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

[GXAlan]

Kenwood L-08C Pre-Amplifier Measurements (Vintage Audio)

Part 1: Kenwood L-08M Monoblock Amplifier Review

Kenwood L-08M Monoblock Amplifier (Vintage Review)

Kenwood L-08M Monoblock Amplifier Review (Vintage Gear; QuirkAudio restored) Where were you in 1980? In Tokyo, Japan, a small team of engineers released the most sophisticated amplifier of its time... A bit of history In the 1970's, an elite team of veteran Trio-Kenwood engineers left the...

www.audiosciencereview.com

If you haven't read Part 1, please give that a read first. There's a much better description of the history of this product line in part one. If you haven't read Part 1 and just want to continue, then spoiler alert... the L-08M was coming surprisingly close to the type of performance we get from HypeX NC500 amplifieres, made more impressive since this was achieved in 1980 with the benefits of 1V input sensitivity and the higher gain and 2 years before the compact disc.

What about the matching L-08C pre-amp? This L-08C was recapped and restored by Peter at QuirkAudio. Thankfully, while the pre-amp is made with a lot of anti-magnetic material (plastic), it has done much better surviving 42 years as it's quite lightweight. This is also a very rare 120V unit. From the outside, you cannot tell that it's anything special.

Test setup
Panasonic UB9000 RCA out (2.1V) into Kenwood
--> 4V out from regular RCA jacks (1m cable) versus 2 meter Sigma Drive cables
--> generic RCA to XLR input adapter from Amazon
--> E1DA Cosmos ADC Grade A

Just like the L-08M, the marketing brochures seem make it seem smaller than it really is. Although it's not very tall, it's deeper than most traditional audio gear. Here's a top-down view of the Kenwood L-08C compared to a Marantz Dolby Atmos 7.2 receiver.

Like the L-08M, the L-08C boasted a very impressive set of advertised specifications that would still be competitive today in 2021. 106 dB SNR and frequency response of DC-850 kHz!

Unique to the L-08C was the ability to drive the amplifier with standard RCA cables or the option of using a fancy Sigma drive cable which applied negative feedback to the pre-amp output based upon a remote sensing strategy of the RCA inputs. Does it work?

Short answer? Yes.

We pretty much have a pre-amplifier that matches the advertised specifications of 106 dB SNR and is essentially transparent to the source (a Panasonic UB9000 with a modern AKM AK4493 DAC for a 1 kHz test tone where the E1DA Cosmos is optimally calibrated.)

This was sold to the public 2 years before the introduction of the compact disc.
(thanks @restorer-john for correcting my dates)

The anonymous design team at Kenwood for the L-08C and L-08M in 1980 truly deserve their spot in the audiophile history books. Even in 1980, they have exceeded the performance of the modest test gear that I have!

@amirm @restorer-john

 

[restorer-john]

This was sold to the public 5 years before the compact disc.

Bear in mind, The Compact Disc was officially released for sale in October 1982 (Japan) and the L08c/L08m earliest brochure date I can see is July 1981, so we have an approximate 1 year difference. The L08c/m pair also does not appear in any general brochures until 1982. If you are in any doubt, check the date codes on the internal devices or caps that weren't replaced by your tech.

The L05/7 m/c were available in 1977.

 

[GXAlan]

Bear in mind, The Compact Disc was officially released for sale in October 1982 (Japan) and the L08c/L08m earliest brochure date I can see is July 1981, so we have an approximate 1 year difference. The L08c/m pair also does not appear in any general brochures until 1982. If you are in any doubt, check the date codes on the internal devices or caps that weren't replaced by your tech.

The L05/7 m/c were available in 1977.

Ah! I will correct the CD date -- I was using 1985 for the US introduction of the CD.

The L-08C was introduced in Japan in 1980. It is possible that European/US/Australian exports were 1981.

