Pultec Low Frequency Calculation
- Thread starter Bigorno
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ruffrecords
Well-known member
That is probably because there is no agreed standard way of calculating this.
With the inductor base high boost it is easy because all you need to do is calculate the resonant frequency for the values of L and C.
With boosting and shelving curves there are usually two RC time constants, one that define the frequency at which the response begins to change and the other that defines the frequency at which is flattens out again. The second one often, but not always, corresponds to the nominal boost/cut frequency. The first can be five to ten times greater of lesser (depending on if it is a boost or cut).
Of course, Pultec never divulged any of these resiliencies other than the nominal one printed on the front panel. if you look at the curves published by Pultec you can estimate the two RC frequencies for each nominal frequency and try to work out how these are related. I did this and found that the relationship is not constant (I have no idea why) so it is not really possible to create a general rule for calculating them. In my poor man's Pultec EQP1A I compromised by fixing the ration of these frequencies so I could generate a rule and a spreadsheet for calculating the RC values.
Cheers
Ian
With the inductor base high boost it is easy because all you need to do is calculate the resonant frequency for the values of L and C.
With boosting and shelving curves there are usually two RC time constants, one that define the frequency at which the response begins to change and the other that defines the frequency at which is flattens out again. The second one often, but not always, corresponds to the nominal boost/cut frequency. The first can be five to ten times greater of lesser (depending on if it is a boost or cut).
Of course, Pultec never divulged any of these resiliencies other than the nominal one printed on the front panel. if you look at the curves published by Pultec you can estimate the two RC frequencies for each nominal frequency and try to work out how these are related. I did this and found that the relationship is not constant (I have no idea why) so it is not really possible to create a general rule for calculating them. In my poor man's Pultec EQP1A I compromised by fixing the ration of these frequencies so I could generate a rule and a spreadsheet for calculating the RC values.
Cheers
Ian
CJ
Well-known member
a quck way is to get a bunch of caps and have a pair of clip leads coming off the cap hookup points,
then you just plug and play till you find the freqs you want,
you will find that one value cap will eq a certain song very well, but not the next production you play, Epic, Capitol, A and M, they all have their rooms and own sounds, you will find that certain cap values will work for one recording engineer and room, but not the next, but certain record companies have the same sound for each artist because it was recorded in the same room with the same equipment,
so it is a compromise, there is no perfect value for the pultec, so add more values than stock for more flexibility,
this will allow you to try two caps of same value but different makes,
like wima vs wax and paper vs orange drops vs whatever you can find,
it is a lot of fun doing this, beats smokin crack any ol day, :
did you check the Meta on EQ?
here>
http://www.groupdiy.com/index.php?topic=16761
then you just plug and play till you find the freqs you want,
you will find that one value cap will eq a certain song very well, but not the next production you play, Epic, Capitol, A and M, they all have their rooms and own sounds, you will find that certain cap values will work for one recording engineer and room, but not the next, but certain record companies have the same sound for each artist because it was recorded in the same room with the same equipment,
so it is a compromise, there is no perfect value for the pultec, so add more values than stock for more flexibility,
this will allow you to try two caps of same value but different makes,
like wima vs wax and paper vs orange drops vs whatever you can find,
it is a lot of fun doing this, beats smokin crack any ol day, :
did you check the Meta on EQ?
here>
http://www.groupdiy.com/index.php?topic=16761
Hi,
I found something perhaps interesting, see attached file.
My estimation is based on the Gyraf Audio type schematic.
Here are the equations:
Bass Boost:
Cap value (nF) = 6444 x Frequency (Hz)-1.15
Bass Cut:
Cap value (nF) = 2934 x Frequency (Hz)-1.18
Hi Cut:
Cap value (nF) = 1989133 x Frequency (Hz)-1.09
Hope it could help someone
I found something perhaps interesting, see attached file.
My estimation is based on the Gyraf Audio type schematic.
Here are the equations:
Bass Boost:
Cap value (nF) = 6444 x Frequency (Hz)-1.15
Bass Cut:
Cap value (nF) = 2934 x Frequency (Hz)-1.18
Hi Cut:
Cap value (nF) = 1989133 x Frequency (Hz)-1.09
Hope it could help someone
