Anyone tried modding active ATCs

Hi, I am considering having a look into ATC20A and possibilities for modding. What I would sonically like to improve is a transparency in upper mid and HF - I found a performance in this region a bit compromised (lack of air, a certain "thickness" of the sound). One option would be to upgrade the tweeter once the new ATC driver is ready. Another - and more likely to make a serious difference - would be to consider recapping and rewiring with something better. And finally - it is possible to do serious modding and interfere with the design solutions - like separating PSUs from power amps and active crossovers, bypassing caps etc as Markus suggested.
However it is impossible to find anything on the net about this, with exception that someone on Audio Asylum was raving about putting Black Gates into his ATC preamp.
I am wondering if anyone has a certain experience with this or at least knows someone who succesfully did it.
Cheers Gordan

 

Hi Gordan - my experience with blackgates has been that kit sounds better without them! I'm in a minority here i think, but not alone - hasve spoken to several audiophiles with the same view.

 

Super-tweeters? The tweeter in the ATCs is quite directional at the top end which may be the cause of lack of air.

I am going to give some to Larkrise soon, maybe he would lend them to you for a play as well? You should be able to connect any stand-alone super-tweeter on to the same power-amp output as the normal tweeter runs from.

 

Can you please explain what "directional" means in this case? I have several complaints about the ATC HF performance but the main ones are a) extension (i.e. early roll off) b) a character of instruments - they definitely lack absolute refinement, they tend to sound too "thick", which might be a consequence of c) lack of air....

For quite some time I've thought this is all down to upstream componenets but after playing with 2-digit number of preamps, several different CDPs and cables this has pretty much remained all the time so I assume this is ATC in-house thing.

Don't get me wrong - my wife (with better ears than me) would now say I'm splitting hairs but I really do love everything else what this speaker does. Midrange and even bass performance (for 20 liter box) is second to none. In case I would manage to sort this thing out I assume I wouldn't really need to change this speaker until it falls apart in 20 years or so.....

Tenson, I've heard about a small group of HK audiophiles who are using ATCs with supertweeters with stunning result. Can you pls just elaborate how would I be able to connect the supertweeters when there are no any additional outputs or whatsoever on my active boxes.

 

sorry i forgot this - tenson thanks for the offer the only problem is that i am based at a completely different part of our planet, so realistically not possible (at least not without having a private jet....

 

I suspect the lack of extension and lack of air are down to the same thing - high directionality at the extreme top end.

I think this is the tweeter, right?

http://www.madisound.com/cgi-bin/index.cgi?cart_id=6075.25902&pid=1325

If you open the PDF file about the tweeter you can see the frequency response on axis and also 30degree (green) and 60degree (red) off-axis.

30degrees off axis at 20KHz the response is down as much as 15dB. This is a lot. While you may get a flat response when listening directly to the tweeter, if you at not directly in front of the speaker you will get a rolled off top end. Not only this but the lack of air is because even if you are in front of the speaker, the reflections from the room will be very rolled off at the top end meaning the over-all power response in-room will be rolled off even when the direct sound is not.

What you need is a tweeter with wide dispersion so that even the reflections are extended right up to 20KHz or so. The super-tweeters like the ones I will send to Larkrise are only about 3-5dB down at 30degreese off-axis at 20KHz. - but this is exceptionally wide dispersion.

If you open the amp in the ATCs you should be able to find the wires that connect to the tweeter. you should I think, be able to hook a passive super-tweeter on to this same line and drive it from the ATCs tweeter amp.

Hope all that makes sense, rushed typing it a bit!

 

I think he means the tweeter have a narrow beam like a torch....

I fitted artist's monster active atc speakers with good xlr cables from his ecs [?] pre ...transformed the performance ...pm him

in original guise they sound much as you described.....after you had to ask was it the same track being played....definately the woolly blanket had been lifted from the speakers. Subsequent tracks sound light airy and musical with bass to die for .

So the issue may lie elsewhere ....I'd also agree with larkrise and find blackgate execrable...

 

tenson, no it's not that tweeter - the one you linked is a very old vifa tweeter that was replaced with the one i have, a roundish one with 3 screws for the dome and 3 screws for mounting the tweeter into a baffle, looking very similar to
http://www.madisound.com/cgi-bin/index.cgi?cart_id=6075.25902&pid=1331
except it has 3 mounting screws instead of 4...

 

Could you get a picture of the tweeter or maybe even take it out and see what serial number it has?

 

Thanks Fox. Interesting about the different face-plate having that small waveguide in it. This will give a narrower dispersion at the high frequencies. The stock Vifa is not at all bad for off-axis dispersion but with that waveguide it will be considerably narrower. Probably about the same as the little tweeter I linked to earlier. I would say the same still seems likely - that the tight dispersion in the top octave is not something you like that much since it generally stops a speaker sounding very 'airy'.

