Kenwood L-08M Monoblock Amplifier (Vintage Review)

[Blumlein 88]

@amirm
I'd vote for this to get a spot on the home page.

 

[tomchris]

I really like to see the Sigma Drive tested and measured after Peter from QuirkAudio has checked and tweaked it.

 

[charleski]

One further proof and reminder of how great the Japanese designs of the 70 and 80's were. Across the board. It pains to realize how great a disservice the High End Adio press TAS, S'Phile and their ilks , did to the hobby and industry in general.

Yes indeed. One of the Great Audio Myths that's done so much damage to 'high-end' audio is the story that Japanese manufacturers went chasing ever-lower THD numbers back in the '70s and ended up producing amplifiers that sounded terrible. One has to suspect that this originated from a blend of racism and the realisation that many US/European manufacturers of the time simply couldn't match the technical skills the Japanese had developed, so they decided to pretend these skills didn't matter.

 

[restorer-john]

Yes indeed. One of the Great Audio Myths that's done so much damage to 'high-end' audio is the story that Japanese manufacturers went chasing ever-lower THD numbers back in the '70s and ended up producing amplifiers that sounded terrible. One has to suspect that this originated from a blend of racism and the realisation that many US/European manufacturers of the time simply couldn't match the technical skills the Japanese had developed, so they decided to pretend these skills didn't matter.

Or they just blatantly lied.

My collection encompasses mostly late 70s, 80s and into the 90s, Japanese gear. Basically designs conceived and marketed before the Japanese crash and the 'lost decade' of stifled innovation, slashed budgets and cheapening of costs/build right to the edge of fitness for purpose. Now we have a generation or two who have never experienced mass-marketed quality in anything but a smartphone.

The difference in absolute care, quality, construction and performance of gear makes pretty much everything I see these days, make me yawn. I love all HiFi, but it's impossible to get excited for much of the stuff being pushed on consumers in the last few decades.

 

[GXAlan]

Or they just blatantly lied.

My collection encompasses mostly late 70s, 80s and into the 90s, Japanese gear. Basically designs conceived and marketed before the Japanese crash and the 'lost decade' of stifled innovation, slashed budgets and cheapening of costs/build right to the edge of fitness for purpose. Now we have a generation or two who have never experienced mass-marketed quality in anything but a smartphone.

The difference in absolute care, quality, construction and performance of gear makes pretty much everything I see these days, make me yawn. I love all HiFi, but it's impossible to get excited for much of the stuff being pushed on consumers in the last few decades.

What is great is the regular non fancy stuff that we would call mid fi still had really premium build and you would be giving up number of inputs or power.

That said, I think the customers was also different. A good perspective is that the JBL L100 was an incredibly popular selling speaker. It sold for $273/each, or $4000 a pair when accounting for inflation.

Imagine going to a mainstream store and thinking that the $4000 speaker is the most popular one!

There are still L100’s with original drivers still going strong. Most are damaged from being dropped or being soaked in water. The L100’s used cloth surrounds so they did not have to deal with foam rot.

 

[AnalogSteph]

The signal chain is Panasonic UB9000 -- balanced-2V --> Marantz PM-11s2 as pre-amp --single ended--> Kenwood L-08m --Vishay Dale 1% NH-250 4.48 ohm resistor -- AUX in -> E1DA Cosmos
I have tested these in the stereo mode of the E1DA and ultimately used the AUX input for my final tests.

The Cosmos ADC has low input impedance, for both differential and common mode. This results in modest suppression of ground loop issues, which is why you're seeing some interference. It shouldn't be too bad if you choose the least sensitive setting as input impedance goes up accordingly, but don't expect any miracles in terms of CMRR. You're not the first one to stumble over this.

Topping D10s + E1DA Cosmos ADC as a measuring system

This combo make an excellent low cost measuring system, enabling to measure harmonic distortion components down to -130dBr, at about 300 EUR total price. I use the D10s with Olimex USB isolator to avoid signal ground loops. Below please see the measurement of my discrete preamplifier Dispre 2 -...

audiosciencereview.com

 

[anmpr1]

1) A good perspective is that the JBL L100 was an incredibly popular selling speaker. It sold for $273/each, or $4000 a pair when accounting for inflation.

2) There are still L100’s with original drivers still going strong. Most are damaged from being dropped or being soaked in water. The L100’s used cloth surrounds so they did not have to deal with foam rot.

