AU999 Bass EQ control mod

Discussion in 'Exclusively Sansui' started by kevzep, Nov 17, 2012.

  1. kevzep

    kevzep Its all about the Music Subscriber

    As promised here is the mod I have been mentioning around the forum lately...
    Unfortunately I did not do any before and after graphs, I was working on it with my analyzer, but was entrenched in the progress I was making.....

    What the mod does, is it changes the "slope" of the curve, so that a greater range of frequency has a larger boost, and as a result there is a steeper slope from the centre frequency.

    Also there is more gain in the Bass EQ so there is now a 15db boost at the centre frequency....

    The resulting sound is the creamy fat bass when you boost it now.
    In fact the 200hz and 400hz options sound more like what you would expect, whereas in standard trim its all a bit disappointing....

    All you need is 4 resistors.
    2 x 1meg (1/4watt metal films)
    2 x 2.2kΩ (1/4watt metal films)

    First picture shows the area you are working in. Its hard to follow the nonsense which happens around these switches with the circuit diagram, took me a while to figure out the signal flow in there, but you dont really need to worry about this to do this mod.
    [​IMG]

    The 1meg resistors are the ones in the plastic sleeve, in this pic you should be able to see where they terminate. You will see the existing ones in your unit there and simply just remove the old ones and put the new ones in.
    [​IMG]
    On this end you can see the two Blue 2.2kΩ resistors which are the next ones to do....
    [​IMG]
    Yeah, its a little messy in there, I was swapping out so many resistors I made a bit of a mess which I need to tidy up, not a lot of room to move in there....
    Ask questions, and most of all, enjoy!!
     
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  2. squillo

    squillo New Member

    Messages:
    9
    Location:
    Rome - Italy
    Hi kev!
    If I well remember in a previous post, You wrote that this mod must be implement after the mod to the pre-am section. Correct?

    ciao
    Rug955i
     
  3. kevzep

    kevzep Its all about the Music Subscriber

    Yes to get the best performance you need to do both mods.
    The pre-amp is very short of headroom already and this mod will use more headroom....
     
  4. GeoKost

    GeoKost Well-Known Member

    Messages:
    525
    Location:
    Mount Ida, Arkansas
    Thanks Kevin. Now to round up some resistors. :yes:

    George.
     
  5. Jpdspin

    Jpdspin Member

    Messages:
    51
    Location:
    Bomont,Montréal. Québec
    Hello to the happy Sansui 999 Owner.
    I will be doing the EQ mod next week. I still have to say, I'm so happy with the pre-amp mod. I love my 999.Thank's again Kev.:tresbon:
    The recap job was made by a friend well experience in the vintage stuff. I was not very good in electronics. I'm still not the best but I'm reading a lot. Project by project I'm getting better. At that time I only ask my friend to do the cap, I didn't know what to do with the transistors, neither the resistors.

    For now, I'm following Tnsilver on the 9090 adventure recap. I just bought a fantastic 9090 and I ordered the parts to do a recap and diodes, resistors, changes. So doing that I was thinking about my Sansui AU999. I read the thrilling story on Tobij17 AU999 recap and happy-end. Now I'm asking my self, what should be done to make sure that my 999 will go for a long ride. Knowing that the caps are done, what's next ( I would like to stand in the middle and change the parts that can be problematic ).
    Kev mention that« I have BHC 80V 10,000µf caps in mine, I also put a bigger bridge rectifier in mine to handle the start up "in-rush" current.»In my Sansui the bridge rectifier was not change ( my caps 80v 10,000µF ) should I do-it, or is there more important things to do before. I just learn I to do the Bias and DC offset test. So I'M going to test those when I come back home.I know that the balance check is not perfect. The right channel is a little bit lower than the left.
    I did read the article on the fusible resistors ( It doesn't seem to have those on the 999). I was looking for a article on the transistors, to learn more, but I didn't found, any link would be welcome.
    Now I know How my multimetre works, know that is not precise and I have to change it.
    If you have any suggestions on what should keep me working, for the winter time, I would be very, very Happy:yes:
    I will come back with the after Bass EQ control mod.

    Jpdspin
     
  6. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    11,638
    Location:
    Long Beach, CA
    Kevin, I'm doing this mod to a 999 built in July '71. It appears to already have resistors in those positions. They are not the same value as the ones you recommend but look to be identically positioned. Did you replace existing resistors with resistors of different values?

    Here's a picture.

    - Pete
     

    Attached Files:

     

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  7. kevzep

    kevzep Its all about the Music Subscriber

    Yes Pete, you need to replace those resistors with the 1meg and 2.2kΩ resistors.
    The 1meg ones are the ones you can see in my picture which are in the plastic sleeve.
    The 2.2kΩ ones are the blue ones on the actual rotary switch....

    Then boy oh boy crank that bass up, you wont know yourself......:thmbsp:
     
  8. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    11,638
    Location:
    Long Beach, CA
    I didn't realize it was a simple swap. Thanks,

    - Pete
     
  9. GeoKost

    GeoKost Well-Known Member

    Messages:
    525
    Location:
    Mount Ida, Arkansas
    Kevin, I tip my hat to you. I finally got around and did the mod this evening. All I can say is Nice! :banana: :yes:

    Tomorrow will be a fun listening day. Have to go to a birthday party for now. Not mine.

