Kenwood L-05M Vintage Amplifier Review

[IAtaman]

Love vintage amp review. Wish there were more photos of the internals, maybe in an 18+ area of the forum.

It’s the performance. I can say the SINAD same as Torque in car because torque will win the race. The wattage is same as Horsepower but SINAD is the Torque

That makes no sense. Neither the electrical part nor the mechanical.

My conclusion is that some people are very susceptible to nostalgia.

I am one of them. Nothing sounds as good as the sounds of your childhood.

 

[fpitas]

I am one of them. Nothing sounds as good as the sounds of your childhood.

I'm glad for you. But still glad that nostalgia has little appeal to me

 

[MinMan]

I've always thought that this power amp might measure well.
I have three stereo KA-8100 integrated amps with similar gain stages.
They conveniently permit bypassing the pre-amp section (see back panel). maybe I can use them with my 5.1 Cabasse MTM set up... someday.


Ordinarily I disdaine nostalgia - I'm not convinced using these would demonstrate otherwise.

 

[Mart68]

Love vintage amp review. Wish there were more photos of the internals, maybe in an 18+ area of the forum.

 

[fordiebianco]

I was right with you until the FM part. FM is near dead except for car radios.

Funnily neither in the UK nor in the ROI. In the Republic they even abandoned DAB due to lack of uptake and continue with FM.

 

[Labjr]

I wasn't commenting about lack of interest in FM. Just that most older receivers seem to have poor sensitivity on FM band. My thirty old cheapo boom box has better reception and does a better job of locking onto the FM stereo subcarrier.

 

[ConnorG]

Filter capacitors age just as other electrolytic capacitors do. I restore audio equipment daily and can say with confidence that the DC leakage, ESR, and capacitance have all drifted in the original filter capacitors. There are many mods that can be done to the power supplies in the L series gear to greatly improve them that don’t involve adding a SMPS

 

[amirm]

@amirm how is that you are showing SNR at 5W at 96dB but the FFT also at 5W showing a lot of spikes higher than 90dB. 120Hz is peaking around 86dB for example. Perhaps in misinterpreting

Good catch. You have read it right. I just checked the SNR project settings and while it uses a slightly narrower bandwidth (20 to 20 kHz instead of 22.4 kHz in dashboard), there is no difference in measurements otherwise. The SNR test is very quick though. So perhaps the power supply noise is less when the unit is fed a signal for a fraction of second in SNR test as opposed to continuous in dashboard. Will have to think about this more....

 

[Vear]

I had the amp featured in this review partially restored by Precision Audio Restorations. I keep these as spare amps and it was at my request that Leo at Precision did not replace the large filter capacitors. I can say that driven by my Benchmark DAC2HGC the L05Ms are as silent as the AHB2 (ear to tweeter) with the volume turned all the way up. Regardless, the AP Analyzer does not lie and there is some inaudible PS noise. I kind of wish I would have replaced the large filter cap and the old ceramics (with COG or silver mica) before sending it to @amirm for testing. This way we could have definitively ruled out all old components and known for sure that the noise is due to the signal path crossing below the PS as mentioned.

I'm not an expert at reading measurements (and please correct me if I'm wrong) but considering the above I think this amp still performed phenomenally, albeit held back by the chosen SINAD ranking method. This is a partially restored 45 year old amplifier and it was able to clear 16bits at 5W! This is with high gain and RCA inputs. Remember this amp was produced years before the CD format was released. I haven't looked at all the test results here on ASR but it seems many A/B amps have trouble with that even today (even if their SINAD numbers are better).

I also found the frequency response graph to be one of the flattest I've seen here on ASR, there's not even a hint of a drop. Not even the AHB2 rides the rail like that. Inaudible yes, but very cool to see from an engineering standpoint nonetheless.

Somewhere, Kenwood/Trio Lab engineers from a half century ago are smiling.