1) My L100 cost (1975) I believe, $333.00 USD. At the time the JBL consumer line was 'fair traded' which meant they were not discounted. However dealers would make you a deal in a system, adjusting the overall price down. You could buy the 4311 for less, but then you didn't get the cosmetics.

Back then, JBL were made in the LA factory; it is interesting to ponder the fact that JBL is now selling a made in Indonesia (I think that's where they are built) L100 Classic for the same (inflation adjusted) price.

L100 popularity was due to several factors. First, the rock and roll angle can't be discounted. Everyone remembers the Maxell 'blown away' thing.

Next, it was an era of 'polite' sounding acoustic suspension loudspeakers, which although were probably better 'balanced' sonically, yet had a sort of 'closed in' and muffled sound. Plus, those generally required a lot of watts to play loud, and watts were expensive back then. JBL had a more 'open' and unboxy sound, were more sensitive, playing louder with less amplifier.

Finally, the cosmetic factor. No one had encountered a loudspeaker with a blue or orange 3D foam grill. That was certainly a selling feature.

2) JBL drivers were first rate from a build standpoint. The L100 crossover was minimal, and the box unbraced. You often find the LE25 tweeters damaged, because someone pushed it in. Otherwise, all drivers are probably still functioning. The foam grill typically disintegrated over the years.

It would surprise me if many were 'soaked' in water. If by that you mean flood damaged. No doubt many had water (or beer) spilled on the wood tops. However the veneer was actually thick enough for it to be sanded and refinished. Many were likely dropped, during moves and such.

As far as the Kenwood L-series? In the US those products had very limited distribution. From Japan, at the higher end, Yamaha product was pretty common, along with the Sony VFET line. Accuphase. Then probably Lux. In the more 'exclusive' shops you might find Stax, and maybe a few others. Sansui and Marantz made some expensive gear, but they were mostly relegated to 'Pioneer' status--that is, rather prole and geared toward the mid ranges. I suspect that most top tier Japanese electronics were as good as, if not better, than most of the boutique stuff the 'high end' touted in their magazines, and in their audio salons.

 

[restorer-john]

@AnalogSteph Your avatar "I only give negative feedback" could be interpreted as meaning: Your maximum output is reduced, although the errors are less. But it could be also argued you are less likely to stray from the

1) My L100 cost (1975) I believe, $333.00 USD. At the time the JBL consumer line was 'fair traded' which meant they were not discounted. However dealers would make you a deal in a system, adjusting the overall price down. You could buy the 4311 for less, but then you didn't get the cosmetics.

Back then, JBL were made in the LA factory; it is interesting to ponder the fact that JBL is now selling a made in Indonesia (I think that's where they are built) L100 Classic for the same (inflation adjusted) price.

L100 popularity was due to several factors. First, the rock and roll angle can't be discounted. Everyone remembers the Maxell 'blown away' thing.

Next, it was an era of 'polite' sounding acoustic suspension loudspeakers, which although were probably better 'balanced' sonically, yet had a sort of 'closed in' and muffled sound. Plus, those generally required a lot of watts to play loud, and watts were expensive back then. JBL had a more 'open' and unboxy sound, were more sensitive, playing louder with less amplifier.

Finally, the cosmetic factor. No one had encountered a loudspeaker with a blue or orange 3D foam grill. That was certainly a selling feature.

2) JBL drivers were first rate from a build standpoint. The L100 crossover was minimal, and the box unbraced. You often find the LE25 tweeters damaged, because someone pushed it in. Otherwise, all drivers are probably still functioning. The foam grill typically disintegrated over the years.

It would surprise me if many were 'soaked' in water. If by that you mean flood damaged. No doubt many had water (or beer) spilled on the wood tops. However the veneer was actually thick enough for it to be sanded and refinished. Many were likely dropped, during moves and such.

As far as the Kenwood L-series? In the US those products had very limited distribution. From Japan, at the higher end, Yamaha product was pretty common, along with the Sony VFET line. Accuphase. Then probably Lux. In the more 'exclusive' shops you might find Stax, and maybe a few others. Sansui and Marantz made some expensive gear, but they were mostly relegated to 'Pioneer' status--that is, rather prole and geared toward the mid ranges. I suspect that most top tier Japanese electronics were as good as, if not better, than most of the boutique stuff the 'high end' touted in their magazines, and in their audio salons.

From a man who was there at the time.

 

[SIY]

I had some LO-7Ms in my living room for a while- they eventually blew up. I found out later that my experience was not uncommon. Superb performance, though, so your measurements don't surprise me.