On the other hand it might just not be a very good tweeter.

If you just want to experiment to find out what you don’t like about the ATC tweeter, the Vifa XT25TG30 is an incredibly good tweeter that looks as though it would work suitably as a drop in replacement (assuming 4th order crossover?). It is still quite directive in the highs though, so if you find this tweeter a good improvement it may not be the directivity that you find an issue. If you don’t find it a huge amount better then you know it is probably the directivity, since everything else about this tweeter is superb. It is cheap enough to try it and see, as they are around £40 each (a bargain given the performance).

http://www.tymphany.com/datasheet/printview.php?id=112

 

Surely every tweeter with real-world dimensions is, though: unavoidable physics.

 

Well really I was suggesting it to anubisgrau.

Felix, there is quite a large difference between many tweeters in the off axis dispersion at the top extreme. The XT25, D26NC55 and by the sounds of it the vifa with the ATC face-plate all have pretty tight dispersion. The XT25 I think is mainly due to the dual concentric rings that produce destructive interference off axis. Most of these are around 10-15dB off axis.

There are many other tweeters that are more like only 6-10dB off axis. Especially if you look at 3/4" domes instead of 1", which is perfectly doable with a 4th order electrical slope at 2.8KHz. Something like the Seas 22TAFG (as I also suggested for Robs H2s) may be a good option, though it is 1dB more sensitive and the Vifa in the ATC and smaller so would need a bit of work to make it fit the gap.

 

Yes, but my point was - at a given frequency, the dispersion depends to first-order approximation n the diameter of the dome, that's all there is to it. For a specific tweeter you have to look at (or ask for) a plot, but don't expect major surprises. And of course real power handlng goes with the inverse of diameter, more or less.

 

There are more factors at work than just the pure diameter of the dome - I suppose this sets the widest dispersion limit though. For example, the shape of the dome (or even inverted dome!), the face plate around it, the dome surround and any phase plugs / modification. At such small wavelengths as 10-20KHz these small things can all have an effect, especially when combined. As such you can find considerable differences in top end dispersion and response between different 1" domes. Compare, just as an example picked from some PDFs I have on hand, the ScanSpeak AirCirca vs the Vifa D26NC55. Then also consider the Focal TC90K as the H2s have, and although it rolls off early, the off axis response very closely matches the on axis response. Though it is still a '1" dome".

 

Rather then mess with the Atc's use a pair of super tweeters

 

That definitely makes sense so why not do that anubisgrau?

 

to be frank if i would need to stay with a dome tweeter, i would rather wait for a while until ATC releases their long time anounced in-house tweeter for active series. i would feel a bit silly changing the whole baffle to install SEAS and than to be tempted to do that once again.

actually - this goes to technically competent - after recently hearing probably the best tweeter one can buy for relatively sane money - RAAL short ribbon - and if i would need to replace the whole baffle, than i would much rather consider an extreme solution to address the HF transparency issue of ATC: dropping RAAL tweeter.

http://www.raalribbon.com/products_flatfoil_70-10.htm

apart from physical work (cutting a completely new baffle) - what kind of adjustments with active crossover should be done to make this possible and functional (and feasable after all).

comments please

 

just to add: ATC 20A are crossed over at 2.8 khz

RAAL recommends when used passive 4th order L-R at 2.8 khz

what kind of issues are to be expected?

 

That is a nice tweeter, I have a pair sitting on my floor as we speak. Besides the rising high frequency response, which Aleks says is on purpose as he feels it sounds best, there should be no real problems as far as I can tell. You would need an L-pad resistor network to drop the sensitivity in line with what the ATCs expect, though. You could also adjust the HF rise by playing with one of the resistor values. I would also trim the bottom of the face-plate off to get it as close to the mid/woofer as possible.

I would make a new baffle out of MDF to try the Raal first, rather than cutting up the ATC one. If it works well then you can do as you like, if not at least you can go back and sell the Raal.

 

thanks, great and fast response.

well a good thing is that the RAAL is one of the few great audio products from my country (apart from karan, korato and NAT, to start with) so i think i can find a pair to borrow and play a bit with them.

also not sure i would stick with the original ATC baffle - in case i ever need to sell the ATCs i guess it would wiser to keep the original tweeters and a baffle untouched and reassemble them. who would really but used ATC 20 A pro with RAAL ribbon tweeters - sounds like a real experiment.

ATC 20 pro baffle doesn't look like the easiest to make but than it's not a rocket science.