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Altec Attenuation Circuit Help

Discussion in 'The Lansing Legacy' started by WntrMute2, Jul 15, 2018.

  1. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    I am trying to add the 30923 attenuation circuit into my cloned N-800-F crossover. The area circled in red is replaced by a 16ohm L-pad. I am need to figure out where to splice the 30923 circuit into the crossover.
    Any assistance would be appreciated! I also would probably use the L-pad mentioned in the text. Additionally, how accurate must the resistor values be? It is hard to source high watt 7.8ohm and 13ohm resistors. Thanks in advance! Screen Shot 2018-07-14 at 9.50.41 AM copy.png
    N-800F Schematic copy.jpg

    20171231_184858-3 copy.jpg
    I moved this query from the general speaker forum to here. I hope the Moderators are OK with that.
     

     

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  2. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    ( I thought ) the first bit of text positioned immediately after the Green circle ( in the 1st pic ) described pretty clearly where to put the 30923 filter.

    Looking at the second pic ( the preceeding text says ) to put the 30923 filter immediately before the red circled area ( right after the L1 coil junction ).

    Use 8 ohm resistors ( for R1 ) and anywhere from a 12 to 32 ohm resistor ( for R2, the resistor that goes to ground ).
    - The higher the value of R2, the less the midrange is attenuated.
    - It's best to determine this value by ear ( listening > IME ) .
     
    Last edited: Jul 18, 2018
  3. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    I have a bit more drawn out but I still would like to figure out how to use an L-pad in place of the resistor network of R-1s and R-2. I know what the words say but it is hard for me to put the words into the schematic. Thoughts?
    Thanks for any and all help.
     
  4. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    Here ya go;

    30923_16Ohm wiring_.png

    This re-uses your existing variable Lpad ( 16 ohm I guess? ) within the mid-range reduction circuit ( typically called the 30923 circuit ).
    HF frequencies bypass the resistors by making their way through C2 ( while midrange frequencies are held back > re-balancing HF to MR ).

    In this circuit version, HF is now turned up full ( all the time ) since we want to only attenuate the mid-range frequencies ( of the 802/806 ).
    - ( IOW, with this 30923 configuration/variation , it's only the mid-range that gets turned up or down )

    Note: C2 is larger than is typically mentioned. You can vary it from 3uF to 6.8uF, adjust to your own taste.

    Truthfully, if your 806/802 has enough HF to satisfy your needs for HF full up ( all the while padding the midrange down ) then things will work out for you.
    - This ( satisfaction ) will depend on the diaphragm type found in your 806/802 ( since some have more HF extension than others ).

    - IME, the 30923 only works properly with driver/diaphragm combos that are endowed with at least 92-93db of HF ( as measured at 10K ).

    If your combo measures anything like the following ( Zilch ) measurement ( typical of many 806's ), then no matter which circuit you use ( apart from bi-Amping ), your driver will always seem to be HF deficient ( since the overall speaker midrange efficiency is up in the high 90's ).

    [​IMG]

    :)
     
    Last edited: Jul 16, 2018
    UncleBingo likes this.
  5. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    Thanks very much EarlK. You have been most helpful! I guess i should have mentioned I am currently running 802-D CDs. I don't know if they have more HF energy than the 806-As that are stock. I just put them in over the weekend.
     
  6. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    Hi,

    You're welcome.

    I don't know why I figured you had 806's, anyways, I've already modified my last post ( actually, quite a few times while trying to build some clarity, HA! ).

    This evening I'm going to post another ( simpler ) mid-range suppression circuit.

    :)
     
    Last edited: Jul 16, 2018

     

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  7. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    Hi,

    Here's a simpler ( RC ) RC correction circuit for you to try ( it'll give the same results as a full blown 30923 ) but it's not as flexible/adjustable .
    It utilizes what you currently have wired in place ( you just add parts to it ).

    SimpleRC_16Ohm wiring_.png

    To use it.

    Simply adjust your horn level to where you think the mid-range output is balanced to the woofer & then add a 3uF - 6uF cap ( wired across terminal 3 + 2 of your variable Lpad ) to restore the HF.

    IME, adding any more than 9uF of capacitance ( in this position ) is self-defeating as one is simply allowing the mid-range to bleed back through this HF bypass route .

    :)
     
    Last edited: Jul 18, 2018
  8. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    WM2

    Are you able to tell me about the diaphragms in your 802D's ?

    Are they the original 16 ohm Altec stock ? ( or GPA replacements ? )

    Do you know the part numbers?

    Have your drivers ever been re-magnetized ?

    :)
     
  9. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    Thanks for the many options you've provided. I think I'm going to try to incorporate the 30923 into a new build laid out somewhat like this.

