Kenwood Basic C1 Preamplifier Restoration/Upgrade

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by Leestereo, Aug 14, 2014.

  1. Anti_Skate

    Anti_Skate Well-Known Member

    Messages:
    543
    Location:
    Somewhere in Mid Michigan
    I've been listening to this unit for a couple days now, and the improvement is quite dramatic. The sound stage seems deeper and wider on both cd and phono. Nice tight bass and more detail in the mid to high end.
    The phono section is much improved, with more definition throughout the range. Seems to be a good match to the Ortofon OM10 I'm currently using.

    This was well worth the time and effort, and the cost was pretty cheap even with replacing the relay, under $40.

    One word of caution.
    The subsonic filter switch is kinda delicate and comes apart pretty easy when manipulating the board around. Be careful not to bump it around to much.

    Thank you Leestereo for this wonderful mod.
     
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  2. Leestereo

    Leestereo Super Member

    Messages:
    2,042
    Location:
    Ottawa, ON
    Anti_Skate: Happy to hear that the restoration/upgrade of your C1 worked out so well!
     
  3. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    I just decided that being I was back in touch with Dan (DRM) that I would buy his kit to re cap the C2. The only other thing that I will do as of now is replace the op amps and put in the socket to "roll" them with others. I am glad I did this because I simply do not have the vision, know how or patience to try much more for now anyway. I knew that being this was my very first total shotgun re cap that it was not to be easy for me. So far with the kit it has been quite manageable. I cannot say how glad I am that the kit was marked with the part positions on the actual board. I did find that my C2 had one extra capacitor a 47 uF 100v (best I recall) on one of the boards that was not included in the kit. I think I can quite easily live with that ! I ordered the NE5532P / NE5532 op amps with DIP 8 sockets. Hope I did not screw up. Either way this has been one happy project for me. I will check back in with you guys and see what you have to say about my choices. The good thing is that I have another one to do (a C1) and that was my original pre amp that my Daughter and I used to listen to (James Brown and dancing together) when she was a little girl. She is all grown up now but the original C1 and M2 mates make me remember some really good ole days. Thank you all for your help.
     
  4. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    OK, I am trying to sort this op amp issue. I guess I do not understand. I ordered 4 NE5532P/NE5532 Op amps and Installed two of them (with sockets) one on the tone control board and one on the filter board. The one that came out of the filter board was a 4560DN JRC. The one that came out of the tone control board was a 4560DN JRC as well. Both of these were replaced with the NE5532P Op amps. On the EQ amp there was a 4560DN JRC. I have not replaced it yet. (Pretty easy to access). Now, on the flat amp there is a JO41DD JRC (I have not replaced it yet). So in this C2 I have four Op amps (as far as I can see??) Three that are the same part number (4560DN) and one that is a different part number (JO41DD JRC). That means I have three of the same and one that is a different op amp. What do I put where and where is the phono op amp that everyone speaks of ?? I have 2 LME 49860NA Op amps as well if I can use them. So far I have only used the AUX 1 input, I have not tried any other input and it sounds great but seems to lack gain (I suppose) as the volume has to be turned up pretty high before the volume gets loud. I am using a DRM rebuilt M2 amp . Help me please..Thanks.
     
  5. Anti_Skate

    Anti_Skate Well-Known Member

    Messages:
    543
    Location:
    Somewhere in Mid Michigan
    I'm not sure about the c2 but in the c1 there was a resistor change when swapping the op amps. Presumably to change the gain of the amp to match the original circuit.
     
  6. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    Lordy, if its in the C1 it is almost certainly in the C2 as well. I will have to admit right now that it was my fault about the volume level thing. I guess I had the gain / volume level one of the two turned down. Levels are great now. Hope someone chimes in about the resistor change as well as the op amp swaps..Thanks Anti_Skate.
     

     

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  7. Leestereo

    Leestereo Super Member

    Messages:
    2,042
    Location:
    Ottawa, ON
    In the C2 schematic, Kenwood refers to the phono op amp as the "Eq Amp". The flat amp (i.e., line stage) is a 2041DD op amp.
     
  8. Leestereo

    Leestereo Super Member

    Messages:
    2,042
    Location:
    Ottawa, ON
    In the C1 preamplifier, it is the output load resistors (R41/R42) for the final op amp that are changed to 56.2kohm resistors. This will not affect the gain of the circuit. In the C2, the corresponding resistors are R55/R56 and they are already specified as 56kohm.
     
  9. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    OK, after looking again I did find that the "Eq Amp" was the phono section..Took me a while to put it together in my head as I kept looking for the phono section that did not exist so thank you for replying so I know my thinking and reading of the schematic are verified. This is where you recommend a NJM4580DD op amp if my reading of the thread is correct. The other three op amps should be NJM2068DD. If I am reading correctly. Please tell me I am right..I have a slew of op amps now that I ordered wrong somehow. I think I was reading multiple threads at different times as I wrote down the parts I needed. Thanks Leestereo.

