Val_r

How to determine exact cutoff freq. in a pultec filter?
« on: February 12, 2009, 04:15:15 AM »
Hi,

Ex.: I want to determine the actual cut-off frequency of the low boost section of eqp-1a filter (shelving).
How is it done?
Should I turn the pot to max and measure the freq. when it reaches +14dB?
The same for the hi-cut section?

 ::)
Ok, cool ! Jahmekya


Luny Tune

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #1 on: February 12, 2009, 04:27:57 AM »
Why?

And I mean that in the most helpful sense. :)

Is it to determine whether or not a second unit will perform exactly the same and being able to measure and correct it based on your measurement?
Or is it just to find out how it's done?
Is it to match a diy version to an original?
Or...?

gyraf

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #2 on: February 12, 2009, 04:32:09 AM »
For shelving filters you specify them at their -3dB points - in this case when turned full-on (though subjectively this standardized frequency marking will often not make sense in use)

Jakob E.
..note to self: don't let Harman run your company..

EmRR

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #3 on: February 12, 2009, 09:57:55 AM »
Yes, you have to decide on a standard and quote it, which in this case may mean determining what standard Pultec used.    Another EQ of that era, the Langevin 251A, specified the freq at which maximum cut occurs.  Also maximum boost for the low band.  So 40 and 100 are used, but it really effects everything up to a The high boost bands being bell shapes quote the center freq as is normal. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

Val_r

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #4 on: February 12, 2009, 12:46:53 PM »
Yes, you have to decide on a standard and quote it, which in this case may mean determining what standard Pultec used.

This is what I would like to know.
Were they using the |3dB| points as a standard?
 ???

Quote
The high boost bands being bell shapes quote the center freq as is normal.
Obvious.
Ok, cool ! Jahmekya

CJ

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #5 on: February 12, 2009, 08:59:04 PM »
there are some scans of the original EQ Curves from the manual floating.
Or do you have those already.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Val_r

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #6 on: February 13, 2009, 03:09:05 AM »
Thank you CJ !
I've found the manual with the curves.
So, from it, I can see that the standard for taking the frequency indication is not the |3dB| point, but the max. excurion of the filter (+/- 14 dB).
As seen from the curves, the 100Hz boost plot shows it's boost of +13dB at 100Hz,
the Attenuate section for the same frq. shows it's cut of -17dB at 100Hz.

Hope it is clear for others about how to check for correct filter response.
Thank you again.

Respect,

Val
Ok, cool ! Jahmekya

CJ

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #7 on: February 13, 2009, 03:27:07 AM »
Pretty crude, it is that Ni output that everybody loves.

If you want to blueprint that thing, you can change all the pots to stepped things and dial it in any way you want.

You need a pultec for every song, otherwise, everything comes out eq'ed the same!
So like, for a killer album, build 12 pultecs, all different cap values.

Sparky, sounds like your serious.
Here is what you do.
Get three 19 inch racks.
Load each one with nothing but turet  boards full of every cap known to man.
Do this for each section, boost hi, lo.

You will have a pultec from Tierra del Fuego.
Just patch everything.


« Last Edit: February 13, 2009, 03:35:00 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Val_r

Re: How to determine exact cutoff freq. in a pultec filter?
« Reply #8 on: February 14, 2009, 02:31:24 AM »
Pretty crude, it is that Ni output that everybody loves.

Yeah man! And the toroidal core ferrite inductor, as well.

Quote
You need a pultec for every song, otherwise, everything comes out eq'ed the same!
So like, for a killer album, build 12 pultecs, all different cap values.

Or a 32 pos. relay based freq. setting switch.

Quote
Sparky, sounds like your serious.
Here is what you do.
Get three 19 inch racks.
Load each one with nothing but turet  boards full of every cap known to man.
Do this for each section, boost hi, lo.

You will have a pultec from Tierra del Fuego.
Just patch everything.

Uhu. 8)
Ok, cool ! Jahmekya

 

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