Passive crossover

After much serching I found the details of the passive crossover I used with my 511b, 2x416a IB setup I built many years ago. The design comes from Audio Magazine, November 1969 issue. Using iron core mil spec inductors and a few resistors & capacitors it was fairly inexpensive when built. I had the added bonus of an employee discount from the distributor I worked for at that time.

I have scanned the article in high resolution B&W, but the file size for each page, one of the cover and three of the text are still in the 2.5mb each, range.

Should anyone want to go to their local library & try and find it for their own education, I'd encourage it. Otherwise, if you're an electronics whiz, you might just find it entertaining. My own library

Dialup internet service makes it a lengthly process to send here, although I could try, but it would require 4 full screens to display. I would not object to sending out a few copies my snail mail.

I looked at a nov 69 Audio issue and came up empty.

?? Don

I've been fighting with computer problems for some time trying to put some key features of that article here with poor results, mostly giving up. And it looks like tonight isn't any different. PM me with an email address. I'll send it to you. I assure you, that issue is correct. Article begins on pg 52. " Passive crossover for bi amplifier systems."

Trying to post a link to archive.org read it online

Lots of nice stuff there BTW

https://archive.org/stream/am-1969-1...e/n53/mode/2up

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Originally Posted by Old Guy

Trying to post a link to archive.org read it online

Lots of nice stuff there BTW

https://archive.org/stream/am-1969-1...e/n53/mode/2up

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Wonderful resource!

Thank you!

At the repair shop....

Needed to send this other jpg in another panel. Moderator may combine if he chooses.

Very cool stuff gentlemen!!! Thanks for sharing!!!

A not of caution with passive low level crossovers. They do need to "see" close to the correct output load. With the input of most solid state gear being very hi-z, it's often good to connect a 610 Ohm resistor across the output of the filter. 610 ohm and the 50k of the solid state amp works out to around 600, close enough for rock and Roll anyway.

I think you're saying that in the circut I posted,which has 600 ohm resistors, that's close enough.

Was addressing filters in general. Altec made passive line level units, as did others, mostly a caution for folks using any of them.

BTW 600 isn't a standard value, 610 used to be. 620 is readily available.

Better to be slightly on the high side than low side.

might find some things in here -


AmericanRadioHistory.Com - Documenting the History of Radio TV and FM broadcasting

I only read the article once, but I like the idea of a passive line level crossover and it looks simple enough that even I, a novice in electronics should be able to solder up. Is there enough info in the article to design a 1000hz crossover? I can't do the math, but my son is a physicist, so I assume he can. :)

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Originally Posted by VolvoHeretic

I only read the article once, but I like the idea of a passive line level crossover and it looks simple enough that even I, a novice in electronics should be able to solder up. Is there enough info in the article to design a 1000hz crossover? I can't do the math, but my son is a physicist, so I assume he can. :)

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Unless you're going to do it right with an output transformer or an active buffer / make-up gain section, you may as well go with a normal active two-way crossover a la Rane AC22 which is trivially inexpensive second hand and less expensive than a single high-quality transformer.

It's worth noting that input impedance specifications particularly on solid-state electronics are nominal and assume a very low impedance and non-reactive output feeding said input. Unless you've got the schematics on-hand or are willing to measure, you won't have much clue on reactance at the input (coupling capacitors, for instance) and its attendent effect on your crossover point.

BobR

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Originally Posted by Old Guy

Was addressing filters in general. Altec made passive line level units, as did others, mostly a caution for folks using any of them.

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Good advice.

It was trivial to use passive units in spite of their inaccuracy and generally bad phase characteristics when inputs and outputs and the entire world were 600 ohm transformer-coupled; they definitely won't perform as advertised otherwise.

BobR

As Bob said, actives are cheap, but for some, DIY is the way to go..for instance Rod Elliot has a bunch of stuff on his site...

