVie’s voice leads the band and the nuances to the words are clear, drum whacks and guitar plucks too.

Conclusion:
This is no numbed out black box amplifier. This is a beautifully executed musical tool which will engage you in the listening process. Due to its power your speakers wont’ need much to perform and 4 ohm speakers need not be avoided. You get lucky from time to time in this hobby of vintage gear as did we in this purchase. Now I wonder if I will ever see a KA-7020 surface?

 

[Ishmael]

Here are the nudies as clean as I could get without risking the really small stuff (yes more cleaning is in order looking at the pictures, guess that's what weekends are for).

 

[carcrazy]

Nice amp, it looks like it is very well built. Congratulations.

 

[Ishmael]

Thanks car it really does look and sound that way. I will remove the bottom plate later this weekend to deoxit and then fader lube all the pots. I am hoping again to get lucky given the clean lay out encountered so far and have easy access to them.

 

[Ishmael]

A final request to the Kenwood room. Does anyone know how I would purchase or get a service manual for this amplifier? Caveat-I know there are a couple online free manual websites, but in looking at their preview they list an all in one service manual for the KA-701, KA-7010 and KA-7011 so I am uncertain as to which amplifier is covered, though it could be all three. However, I don't know anything about these sites and don't want to risk downloading something from their site, their pdf download software, when I can't be sure it won't include spy, mal-ware too. So if you have used any of these sites without the blue screen of death popping up on your computer three months later do let me know. Final, final, does anyone know the DC offset values for this amplifier (the main reason behind the search for the service manual)? I don't want to risk a pair of speakers. Thanks for any help you can provide.

 

[Ishmael]

Into each life a little rust must fall. As you can see there are spots of rust here and there on the transformer covers. So I took some rust inhibitor and with my smallest auto detail brushes applied a layer of rust inhibitor (the white stuff you see). This will turn black, chemically inhibiting the rust and leaving a coating over the rust. Final, shot is the same area after a coat of black paint over the rust inhibitor. Next, removing the face plate to clean the pots/controls.

 

[Ishmael]

A good evenings work. All the controls have been cleaned with deOxit, in some cases twice as I ran out at the end, but managed to purchase another spray can locally. The face plate has been cleaned and two control knobs which came apart, they have a metal shell glued over a plastic part that fits on the shaft, have been re-glued. Fired it up and there is no noise at all coming from the balance as there was before, or, through any of the other tone controls.

I will let the glue set for the night and then bring this in tomorrow to try out with our bedroom system. This is a quite powerful amplifier and easily drove the New Large Advent speakers in our garage. Thanks again for your suggestions.

I would highly recommend this amplifier if you ever come across one. While I have not heard, and given their rarity will likely never hear the Kenwood 500, 600, 650 line of integrated amplifiers, at least from the specifications perhaps these two dual power amplifiers, KA-7010 and KA-7020, may give you a taste of the same.

 

[Charliep127]

I have an opportunity to pick up one of these for 5 bucks... needless to say I'm going to do it. But do you know if these are compatible with remotes? This one isn't coming with one.

 

[Warpserver]

Looking at pictures of the front and back, most likely no.

There's no remote sensor on the front or plugin for one on the front or back.

 

[Kingshead]

Yes, Kenwood has been building dual mono integrated amplifiers for quite some time, check out the clean layout of the KA-7300. I have one powering my Infinity Modulus speakers in the bedroom, the pre outs and main ins were very useful for connecting the Modulus sub.

 

[SicMan]

The KA9100 KA9150 is a good example too .. and they sound great for 90 - 100 W / Channel

 

[diepbtt]

A good evenings work. All the controls have been cleaned with deOxit, in some cases twice as I ran out at the end, but managed to purchase another spray can locally. The face plate has been cleaned and two control knobs which came apart, they have a metal shell glued over a plastic part that fits on the shaft, have been re-glued. Fired it up and there is no noise at all coming from the balance as there was before, or, through any of the other tone controls.

I will let the glue set for the night and then bring this in tomorrow to try out with our bedroom system. This is a quite powerful amplifier and easily drove the New Large Advent speakers in our garage. Thanks again for your suggestions.

I would highly recommend this amplifier if you ever come across one. While I have not heard, and given their rarity will likely never hear the Kenwood 500, 600, 650 line of integrated amplifiers, at least from the specifications perhaps these two dual power amplifiers, KA-7010 and KA-7020, may give you a taste of the same.

I have a kenwood KA-7020, a upgrade version of KA-7010. Curently i do recap- work as i find many Brown ELNA caps are leaked and destroyed some places of the mainboard.

I do not find these polarized 2,2uF/100V in my country but non-polar ERO 1813 2,2uF/250V are available. Could someone know that i can use it for polarized electrolytic caps?

These ones are in power amp final stage.


Thanks

 

[KingBubba]

I see it has those damned remote switches with the linkage from the front panel. The Pioneer SX 3800 has a whole set of those which are a misery to work on. I hope yours are easier. Definitely a fine looking machine. Enjoy.

 

[Ishmael]

Charliep sorry for late reply, no there is no remote. This is an all manual control integrated amplifier, but well worth the effort to get up and adjust the controls.

 

[JimSurreyUK]

Yes, Kenwood has been building dual mono integrated amplifiers for quite some time, check out the clean layout of the KA-7300. I have one powering my Infinity Modulus speakers in the bedroom, the pre outs and main ins were very useful for connecting the Modulus sub.

if my amp looked like that inside, i'd replace the metal covers with perspex, with subtle fan ventilation and have it set up on the coffee table so i could look at it, yum

 

[ProudArmyBra]

So I aquired one of these.

Does anyone know the actual rail voltage. It has 4x 7500uf caps at 71V fromt he factory.?71V caps are not the norm today.

I was also wondering if these are snap in caps or bolt in?

The amp is in my basment wrapped in plastic it will be weeks before I can take it apart. Would be nice to get parts comming.


Parts are terrible to try to get ones hands on.

 

[chazix]

actual rail voltage

Welcome to AK. I'm puzzled, though. I surmise that you have service info, which (at least in the doc available on elektrotanya.com) has the voltages.

Yep, 71V caps are uncommon today. You can go higher without a second thought. If you're thinking of going lower, like the 63V that's common at the time I'm writing, I guess I'll say that I wouldn't, myself. Having a healthy margin on that rating is A Good Thing.

From pictures on the interwebospheres, I reckon that snap-in (or plain old radial) caps were used. I think it would be a mistake to order parts before you've had hands-on.

Another thing that puzzles me about this post is that I feel like getting passive components for vintage gear is astonishingly easy. Have you tried Mouser or Digi-Key, both of which will let you search for parts that match a desired diameter, height, and lead spacing? (All of which you'll want to consider, especially lead spacing. And you may find that upping the voltage rating helps in matching the physical specs.)

(Edited for typo)

 

[Semanon]

Totally agree with @chazix. Wait until you open the unit, then verify things like cap size, lead spacing, mount type, etc., before ordering from Mouser/Digikey. If they don’t have an exact match, go up a bit in voltage and/or capacitance. You can always ask here if you are unsure.

My last point: try it for a while before doing a rebuild. Start it up on a dim bulb tester, clean controls that need it, blow out the dust, look for obvious problems, and enjoy. Then if you feel the need to recondition it, you will have a baseline against which to compare. IME, power supply caps are the last to go out of spec. I often don’t replace them when aiming for sonic improvement, unless they are leaking or bulging.