    Thank you as I have a C1 that I will restore as well using the information found here. I will not buy a "kit" for the C1 I want to go full tilt upgrade on this one..
     
  10. Leestereo

    Leestereo Super Member

    Messages:
    2,042
    Location:
    Ottawa, ON
    Yes, I suggest using a 4580DD for the phono stage since it has a lower noise specification in a RIAA circuit. And the Flat Amp, Tone Amp and the Filter Amp can all use the 2068DD. Note that if you want to use the aforementioned op amps, you should also replace the 20V zener diodes at D11-D14 with precision (2%) 16V BZX85B zeners to lower the rail voltages (the stock rail voltage is ~18.6V which is too high, even for the stock 4560 op amp).
     
  11. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    At this point you have lead me completely thru all I need to know Leestereo. Thank you so.
     

     

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  12. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    Just wanted to check in and say that I realize that this thread was created and was directed towards a C1 restoration / upgrade /modification, not a re cap for a C2. and that is basically what I needed to do. By reading and asking questions I was still able to follow directions to the point that I could complete the C2 job anyway and upgrade to an even better sound as well as well as upgrade the reliability of my loved C2. Not only that but I know for a fact that I can do my C1 as well. What I want to do is thank all who helped especially Leestereo as this would not have been possible for me if not for his help. It also forced me to pay closer attention to schematics and my part numbers as well. That in it self was a huge help going forward with other projects. I have no official training of any kind working with repair / restoration of Vintage Hi Fi however with the help of people like Leestereo and the others who have helped so much here at Audiokarma and The Polk Audio site I have learned an awful lot about this hobby that I love so much. Thanks again. Jim H.
     
  13. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    I feel like I know the C1 and C2 very well now. Doing this gave me the confidence to tackle a much bigger job. A complete re cap of my Parasound HCA 1206. Not for the feint of heart that one...A real booger bear that one was. Anyhow, now I am confident in ordering from Mouser and installing all the parts without the smoke that comes out (and does not go back in). Thanks all, especially Leestereo. I hope I can help someone some day like you all did for me.
     
  14. Leestereo

    Leestereo Super Member

    Messages:
    2,042
    Location:
    Ottawa, ON
    Glad to help, vsat88.
    How do you like your restored/upgraded C1 & C2?
     
  15. vsat88

    vsat88 Like my Bluetooth ?

    Messages:
    555
    Location:
    Phenix City, AL.
    I really like the C2. I always have. I did not do all of the suggested upgrades. I really wanted to do the C1 with all the recommended parts and the C2 back basically stock. Could not help myself though, put in new op amps and did the diode upgrade in the power supply. I am really happy with it. The phonograph section is boss ! Before I did the re cap the C2 had a weird fault. When you first turned it on it would sound well, OK however after it played a short period of time the volume would drop off. No problem with that now. It is being used in my main setup now. Very smooth and no reason whatsoever to use any tone controls or loudness button. Not that I would use them anyway. thanks again. I typed this on my phone so sorry for any miatakes..Oh, when I do the C1 and my buddy's C2 I will check back in
     
  16. tri_pod

    tri_pod Active Member

    Messages:
    142
    Location:
    Cape Town South Africa
    Thanks for this thread on the C1. My own is still stock and sounds better than a much newer Rotel RC980BX.

    tri_pod
     

     

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  17. Karl vd Berg

    Karl vd Berg Super Member

    Messages:
    1,953
    Hi, Leestereo.

    Just a quick question about C7 and C8 (220uF bipolars). Could these be replaced by a ready polarized 330uF in case MUSE 220uF bipolar ones are not available soon?
    Or, would rather be better to keep the original 220uF value, but with fresh polarized ones in this position? Thanks and nice restoration.
     
  18. Leestereo

    Leestereo Super Member

    Messages:
    2,042
    Location:
    Ottawa, ON
    Hi Karl,
    A bi-polar type is best for C7/C8; if the 220µF are not available, 100µF capacitors can also be used (the F3 cut-off is still acceptably low at 2.5Hz).
     
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  19. Karl vd Berg

    Karl vd Berg Super Member

    Messages:
    1,953
    Okay, thank you! :thumbsup:

    [edit]

    I'll wait to have the proper MUSE bipolar caps for the electrolytic positions, but meanwhile let me share a picture of this C1 I'm working on. It's a VERY nice preamp indeed!

    I'm trying now an LM4562 (IC1) and stock NJM2043 went to IC2. Also 16V zeners (1.3W) replaced the stock 18V ones. PSU has 2200uF/35V and 470uF/35V as you suggested. Film caps replacing the stock 1uF. Thank you for this reference thread!

    [​IMG]
     
    Last edited: Jul 12, 2016
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  20. Karl vd Berg

    Karl vd Berg Super Member

    Messages:
    1,953
    Just one more question: does it worth to replace the output relay with a new one? And, if yes, which one? The service manuals (for both C1 and C2) don't specify model, voltage nor current max ratings...
     

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