    IMG_20180717_174056.jpg

    The green rectangle is the new network. I was planning on making the 13ohm resistor easily removable but it occurred to me that I could use a good quality potentiometer. I have a couple of 33ohm Russian surplus pots that should fit nicely. Thoughts? Also, what wattage resistors would you recommend?

    Thanks for all the assistance!
     
  10. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    Original 16ohm diaphragms according the guy I bought them from. I had them apart but did not get the part numbers off of them. The magnets have not been recharged as far as I know.
     
  11. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    The schematic looks electrically correct ( even though the 10.5uF cap within the bass circuit leg seems to have been partially erased ).

    Putting the ( Russian ) 33ohm surplus pot in place of the 13ohm resistor makes good sense.

    10 watt resistors are more than good enough for all ( but the most over the top ) home listening ( IME ).
    - I also use a lot of 5 watt resistors in my external Altec 288 horn circuits ( they never get warm ).

    What woofers are you using ?

    I'm out-to-lunch as far as knowing much about your project ( is it documented somewhere else ? ).

    :)
     

     

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  12. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    The 10.5uf cap will be there. It looks fine on the pic from my end - weird.
    My woofers are dual 414-A's 16ohm wired in parallel for a 8ohm load. The original CDs are 806-A's 16ohm.
    I don't really have a "build" as I bought these Heathkit AS-21 Legattos over the winter. Then had a friend refinish them as best as he could and they look presentable. I cloned the N-800-F crossover and have them mounted outboard. The sound is really good. Just this weekend I swapped in the 802-D drivers. That is a 40 screw adventure! I roughed together some grills as the wife wanted them a little more finished when company came over for a listen in the Dungeon of Delites. Our breezeway system is much more presentable.

    20180213_101557.jpg

    20180126_174916.jpg

    20180304_163807.jpg

    Im driving these with a pair of SET 300b's I recently built with parts sourced from Min Yang.

    IMG_20180508_182704.jpg

    IMG_20180505_083815.jpg
     
    olson_jr and EarlK like this.
  13. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    Beautiful!

    :)
     
  14. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    Thanks Early.
     
  15. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    Parts are on order from Mouser and Parts Connexion. Will work on them hopefully next week. One other question. In the Altec schematic, there is the HF attenuation circuit consisting of a 20ohm resistor and a 25ohm potentiometer. I had replaced that with a 16ohm L-Pad. Is there an advantage to one over the other? I now have the proper pots to recreate that circuit as Altec intended.
     
  16. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    There's no easy/simple answer to that question ( ie; the 16R Variable Lpad vs modified 25R Potentiometer ) .

    Personally, I'd build both to see which offers the best performance.

    Do you have any measurement gear for capturing live sound?

    Nowadays, anyone messing around with this stuff should at least have a smart phone app ( that does a minumum of a 1/3 octave RTA ) along with a small calibrated test mic .

    This Dayton seems ( good ) + popular.

    imm-6 test mic phones


    :)
     

     

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  17. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    I have the REV software and that mic as well as the RTA app on an old iPad which is much easier to use. Will be able to post graphs. Just not until the weekend for the old stuff.
     
  18. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    I slapped together a mock-up this morning and tied it into one speaker. Ran some pink noise and tested with the IPad's RTA app.

    First, no 30923 circuit.
    IMG_20180721_123320.jpg

    With 30923. 13ohms dialed in with potentiometer.

    MVIMG_20180721_123723.jpg

    Comments welcome.
     
  19. EarlK

    EarlK Well-Known Member

    Messages:
    547
    Location:
    Richmond Hill, Ont.
    Is this with the horn level full up ( after the 30923 has been inserted/activated ) ?

    Could you back out to 3ft ( on-axis with the center of the horn ) and take another reading ( + then post that pic ) .

    Is the 30923 using the 3uF cap over the 8R+8R+33R ( pot. dialed to 13R ) ?

    Overall, I would have expected more attenuation from 2K to 6K than what I'm seeing.

    You might try more 30923 attenuation, dialed in on the 33R Pot. ( ie; 6R or so, instead of 13R ) / then ( if there's any drive level left ) turn up the whole horn circuit .

    All in all, it looks like a set of tweeters may be in your future ( or new GPA diaphragms, plus a remag ).

    :)
     
    Last edited: Jul 21, 2018
  20. WntrMute2

    WntrMute2 AK Subscriber Subscriber

    Messages:
    1,744
    Location:
    Royal Oak, Michigan
    I will try your suggestions. The diaphragms are original as far as I know. I'm not sure I can find a better tweeter than the 802-Ds though. Maybe a remag is in order. The cap value is the 3.3uf over 8.0 + 8.0 + 13ohms. I'll try some lower value caps.
     

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