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Moog Parametric EQ

Discussion in 'Electronic Repair Modifications DIY' started by peterc, Dec 5, 2002.

  1. peterc

    peterc Guest

    Hi all

    Has anyone used this unit or seen a circuit diagram of it? It seems to have a "holy grail" image attached to it, like most of the gear Bob Moog designed.

    Some links of interest :

    & now the big question : A good DIY project?

  2. gyraf

    gyraf Guest

    As far as I can see, there's nothing new here:




    I think this is just the good old american "lets' try to patent something that is already invented" -scheme that is at work here.

    So I think this is more a result of poor american patent laws than of real creativity..

    Jakob E
  3. tosch

    tosch Guest

    I will participate in the first time. I was using Moog Parametric EQ
    . It is very unique EQ. There was time when I was going also to produce the clone, too.
    However, because two was able to be bought fortunately, it did not
    make it.

    It is very often effective.
    The phase changes too much.
    The sound is ahead when using it for the line recording etc. of BASS
    because the input circuit is unique. Problem at clone

    Anyway, it changes in dramatic form.
    It's need special VR


    Although it is good to do DIY, and parts are saved, savings decrease..
  4. gyraf

    gyraf Guest

    Hi Tosch,

    Welcome here!

    It's good to have people from your part of the world in this forum!

    Jakob Erland
    Gyraf Audio
  5. peterc

    peterc Guest

    Hey Tosch

    Thanks for the reply & the info about this box of tricks.

    I'm a bit confused about "VR"? Could you tell me more? Do you have a schematic by any chance?

    Once again tahnks, & welcome

  6. tosch

    tosch Guest

    Thank you for welcoming

    I have built a prototype ten years or more ago.
    I used the rotary switch for the change of special VR.(Variable resistor)
    I thought that the pot of frequency was dual C(revlog type) or W curve.

    >Do you have a schematic by any chance?
    Yes, When I was going to make the schematic and dissolved, the very kind wiring diagram was contained. The parts list and the part arrangement plan were also contained. Though regrettable, the experimental model does not remain.

    I consider how to send.


    Although it is good to do DIY, and parts are saved, savings decrease..
  7. Kev

    Kev Well-Known Member

    tosch !

    is that who I think it is ??

    Hi and welcome to tech talk .

    I'm glad Jakob spotted that cos I must have been asleep for a day or so. I really am starting to miss things I should be seeing. Sleep ... I need a week of sleeeeep.

    It is very good to have you here ... wavey.gif
  8. tosch

    tosch Guest

    It is strange English usage.
    I rearranged the NEVE EQ.
    A phase changes like EQ of moog. However, it is regrettable that variable of Q is not made.


  9. Kev

    Kev Well-Known Member

    Looks like a 51 series EQ board.

    I've done much work on these.
    The transistor output stage gives me the most grief and tracing broken tracks on the PCB.

    the transformers ?? one is an old Neve and the other is ??? I can't read the writing.
  10. Bo Hansén

    Bo Hansén Active Member


    Yes, this eq are a very nice sounding unit, but it have some unusal circuit design.

    (the eq section is a "gyrator to ground" type circuit, like graphic eq designs)

    In the input amp it it have treble pre-emphasis and in the output amp it have treble de-emphasis
    to improve the treble headroom and signal to noise.

    Regarding the hard to get VR/potentiometers,
    the freq. sweep pot I think is ok, because it is usal to use dual reverse logaritmic types as sweep pot, and you can find this as a spare from some console manufactures, but the unusal potentiometer in this Moog eq is the variable Q, and what I remember it was a dual type with some 100 ohms in one half and some K ohms in the other half with different curves, so this one can be hard to get.

  11. Bo Hansén

    Bo Hansén Active Member

    Sorry, wrong again.

    Regarding pre/de-emphasis, it worse the treble headroom (not improve) but it improve the signal to noise.

  12. peterc

    peterc Guest

    I have the schem here.


    I will leave it up for a few days.

    I thought of doing a 3 way toggle for the Q to get around the dodgy dual pot in there.

  13. Mark Burnley

    Mark Burnley Guest



  14. NewYorkDave

    NewYorkDave Guest

    Note that the schematic looks tiny on the webpage, but if you right-click and "save as", you'll download a full-sized image.

    Thanks for posting that.

    Shame about those 4558's. Yuck...
  15. NewYorkDave

    NewYorkDave Guest

    By the way, for a similar concept, see the Orban 622.

    I own one and it's a nice EQ.

    Orban 622 manual/schematic (PDF)
  16. Bo Hansén

    Bo Hansén Active Member

    Yes, I remember right, the sweep frequency pot was a typical 100 kohm reverse log that you can find in the most of parametric eq designs, easy to get as sperepart, but width/Q pot are very unusal 500 ohm linear and 50 kohm logaritmic, that one can be hard to find.

    Vishay (Sfernice) make spec. pots on order, min. order aprox. 25 to 50 pcs.
    (the P11 03 PA11 white plastic square type)

    I think I have some plotted curve for this eq, I will se if I can find them and display them here.

  17. Bo Hansén

    Bo Hansén Active Member

    Hallo guy´s,

    I find the Moog MKPE 304A parametric eq plotting that I have done in 1987, and here it is:

  18. tk1

    tk1 Member

    Hi there, I just found this forum after doing a search for Moog Parametric EQ. I bought one of these recently and I love the way it sounds! Only thing is the 'drive' control's not working :'( It's totally unresponsive... I was hoping to get some advice from some of you folks on here regarding the matter. Does this sound familiar, has anyone had this, is it fixable and how? Thanks in advance.

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