Active analogue crossover full balanced

Hi, I'm back here again looking for help. I have a version of the loudspeakers from Troels Gravesen: the ATS . In them I eliminated the crossover of the wofers to use a Hypex Fusion 501. The cutoff frequency and order is the same as in the passive version. I use a Mcintosh c1100 preamp and an MC452 power amplifier. Now I am interested in incorporating an active crossover to make the 452 only amplify from 200hz (mids and tweeter) since the Hypex is in charge of 200hz and below. In particular I'm looking for a fully balanced active analogue crossover since the pre and power amp are full balanced. I'm not interested in digital crossover. I would like to know quality alternatives that do not deteriorate the signal between the pre and the power amplifier. If there is a thread dealing with this topic, please let me know. Thanks.


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I built the Nelson Pass designed LX-mini/6-12 active crossover. I built two pcb's for a Balanced version, I changed the upper J113 JFET's and used 2SK170bl with an Idss of 8 mA or more to reduce noise. There is a very nice and easy app to calculate the the resistors and capacitor values for the crossover in the 6-24 crossover article.
The 6-24 can be built the same as the 6-12 version, the 6-24 allows for far more adjustment of the center point and slope.
Both kits are available from the diystore.
I’m no expert, but I suspect a fully balanced setup will quite happily show a really bad CMRR, unless you take extensive care getting the symmetry top notch (0,1% tolerance components, optimal print layout and the like….).

Probably wiser to build a differential input, process unbalanced and end with a balanced output. That could be accomplished with standard PCB layouts from Rod Elliot or alike.
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Hello, thank you very much for the answers and apologise for my late reply.

I am not a specialised diyer although I have the possibility of commissioning a project from people who do have experience. Within the commercial models I am especially struck by this active crossover for its good reviews and reasonable price but I am not sure if it is full balanced or not, and I do not know ratings from real users either.

Another trademark is this, but I haven't found real ratings either.

I have also found this kit quite economical and simple.

Elwood, the Nelson Pass filter seems very popular. I am not qualified for such a project. I would need outside help.

Mark, I propose a full balanced filter from the logic of respecting the design of the pre and the power amp.

Alex, thank you for sharing your project. A very interesting story but that level of project is totally beyond my means


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the Nelson Pass filter seems very popular. I am not qualified for such a project. I would need outside help.

You need to buy something built?

Any 2 mono XOs, like the Pass LX-mini or 6-24, can be wired identically and one used to filter each phase to get a balanced XO. I imagine one board above the other facing each other.

Off the shelf analog will not be as versatile, be hard to find, and lots of bucks.

Marchand might be able to build what you need, but IME, their Op-amp based filters are not as transparent as the Pass FET XOs.

If you are lucky, you can find a competant DIYer who can help out. The sirst 2 repeat Tony.
Never heard of these guys, but kinda pretty:


You might be able to find a used one, or we could talk Pass into the next generation?


Not sure if they still sell this one:


You’d have to find one used, they have gone digital.


You may think you improve performance, but with these textbook active crossovers you are basically ruining the performance of the original very expensive TG design.
Why? Because the original x/o design takes drivers' SPL irregularaties into consideration in order to produce acoustically correct filter slopes. Your active textbook analogue filter does not do that: the slopes are only electrically correct. In combination with real loudspeakers the results rank from so-so/slightly incorrect to complete disaster.
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I don't believe in telling folks what to want ....what not to's not our business to do so, imho
I Just hate to see folks going down expensive paths that probably won't pan out to be up to their expectations...

The all-analog crossover or equalizer route is a costly path for sure...I know, as i still have some of that gear.
And it still works great, and sounds great !!

But that gear has proven to be no better than my digital stuff, that costs so much less, and offers greater precession, and more types and orders of crossovers, ......same advantages for EQs .

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Hello, thanks again for the contributions.
Hello,Boden, the ATS have already been modified in relation to the original design. I have changed the tweeter (it is interesting to see how TG used several before deciding on scanspeak for reasons of “personal taste”), and I have replaced the woofer filter with a Hypex Fusion 501 module, by the way, under the supervision of TG. I understand that I can keep the passive filter (mids and high) cutting at the 200hz established in the design because my fundamental intention is to ensure that the power amplifier only works from 200hz to operate in a more relaxed and solvent way.

