Passive Baxandal EQ and phase?

I have a question about phase and passive eq's. I'm making a Baxandal passive eq and hoping to use it in front of my TAB or Neve mic pre for line level work. Will the phase be out of wack by doing this? and if so how can I make it work?
Thank you.

I'm not trying to be a wiseass, but truthfully there's no such thing as a passive Baxandall EQ. Baxandall's EQ was active. And your question is vague: what do you mean by "will the phase be out of wack?" Just about any equalizer is going to alter the phase-frequency characteristic of the signal. In fact, this is a by-product of what makes them work in the first place.

The best thing to do, with questions like this, is to post a schematic of what you want to do, rather than expect readers to know what you have in mind from a very incomplete description.

I'm sorry I guess I was talking about inverting the gain as opposed to phase. I was thinking that when the gain is inverted the negative becomes the positive and the positive the negative (which is what I meant about being out of phase, perhaps the wrong term sorry), but I'm not sure, I'm not very educated in electronics.

I tried to enter a picture and haven't had luck. Here is the link
amps.zugster.net/articles/tonestacks
Gyraf had given me the impression in the past that the Baxandall eq was a passive design, I must have misunderstood him, sorry about that. [/img]bax-scem.gif

Here was the original question perhaps I should have just continued this topic were Gyraf answered a question for me relating to passive eq's.


groupdiy.com/index.php?topic=8740&highlight=baxandall

[quote author="Gyraf"]For a full-passive type you could look into how it's done in tube guitar amplifiers. My favorite simple-eq is the baxandall type, but that takes at least one tube or transistor, as it needs inverting gain to work. [/quote]

What I mean is: the baxandall type tone control is not passive (as it requires an active gain component). For full-passive eq's that are simple, look into guitar-amp type tonecontrols - there's many schematics around.

If you by phase wack mean absolute phase, then you're right that the baxandall type eq will reverse your abs.phase, but you could mount it with a phase-reverse stage if you need it..

Jakob E.

Well, if you use it with a mic pre, just hit the polarity switch there...

Samuel

Thanks that is what I meant sorry for the confusion. The schematic I'm working from is called a "Passive Baxandall Tone stack" So by reversing the phase on the preamp I think It will work without power running to the eq, correct?

[quote author="Coldsnow"]... I was talking about inverting the gain as opposed to phase ...[/quote]
Best if you think that the gain doesn't actually invert, the polarity inverts.

Polarity is one thing. Phase is another... Again, this is intended only to steer you towards the correct line of thinking so that things will hopefully click into place later on.

Polarity(not phase) has no effect on whether something will work or not if it's passive. There's no real way to invert the polarity of a non-differential signal passively without a transformer.

I don't see what you're really asking very clearly, but if you're asking if swapping the signal and ground lines will correct for a polarity inversion elsewhere I'd say don't do it. Usually (though not always) you end up with nothing.

Ok so would adding an input trans 600/600 ohm and wiring the input positive to the negative of the circuit and visa versa might work?
Or would a 1 to 1 output tranny work if wired that way? I'm thinking the output would not work because it is passive but I'm not sure.
Thanks again

I'm pretty sure I'm starting to grasp what you want to do, and when I get back from the greenmarket later today I'll post some suggestions for you. I will say this right now: you're mistaken in thinking that the passive EQ inverts the signal polarity. It does not. More details in a few hours... Now I'm off to buy some tomatoes! :grin:

OK, I'm back.

Coldsnow, correct me if I'm wrong, but it sounds like what you want to do is to connect a simple passive Bass-Treble control between a line-level source and a mic preamp. The circuit you want to use was mistakenly referred to as a "Baxandall", which threw the whole matter into confusion because now everybody thinks you're talking about a specific active EQ circuit that reverses signal polarity. But I'm pretty sure this is the circuit you're talking about:


I adjusted the values to give curves more usable for full-range music. The values you usually see in guitar amps give more of an upper-midrange boost which is great for guitar but not so good for program material. Here are the curves:


This passive circuit does not invert the signal polarity, so you don't have to worry about that. It will cause phase shifts at the frequencies of equalization, but all practical equalizers do that.

We have to scale the component values to fit the lower impedances involved with a mic preamp input circuit. The mic preamp will typically work best from a source impedance of 150 to 200 ohms with a mean signal level of -40 to -20dBU. The EQ should work into a load of about 1K and its nominal attenuation is only about 22dB. Also it would be a good idea to isolate the EQ from the reactive elements of the mic preamp input transformer. So we add a pad at the output of the EQ, which adds about 15dB more loss and reflects a load of about 1.2K to the EQ, and about 200 ohms to the mic preamp.


It's very important that the EQ is driven from a low source impedance (as noted on the schematic); otherwise, the curves will become very screwy and the "flat" (midpoint) position will be anything but!

If you want a slightly more sophisticated passive EQ that can be inserted between a line level source and a mic preamp, let me know. I designed one a while ago.

That Passive circuit is Massive, NYD.
Imma stick it in the control amp front end of my fairchild clone.
kinda vary what freq's get limited. I have some gain i can burn off too.
Peace,
lar

This is fun to play with filters....
http://www.duncanamps.com/tsc/index.html


"Tone stack types: Fender modern, Vox, Marshall, James (passive predecessor to Baxandall)..."

:guinness:
Fabio

Larrchild,

I saw your site -very very very nicely done indeed!

(nice avatar too, BTW... I have the same birthday as Pater Sellers did, also as did his colleague Sir Harry Seacombe...)

That 670 clone... oh, I have so many questions... I should probaby contact you via PM...

Keith

I had heard Dr. Strangelove was Elvis' favourite film. He watched it constantly. So do I. =)


Sellers was supposed to play the bomber pilot too. But he broke his leg.
That would have been 3 roles in the film.

Trivia: "When Slim Pickens says "A fellow could have a pretty good time in Vegas" watch his lips..he really says "Dallas" but they dubbed it out after Kennedy got shot.

Ok, I have to breadboard a passive eq now=)

Would've been four, no?

Mandrake the President, Strangelove makes three.

Keith

yes yes. I knew it was 4 and i kept looking at it. Thank you. Doh!

That sounds more real. I believe it. cool.
Why scour the film trivia boards?...hang here.

Passive's goin good, just adjusting for my load and source imp. =)

you HAVE TO see Rod Steiger as Mr. Joyboy in this film

Click to expand...

I'm still recovering from "The Illustrated Man"

Haskell Wexler rules.

When I'm not breathing lead, I am a cinematographer: http://www.imdb.com/name/nm0418377/

We worship him.

[quote author="buttachunk"]Has anyone here seen "The Loved One"[/quote]

Yes, I've seen it. It's great :thumb:

We often quote Strangelove at my job.
"No fighting in the war room!"

We worship him.

Click to expand...

He's up there with, say, Greg Tolland? :grin: