Phono Stage upgrade to complement Dohmann Helix One Mk 2

Velodyne DD+, 15 or 18 inches.

ML probably make a good woofer too.

If you are going to draw conclusions by reading websites, you’re likely to do nothing. It is impossible to conceive that a high pass filter would have zero (measurable) effect on the upper frequencies, mostly in terms of phase shift, not distortion so much, unless you use a bad electronic crossover. The question is can you hear it and if you hear it do you like it? The reason for using 6db/octave (passive with just a capacitor or active using an electronic crossover) is to do as little damage as possible to frequencies above the crossover point, in terms of phase shift. If you have questions about the ML subwoofers, it would be best to either look for a good review on line or to call ML and ask. I don’t know how I got into the role of a person urging you to try a subwoofer. In the Velodyne website and elsewhere at sites selling Velodyne, there are usually good photos of the back of the subwoof showing connectivity. I looked at a few last night. For me it was easy to see there are inputs for the preamplifier output, outputs for high frequencies to go to a main amplifier, and of course the low frequencies go to the built in amplifier that drives the woofer. There are many other choices of connectivity also offered; one would not be using every single input and output in any single installation. If you buy a Velodyne, there will be a book explaining in great detail how to install and use. Never fear that.  Better yet, in your case I recommend you get a local dealer to do the install and explain it to you along the way.

@lewm

because of the quality components of the pre- and amp, I am leaning towards an capacitor HPF, as opposed to running it through the sub, which just has a standard 6db per octave HPF, which would just be a standard, probably low-grade capacitor, correct?  A silver Duelund CAST capacitor in line with the two components, and then a separate line to the subs: it seems that Martin Logan subs might fit in the system better, since they also make ESL, and are more designed for a two channel system.  It seems that the Velodyne is for multi-channel home theatre use.

@drbond , you will hate any analog high pass filter. To operate a subwoofer correctly all filters have to be digital. The highest quality units now use 64 bit floating point processors and have none of the issues older units had like the volume control problem. Conversions in and out of 24/192 are invisible. 

@lewm correct. IMHO the Velodyns are mid Fi. The Balanced Force MLs are superior in every way The Magicos Q series, also balanced force, are the best on the market because of their extremely stiff, heavy enclosures. Because the electronics in all subwoofers are sort of second rate I prefer passive ones. You can only get these in kit form or build them yourself. Otherwise you can just bypass the electronics. This is mandatory for the filter section. Some class D amps are tolerable for subwoofer duty but the best bass I have heard comes from A, AB amplifiers with vanishingly low output impedances. The JC 1 is a killer subwoofer amp. These produce way too much heat to put in an enclosure. Only Class D amps are efficient enough for that.

@mijostyn

Understanding that digital LPF is better for sub woofers, can a high grade analog capacitor (e.g. silver Duelund CAST) be used for the HPF to the ESL with good results?  What’s the main disadvantage to using an analog HPF via an in line capacitor and a digital LPF to a subwoofer?

What are the higher end passive sub woofers on the market? (I do have an extra couple of amplifiers (class A and AB) sitting around).

I only chose Velodyne as an example of a good company that’s been making and selling subwoofers for at least 30 years. I am aware that for very big bucks Magico and others also make subwoofers. I’ve never heard them and the question was how to incorporate a subwoofer with minimum effort not what’s the best subwoofer. I don’t live in your world of absolute certainty and perfection but you’re entitled to your opinion. However it would be nice if you acknowledged that you’re stating an opinion or in this case a set of various opinions.