diggy fresh

Pultec hlf-3c
« on: August 10, 2016, 12:56:40 PM »
Hi all!

I recently started messing with winding inductors and passive eqs and i'm looking to make a passive Pultec Hlf-3c.
I don't have much experience yet with filters and i'm starting to study them. (autodidact)
I have a few questions for more experienced people.


here's the only info on it i was able to find:  (schematic included):

http://www.gyraf.dk/schematics/Pultec_HLF3.pdf

(many thanks to Gyraf and the guy who took the time to reverse engineer this!!!)



Did anybody was able to make a version using these schematics?


I'm looking for an online calculator for this topology of filters to be able to tweak the capacitors to fit the tolerance of my self-wound inductor,  i don't know enough about filters to identify the topology of the Hlf.

Anybody can identify the topology??   i'm guessing it's "constant something" , bridge-t someting?  pi? chebyshev?
help would be appreciated.


Also, i read this passive filter needs 600 ohm source and load to function correctly.  How will this filter react with modern source and loads??  I'll probably be driving the filter with the output of my soundcard (50 ohm) and back in a modern line input.


thanks for the help! any info would be appreciated.

John


English is my second language, apologies

Autodidact audio geek, constantly learning.

Very interested in old technology, i mostly learn from the info you guys share on here, so thanks!


diggy fresh

Re: Pultec hlf-3c
« Reply #1 on: August 12, 2016, 11:15:01 AM »
ok, i think i got it,

the high-pass section is "Butterworth Tee LC High Pass Filter"  with an impedance of 500 ohm

and the low pass section is  "Butterworth Tee LC low Pass Filter" also 500 ohm.

i was able to calculate the lp and hp sections using these:

http://www.calculatoredge.com/electronics/bw%20tee%20high%20pass.htm

http://www.calculatoredge.com/electronics/bw%20tee%20low%20pass.htm


It didn't work for me when i first posted because i was trying to use the calculator in reverse ( to calculate the frequency with my exact component value). still looking.



I'm still curious what the effect will be with "modern" source and load impedance, anybody?
English is my second language, apologies

Autodidact audio geek, constantly learning.

Very interested in old technology, i mostly learn from the info you guys share on here, so thanks!

EmRR

Re: Pultec hlf-3c
« Reply #2 on: August 12, 2016, 12:12:34 PM »
Search my posts.  altec, langevin, etc.  This has been covered to death by many people. 
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

diggy fresh

Re: Pultec hlf-3c
« Reply #3 on: August 13, 2016, 12:35:15 PM »
Thanks Emrr,  hadn't thought of searching for altec and langevin threads thanks, i started.


The HLF-3c is similar in topology to Newyorkdave's passive filter, minus thye "brf" input part.

http://twin-x.com/groupdiy/albums/userpics/FilterPanelConcept.png


I get from the various threads that loading etc will affect the knee or resonance of the filters, i am very interested in this effect.


Emrr,   i saw in the old "passive filter panel" thread by Newyorkdave you mentioned:

"I was thinking this afternoon about using ........a 500 ohm input rheostat in series for trimmable ringing.   The rheostat is nice as an extra effect sometimes.   And an output load resistor on a switch."

I am very interested in this.  so as i understand, you would put a 500 ohm pot in SERIES with the input ? and a swith on the output which puts a resistors in PARALLEL with the load?   what values of resistors would you recommend for the load switch? 



Also another question:
 For the low pass section with the two identical inductors in series, how important the matching between them?   What would be the effect of a slight mismatch?  I have a difference of 1mh between some taps and slighlty more for others. Would the filter be less effective? less sharp?  the frequency would drift a little?


Also, anybody knows of an online calculator like the ones i posted above where i could "reverse" the formula?
I would like to calculate the frequency with the component values instead of calculating the component values for a given frequency.

Thanks!
J




English is my second language, apologies

Autodidact audio geek, constantly learning.

Very interested in old technology, i mostly learn from the info you guys share on here, so thanks!

Re: Pultec hlf-3c
« Reply #4 on: July 16, 2020, 05:37:58 AM »
Hello, someone who can take me out of my ignorance and enlighten me on how to calculate what inductance and what capacitance to mount so that it filters at the desired frequency, that is to say that in a filter it passes high chebyshev it achieves a filtering in for example 7500hz that inductor And what condenser do I have to put to achieve a filter with an enhancement of at least 5 / 10db of narrow bell, and a drop of about 20db.
Thank you very much in advance.