Pultec type (passive) equalizer

[lohk]

Does anybody have any idea how to wind precise inductors (for passive filters) without a inductance meter ?
Is there a webside to explain this ?

I want to make a Pultec EQ for my studio; I recently found the schematic in the net
( [url]http://www.gyraf.mobilixnet.dk/ [/url] ).


Klaus

 

[djk]

Buy an LCR meter.USD$50 from MCM 72-6634.The USD$189 MCM 72-960 is much better.

 

[lohk]

Thank you, that really was an answer to my question...

 

[otto88]

PULTEC Style EQP-1A EQP1A Complete Filter Unit New:

eBay Australia: Buy new & used fashion, electronics & home d?r

 

[prairiemystic]

For the Pultec coils, use telecom grade ferrite pot cores - not SMPS ferrites.
Sowter makes the inductors and transformers too.

 

[Tajzmaj]

Klaus. It will be hard without lcr meter. You ca calculate coils but in reality it is batter to measure too.
I made 2 gyraf's pultec units and work fine... With coils which I bought cheap from Farnell.
Later I made 2 units with solid state output. 1073 type. On my opinion those sounds even batter than gyraf's tube output which is very sensitive of which opt you use. With Lundahl 5402 which was used by Jakob I was't quite happy with low end.....
Best regards, Taj

 

[otto88]

prairiemystic

What is the advantage of telecom grade ferrite pot cores?

Cheers

 

[prairiemystic]

Pultec Inductors - ferrite material etc.

The vast majority of ferrites out there are designed for switching power supply applications. They are optimised for high flux-density and I find they sound quite poor with audio signals. Just too much distortion for my taste.

When I spoke with engineers from Neosid, they said for low distortion I should go with a P11 ferrite material from Neosid/MMG/TTI. The P11 material is used in filters and mainly in POTS (analog) telephony. P12 material would work too.

There is a Siemens research paper out there that showed transformer distortion is related to core geometry and symmetry. I went with larger RM-10 pot core has low CDF ("core distortion factor") whereas E-cores seemed much worse. Some info in this Siemens/EPCOS app. note pg. 6/22 or 133:
[url]http://www.thierry-lequeu.fr/data/AN-EPCOS.pdf[/URL]

To summarize, I would avoid using power magnetics for a Pultec clone filter inductor.

 

[musician0001]

I want to build just the passive part of an MEQ5, without its input transformer. I want to use it as a module to be inserted (via TRS) before a guitar amp or right after the input transformer of a mic preamp or before its output transformer. Anyone can please tell me if this can be done or not?