Pultec filter section question

[rafafredd]

[quote author="kubi"]:?: Seems like I missed that day of school! :shock:
Please could you be more specific on what I should watch out for? Or please feel free to feed my mailbox if you have the schematics at hand.:grin:

Thank you very much in advance![/quote]

This is the NYDave passive EQ circuit. It´s up on my list of TO DO projects. Find it at the meta or try a search.

 

[NewYorkDave]

CJ: Yeah, I talked to Fearn at the 2001 AES and he told me that he uses a cathode follower in front of his filter section.

Rafael: I've made some tweaks to the reactive elements in my EQ circuit to give somewhat narrower peaking curves. I'll post them one of these days :grin:

 

[rafafredd]

WOW! And this was already a killer circuit...

 

[NewYorkDave]

Kubi,

The inductor/capacitor values on my early schematics produced very broad curves that you may have not found to your liking, especially when the center frequencies were close enough for the curves to overlap. I'm putting out a new set of inductor/cap values that will produce some narrower curves that you may find more useful.

 

[CJ]

if you want a notch filter, just rip out the 270 ohm q resistor on the MEQ-5 mid cut circuit.
simulate it to see how steep.
i didn't like the sound of it too much. tolerable at low db cut levels but after that, pure garbage.

 

[clintrubber]

Just curious who actually did add additional bands. How did it turn out ?

 

[Val_r]

[quote author="NewYorkDave"]Kubi,

The inductor/capacitor values on my early schematics produced very broad curves that you may have not found to your liking, especially when the center frequencies were close enough for the curves to overlap. I'm putting out a new set of inductor/cap values that will produce some narrower curves that you may find more useful.[/quote]

Can you post the new set of values?

Thank you,

Val

:roll:

 

[NewYorkDave]

Circuit

Table of Values

 

[Klaus Mogensen]

I have been playing around with making a pcb in Gyraf style of the
mid cut version of the MEQ5 eq.

http://www.gyraf.dk/gy_pd/pultec/meq5.gif

I can't really afford the expensive switches so I decided to split it in two
bands of six positions using two lorlin 2x6 switches, which also avoids all the annoying wiring.

Here is the layout:

http://groupdiy.twin-x.com/displayimage.php?album=random&cat=10093&pos=-674

The left portion is the low mid cut and the section to rigth is the high
mid cut. The positions goes approx. as follows:

Low mid cut: 300 Hz, 500, 700, 1000, 1500, 2000

High midcut: 1500, 2000, 3000, 4000, 5000, 7000

I skipped the 200 Hz value to avoid the 420 mH inductor and to have two
over lapping bands. Some of the inductor values are hard to get
so I made the option of using a series combination of two inductors
(the 227 mH and the 145 mH value).

For the bandwidth I used a 47 Ohm fixed resistor and a 1k lin pot.

I haven't listened to it yet, but only measured it with an audioanalyzor,
which gave a total insertion loss of 6 dB. I have the measurements on
another computer and can post them another day.

Here's the PCB

http://groupdiy.twin-x.com/displayimage.php?album=random&cat=10093&pos=-673


Btw, I don't what to do with the 2k2 rev log pot. So far I have only used
a linear.
It is really easy and fast to make.
Best, Klaus :grin:

 

[laitue5]

Only 6db loss? It could be integrated easily in a microphone preamp design without adding another gain block? Or maybe in an opamp?s feedback?

 

[Klaus Mogensen]

Yes, it should be possible to insert in a preamp.

Here are some measurements:

A bandwidth sweep:

and a frequency sweep:

The insertion loss is seen in the first graphs (difference between green
and white)

Good luck.

Klaus

 

[Klaus Mogensen]

OK. quite poor quality of the pictures.

Look here:

http://groupdiy.twin-x.com/index.php?cat=10093

or maybe

http://groupdiy.twin-x.com/albums/userpics/10093/thumb_LowPos2HighPos3c.jpg
http://groupdiy.twin-x.com/albums/userpics/10093/thumb_LowPos2HighPos3d.jpg
http://groupdiy.twin-x.com/albums/userpics/10093/thumb_bandwidth%201k%20lin%20max.jpg
http://groupdiy.twin-x.com/albums/userpics/10093/thumb_high%20pos1-4.jpg

 

[clintrubber]

[quote author="Klaus Mogensen"]I have been playing around with making a pcb in Gyraf style of the
mid cut version of the MEQ5 eq.[/quote]

Nice ! :thumb:


While on the subject of modding, the thought struck me
that it'd be both easy & imho of practical use to add a
simple DPDT-switch per section to have the option of changing CUT into BOOST.


