Kenwood Basic C2 Preamplifier Restoration/Upgrade

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by vsat88, Apr 20, 2017.

  1. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Myself and a few others have been posting in a C1 thread and we wanted to break away from doing so by starting a thread about the C2 Kenwood Basic Preamplifier so the information would be easy to find if others needed it. We were going to detail the upgrades and restoration to this unit a bit at the time. . I would like to thank @Leestereo for starting the C1 thread that this thread was named after. You will find a plethora of fine information and facts about both units here :
    http://www.audiokarma.org/forums/in...c-c1-preamplifier-restoration-upgrade.609337/
    More to come..Thanks for watching !
     
    Rodrigan and Karl vd Berg like this.
  2. Karl vd Berg

    Karl vd Berg Super Member

    Messages:
    1,839
    Nice! :thumbsup:

    The C2 is a complete and nice preamp. Having seen quickly the schematic, it has nice/really good components in it, so how do you describe the sound of your unit?
     
  3. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Mine sounds like you explained on your C1 before the upgrades. "turning the volume up high and there was no bass and weak sound" I cant really say it sounds bad. I do not know exactly how to explain it except kind of as you said, weak and little bass. and I have to turn the volume up too far to it to go louder. Its clear as a bell but for a dOUK aUDIO 40.00 tube 12V preamp to sound better than the C2, that is just not right. I have tried everything I can think of. Upgraded the Op amps, a complete capacitor shotgun, diodes swapped with the 16V fast recovery ones, cleaned every switch, every pot. It all works perfectly. It just does not sound as nice as I think it should. I will have to say that I do not use any loudness treble or bass controls. I run every bit of my equipment that way. To me if I have to use that then something is not right to start with. I am using a matching Basic M2 amp as well. Both gain controls are all the way up on the amp..I may just sell it and buy a American made preamp as I have a B&K ST-202+ Amp and my speakers are Polk Audio SDA-SRS 's so, maybe go all Americian made equipment ??
     
  4. jheu02

    jheu02 AK Subscriber Subscriber

    Messages:
    2,933
    Location:
    North Carolina
    vsat88 and Karl vd Berg like this.
  5. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Thank you John. I want to say this as well. I had completely forgotten that you had posted all of your restore. In fact after reading it again I found that in the past I had referenced it more than once during parts of my upgrade. I had thought there was more information here at AK in regard to the C2 but had read so much in the past that I had forgotten where. I am at a temporary stopping point now as far as work go's on the C2 due to illness in the family. I will get back here as soon as I can to document more. Thanks for adding the crosslink !
     
    Last edited: Apr 24, 2017
  6. 24Vboost

    24Vboost Active Member

    Messages:
    313
    Hi guys.

    I am new here and just caught the tail end of the resto on the C1, I just bought this preamp yesterday and hope that pre is okay. By reading your post vsta88 is the turning up the volume to get any sound have to do with the 5V pre output? I actually do not know what that means only the my old Yamaha CX600u had 8.5V so I am thinking if a preamp has that voltage higher you would not have to crank it as much...

    The bass for the pre does it suck then? I was hoping for fine a replacement for my Yamaha I mistakenly sold as it ran my Nikko Alpha II nicely. The 'db' is higher on the Kenwood too and I was hoping the sound grade would be a bit better...but I am here to learn from the pros...

    If there is a rebuild you guys suggest to upgrade the C1 may I ask where I would find that thread and may I ask for permission to copy the contents and save (the original author as I do not wish to start any issues on copyrights etc...)!

    Thanks guys nice to meet you virtually!
     
  7. jheu02

    jheu02 AK Subscriber Subscriber

    Messages:
    2,933
    Location:
    North Carolina
    Look here.
     
    24Vboost likes this.
  8. 24Vboost

    24Vboost Active Member

    Messages:
    313
    Thanks I saw this but forgot where to find it...guess just type it in!!!!!
     
  9. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    What John said ^^
    And no, the bass does not suck on either the C1 or C2. They are both fine amplifiers. I just want more of a good thing I guess : )
     
  10. Broesel02

    Broesel02 New Member

    Messages:
    36
    Location:
    Siegburg, Germany
    The Kenwood Basic C2 is a very fine Preamp. Moreover, it is easy to fix it up. I have made many of them


    img1.JPG


    and don’t forget to clean up the switches

    IMG_0959.JPG

    Richard
     
    Rodrigan likes this.
  11. Ross6860

    Ross6860 AK Subscriber Subscriber

    Messages:
    1,154
    Location:
    Ohio
    Just got a Basic C1 from a fellow AK'r with a Basic M1a amplifier.

    I also have had a a Basic C2 pre-amp for a while.

