Kenwood L-05M Vintage Amplifier Review

[GXAlan]

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

Again, the challenge is that you are looking at a single test tone, not the whole set of data. As @amirm says, if that single graph was all you needed, he wouldn’t take the time to do all of the other measurements.

What I like to do is to draw the line at around a number that makes sense to you, say -100 dB. If you draw the line across, you can see the bottom one has almost no spikes above -100 dB whereas the L-05m does. So the bottom one is more transparent. The computed number lets you see overall and drawing the line lets you identify the outliers.

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

Yup. The L-05m uses differential amplifiers which were direct coupled which do in fact provide gain at DC. An capacitive coupled one has inherent DC protection but has band pass characteristics.

Direct-coupled amplifier - Wikipedia

en.m.wikipedia.org

Some DC will be compensated by the differential amplifier, but in order to protect about DC current going to the speaker the Kenwood’s have a protection circuit.

 

[Ken Tajalli]

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

I am just dropping in.
DC can also mean Direct Coupled in amplifier specs.
It does not necessarily mean Direct Current.
I have not seen an amp with DC amplification capabilities .

 

[restorer-john]

I am just dropping in.
DC can also mean Direct Coupled in amplifier specs.
It does not necessarily mean Direct Current.
I have not seen an amp with DC amplification capabilities .

Plenty of audio amplifiers will happily amplify DC. However, their DC protector circuits will prevent them doing so, once the output voltage exceeds a threshold. Obviously speakers do not take kindly to massive DC offsets.

 

[pma]

However, their DC protector circuits will prevent them doing so, once the output voltage exceeds a threshold.

- which is in case of Ncore 12Vdc if both channels have the same dc offset or 24Vdc if only one channel has the dc offset and the other has 0V offset (summation divider from L and R goes to one comparator set at 12V threshold). And their tech support tells you that "sound source must not have DC at the output". So it goes, the Times They Are A-changin'.

 

[restorer-john]

- which is in case of Ncore 12Vdc if both channels have the same dc offset or 24Vdc if only one channel has the dc offset and the other has 0V offset (summation divider from L and R goes to one comparator set at 12V threshold). And their tech support tells you that "sound source must not have DC at the output". So it goes, the Times They Are A-changin'.

I knew you would likely see that and comment

 

[anchan]

The first is likely to sound noisier even with reasonably efficient speakers. The 86dB peak at 120Hz as well as the spray of noise from 200-2k a centered around -100dB (+/-) will be audible with ear against the speaker.

The second is around 10dB less noisy and from my experience once you’re in the minus 110-120dB noise range things are noticeably quieter.

Remember these charts are at 5W so to see what the noise floor is without signal add 15dB to everything. In that case the first one’s -86dB at 120Hz peak becomes -70dB with reference to 1 volt which may be audible.

-85 to -90db H2 is not bad to me and not much worse than the first so I would choose the second amp as likely better sounding

 

[Vear]

The first is likely to sound noisier even with reasonably efficient speakers. The 86dB peak at 120Hz as well as the spray of noise from 200-2k a centered around -100dB (+/-) will be audible with ear against the speaker.

The second is around 10dB less noisy and from my experience once you’re in the minus 110-120dB noise range things are noticeably quieter.

Remember these charts are at 5W so to see what the noise floor is without signal add 15dB to everything. In that case the first one’s -86dB at 120Hz peak becomes -70dB with reference to 1 volt which may be audible.

-85 to -90db H2 is not bad to me and not much worse than the first so I would choose the second amp as likely better sounding

I assume you're referring to the two in post #121. What's your opinion on the two in post #119?

 

[SirPaulGerman]

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

What do you think is better HK775 or the Kenwood L-05 ?

 

[Doodski]

I restore audio equipment daily

Lucky lucky lucky you! A mainline or a sideline job of restoring gear is a great gig. I checked out your YouTube videos and you have worked on some pretty interesting gear. I reallly like this one. I consider this era of Sansui gear to be some of the most beautiful gear ever made.

 

[Jazz]

Poll added. I tend to not rate vintage gear and hence the absence of panther....

You need new figurines for vintage. Maybe some little dinosaurs? T-Rex (top meat eater) is Great, Triceratops (many horns) is Fine, Brontosaurus (gets the job done) is Not terrible, Hadrosaurids (duck billed) is poor.

 

[ConnorG]

What do you think is better HK775 or the Kenwood L-05 ?

