White passive EQ with boost and cut

Hey guys,

Here is the manual, including schematics for my White Instruments LCR passive EQ. It has cut only. Do you see any way to convert it and get both boost and cut? I remember NYDave talking about putting knobs in the middle position, but I want a flat characteristic in zero.

http://www.whiteinstruments.com/4220-archive.pdf

Nope, there is no way to make a passive (unamplified) equalizer with boost capability and unity gain in neutral.

What you do in a passive eq - like the pultec eq stage - is that you cut all frequencies linearly by the amount you want to be able to boost it, and then you add a frequency selective circuit to "let through", ie. not cut, the material you want to "boost".

But this leaves you with an eq stage gain loss of the same size as your maximum possible boost (or unity gain only for the max-boosted part of the signal).

No easy way around that, I fear..

Jakob E.

[quote author="Marik"] Do you see any way to convert it and get both boost and cut?
http://www.whiteinstruments.com/4220-archive.pdf[/quote]
To make load resistance negative...?
Use tunnel (Esaki) diode or other shit.
Or negative impedance convertor?
But you loose advantages of passive circuit (low noise, high dynamic
ratio, etc)
xvlk

[quote author="Marik"]Hey guys,
Do you see any way to convert it and get both boost and cut? http://www.whiteinstruments.com/4220-archive.pdf[/quote]
Marik,
I have an idea; you need four this units to make it in stereo.
(and no changes inside its)
I explain you one channel:
input_resistance,passive_eq_1, terminating resistance, amplifier,
input_resistance, negative_impedance_converter, passive_eq_2,
negative_impedance_converter,terminating_resistance

You can do with passive_eq_1 cuts
and with passive_eq_2 boosts.

Replay me, if you have interest.
You must DIY four Antoniou converters, think, it is no problem.
From transistors are rather complicated, from op amps it is
trivial.

xvlk

Some trivial example of negative impedance convertor and
connection of its to your 4220 s is here.

(you must cut and paste link below to the other browser)
http://mujweb.cz/www/xvlkxvlk/niks.jpg

Remember, that it have two sides which depends on circuit
impedance ratios. If you interchanges it,
you gets oscillator.
xvlk

[quote author="gyraf"]Nope, there is no way to make a passive (unamplified) equalizer with boost capability and unity gain in neutral.

What you do in a passive eq - like the pultec eq stage - is that you cut all frequencies linearly by the amount you want to be able to boost it, and then you add a frequency selective circuit to "let through", ie. not cut, the material you want to "boost".

But this leaves you with an eq stage gain loss of the same size as your maximum possible boost (or unity gain only for the max-boosted part of the signal).

No easy way around that, I fear..

Jakob E.[/quote]

Thanks Jakob,

I don't care much about unity gain in neutral--I have plenty of gain to compensate for that. What I meant by "flat" is that I would imagine that if I cut all the frequencies let's say by 6db, to be able to boost them next, I would get a "wavy" frequency response. No?

I have an idea; you need four this units to make it in stereo.

Click to expand...

xvlk,

Unfortunately, that's not an option--I have two units only.

What's the application?

You may wind up with spikes in the curve due to the differences (in matching freq's) between the two units. That said, if you have a chain where you're EQing a mic or source to "reshape or accommodate" a mic's response then boosting before tape, there will be very few obvious artifacts in the final signal (to the ear, not a scope).

I do this with my semi-parametric eq's all the time - usually to an extreme, though.


-james

Did I talk about running the knobs in the center position? I don't recall that, but then again, there's a lot of things I have trouble remembering anymore. :wink:

The 4220 is a cut-only unit, like all passive EQs, that appears to be designed for tuning out "humps" in room response. It's intended to be run at the zero loss position except for those frequencies that need to be "tuned out." It's highly unlikely that the curves of each band have a perfect enough overlap to give a truly "flat" response with all controls at center. More probable is that centering all controls will give you some low amplitude peaks and valleys up and down the audio range. There are several passive EQs that are designed to be flat (relative to their insertion loss) at the center position, but this is not one of them. The passive EQ design I published here a while back, as well as others such as the Cinema Engineering 4031B, Langevin EQ251A, etc., are capable of a flat response with boost and cut possible, relative to the nominal insertion loss.

An EQ like the 4220 can be used successfully for music, but it requires a different way of thinking. You have to think in terms of what needs to be attenuated, rather than what you want to hear more of. As an example, if a male vocal track sounded "boxy", you would apply a cut around, say, 300 or 400Hz, rather than attempting to boost the 5kHz "presence" range. Actually, you'll often get better results by thinking subtractively regardless of the particular type of EQ you're using.