    I don't find them lacking. I just started playing with the C1/M1a combo tonight. Volume on 2 got me the "can you turn that down a bit" request from the second floor.

    Depending on source material and volume, I do have to run the loudness at 2 and the bass at +1. But this is running through Infinity RS5b, which are pretty hot on the high-end and mid-range, especially at low to mid volume levels. They are also not a real easy speaker to drive, not bad, but they do like a bit of clean power. Start cranking the volume and the bass starts to come in. Different speakers will probably respond differently. Running a pair of Klipsch or Large Advents (or two pair of Large Advents:)) should be a piece of cake.

    Dollar-for-dollar it's hard to beat these "budget" pre-amps.

    I may send them out for a complete overhaul at some point, but for now they appear to run just fine. I guess I do prefer the Apt Holman, but it was quite a bit more expensive.
     
  12. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
  13. jheu02

    jheu02 AK Subscriber Subscriber

    Messages:
    2,933
    Location:
    North Carolina
    You could, but they'd be better used elswhere. I like using high temp, low ESR caps in the PS like Panasonic FM, FR, FC or Nichicon PW, HE, PM.
     
    Karl vd Berg likes this.
  14. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Got the Panasonic's on order from Mouser now. Just throwing it out there to see what others thought. Thanks !
     
  15. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Hey, wanted to update the thread and say that I do have new Panasonic low ESR caps OTW from Mouser for the PS in the C 2. I did not take the top off to see what exactly I used as far as brand name capacitors but I had a few images I made and I can see that they were all nichion caps. I would like to say that what I stated above as far as the C2 not sounding as good as the cheap dOUK aUDIO tube Preamp is not so. I do not know what was going on when I so call tested them both in my system but the tube pre does NOT sound better. Perhaps I had one or more of the tone controls in the wrong position at the time I listened. In fact I really don't know what went on but that tube pre does not sound as good..period.
     
    Rodrigan likes this.
  16. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Here are a few images of the C2 rebuild. These were taken months ago. Just an upload for posterity's sake. Perhaps someone will benefit. The images with the brown caps are the old. The black cap images are the new. The JRC Op amp is the old, the Texas Instruments, I think they are TI anyway are the new complete with standoffs. Part numbers are as seen on the Op Amps.
     

    Attached Files:

    Last edited: Jun 1, 2017
    Rodrigan likes this.
  17. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Anonymous said...

    "Actually, it is easy to disassemble if one keeps in mind that all three boards and the faceplate is one assembly and the pan is just another piece. Takes 5 minutes to take it apart and put it back together."

    " Major issue with C2 is that Opamps used in it are designed to operate at +/-18V max. The actual power applied is actually greater than this voltage. As a result they often go bad. What is worse - they take input JFETs down too. Therefore if you get your hands on C2 - replace opamps with +/-22V ones (NE5532 for instance). They will sound better too."

    I think I will take all of my on board switches off too as I still cannot seem to get them clean enough. It takes me a lot of time to finish a project BTW. I always get caught up with something else. Yes sir, ADD bad this one.
     
    Last edited: Jun 1, 2017
  18. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Thought I had read that you guys used Panasonic 390uF 35V in the PS so that is what I ordered however when I opened mine up I see an area marked "power supply but that area has 100 uF 50v Caps x 6 C 75,76 - C 71,72,73,74. In the flat amp area C 23, C 24 there are two 47uF 35V so where do the 390uF 35v Panasonic caps go ?
     
  19. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    488
    Location:
    Phenix City, AL.
    Here are a few images for reference..Perhaps I am confused I and I am supposed to put them in the flat amp section near the op amp ?
     

    Attached Files:

  20. jheu02

    jheu02 AK Subscriber Subscriber

    Messages:
    2,933
    Location:
    North Carolina
    I found a post in Leestereo's Basic C1 restoration where that was done by Karl. Quoted here:

    "I had to do the same with the previous Nippon Chemicon's KMF at PSU, turning the volume up high and there was no bass and weak sound. Now it's different, the sound is much more present, full, nicer. I think that may be room for further improvement, with C0G multi layer ceramic caps, soft recovery rectifiers and a couple of fresh Panasonic FC caps in the PSU...

    I have the Basic C1 unit, the C45 and C46 follow the new 16V Zeners, before the opamps, and I'm using here PW's 390uF/35V (stock ones were Elna 330uF/25V).

    I have to see the schematic of C2, and will help you for sure :)

    Edit: do you have a thread for your C2 unit?"

    http://www.audiokarma.org/forums/in...reamplifier-restoration-upgrade.609337/page-6 post # 106

    It may not apply to your C2...Karl was working on a C1.
     

Share This Page