Phono Stage upgrade to complement Dohmann Helix One Mk 2

Holmz, I am no fan of the REL approach, for the reason that if you drive the subwoofer off the main amplifier output, then neither the main amplifier nor the main speaker derives any benefit in terms of reducing the workload inherent to reproducing the lowest bass frequencies.

Well I am not sure what the REL approach is other than reading @Rauls words that it derives the input from line level rather than RCAs or XLRs. So it sounded like the it was similar to a Vandersteen, however the manual is a bit light light on specifics… other than that there are the speaker inputs.
But whether the main amp to speakers are high pass filtered did not pop out.
It was 30 pages and i skimmed it, so maybe I missed it… but it does seem like it is not the same as how the Vandy unit works. That unit HPF the main speakers, and then the sub rebuilds the bass back up to where it should have been without a HPF going to the main speakers.

Moreover, any distortion in the output of the main amplifier is presented to the REL subwoofer amplifier at its input. Unfortunately, I long ago concluded that you cannot obtain all the major benefits of subwoofing unless you’re willing to add a high pass filter on the main amplifier.

Well that is what I posted a while ago, and it was a high pass filter to derive that benefit that you point out.
Then the sub rebuilds the signal back to where it should be at.

One can roll their own capacitor, or use a host of HPF to do that at various price points from a capacitor to a Harrison labs one at $50 to ones at kilo$...

Holmz, was that "humerus" or "humorous"? And why did you find it humorous?

I read too much Homer in my youth, as I had a great 7th and 8th grade literature teacher. And hence the spell checker is Greek to me.

I truly did wonder why you thought Raul’s quote was humorous. Along the way, I could not resist the anatomical pun. However, I do know that autocorrect is a bitch.

My understanding of the classic REL set up is that the signal to the REL subwoofer is derived at the interface between the main amplifier and the main speaker. That full range signal is routed to the input of the REL subwoof amplifier which has a low pass filter before its input. The REL subwoof thus augments the main speaker at very low frequencies. This method does not result in reducing the bass frequency burden on the main amplifier or even the main speaker. Perhaps I’ve got it wrong. I suppose all this belongs on another forum, but drbond seems interested, and he is the originator of this thread. Otherwise, sorry for the digression.

drbond, The classic approach is to drive an electronic crossover from the preamplifier.  The electronic crossover has built in active high and low pass filters, usually with adjustments for cut-off frequencies and a choice of filter slope.  Sometimes an electronic crossover can also add gain to the signal.  Raul and I were talking about using an electronic crossover only for a low pass filter to the subwoofer.  The frequencies above low bass would go direct to the main amplifier, but at the input of the main amplifier, all you need to do is to add a single capacitor in series with the signal.  That capacitor in conjunction with the input impedance of the amplifier will act as a passive high pass filter with a gentle slope of 6db/octave.  For that, you would like to have a preamplifier with two pairs of output jacks, but it's not really mandatory; you can derive a second output between the main amp and the electronic crossover you use to provide the low pass filter to the subwoof.  I like this second option because the high pass signal does not have to go through a second circuit.  Trade-off is something called "insertion loss"; you lose a little gain in a passive filter, usually inconsequential.

Too late to edit my post above, but for completeness I thought I should add that an active electronic crossover is called "active" because it does add gain, to correct for the above mentioned insertion loss of any filter. The steeper the slope of the filter, the more is the insertion loss, and the more gain is added by a typical electronic crossover to compensate.  The two best and most expensive electronic crossovers I know about are the Pass XVR1 and the Bryston.  Pass can do 6, 12, 18, or 24db/octave slopes.  A passive filter, like just adding a capacitor in series with the signal going to the main amplifier to create a high pass filter, is pretty much limited to 6db/octave, also called a "Butterworth" filter. Steeper slopes CAN be executed passively, but insertion loss goes up accordingly.  You want a steep slope on the low pass filter going to the subwoof, because you don't want the subwoof contributing to midrange and treble, where it is likely to add distortion. In most cases, however, you can get by with a 6db/octave slope on the high pass filter, if your main speaker has full range capabilities.  Exactly where to set the crossover points is a matter of experimentation.

Dear @drbond : You already know that in the audio world always exist trade-offs when we want to make some room/system changes, nothing is perfect so don’t try to look for because just does not exist.

You need only a high pass because the low pass is made it by the sub’s. Now you can have that high pass with and active external crossover or you can do it at the input of your amps and for me this is the best high-pass trade-off because you add almost nothing: no added electronics, cables and input/output connectors.

The signal that goes to the amps from the CH goes directly or through the external high-pass filter and from your CH goes too directly to the subs. Btw, usually the high-pass filter setting up is in the 80hz-100 hz and you do not needs that the external/internal high-pass has additional gain because the high-pass gain is handled by the preamp. The gain of the low-pass by the sub's.

That’s it.

R.

@lewm : " I truly did wonder why you thought Raul’s quote was humorous. " . Easy, because he did not think in that way before. Seems to me that is his way of audio life kind of think because he posted twice something with no sense in reference to what I posted about sub’s, he said twice: " you was not the first person to said that " .

But where in hell posted I that " I was the first audiophile to said that " ?

Dear @drbond : lewm posted " You want a steep slope on the low pass filter going to the subwoof, because you don’t want the subwoof contributing to midrange ..."

Normaly subs comes with 12db/18db filter shape and the users always can change the low-pass frequency that at the end the sub internal dsp will tell us and through listening tests we can confirm is rigth or we can play with the sub crossover set-up characteristics till we are satisfied with. The Velodyne low-pass shape by default is 24db ( steep as lew posted. ) but selectable and its high-pass shape is 6db. My old Velodyne low-pass filter shape " initial 12db, 48db ultimate ", is what I read in its manufacturer specs.

In the other side, adding sub’s in any room/system means too that maybe we can need some kind of different room treatment maybe not or we can find out that we need to move a little the main speaker positions.

Subwoofers per se is not a " key on hand " solution to open the " door ", we always need some kind of work for the room/system good integration.

R.