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Old 14th October 2010, 06:06 PM   #1
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Default ATC active crossovers / amps info

Hi. I'm a (small) studio owner and enthusiast working on a lot of audio related DIY projects. I'd like to get my feet wet with three way active speakers (i.e. active crossover and separate amplifiers) built on ATC drivers. Something like a wilmslow system, but activated.

What I'd like to ask is if anyone knows how the active crossovers are done in, say, activated SCM100/SCM150 and what kind of amps are specified for that kind of design.

I didn't find any public info shared here nor did anyone at ATC respond to my pleas..

The project is some months away, but I really like to read up on projects before starting them. In any case, if you have some info and are willing to share, please do

Cheers,
B.
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Old 25th October 2010, 03:33 PM   #2
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Hi baadc0de

I am currently doing a similar project using ATC drivers. Though i don't have any specific information to offer about how ATC do things in their commercial designs, i can tell you my thoughts and conclusions so far.

I originally intended to built an active SCM-50A clone type speaker but using a ribbon for the tweeter. Having got hold of some 12" studio bass units, i started thinking instead to do a SCM-100A clone, and am now actually thinking of a four way. As yet no speaker is actually built, i just have all the parts. (mid range is the ATC "super").

I don't know how much experience you have building speakers. Myself, it's my first go. For crossovers, i didn't see much point going analogue active as ATC do. Digital crossovers are very flexible for DIY and quite cheap. I bought a Behringer DCX2496 which can do 3-way. I have one with the Jan Didden volume control. But since i started thinking 4-way, i actually preferred the Minidsp solution and have recently bought two of those, and the minidigi input boards. This kit will give you lots of flexibility to tailor the crossovers and get the sound you want. Coupled with room measurement software and a calibrated mic, you should be able to get good results - i say 'should' - i haven't done it yet. In the ATC designs, i believe there is some equalisation employed to allow the mid-dome to be used as low as they do, something like 380Hz. With a digital crossover you can experiment with all that. You could go sealed and use a linkwitz transform now available on minidsp.

For power amps, i built a number of them from a design in a book. But it takes a lot of time. There are many good modules out there from various manufacturers, its a no brainer to buy those if time is a constraint. Connexelectronic worth considering. Depending on budget, Hypex modules another option. I think these are going to compete very well with anything ATC puts in (which i think are class A/B). Perhaps a bridged stereo amp for the bass and another stereo amp for mid and treble. Digital amps typically need less heatsinking.

In terms of cabinets, i think wilmslow will allow you to buy just the CAD drawings. Speaking with them a while ago, they said the stated 'liter' volume on their website includes a compartment for housing the crossovers. So in reality, less volume is needed.

As i said, i don't know your experience with speaker building, perhaps all this is already well known to you.

Good luck with your project, please post some pictures if you have some success.

Also, have you seen this project with ATC drivers?:

project 10
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Old 25th October 2010, 04:07 PM   #3
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ATC amps are class a/b jobs but run in class a until 2/3 of rated output.
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Old 25th October 2010, 06:54 PM   #4
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Thanks for the responses guys.

No, this is my first DIY speaker project.. it's to be built as a stereo reference pair to have in a control room of a project studio, so I'd like to get close to the baseline spec of an active ATC system and then tweak from this 'known good' configuration..

That said, a behringer digital xover could to the trick, I might do that actually. It's available off the shelf, is configurable and once I'm happy with the settings I can just make myself an analogue counterpart. DIYing a few class A huge power amplifiers shouldn't be too much of a problem either (I like the challenge and have built tons of studio gear, even guitar tube amplifiers).

ATC "super" - that's not the one included (or available) from the wilmslow site, right?

Cheers!
B
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Old 25th October 2010, 10:25 PM   #5
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How much of a time delay does the Behringer digital crossover produce?
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Old 25th October 2010, 11:58 PM   #6
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Baadc0de, just build it up with the DCX either leaving it there or doing the analogue clone later as you said. If ATC have specific filters or EQ designed into their electronics you won't ever know unless you measure their implementation and copy it.

Just build what you want, measure them and tweak to taste.

I heard an active set of ATC about 10 years ago, don't recall the model # now, but 15" 3 way based and I thought they were excellent, but too much for my wallet. This was in one of the now defunct audio stores here and I thought they were better than many of the much more expensive systems on offer there.

I will enjoy watching a build thread for these.

Quote:
Originally Posted by David Gatti View Post
How much of a time delay does the Behringer digital crossover produce?
Latency analogue in-out is specified at <1ms but it can set >500ms from memory.
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Old 26th October 2010, 12:44 AM   #7
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Quote:
Originally Posted by Brett View Post
Baadc0de, just build it up with the DCX either leaving it there or doing the analogue clone later as you said. If ATC have specific filters or EQ designed into their electronics you won't ever know unless you measure their implementation and copy it.(...)
Could be similar to the/a passive xover. But probably is not, because there's not the same issues with phase as you have in passives vs. amps. Only the phase from the point source/driver to driver and not from passive xover components.
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Last edited by Inductor; 26th October 2010 at 12:48 AM. Reason: ATC Amp
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Old 26th October 2010, 02:26 AM   #8
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Wow, state the obvious.
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Old 26th October 2010, 09:36 AM   #9
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Unfortunately Wilmslow don't sell the "super" mid range dome (SM75-150S). I wonder though how much difference there really is between the "normal" version they sell and the super. And the super is a lot more money too. If you do want the super, you might be able to get it direct from ATC. I'm not sure what they're policy is, i know they restrict distribution of their Super Linear Bass drivers but not sure about the mid range. (they quoted me around £470 inc VAT per unit if i remember correctly).

There are some SM75-150 currently on ebay UK:

ATC SM75-150 midrange Mitteltöner pair speaker on eBay (end time 26-Oct-10 16:07:17 BST)


Just remember if you go the DCX route, and want to use its digital input, you'll need some sort of ganged volume control for it (e.g. Jan Didden design). Otherwise, you can just use the analogue ins with a stereo pre-amp before the DCX.

The DCX has numerous filter curves. If you were to prototype using the LR24 curves then it should be quite straight forward to transfer it over to the Elliot Sounds LRX424 analogue active crossover PCBs at a later stage:

Project 125
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Old 26th October 2010, 11:51 AM   #10
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Browsing on the 'net it seems that ATC restrict usage of their 'SL' series drivers to their own speakers and 'S' are hard to get (and as mrwireless pointed out, they're not cheap at all). I'd still like to get as close to the SL using line as possible for starters and then tweak from there, so if anyone has a suggestion, don't hesitate to voice it.

The idea of prototyping on a DCX and then transferring that to lrx424 is exactly what I had in mind. How fortunate that there's a compatible PCB project ready made.

Thank's a lot for the suggestions made thus far
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