Phono Stage upgrade to complement Dohmann Helix One Mk 2

Drbond, the filters built into most subwoofer electronics are active and analog. Unless explicitly stated, the filters in an outboard electronic crossover are analog.The only passive filter mentioned so far is the idea of using a capacitor in series with the main amplifier input to effect a simple 6db high pass filter. Everything else is active . If you want digital filtering I know nothing about what’s available, and I personally wouldn’t go in that direction.

@lewm 

Thanks for the clarification.  My favorite pieces involve the cello or cello and piano.  (Yes, Bach, but also Beethoven and Brahms.)  Consequently, I was thinking that the crossover should be below the lowest cello note, which is 44 Hz, as I wouldn't want the cello to sound like it's jumping around. 

 

Hmmm…this subwoofer project is looking complicated:

often it does…
Many do it digitally, and that is a lot easier some ways.
However if the main analogue chain is nice, then we can complicate it with an analogue approach, which is in fact a bit simpler.
(But there are many ways to skin a cat)

it seems like an ideal approach would be an in line high pass filter after my pre-amplifier, but this would have to be an analog filter, correct?

That is one way, and usually it is the one that has the minimum detriment to the signal chain. And even with this HPF, one can use some DSP on the sub to flatten the response a bit.

(I can see myself reacting to a cello that sounds like it’s in one place for the higher notes, and another for the lower strings/notes…)

A cello sounds like it is in the same place as the higher notes of the instruments harmonics locate the cello, and low notes reinforce the fundamental tone.

When it is done right then it is not apparent that the sub is even on.
But if one turns the sub off, then it is apparent.

And it often sounds best when it is turned up to the point that it is apparent and backed off to the point where it almost seems like it is not contributing.

Set up well it is like PFM (Pure Magic).

…or replace my pre-amplifier, which I really enjoy listening to, with a digital pre amplifier that has filters built into it…which I am averse to do…

It is ^here^ where the in-line HPF is an elegant solution.
It sound great now, you just a bit more of low notes, and remove having to force the main speakers from trying too hard to play those low notes.

With the HPF, one just tapers off a major portion of the power to the main speakers, as the lion’s share of power is used for pushing air in the low notes. And then the sub takes that over and tapers off the power as the notes enter back into the main speakers in a smooth fashion.

And then all the IMD and Doppler distortion of the panels having to wave back-n-forth as the high note are also coming off of it… becomes reduced as most of that waving gets shed to the sub.

Doing this at a knee of 100Hz is not uncommon with a 1st order slope.
Some people go high with higher slopes.
And if the sub resonates or has harmonic, or noises, that locate it in the room, they they might cross it over lower.

If one fancies the idea biasing the dielectics, then the HPF get some extra stuff in it, but it behaves like a single capacitor.

drbond, This thread can go on and on with different ones of us giving you different advice. To avoid further confusion, I suggest you read up on the options by searching on line.  Terms you need to understand are "active crossover", "passive crossover", and something about how slope of the high and low pass filters comes into play. I don't agree with Holmz in some cases, but for me to debate Holmz here would only confuse you further. Suffice to say, as I said before, a properly integrated subwoofer will not give you the sensation that the cello is jumping from main speaker to subwoofer and back again.  On that score, Holmz and I agree. On the other hand, I am not a fan of digital filtering or digital shaping of the response.

@rsf507 talking about $60,000 Phono stages is not that relevant to most people either. 

@rauliruegas , since I design and build my own subwoofers and analyze the results I know a lot more about it than most audiophiles. Putting a 1st order high pass filter on the amplifier input is a last resort. 4th order is more like it. You are much better off with a digital 4th order high pass filter than an analog one.