Modding a Kenwood L 1000 M

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spiderr

Member
Joined 2020
Good evening,
hope you are well.
Just brought home 4 pcs of equipments from the Kenwood L1000 series:

1. L1000D CD player,
2. L1000T Tuner,
3. L1000C Preamp and
4. L1000M Power amp

And I think I need some help/advice...

The whole system powers up but got a couple of issues :
1. L1000M Power amp few times went into standby mode (after restarting plays well)
2. after a few hours L1000D CD player stooped working properly ( it reads CD’s well but can not get the sound).

Can you please advise me where or whom I should seek for a good pro service (optional upgrade) of my new beasts ?
I'm Northamptonshire UK based.
Thanks
Best
Marcin

P.S. Sorry for my English it is not my 1 language
 
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radkosechko

Member
Joined 2008
his047 said:
THE CAPS THAT I THINK SHOULD BE BYPASSED ARE C51,51,53,54; C39,C40; C31, 32; C35, 37; C17,18; C9,10,11,12; C19,20,21,22; C31, 32. (sorry about the shouting: my CapsLock was stuck). They can be found on the main boar and the auxiliary board.
Thanks for the advice concerning the OpAmps. I am no expert on those and am only relaying the advice given by High Fidelity in around 1994 (this also goes for the Inductors). They suggested mounting all ICs in (gold-plated) sockets so that later substitutions would be easier. I have heard good things about the LM series but have not tried it.
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Hi All,
Bought a L1000C last summer. Good preamp, but sounded dull, as if through a blanket or curtain.
Last night I removed all the 100 uH inductors, and all the capacitors on the signal path, as described by his047.
Now, it is completely different device. Sound as it should, clear, detailed, exact. The curtain is gone.
If you want to really enjoy the preamp, this is a must-do. I will upgrade the op amps later on, thinking about LME492720 and/or OPA2604.
Thanks his047!!!
 
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radkosechko

Member
Joined 2008
his047 said:
The original suggestion was to use OP275. To be honest, you have done by far the most important/audible modification. The change in ICs is noticeable, but not as stunning as bypassing the caps.
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Oh, yes, that is so true! I did change the line amp op amps, as I had just two OPA2604, and no other better options available at home. But, I will buy some OP275s, and will have a go. Apart from that, will fit sockets for the op amps, so I can easily swap and try different ones. I still do not understand why did these guys put sooooo many capacitors in the signal path, when actually, they are not needed.
 
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his047

Member
Joined 2008
The most likely explanation is that they were trying to meet ALL possible radio-emission demands worldwide. However, that does not explain the plethora of Elcos, so your guess is as good as mine.

The upsetting thing is that Kenwood managed to seriously downgrade a very, very good preamp to something good, but not outstanding. And I must admit that I like the design, which I think is just gorgeous and not at all a 'rather bland looking and sloppily designed..."melted ice-cream design"'.
 
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pitbul

Member
Joined 2011
Info for anybody who will upgrade OPAMPs in this preamp, it is mandatory to place bypass caps near the legs 4 & 8 (supply pins). These caps reduce self oscilation of the opamp. Power supply lines on the PCB are long and there are no fast caps on it. When upgaded to LM4562 this work is must.
Another thing to minimise noise is to connect ground plane on upper side of the PCB board (tone control/output), you will find place where it could be easily done by placing some solder. Do not have picture of this work, but carefull observation will reveal it.
Bypass caps are 100nF/63V (or 50V) X7R.
 
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