HK775’s are terrible from a design, layout, reliability, and servicing point of view. I restored a pair about a year ago, and that is the last pair I will ever touch. They sound phenomenal though which is one of their only redeeming qualities. Oh, and their aesthetics …I do wonder how they measure though.

 

[Oldasdrt]

Great that you were able to find parts, I had a Pioneer VSX D1S,circa 90, that had a bit of H2O damage from Hurricane Andrew, the tech told me the output transistors weren't available in 91,,

 

[Labjr]

IMO, Harmon Kardon was a cut above most of the other Japanese made stuff in the late 70's into the mid 80's. However, the design of their amplfier circuits was more complex. I had 2-3 of their ampfliers because a local dealer heavily discounted HK which made it a better value than Yamaha which was almost never disounted. I still like the color of the champagne gold faceplates.

 

[Labjr]

Great that you were able to find parts, I had a Pioneer VSX D1S,circa 90, that had a bit of H2O damage from Hurricane Andrew, the tech told me the output transistors weren't available in 91,,

I serviced Hi-Fi and remember Japanese transistors were fairly easy to source back then. Perhaps the technician didn't want to work on your receiver? I didn't particularly like working on those multi-channel receivers because a lot of them seemed like throwaways.

 

[Oldasdrt]

I serviced Hi-Fi and remember Japanese transistors were fairly easy to source back then. Perhaps the technician didn't want to work on your receiver? I didn't particularly like working on those multi-channel receivers because a lot of them seemed like throwaways.

Could be, but I found it strange to not be able to find the part, the Rec wasn't a throwaway, but at the time there wasn't an internet either, before I powered it up I did blow it out with a hair dryer on low

 

[crossrh]

Thanks to @GXAlan for mentioning the L-O8M in the Monoprice HTP-1 thread on AVSFORUM, which led me to this thread.
I bought two of these new in 1984 for $200 each. I still use them today, completely unmodified/unrestored, along with my AGI 511A preamp.
I emailed Peter at QuirkAudio about refurbishing the L-O5Ms and the 511A. 30 minutes later he called me, and will send estimates in a few weeks.
I wonder if there is any interest in me sending these unmolested L-O5Ms to Amir for further review before I send them to Peter.

 

[Doodski]

Thanks to @GXAlan for mentioning the L-O8M in the Monoprice HTP-1 thread on AVSFORUM, which led me to this thread.
I bought two of these new in 1984 for $200 each. I still use them today, completely unmodified/unrestored, along with my AGI 511A preamp.
I emailed Peter at QuirkAudio about refurbishing the L-O5Ms and the 511A. 30 minutes later he called me, and will send estimates in a few weeks.
I wonder if there is any interest in me sending these unmolested L-O5Ms to Amir for further review before I send them to Peter.

A before and after test would be very cool. Before the service restoring and then after that test again.

 

[SirPaulGerman]

Are the MK2 version of the amp, much better than the originals ?


The only difference in the spec is the frequency response
Frequency response: 1Hz to 50kHz MK1
Frequency response: 1Hz to 600kHz MK2

Should I be worry about the Frequency response ?

 

[ConnorG]

Are the MK2 version of the amp, much better than the originals ?


The only difference in the spec is the frequency response
Frequency response: 1Hz to 50kHz MK1
Frequency response: 1Hz to 600kHz MK2

Should I be worry about the Frequency response ?

I assume you’re talking about the L-07M here, as the L-05M never had a second revision…

Having resorted and listened to both the Mk1 and Mk2 L-07Ms, I can say without a shadow of a doubt that the Mk2 is the better of the two. The only physical differences between the two are the amplifier driver boards and the output devices used (much higher gain bandwidth devices used in the Mk2 version). The power supplies and chassis are the same, minus the anodizing color. Sound quality wise, the Mk2 outperforms the Mk1 by a fair margin. The Mk1’s have a tendency to sound harsh when pushed whereas the Mk2’s retain their composure. Bass control on the Mk2 is even better than the mk1 which is saying a lot, as the mk1’s are already very tight and controlled.

The problems with the Mk2 relate to some of the components used drifting, as well as a poorly implemented ground scheme from the factory. Overtime these issues will cause the amps to go into parasitic oscillation which will kill them in short order. I highly recommend having a technician restore L-07M’s (especially the mk2 version) before any use.

 

[SirPaulGerman]

So in the end, the MK1 version will last longer and wont oscillate