Here is some example on passive boost and cut equalizers, as Jakob say before, the +dB you want in boost position you lose in flat position, but a aprox. +12 dB gain make up amp (in good discrete design) after the eq circuit are not a disadvantage for the passive eq character.

--Bo

Thank you Gentlemen,

Basically, I need a nice passive EQ for mastering, as I am not satisfied with quality of Protools EQ's. Of course it would be nice to use at least inductors from White, but first I need to measure them...

NYDave,

I made a search, but could not find your passive EQ. Was it here, or on TT? Could you please give me a lead.
Pultec would be another possibility, but I am not really into cloning, so would rather go for an original design.... and support our folks... at least morally :thumb:

Even though it will increase the insertion loss, I recommend a 4:1 stepdown transformer at the input to ensure that the EQ is always driven from a very low source impedance. Or, you could use an active buffer as long as its output Z is under 60 ohms. When the source Z rises above 60 ohms, the amount of "boost" becomes limited. This is a consequence of this simple "inverted L" type circuit. The payoff from this simple circuit, though, is that half the inductors and caps of a constant-impedance type are required.

Using proportionately higher values of "L" and lower values of "C" will give you sharper curves. The values chosen yield fairly broad curves that should be found to be "musically useful." The general shape and center frequencies of most of the curves were inspired by those of the Langevin passive EQ.

By the way, instead of stripping the 4220 of its inductors, why not sell it and use the money toward whatever DIY solution you choose? I happen to own three 4220s, and I might be interested in a fourth if the price were right :grin:

> White Instruments LCR passive EQ. It has cut only. Do you see any way to convert it and get both boost and cut?

Do Not Mess With It!!!

Those passive cut EQs are absolutely perfect for PA EQ. More people should use them instead of active boost-cut EQ. When I was "forced" to use one of them to earn beer-money, the performers loved it. Used with discretion, it can give 6dB or 12dB more gain before feedback, and I think it corrects the phase response better than any other EQ.

It would be trivial to add an amp and make it boost-only. But that would be stupid. Making it boost-cut really means destroying it. Since you can buy fine EQs for small bucks, why kill the soul of a perfect tool?

[quote author="PRR"] why kill the soul of a perfect tool?[/quote]

PRR,

I like convicing reasons :grin:

NYDave,

Let me think if I can find use for them the way they are, or even better... PM me with your offer.

How a "Z" section looks like? What do you mean by "half the inductors and caps of a constant-impedance type are required"?

Marik;
I though I knew you better than that.

P ro Tool s will not ever sound good.
Use the passive EQ and you will like it.
Throw that p ro tool s stuff in the trash can.

[quote author="adrianh"]Marik;
I though I knew you better than that.

P ro Tool s will not ever sound good.
Use the passive EQ and you will like it.
Throw that p ro tool s stuff in the trash can.[/quote]

Hey Adrian,

Sorry if disappointed you :grin:
I afraid I have to stick with PT--you know, to cut a tape is not much fun. If you ever were into classical music editing, you know what I mean. Sometimes I have to do up to 100 cuts in 5 minute piece. But all the processing I do out of software. I had quite a few EQ's, but did not like any of them. The White sounds much better, but lacks a boost, so I gonna give a try some passives.

Marik,

I made Daves passive and I've been using it alot. It sounds great.

I made six of them in one box. Each has 3 bands with six frequencys for each band. the high band has selectable Q and peak or shelf.

I used an SRPP stage like in the Gyraf pultec for make up.

I used 600:600 transformer for input.

So Dave are you saying I could get more boost if I used a 4:1 input transformer?

Bluebird,

I found your MAGNIFICIENT EQ! Wanna trade for ribbon mics? :grin:
It's strange--when I made a search that thread did not come out. Ha! it's always a good idea to look at meta, first.

I gotta do some homework, read Audio Passive Network Design book, and then see...

[quote author="bluebird"]So Dave are you saying I could get more boost if I used a 4:1 input transformer?[/quote]

Likely, yes. If whatever you're plugging into the EQ has an output impedance of more than 60 ohms--and there's a pretty good chance it does--then the stepdown transformer would help, but at the cost of an extra 12dB of insertion loss, for a total of 22dB at the "flat" setting. Luckily, 22dB is only 12.6X gain, which isn't terribly hard to provide cleanly.

It sounds to me like your looking for tartan coloured paint

Cheers

R