Mark, a digital filter for medium and high frequencies was completely ruled out. I use several analog sources and a tube preamp. It doesn't make sense to me to do an AD and DA conversion in my setup. I can control the more complicated frequencies through Hypex DSP.

planet10, thanks for the links, I've been looking for second-hand filters and there isn't much. It seems that the Nelson Pass filter is the most popular around here. I think it's the safest option if I want to go the DIY route.


I added analog equalization to my modular analog preamp. It equalizes the speakers and has 36 dB/octave (sixth order) 20 Hz high pass filter a la Rod Elliot. I used the best parts available (resistors and capacitors), I buy everything in lots of at least ten so I get a discount, used 4562 op amps, and just the parts to populate two small boards was about $60. That was a few years ago so it's more now. I made my own boards (didn't buy ESP's boards but I might next time).

You can't switch it out of the circuit without opening up the unit. After two years of listening to it I would say that it adds nothing except what it's supposed to. It reduces distortion big time and greatly increases max SPL. If it was fatiguing I would have pulled it out by now.

Analog solutions are expensive, and not as versatile as digital solutions. I think an analog circuit can be as precise as a digital circuit but it'll cost you. For my application it's worth it because I still have bragging rights that my whole signal path is analog. I can't imagine a digital circuit performing this transparently, but I could be wrong.
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could you share any more details about your setup please ? I have the option to use digital but also like the idea of a well designed analogue active crossover I have a bss unit which you can swap out the card for different frequencies a cheap dbx unit and have been really interested in the xkitz crossovers
Not a crossover but a fairly standard analog preamp with bass and treble controls, conventional tape monitor, and digital controls including a mute circuit on the output that makes sure there's never any pops or clicks.

High filter is Rod Eliot's infrasonic filter works great. Bass/treble are Walt Jung's precision tone controls; I've been building them since the 1970s.

You could build a whole active crossover etc from Eliot's website . I'be built a few of his circuits and they're well thought out. It's worth your while to browse his projects if you're into DIY electronics.
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Mark, I propose a full balanced filter from the logic of respecting the design of the pre and the power amp.
Hope you find exactly what you want! Like i said, don't mean to tell anyone what to want.

I added analog equalization to my modular analog preamp.

I did too, when i was still into classic all-analog, and took my first step away from shunning EQ's, etc.

Manley's Massive Passive...still a great piece of gear for me...
Mark, I propose a full balanced filter from the logic of respecting the design of the pre and the power amp.
I suggest you do some reading about the why and why not of balanced signal transport and processing. It basically boils down to this: balanced drive is advantageous for microphones and in cases gear is spaced far apart, as in more than 10m. There is no advantage in building balanced signal processing. It’s expensive and needlessly complicated. And a well-designed balanced driver or input should process any unbalanced signal perfectly.
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Even as I do not agree on your "analog only" idea, as rebuilding the passive filter in active analog is a huge problem, close to impossible DIYS, I want to warn you about one trap:
Most analog, balanced x-over convert the balanced signal into a single ended, process it (analog) and then convert it to balanced again. That is standard procedure.
So your idea will send the signal through a large handfull of OP-amps, in most cases something very "low end". If you find an NE5533 inside an active x-over, this will be a very, very good part. So your valueable, Macintosh processed signal will pass through a 50 Cent part multiple times and maybe some balanced/single and back special IC.
Informed people may argue, that your analog signal has been sent through about 200 OP-amps of much lower quality than the 5533 anyhow, before being pressed on vinyl or any other medium. Just think about it.

As an alternative, just try out some DSP'ed X-over, even if you don't plan to keep it. Just to compare how a simply "high passed" and "high pass plus frequency correction" (just as the analog TG x-over does), sound.
Of course, if you do not measure the response, things get extremely subjective and variable anyway.
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small correction: its usually the NE5534A or NE5532 (8pin), not NE5533 (14pin, a dual 5534 complete with compensation and balance inputs, but noone really uses them and they are becoming unobtainium).

Recordings might have had the signal through a few dozen opamps, not 200, if you think about it... Yes a whole mixing desk might have 200 opamps, but each channel is much less, and signals go through one channel and a master mixdown, and possibly an external effects box.
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