"Sigma Drive" was well-known outside of marketing as "remote sensing." Very common in lab power supplies and measurement systems for low resistances.

 

[restorer-john]

I had some LO-7Ms in my living room for a while- they eventually blew up. I found out later that my experience was not uncommon. Superb performance, though, so your measurements don't surprise me.

"Sigma Drive" was well-known outside of marketing as "remote sensing." Very common in lab power supplies and measurement systems for low resistances.

The L07m did not implement sigma drive. And neither did the L07mkIIs. How did you manage to blow them up?

I've owned 9 of them and apart from vintage 'blag flag' cap issues and oscillation, they are a beautiful design.

Sigma drive came afterwards, in the the L08M and a bunch of integrateds as well as the L1000 and some other models I can't recall...

 

[anmpr1]

This may have been mentioned somewhere, but for interesting Japanese designs, check out the Skyfy YT video of the Sony TA-N1 amplifier and matching preamp. They take the lid off, so you can see the construction love. These were later pieces than the Kenwood, from 1999. Most people wouldn't think of a hunk of aluminum and iron to be pretty, but that's why we are audiophiles, I guess.

 

[Chr1]

Presumably the heatsinks are oriented horizontally to be aesthetically more pleasing.
ie pretty....
Have to say that I think that it is one "sexy" Sony power amp.
Like the Kenwood: Me likey.

 

[ConnorG]

The L-08M’s were and still are fantastic amplifiers. I’ve had the privilege to restore and use a pair of these gorgeous amplifiers recently. They are among some of the best I have heard in my system. Everything OP stated is exactly how I hear them.

A link to a thread on the restoration I performed can be found here.

I also have a small video on my channel showcasing the L-08M’s playing some music here.

Thanks OP for putting this thread together. I own a pair of L-07M’s, L-07MII’s, and recently sold my pair of L-06M’s which also sported Kenwood’s Σ drive. I have a pair of L-07MII’s with me now for restoration as well, which I’m almost done with. They are another pair of fantastic amplifiers from Kenwood’s golden age. I will have a video documenting their restoration on my YouTube page within the week for those interested.

 

[ConnorG]

One further proof and reminder of how great the Japanese designs of the 70 and 80's were. Across the board. It pains to realize how great a disservice the High End Adio press TAS, S'Phile and their ilks , did to the hobby and industry in general.
I would like similar tests/reviews for some , generally unknown (Japanese) speakers of the same period. We know a lot about Yamaha efforts (NS-1000, etc) but little else about others, in particular Technics... They made several SB-xxx "Linear Phase", some of which, were said to be superb.
Congrats and thanks to the OP @GXAlan

Peace.

I agree almost fully. Harry Pearson of TAS actually used the L-07M's in his reference system for years because he liked them so much. I will share scans I took of his review in a 1977 issue of The Absolute Sound.

--But yes. The anti-Japanese vitriol masked with a patronizing attitude was apparent in spades when reading many hifi review magazines of the 70's into the 90's. "The Audio Critic" magazine was a clear example of this on countless occasions.

 

[anmpr1]

I agree almost fully. Harry Pearson of TAS actually used the L-07M's in his reference system for years because he liked them so much. I will share scans I took of his review in a 1977 issue of The Absolute Sound.

--But yes. The anti-Japanese vitriol masked with a patronizing attitude was apparent in spades when reading many hifi review magazines of the 70's into the 90's. "The Audio Critic" magazine was a clear example of this on countless occasions.

Thanks for the scan. I was not aware Harry was using them. That surprised me, to tell you the truth. As far as Aczel?--his view (which he later repudiated as idiocy) was that no matter how good a Japanese circuit was, there was an American preamp or amp that was better. This, by the way, was early Gordon Holt's view, also.

At the same time, one must compare that view with his embrace of exotic Japanese MC cartridges. For his part, Holt was more a fan of American MM cartridges. Especially the spherical tip version of the V15. Perhaps that, because he was not aligning his cartridges for lowest distortion?

Alternately, Aczel (under the influence of Mitchell Cotter) was never antagonistic to high end Japanese direct drive record players (in fact, he even listed the mid-range Kenwood 'stone' player as a 'best buy'). Of course they were modified--both SP-10Mk2 examples. First by Cotter, the other by Sao Win.

So the 'anti-Japan' thing was really a mixed bag.

What we find in Pearson's review is the typical nonsense that was (and still is) fashionable. Of course, one might expect actual differences to be evident when comparing an L-07 to a D-150. But probably not in the way Harry reported them.