 

[Doodski]

@Vear it is fortunate that there appears to be plenty of room for measuring and fitting new smoothing caps in the power supply. It should not be too difficult to spec out something and find a proper package. There are supply issues ongoing so maybeee there might be a delay but you still have flexibility in the package size due to the roomy area.

 

[SIY]

Good catch. You have read it right. I just checked the SNR project settings and while it uses a slightly narrower bandwidth (20 to 20 kHz instead of 22.4 kHz in dashboard), there is no difference in measurements otherwise. The SNR test is very quick though. So perhaps the power supply noise is less when the unit is fed a signal for a fraction of second in SNR test as opposed to continuous in dashboard. Will have to think about this more....

Bandpass filter selectivity?

 

[amirm]

Bandpass filter selectivity?

Oh. I need to measure it and see how sharp the end points are. Thanks for mentioning this.

 

[Tovarich007]

I just read this review. Interesting, though we have to keep in mind the reviewed unit is a largely modified version by the owner (most parts have been replaced, not always by original ones, or for improvements by better parts, or because of shortage of original parts). So, Amir hasn't reviewed the exact original L 05M, don't forget this fact when you read or comment this review !

But, all in all, I'm still convinced that good amps of the japanese hifi golden age, from Kenwood, Sansui, Sony, Yamaha, Technics, etc. give many modern designs a run for their money.

Of course, they run generally hot, are heavier, and repairs aren't easy (avaibility af parts issues), Well, theyre not class D à la Hypex nor A/B à la Benchmark, but they're pretty good yet.

 

[sergeauckland]

I just read this review. Interesting, though we have to keep in mind the reviewed unit is a largely modified version by the owner (most parts have been replaced, not always by original ones, or for improvements by better parts, or because of shortage of original parts). So, Amir hasn't reviewed the exact original L 05M, don't forget this fact when you read or comment this review !

But, all in all, I'm still convinced that good amps of the japanese hifi golden age, from Kenwood, Sansui, Sony, Yamaha, Technics, etc. give many modern designs a run for their money.

Of course, they run generally hot, are heavier, and repairs aren't easy (avaibility af parts issues), Well, theyre not class D à la Hypex nor A/B à la Benchmark, but they're pretty good yet.

On that issue, I find the opposite. Electronics of that era used through-hole components and decent sized PC board tracks, so changing components was a lot easier than current Surface Mount withy tiny PCB tracks. As to parts, I accept that's often the case with mechanical parts, occasionally unavailable output devices, but 'general' electronic components are easily available.

I've never had to scrap a vintage amplifier going back to the early 1960s due to unavailability of components, although for example, my Yamaha CR1000 receiver had some dodgy switches which are pretty much unavailable but it works otherwise.

I've just repaired an HMV Model 5114 table radio made in 1952!

S

 

[pseudoid]

Thanks go out to @amirm for another great resto-mod that performs.
It looks to be an inverting power-amp? [ty, @pma]
Why did they call them "DC" amplifiers?

I regret throwing out my "working man's" Adcom GFA-555.
It would have made a good test specimen; like this Kenwood L-05M amp.

 

[GXAlan]

Why did they call them "DC" amplifiers?

There is no capacitor coupling so the amplifier is rated from DC to xxx kHz

 

[Vear]

Can someone tell me how these compare? What are we seeing here? Which one has overall technically better performance?

 

[GXAlan]

I would vote the top one is better because the H2 is higher on the bottom.

Generally have to look at THD (*total*) along with the peaks (what might be audible).

You also have to assume that the L-05m are symmetric since the stereo imbalance is potentially an issue below.

 

[Vear]

I would vote the top one is better because the H2 is higher on the bottom.

Generally have to look at THD (*total*) along with the peaks (what might be audible).

You also have to assume that the L-05m are symmetric since the stereo imbalance is potentially an issue below.

How about these two? Just trying to understand the significance of the differences (especially from 1kHz-20kHz).

 

[pseudoid]

There is no capacitor coupling so the amplifier is rated from DC to xxx kHz

Yes, exactly! It was more a leading question - - "DC" as in one of the biggest enemies of speakers?
yum...