Linkwitz-Riley Electronic Crossover

I should have figured that that article was just to good sounding to be true. My buddy, the "Electrical Engineer Genius" said he could build me a passive line level crossover for $8 with just a capacitor and resistor over a year ago, and that an active crossover was a waste of money, but I am still waiting. :)

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Originally Posted by VolvoHeretic

I should have figured that that article was just to good sounding to be true. My buddy, the "Electrical Engineer Genius" said he could build me a passive line level crossover for $8 with just a capacitor and resistor over a year ago, and that an active crossover was a waste of money, but I am still waiting. :)

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They're called FMODS.

FMODS

Comparing them to an active crossover would be like comparing a bicycle to a fine Italian sports car.

While your genius friend may have a great understanding of electricity in general, he apparently has little understanding of the complexity of an audio signal, or the reactivity of audio components. The folks that make the FMODS simply ignore a lot that might otherwise undermine their marketing.

So,to ask the next question, has anyone used simulation software to check the veracity of the circuit I posted? You gotta remember when it was designed ,using relatively standard methods. I don't think it could get much simpler. I did look at the L-R blurb on Elliots web pages, and it seems his thoughts are well respected. Is one really going to hear, say a 3 db differenced at the crossover point knowing full well that most speakers can't spec their entire range inside of 3 db?

This was simple, had few parts, had to deal with only small voltages instead of lots of power, and I don't think there is any preamp out there worth its salt that can't handle a 3 db insertion loss. ???

Think this thru some more...as has been said that circuit will be affected by what it's hooked to...how can you sim it?

Answer is you can not. You could sim for ONE combination, which would be useless for others.

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Originally Posted by gvasale

So,to ask the next question, has anyone used simulation software to check the veracity of the circuit I posted? You gotta remember when it was designed ,using relatively standard methods. I don't think it could get much simpler.

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No one has performed any calculation because there is no point.

I mentioned that passive networks like this were designed in the era of 600 ohm termination which optimally used transformers for impedance matching (max power transfer), isolation and - most importantly in this instance of tuning a L-C circuit - ensuring that the target bandpass / bandstop frequencies are met.

This circuit uses resistive termination without buffering (isolation) which is NEVER recommended and will NEVER meet target -3 dB points in real circuits. In other words, it won't work.

Thankfully we live in a world where solid-state electronics offer low output / incredibly high input impedances and we have finally moved away from power (0 dBm = 1 mW into 600 ohms) to simple, scalar voltage (0 dBu = 0.775 V) reference for equipment interface. And we have finally dispensed with obscenely expensive phase-altering transformers!

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I did look at the L-R blurb on Elliots web pages, and it seems his thoughts are well respected.

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His thoughts are well respected because they are based on solid audio engineering principle.

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Is one really going to hear, say a 3 db differenced at the crossover point knowing full well that most speakers can't spec their entire range inside of 3 db?

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Depends on where (frequency) and over how broad a range (bandwidth) this 3 dB difference is -- please study the psychoacoustic concept of Equal Loudness (Fletcher-Munson / Equal Loudness Curves).

But in general, yes, a 3 dB difference - particularly in the midband where most crossovers are designed to operate - is audible.

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This was simple, had few parts, had to deal with only small voltages instead of lots of power, and I don't think there is any preamp out there worth its salt that can't handle a 3 db insertion loss. ???

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Yes it is simple because there are critical features missing. Without an exact load or buffering/transformer isolation from outside reactances, this design will not work as intended.

And never mind the insertion loss; it is the poor transfer function (frequency and phase response alteration) that is objectionable.

BobR

[QUOTE=Old Guy;1949811]As Bob said, actives are cheap, but for some, DIY is the way to go..for instance Rod Elliot has a bunch of stuff on his site...

Great recommendation.

Rod Elliot performs an amazing public service through his website Elliott Sound Products - The Audio Pages (Main Index)

Like Siegfried Linkwitz, Elliot accompanies his designs with detailed analysis in simple neophyte language; they have immense pedagogic value not only to students but to all audio enthusiasts of any level.

I'm not ashamed to state that I've purchased and used quite a few of his printed circuit boards as they are extremely convenient; most importantly, his designs are absolutely solid.

BobR

https://www.youtube.com/watch?v=mjfOTRBqpJw