    Thanks again.

    George.

    Here is a link of my before and after pictures.
    http://geokost.zenfolio.com/p194732993
     
    Last edited: Jan 12, 2013
  10. kevzep

    kevzep Its all about the Music Subscriber

    Thank you George, I like mine so much now (my girlfriend in fact uses it more than me and loves the little beast.) I could never get rid of it....
    It was funny how I could let my G22000 go, but not the AU999 after I seem to have finally found the potential in that great little amplifier that I knew was there somewhere.....

    Let us know how your listening goes!!

    I listen to my AU999 with the TU999 playing my friends FM station every morning for about an hour before I get up, it's a real listening pleasure now.....
     
  11. GeoKost

    GeoKost Well-Known Member

    Messages:
    525
    Location:
    Mount Ida, Arkansas
    Rock and Roll, man oh man, what can I say. Did you hear it? I had it turned up. :D You can actually make some pronounced settings, where before, there just was not any adjustment. :thmbsp:

    I would like to have a TU999. There had been a couple on the bay, I just couldn't find myself to get it and it not be packed well. Maybe later.

    I did pick up this G8000 locally with the power amp boards gone. I'm using the tuner in it driving my AU999. I like having the tone defeat switch on the G8000. I have a couple of local FM stations I listen to all the time that I enjoy.

    Fun, fun, fun. :yes: :thmbsp:
     

     

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  12. mikeinit

    mikeinit Something Profound

    Messages:
    45
    Location:
    Minneapolis, MN
    Could it get any better?

    I saw this mod after I had already reassembled from the other mods and recap, so I just got around to it yesterday.

    This is so awesome to have the best sounding system in Minneapolis:banana:

    I have ignited a passion among more than a few friends with this unit!

    Thanks to kevzep, and others!
     
  13. Jpdspin

    Jpdspin Member

    Messages:
    51
    Location:
    Bomont,Montréal. Québec
    Hi Kevin
    I did the mod last week. One thing sure, is that there is not a lot off space to work in that area but I manage to do a nice job anyway.
    So for the result, I can say it is a big improvement, now, something is happening when I play with the bass filter. It didn't only amplified the bass, it open it at the same time.
    I have to say that there is still something missing, for sure I'm playing less with the EQ and I'm not asking my self questions about sound quality on 80% of the repertoire that I'm listening to. I'm not a sound freak, I just like to be in peace with my gear. I have 5 systems install, that I use every week and when I listen to my Akai 1150 I'm not asking my self any questions, I enjoy, that's it!
    On my Sansui AU999 I've got Celestion Ditton 44 with new inside cables and new caps and B&W dm100. I did a switch with my Akai 1150, still sound better!!!
    I'm in my re-capping 9090 project, so when I have more time, I'm going to check what I could do to improve this 999 that I love. I would probably change again the power caps with better quality.

    Thank's again Kevin for your great mods and help.
    I just dream to be in peace with my Sansui 999 one day. For sure i'm getting closer because all of the passionate people on AK.

    JP.
     
  14. kevzep

    kevzep Its all about the Music Subscriber

    I am happy to see you got some good results.......

    If it has not been re-capped, this will help, go for 10,000µf caps for the main supplies....

    Search the threads here and find the transistor upgrades, this can help a lot too.....

    Good luck.....
     
  15. Jpdspin

    Jpdspin Member

    Messages:
    51
    Location:
    Bomont,Montréal. Québec
    Thanks for the advice Kevin, The AU 999 has been re-capped last year with good audio-grade caps except for the main caps, cheaper one's and not enough strong. So I will start with those and work my way threw the transistor, at the same time it should help for my popping sound that hi have now and then.
    I would need a suggestion to. I have the TU 999 that has the gold face knob and I would like to change those for black ones. I was thinking of asking on the forum if someone has the AU 999 with the gold button and TU with the black ones, to do a exchange. My question, do you know where I should place my demand respecting AK rules ?

    For the re-capping of the Main caps, I will finish first mI new old 9090 with the help of Tnsilver and give here some news about my upgrade on the AU 999 after.

    JP.
     
  16. nilsole

    nilsole New Member

    Messages:
    8
    Anybody who have a link to the transistor upgrade to the Au-999? Nils
     

     

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  17. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    11,638
    Location:
    Long Beach, CA
    There is a lot of restoration information in this thread. I believe it links to others. There are several recent ones on this topic. Use the search function. Try searching by the transistor number you want to replace.

    - Pete
     
  18. kevzep

    kevzep Its all about the Music Subscriber

    What transistors are you after in particular?

    Some need to be replaced, others do not.......
     
  19. nilsole

    nilsole New Member

    Messages:
    8
    I have done the preamp mods and bass mods.And i love the new sound of this wonderful amp.It works very well.I just wonder if it can be even better if i replace some of the transistors.It looks stock inside.
     
  20. nilsole

    nilsole New Member

    Messages:
    8
    Thanks LBPete for the link to the recap tread
     

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