Interesting that he managed to blow up a set, by mis-connecting them. That sort of thing happened frequently with reviewers back then.

 

[tomchris]

The Absolute Sound…Abysmal layout, awful pictures and apalling reviews + pictures of trees as page filler

I have always wondered how the Japanese magazine Stereo Sound fared in comparison.

 

[pma]

@GXAlan , I am not sure what I see in your distortion measurements. Would not it be possible to place base frequency (H1, 1kHz) at 0dBr??

Please see this plot as an example

1) Amplitude of your base frequency, 1kHz, is at -15dBFS, without any doubts. The numbers in the top right corner say H2 = -130.8dBFS. OK, but this means that H2 is -115.8dBr below H1. Another number in the top right corner says THD = -127.1dB. This is simply impossible. THD cannot be better than H2 distortion (-115.8dB). I doubt that the distortion calculations of the SW used are correct.

2) Different amplifiers have similar mains frequency spuriae, in your plots. Did you try to check for a residual system error? (measuring cable shorted at amp OUT Lo speaker binding post, amp delivering the power as normally measured).

3) The ultrasound content is suspicious and may indicate to another system issue.

What is the load used, 4ohm, 8ohm? Or without load?

 

[GXAlan]

@GXAlan , I am not sure what I see in your distortion measurements. Would not it be possible to place base frequency (H1, 1kHz) at 0dBr??

Please see this plot as an example

View attachment 234021

1) Amplitude of your base frequency, 1kHz, is at -15dBFS, without any doubts. The numbers in the top right corner say H2 = -130.8dBFS. OK, but this means that H2 is -115.8dBr below H1. Another number in the top right corner says THD = -127.1dB. This is simply impossible. THD cannot be better than H2 distortion (-115.8dB). I doubt that the distortion calculations of the SW used are correct.

2) Different amplifiers have similar mains frequency spuriae, in your plots. Did you try to check for a residual system error? (measuring cable shorted at amp OUT Lo speaker binding post, amp delivering the power as normally measured).

3) The ultrasound content is suspicious and may indicate to another system issue.

What is the load used, 4ohm, 8ohm? Or without load?

Tagging @pkane who can comment on the math. This was before I understood about using dbR for the scale.

1) I think the THD of -127.1dB needs to be corrected by the same amount, so the real THD is -112.14 dB.

2/3) I didn't have a chance to re-test since I plugged the unit back into its actual daily use. The evening plot is completely unchanged. That is, I turned everything off. Went about my evening, and then late at night, I powered everything on and did exactly the same test without changing anything and those ultrasonic spikes were gone. It's clearly something in my house/local power grid that contributed. We have lots of families with solar power and electric vehicles which do put energy back into the grid.

The fact that The 15/20 kHz hump correlated to my LED recessed ceiling lights and the 30/65 kHz fully disappeared at night with no change to the test system suggests that it's external.

4) 4.48 ohm Vishay Dale 1% NH250. Test description and photo in my Marantz tests.

 

[pkane]

Tagging @pkane who can comment on the math. This was before I understood about using dbR for the scale.

1) I think the THD of -127.1dB needs to be corrected by the same amount, so the real THD is -112.14 dB.

2/3) I didn't have a chance to re-test since I plugged the unit back into its actual daily use. The evening plot is completely unchanged. That is, I turned everything off. Went about my evening, and then late at night, I powered everything on and did exactly the same test without changing anything and those ultrasonic spikes were gone. It's clearly something in my house/local power grid that contributed. We have lots of families with solar power and electric vehicles which do put energy back into the grid.

The fact that The 15/20 kHz hump correlated to my LED recessed ceiling lights and the 30/65 kHz fully disappeared at night with no change to the test system suggests that it's external.

4) 4.48 ohm Vishay Dale 1% NH250. Test description and photo in my Marantz tests.

Yes, you can set your units to dBr in Multitone and this will be done automatically for you. If you select dBFS, you'll need to subtract the amplitude of 1kHz tone, in dB, from THD (also in dB) to get the THD value relative to the fundamental.

 

[GXAlan]

Kenwood L-08C Pre-amplifier Review (Vintage Audio, QuirkAudio restored)

Kenwood L-08C Pre-Amplifier Measurements (Vintage Audio) Part 1: Kenwood L-08M Monoblock Amplifier Review https://www.audiosciencereview.com/forum/index.php?threads/kenwood-l-08m-monoblock-amplifier-vintage-review.37756/#post-1327414 If you haven't read Part 1, please give that a read...

www.audiosciencereview.com

L-08C is even better.