Kenwood L-05M Vintage Amplifier Review

[ConnorG]

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

The Mk1 can and will oscillate if the ground implementation isn’t taken care of. It’s a very poor connection that suffers fatigue from stress overtime. Both the Mk1 and Mk2 suffer from this same issue sadly.
Here is the original ground connection on the main PCB. As you can see, it is very poorly done. A small terminal post is soldered into the main PCB, with the large copper ground plane sloppily soldered directly to it. This area is very susceptible to cracking due to heat and physical stress overtime.
Here is my fix for the problem. I used solid core copper wire to connect the copper ground plane directly to the PCB. I added a small loop to the wire to allow a small amount of movement if need be.

 

[Waxx]

The Mk1 can and will oscillate if the ground implementation isn’t taken care of. It’s a very poor connection that suffers fatigue from stress overtime. Both the Mk1 and Mk2 suffer from this same issue sadly.
Here is the original ground connection on the main PCB. As you can see, it is very poorly done. A small terminal post is soldered into the main PCB, with the large copper ground plane sloppily soldered directly to it. This area is very susceptible to cracking due to heat and physical stress overtime.
Here is my fix for the problem. I used solid core copper wire to connect the copper ground plane directly to the PCB. I added a small loop to the wire to allow a small amount of movement if need be.

That's how i fixed a broken MKI about 5 years ago. It was given to me by the former owner, and i could sell it if i could fix it for my own profit.

I did replace the whole copper board (that was cracked and oxidated) with a copper ring terminal (the kind you use on car batteries) that i put between the bolt and the nut.. And I connected the pcb ground to that with a stranded 1.4mm OFC wire (the kind i use as speaker wire). The guy who bought it still use it without any issues anymore. Your way is as good off course, and closer to original state.

 

[SirPaulGerman]

Would it be possible to convert the MK1 to a MK2 ? I know the MK2 has different output transistors

If you have to choose between
The 05 vs 07 mk1 ?

Also to take advantage of the MK2 and 05 amps, do I need a preamp with the same frequency response ?

 

[olds1959special]

I bought four of these used to power Vandersteen 2Ci speakers. One pair has earlier serial numbers, 850xxx and the other pair is 920xxx. The older pair has a lot more dust on the inside. All four amps have the original NEC high speed outputs. I can see the "NEC" on them with a flashlight. All the caps look similar. I was told the older pair was recapped, how can I tell? What should I look for to inspect the amps without opening them up?

 

[restorer-john]

What should I look for to inspect the amps without opening them up?

You lift the bonnet/hood on your car sometimes?

Take off the bottom panel, the side/top covers and take some photographs of the PCBs and post them.

 

[olds1959special]

You lift the bonnet/hood on your car sometimes?

Take off the bottom panel, the side/top covers and take some photographs of the PCBs and post them.

They sound too good to bother doing anything. I just thought if there was anything I could glean from looking through the top cover? Also, I can switch them around and hear each pair on the midrange / treble vs the bass. The newer, cleaner pair sounds a little more robust, why would that be?

 

[restorer-john]

They sound too good to bother doing anything. I just thought if there was anything I could glean from looking through the top cover? Also, I can switch them around and hear each pair on the midrange / treble vs the bass. The newer, cleaner pair sounds a little more robust, why would that be?

Quite possibly it's your imagination. Seriously, just like your car always goes better after a wash and a polish.

I had 7x LO7m (mk1 and mk2s). They all performed/measured virtually identically, both before and after restoration. They were within a watt or two of each other at both 4 and 8 ohms, with 4 ohm clipping around 289W. Powerful and solid, but they go to pieces below 4 ohms. Very agressive current limiting.

 

[Spurs27]

To not replace the big PSU caps is a criminal offence. Amateurish

 

[levimax]

To not replace the big PSU caps is a criminal offence. Amateurish

It is not a good idea to replace anything that is not out of spec. If after measuring the PSU caps they are out of spec for capacitance or ESR then yes replace them but if they are in spec there is no reason to replace them and in fact due to the "bathtub curve" of service life replacing parts unnecessarily will actually reduce reliability.

 

[morillon]

in general the electrochemical "interstage connection" capacitors are to be changed..(and as a precaution, the tantalums with their unfortunate tendency to put into CC ;-))

 

[Spurs27]

It is not a good idea to replace anything that is not out of spec. If after measuring the PSU caps they are out of spec for capacitance or ESR then yes replace them but if they are in spec there is no reason to replace them and in fact due to the "bathtub curve" of service life replacing parts unnecessarily will actually reduce reliability.

 

[SirPaulGerman]

Does anyone agree with this review about the Kenwood amp ?

 

[olds1959special]

Does anyone agree with this review about the Kenwood amp ?

My L-05M sound bright, clean and clinical! Perfect for putting a tube buffer or tube pre amp before it.

 

[SIY]

My L-05M sound bright, clean and clinical! Perfect for putting a tube buffer or tube pre amp before it.

Was it broken?

 

[GXAlan]

Was it broken?

I want to add a comment to this, since I had the L-08M’s which I have shown really nice measurements of here.

I know everyone insists that all amps sound alike if they aren’t broken, and I also agree that all amps sound nearly indistinguishable and that any real or perceived improvement is a fraction of what you would get applying that same budget to the speakers.