TRIO L-08Cの仕様 トリオ

audio-heritage.jp

 

[restorer-john]

The plastic chassis that Kenwood used were, in my opinion just major cost cutting (like all the Japanese at the time). Clearly the antimagnetic aluminium chassis of the 07 series was too expensive, so they just injection moulded a nasty chassis. I actually threw out a KA-1000 (two chassis (PSU+Amp) TOTL integrated because it was such a POS. True story. It had a stupid capacitive touch volume, sigma drive and it's entire chassis had warped and cracked. And the heat-pipe didn't work.

All I kept was the power supply as I figured one day, I'd use it for something. That was nearly 30 years ago and I still have the PSU! I cut off the umbilicals decades ago and threw it in the bin, then retrieved it. It was supposed to be a PSU mule for amplifiers I was developing but life got in the way.

Here it is, notice the L01 markings. The KA-1000 was just a glossed over L-01 right down to the same transformers...

Three transformers in that PSU, one for each channel and another for low level/control etc.

 

[GXAlan]

TRIO-AMP Fan

TRIO-KENWOODと、第一世代のシグマドライブアンプ 1970～80年代は正にオーディオ全盛期だった。現在なら考えられないような、贅沢で魅力的な機器が数多く生まれた。その中には実験的なアンプも数多くあった。その一つにTRIO－KENWOODが考案した「Σ（シグマ）ドライブ」がある。このSPを駆動させる接続方式であるのだが（厳密には接続機器はSPだけに限らず、プリアンプとパワー・アンプ間、CDやチューナーとアンプ間などもあった）、内部の回路もこのシグマドライブ理論に基づいて設計された。

sites.google.com

This is in Japanese but has more information

Google Sites: Sign-in

Access Google Sites with a personal Google account or Google Workspace account (for business use).

sites.google.com

 

[restorer-john]

I was using 1985 for the US introduction of the CD

US release was March 1st 1983, six months after Japanese home market release. That was the deal Sony/Philips struck when Philips were dragging the chain.

Sony (and the consortium of manufacturers) more or less said "all the Japanese manufacturers are ready and you want to delay the release date because you cannot get your products finished in time??" "Screw you, we'll release in Japan and do a worldwide release when you get your act together next year, in six months." Philips had a lot of trouble getting their players to work, letalone be good enough to sell.

 

[GXAlan]

US release was March 1st 1983, six months are Japan release.

OK, fixed!


November 1980 = launch of L-08C

L-08C KENWOOD - ä¸å¤ãªã¼ãã£ãª é«ä¾¡è²·åã»è²©å£² ãã¤ãã¡ã¤å

www.hifido.co.jp

 

[restorer-john]

@GXAlan

You should do a phono (MM) stage overload test as we were talking about overload in one of Amir's recent reviews. The L08c is supposedly rated for 320mV overload which is excellent.

(Just feed in a 600R or so, 1kHz source into the MM input and wind up the level (slowly) from zero mV while monitoring on your FFT the tape outs until the harmonics start to spike, then wind it back a touch and take an input voltage reading)

 

[AndreaT]

Impressive performance. What was its price? Truly ugly looks: even in those days there were Mark Levinsons with aesthetics that still hold, IMO. It would be nice to know a bit more about the variable feedback from the Sigma Drive: was it a re-edition of the classic Harold Stephen Black one or something truly innovative?

 

[Mosfet]

The Kenwood L-02T (tuner) is an admired product too. I know it's just an analog tuner, but there are many obsessed fans out there claiming it's the best of the best.

 

[kchap]

@GXAlan

You should do a phono (MM) stage overload test as we were talking about overload in one of Amir's recent reviews. The L08c is supposedly rated for 320mV overload which is excellent.

Even if the overload was half the published figure, it would still be far better than the recently reviewed Sutherland Phono Pre-amp. Why can't Sutherland achieve similar results.

Edited.

 

[restorer-john]

It would be nice to know a bit more about the variable feedback from the Sigma Drive: was it a re-edition of the classic Harold Stephen Black one or something truly innovative?