Likely it'll be repeating other designs; I didn't check
other circuits yet (like NYDave's design, Tremaine etc etc).


I should add a drawing, but for now let's try it with words:


#1

First step is to connect the L+C-section between 'top' & 'wiper' of the CUT-knob (i.s.o. between 'wiper' & 'gnd'). This reverses the pot-function,
you may want to swap the outer ends of the pot to have 'flat' at CCW again.

Note the topology of this mid-section is now identical to those of the LOW & HIGH-sections, but only 'upside down'.


#2

Wire up a DPDT-switch that can swap the 'in' & 'gnd'-connections of the
complete section.
Postion 'CUT' has the connections as originally; the 2k5-pot is flat @ CCW,
mx-cut @ CW.
For position 'BOOST' the signal source now enters the section at the pot-terminal that's not connected to any L+C, by means of the first half of the DPDT-switch. The original input is grounded by means of the second half of the DPDT. Flat @ CCW, max-boost @ CW.


There'll be some practical things that need to be solved, like pot-laws (maybe) and changing some fixed resistor values to have equal
'flat'-attenuation for both switch positions etc. (so that would require increasing the 510 Ohms resistor to 2k5) and who knows what else.


Bye,

Peter

 

[Klaus Mogensen]

That sounds like a really good idea. I haven't thought about that. Maybe that
is what Manley does in the Massive Passive ?

It is however my intension to use it after the PEQ1A filter boards as an extension in a stereo unit for mixdown. And in the PEQ1A, boosting is already possible, but in e.g. a preAmp it would be very nice.

Right now, I have to wait with finishing building of the unit, because I haven't money for the chassis (4U $100 at least) and the transformers.

Thanks for the suggestion.

 

[solder_city]

that looks great klaus! :thumb:

ive been wanting to build a nice passive eq. i cant decide whether i want to build one of the various pultecs, or a new york dave eq, or something else altogether. i also like the 'white' passive eqs, ive used them in pa system work and theyre simple and great to use

 

[clintrubber]

[quote author="solder_city"]that looks great klaus! :thumb:

ive been wanting to build a nice passive eq. i cant decide whether i want to build one of the various pultecs, or a new york dave eq, or something else altogether. i also like the 'white' passive eqs, ive used them in pa system work and theyre simple and great to use[/quote]
That just seems to beg for a modular approach, like separate passive-EQ & makup-sections.
First just get one of each (obviously) and keep adding alternatives later on. Or just make a EQ-section & grab a suited mic-pre for now.

Most importantly (and hear hear who's saying this ) is to start soldering ! :wink:

 

[NewYorkDave]

[quote author="clintrubber"]
That just seems to beg for a modular approach, like separate passive-EQ & makup-sections.
First just get one of each (obviously) and keep adding alternatives later on. Or just make a EQ-section & grab a suited mic-pre for now.[/quote]

Here's how my EQ can be configured to use any mic pre as a makeup amp. This is how I'm planning to build it myself (when I get around to it!).

Schematic (JPG)

the two 250-ohm resistors perform the function of "RL" in the schematic for my EQ. The actual load seen by the EQ is about 500 ohms instead of the 600 stated on the original schematic. These two resistors also pad the level and impedance down to suitable values for a mic preamp input. And, R11 should be changed from 137 to 100 ohms. These adjustments to the original values compensate for the real-world series resistances of the 10K:600 input transformer and the inductors in the equalizer.

 

[cstella]

Yes! That would be great. I am totally down with the modular approach. In fact I am building some pultecs as well as the NYD Eq to all be put in MOTM modular synth format. Seperate passive modules and perhaps a gain module with say 4 amps with different flavors. But for now I will use some neve pres which have been doing great duty with the NYD passive summer. Thanks so much for all the great info NYD!

 

[Klaus Mogensen]

I'm currently thinking about what to do with the output amp. Do any of you know whether it is possible to mod the Pultec PEQ1a amp to obtain 6 dB more gain without pressing it too hard (total 31 dB).

http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif

or is it necessary to use an additional tube? I'm going for an integrated approach due to space limitations.

 

[synthi]

I remember that I asked the same question some time ago.
Jakob wrote you can`t get more gain out of the design...

Synthi