Gyraf Pultec Frequencies

[Janus Audio]

Since I didn't find the frequencies I needed for my G-Pultec front plate, I decided to use CJs nice explanation  of reactances to calculate them myself.

The rough results are:

Low Freq:
20 Hz
30 Hz
50 Hz
60 Hz
100 Hz
150 Hz

Hi Cut:
28 kHz (better to use 15nF and parallel the 33nF next to the rotary switch so you get 48nF -> about 20 kHz)
14 kHz
12 kHz
10 kHz
7 kHz
5 kHz


For the treble boost section I had to find the crossing of the function for the capacitive reactance Xc = 1/(2 Pi * f * C) and the function for the inductive reactance XL = 2 Pi * f * L to get proper center frequencies for my front plate dial.

XL = Xc
2 Pi * f * L = 1/(2 Pi * f *C)
f =

(1/ (2Pi)² * L * C)

2 Pi is about 6,28 so 2Pi² is about 39,44

f =

(1/39,44*L*C)

The results for the treble boost section are:

2288 Hz (18nF, 269mH)
2887 Hz (18nF, 169mH)
3535 Hz (12nF, 169mH)
7351 Hz (6,8nF, 69mH)
13018 Hz (6,8nF, 22mH)
18688 Hz (3,3nF, 22mH)

For front dials these can be rounded of course 

Sebastian

 

[livingnote]

Now I get a knot in my math over here..can you help me?

When I put in values in the last formula there (in Hz, F, H) what
I get is exceedingly tiny numbers for the frequency...any clue what I'm screwing up?

(Und noch eena mim pultec aus Berlin, kommse rinn, könnse kieken

 

[Harpo]

When I put in values in the last formula there (in Hz, F, H) what
I get is exceedingly tiny numbers for the frequency...any clue what I'm screwing up?

missing parantheses?
for the last example value pair (3n3; 22mH) Excel returns 18678,9225Hz for formula =WURZEL(1/((2*PI())^2*22*3,3*10^-12))

 

[livingnote]

Ah super - yah looks like my rpn skills need some brushing up

Just one thing - I end up with a different value for the second one (18nF, 169mH)=2886 rounded. That was what got my attention before I totally screwed with the calculator  :

 

[kazper]

The results for the treble boost section are:

2288 Hz (18nF, 269mH)
2287 Hz (18nF, 169mH)


For front dials these can be rounded of course 

Sebastian

I thought something looked funny here is what I got. looks like you made an typo

The results for the treble boost section are:

2288 Hz (18nF, 269mH)
2887 Hz (18nF, 169mH)


BTW  thanks, I've wanted to know this when I designed out the G-pultec front panel

 

[hobiesound]

just get the ferroxcube mini ring-core calculator and be lazy like me. It will calculate the missing parameter from either L, C and freq.

greetings,

Thomas

 

[Janus Audio]

I thought something looked funny here is what I got. looks like you made an typo

The results for the treble boost section are:

2288 Hz (18nF, 269mH)
2887 Hz (18nF, 169mH)


BTW  thanks, I've wanted to know this when I designed out the G-pultec front panel

Yeas, thanks for the correction - I just mixed up the numbers copying it from my jotter...

 

[kazper]

I got the boost section combination stuff fairly quick. I don't get the high cut part... can you elaborate on that a little. I'm probably thinking too deep...

Kaz

 

[Janus Audio]

I got the boost section combination stuff fairly quick. I don't get the high cut part... can you elaborate on that a little. I'm probably thinking too deep...

The original Pultec uses 47nF, 94nF and 194nF in the high cut section for 20kHz, 10kHz and 5kHz. So we have about 169R ,169R and 161R capacitive reactance there. I took the 169R and plugged it into the frequency formula f = 1 / (Pi * C * XC) which you get by converting the formula for capacitive reactance (XC = 1 / (Pi * f * C).

For example the G-Pultec uses 33nF+47nF for one frequency (the 33nF are always paralleled). So you have f = 1 /(Pi * 0,00000008 * 169) = 11777Hz (maybe slightly different cause I use 6,28 for Pi).

 

[kazper]

I got the boost section combination stuff fairly quick. I don't get the high cut part... can you elaborate on that a little. I'm probably thinking too deep...

The original Pultec uses 47nF, 94nF and 194nF in the high cut section for 20kHz, 10kHz and 5kHz. So we have about 169R ,169R and 161R capacitive reactance there. I took the 169R and plugged it into the frequency formula f = 1 / (Pi * C * XC) which you get by converting the formula for capacitive reactance (XC = 1 / (Pi * f * C).

For example the G-Pultec uses 33nF+47nF for one frequency (the 33nF are always paralleled). So you have f = 1 /(Pi * 0,00000008 * 169) = 11777Hz (maybe slightly different cause I use 6,28 for Pi).

I just picked up a book after posting this that helped me understand part of this and I'm going to recommend it for DIY. What I couldn't get is the capacitive reactance is in the G-pultec . In CJ's examples it's posted as something picked or estimated I believe but that was in the original pultec schematic.

What I haven't done is actually compare them close. So your thinking the Gpultec and the Real Pultec share the same capacitive reactance?

Book: Handbook for Sound Engineers, Fourth Edition
http://www.amazon.com/Handbook-Sound-Engineers-Fourth-Ballou/dp/0240809696/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1238869999&sr=8-1