Additional feedback path from the end of the interconnect.

 

[restorer-john]

Why can't Sutherland achieve similar results.

They've been building phono stages for a while and know what they are doing. I'd say they consider a typical overload from a scratch/pop as something that you really don't want to fully reproduce if you want to keep your tweeter voicecoils in one piece.

I could argue for a high overload capability and a low overload/soft clipping capability equally validly. Vinyl just doesn't have the dynamic range needed in real terms and clicks and pops are faults anyway. A bit like the so-called 'intersample overs' needing headroom in a DAC. No, you don't need headroom for IS overs- you need recordings that aren't faulty in the first place.

 

[laudio]

The results of part 1 do not surprise me at all. ASR is hung up on anything older than 10 years is technically obsolete based on computer performance standards but in real world nothing modern has bested the great components from back in the 80's days from a pre/amplification point of view. DACs have, but most DAC measurement these days exceed what we can hear anyway and it doesn't matter. Like component reviews like this from back in the days where most folks have no clue.

 

[AndreaT]

The results of part 1 do not surprise me at all. ASR is hung up on anything older than 10 years is technically obsolete based on computer performance standards but in real world nothing modern has bested the great components from back in the 80's days from a pre/amplification point of view. DACs have, but most DAC measurement these days exceed what we can hear anyway and it doesn't matter. Like component reviews like this from back in the days where most folks have no clue.

What are “computer performance standards” for a preamplifier? Did you care to listen to newer DAC/preamps by Okto, Topping, Benchmark? Before CDs we were limited to 40 dB dynamic range, 25dB channels separation, when lucky. Why this anti-progress tirade?
Also, ASR is to be commended for the openness of the forum and the freedom to join for all. I am always interested in new (and old) equipment, and ASR offers a great guidance in these days of disappearing Hi-Fi electronic stores. Those stores, btw, were not a better standard to choose, as too often they were noisy, crowded, and did not offer enough listening experience time to make an informed choice.

 

[valerianf]

Nowadays electronic components are more performant.
But in the 80's japanese audio design team goal was to improve measurable metrics.
They had a design that they were perfecting years after years.
It is no more the way that the design teams are working: how many equipment measured by Amir have poor metrics.
Performance is simply no more the goal of most design teams.

 

[restorer-john]

Before CDs we were limited to 40 dB dynamic range, 25dB channels separation, when lucky. Why this anti-progress tirade?

Cut it out. We had dbx with 110dB dynamic range, Dolby C came out before CD and gave us in the 70dB+ S/N. And open reel.

Preamplifiers are a shadow and I mean a shadow of their former selves. Not even close. Okto, Topping and Benchmark 'preamps' are just linestages with hardly any functionality. Where's the MM stage, the MC stage, the tone controls, the filters, the loudness contours, the multiple inputs, headphone stages and processor loops? Notably absent. They are a tiny sub facet of a real preamplifier.

I have plenty of real preamplifiers- you should try one yourself. And today (because it's pouring rain), just for fun, I'm measuring phono overloads because a bunch of people are interested. Guess what? The worst one so far is a 2015 product. The best one so far is a 1980 product!

 

[The Capstan]

Kenwood L-08C Pre-Amplifier Measurements (Vintage Audio)



Like the L-08M, the L-08C boasted a very impressive set of advertised specifications that would still be competitive today in 2021. 106 dB SNR and frequency response of DC-850 kHz!


@amirm @restorer-john

850KHz of bandwidth on all analogue sources! WOW. I think it is almost a record figure for hi-fi gear.
You could use to boost your MW reception in case you need! Joke apart, indeed impressive!

 

[restorer-john]

850KHz of bandwidth on all analogue sources! WOW. I think it is almost a record figure for hi-fi gear.

Perreaux had very wide range amplifiers...

 

[The Capstan]

ah ah, this is for short-wave reception ;-)
Thanks John.