But I spent over 3000€ importing a set of multi voltage L-08m and then another $1000 having it restored by QuirkAudio, who also has a track record of great measuring upgrades here.

I finally get the set up back and sit down and _______

I don’t like the sound.

Sighted bias should have really made me feel like this was the world’s greatest amp. If anything, I should have said no difference but I know it measures really well and beyond the threshold of hearing.

But no. I don’t like the sound.

Despair? Depression? I actually start going through track after track and it pales in comparison to the Marantz PM-90, also tested here.

I start doing A/B comparisons with plenty of delay and sighted bias. I try to think what I do or do not like about it.

The difference is in the width of the phantom center. Using something like the La La Land Soundtrack, the vocals are very different in perceived width. With the Kenwood, it’s so narrow and with the Marantz it’s wider. With the Kenwood, I can pinpoint the mouth of the singer in my virtual space. With the Marantz, the center seems larger than life and I cannot really point with on finger exactly where the phantom center is but I can point to the region.

Is this cross talk? Some sort of harmonics adding perceived bloom? Subtle difference in FR from the speaker load?

No idea. It was just very interesting that sighted bias, newness bias and wallet bias should have made me love what I just bought and I actually didn’t.

 

[DanielT]

I want to add a comment to this, since I had the L-08M’s which I have shown really nice measurements of here.

I know everyone insists that all amps sound alike if they aren’t broken, and I also agree that all amps sound nearly indistinguishable and that any real or perceived improvement is a fraction of what you would get applying that same budget to the speakers.

But I spent over 3000€ importing a set of multi voltage L-08m and then another $1000 having it restored by QuirkAudio, who also has a track record of great measuring upgrades here.

I finally get the set up back and sit down and _______

I don’t like the sound.

Sighted bias should have really made me feel like this was the world’s greatest amp. If anything, I should have said no difference but I know it measures really well and beyond the threshold of hearing.

But no. I don’t like the sound.

Despair? Depression? I actually start going through track after track and it pales in comparison to the Marantz PM-90, also tested here.

I start doing A/B comparisons with plenty of delay and sighted bias. I try to think what I do or do not like about it.

The difference is in the width of the phantom center. Using something like the La La Land Soundtrack, the vocals are very different in perceived width. With the Kenwood, it’s so narrow and with the Marantz it’s wider. With the Kenwood, I can pinpoint the mouth of the singer in my virtual space. With the Marantz, the center seems larger than life and I cannot really point with on finger exactly where the phantom center is but I can point to the region.

Is this cross talk? Some sort of harmonics adding perceived bloom? Subtle difference in FR from the speaker load?

No idea. It was just very interesting that sighted bias, newness bias and wallet bias should have made me love what I just bought and I actually didn’t.

You said: I want to add a comment to this, since I had the L-08M's which I have shown really nice measurements of here.
But was it before or after QuirkAudio restored it?

From what type of source do you input the signal to your Kenwood L-05M?
What kind of speakers do you use for the listening you describe?

From your description, your Kenwood L-05M seems to be in mono mode.
Please note, my mono suggestion as the root of the problem is just a guess on my part.

 

[SIY]

Sighted bias should have really made me feel like this was the world’s greatest amp.

Not really. That’s not how bias works.

Controls. You need controls.

 

[olds1959special]

Was it broken?

When I play my SMSL D0100 Pro DAC into my Schiit Saga S pre-amp into my four Kenwood L-05M amps powering Vandersteen 2ce Sig II speakers, the sound is unforgivingly fatiguing to my ears, to the point of aggravating my tinnitus (but extremely detailed.) I expect the amps are just providing gain so they are not imparting any warmth to the signal. So my solution was to add a Hagerman Audio Tube Buffer in between the DAC and the pre-amp. Now the sound is wonderful, and the detail level is still very high.

 

[GXAlan]

Not really. That’s not how bias works.

Controls. You need controls.

Agree that you need controls. But we experience lots of things for the first time without comparison, meals, movies, etc. When you think about “money back guarantees” for cables, there was a post that a salesman never saw a return, because there was no difference and people’s biases never pushed them toward a worse sound.

The biggest problem is the variability of the listening response. If you look at the post I made on DSD vs CD layer of the Japanese taiko drums, I was able to successfully ABX the two. What I used to distinguish is that one of the versions gave me ASMR style tingling in the back of the ears. So I had really clear blind testing and could identify which was what depending on whether it gave me tingles.

Then trying to measure and run DeltaWave, we figured out that even though the digital content could null equally with similar volume, the actual DAC output was slightly different in voltage depending if it was fed DSD or PCM.

Great. I abx’d level differences. No new findings.

BUT, when I went to ABX again, no combination of any volume or settings could generate the ASMR effect for any of the music.

Did my ear put down a bit more ear wax so I was hearing something different? Had my brain adapted to whatever was triggering the ASMR tingles? Did the extra day of getting older result in age-related HF loss by one day where something fell below the threhold? Who knows? I just know that one day, there was a difference I could detect AND Foobar ABX the tracks and ever since then, I couldn’t and they sound alike.

 

[SIY]

Agree that you need controls.

Full stop there.