Pultec HF Q - can we reduce gain as Q sharpens? - and now LF question too . . .

[strangeandbouncy]

Hi Radience,


  many thanks! that is good news.



    kindest regards,


      ANdyP

 

[strangeandbouncy]

Hi,


  so I came across this as part of my Berklee mastering course.


 http://www.sengpielaudio.com/calculator-bandwidth.htm


 From this, using the BombFactory plugin version of the EQP1A, I measured the -3dB points for fully broad, and fully narrow settings at 3kHz(actually 3.2kHz!!!!) I calculated Q as 0.6 for broad, and 1.4 for narrow. Using a Filterbank EQ plugin, setting the Q the same, but gain opposite, I could cancel the Pultec gain pretty well. I didn't try phase reversing two signals, but I will.


   I am still debating whether or not to build three positions for Q, (say 0.6, 1.0, and 1.4), or just two.


  I also wonder whether these values will depend on the Inductors used(?)


      Kindest regards,


     ANdyP

 

[ruairioflaherty]

Hi,


  so I came across this as part of my Berklee mastering course.


 http://www.sengpielaudio.com/calculator-bandwidth.htm


 From this, using the BombFactory plugin version of the EQP1A, I measured the -3dB points for fully broad, and fully narrow settings at 3kHz(actually 3.2kHz!!!!) I calculated Q as 0.6 for broad, and 1.4 for narrow. Using a Filterbank EQ plugin, setting the Q the same, but gain opposite, I could cancel the Pultec gain pretty well. I didn't try phase reversing two signals, but I will.


   I am still debating whether or not to build three positions for Q, (say 0.6, 1.0, and 1.4), or just two.


  I also wonder whether these values will depend on the Inductors used(?)


      Kindest regards,


     ANdyP

Hey Andy,

As I said before I think 2 positions would be sufficient - one around 0.6 the other around 1.2.  If you want surgery you'll use something surgical, the Pultec idea is all about broad sweet curves...

Q will depend on the "Q" of the inductors - the Quality factor.  I'm guessing you'll be using a matched pair by someone like Don Audio or Max IOAudio? - if so it'll be a suck it and see affair WRT to Q (but I'm guessing they won't be too far off).

It's highly unlikely with the work schedule but if I get to build something it will be +/- 4 or 6 dB, all passive, no Q control on the high end, all shelves....

Talk soon,
Ruairi

 

[strangeandbouncy]

Hi Ruairi,


    have you got any further with your idea of "rescaling" to allow for a max cut/boost of 4dB? I wish I new more . . . . . ! makes perfect sense to reduce the make-up requirement, and make it up in your other gear.


  Can anyone else chime in? How do we go about it?



    Kindest regards,


      ANdyP

 

[ruairioflaherty]

Hey Andy,

Just finished in the studio, glass of wine in hand, 12.45 am - good times  ;D

I have been thinking more about this and I'll write more when I get a chance.  Basically the classic pultec design throws away level in order to give us it's boost function and if we need a cut it just feeds filtered signal to ground.  We need to rescale the voltage divider that does the initial level drop of circa 18dB.  This is made up of the various series and parallel resistances, some just resistors, others are part of the various pots.  I did some late night math last night and got close to understanding what and how we'd need to change.

I'll try to frame up my thoughts over the weekend and perhaps ask a few questions that might lead us in the right direction.

BTW - is there anything on your mastering course about how to say no?!!

Cheers,
Ruairi

 

[strangeandbouncy]

Hi Ruairi,


  not as yet, but I find my 16 stone frame does bear some influence in that department . . . .


      I always prefer "yes, of course, but have you considered . . . "


    I am still trying to work out what is happening in the Pultec circuitry . . . you are ahead of me for sure!


        You want just shelving in the HF boost. I guess you don't need inductors then?


  I wish I could do some "math" for this myself!


            ANdyP