[Mountain-ear]

Dennis -

I'm not sure how to contact you directly, and it looks like you monitor this board regularly, so here goes...  Have you ever considered designing an external passive crossover similar to the Dahlquist DQ-MX1?  Mine must be 30 years old, and I can tell from my LCR meter that the caps are failing.  Before I start looking at repairs, I thought I would see if you had ever done any work on external, high-level crossovers.

Probably a long shot, but I'd welcome comments from others as well.

Thanks.

Steve

[DMurphy]

Boing.  Here I am.  I'm not quite sure where this crossover is in the chain of components.  An external crossover would not necessarily be any different than an internal one. How exactly is it configured?    In any event, if the values are on the caps, it wouldn't be difficult to replace them, which is certainly the safest thing to do.   

[Mountain-ear]

The crossover sits between the DQ-10 speakers and the DQ-1W subwoofer.  Basically, the amp is connected to the external crossover, and the crossover does it's thing.  It sums the left and right channel signals into one for the subwoofer output.  The left and right channel cut-offs are variable (a three position switch, I believe).  The output of the subwoofer can be phase-adjusted (with a toggle switch - 0 and 180), and the subwoofer output level can be adjusted (L/M/H).  Nothing infinitely variable here.

The guts of the crossover are more or less what you would expect - caps for the cut-off frequencies and resistors for the volume control.  Then there are two items that look to me more like transformers than the inductors I see in conventional cross-over designs.  The caps are all high value, non-polarized generic models (80, 160, and 400 uF).

Sorry I can't provide more detail.  That's about the extent of my technical knowledge.  I guess I was just wondering if you had ever taken a look at one of these rascals to see if the design could be improved.  I a big fan of Jon Dalhquist, but it's been 30 years since he designed this thing.  I'm guessing that the conventional wisdom about cross-overs might have evolved since then.

Whatever comes of this inquiry will likely be temporary.  I'm planning to have a set of HT-3's by this time next year.  Can I interest you or Jim in a trade-in?

[DMurphy]

Thanks for the details.  I'm afraid the DQ-10 is the one piece of audio history that I've never laid my hands on.  In any event, a passive cross to a sub just isn't a very good idea.  I would preserve the historical value of the combo by replacing the electro caps with some inexpensive poly's--Danny Richie has some high value axons that could be paralleled to create the right values--or just get some Bennic electrolytics from Madisound.  And even if I thought I had a stab at improving Jon's design, I would have to have one of the 10's and the sub here in my shop, and that doesn't sound very practical.  Just for grins, where are you located?

[Mountain-ear]

Just outside of Pittsburgh...  If you're ever in the area, drop me a line.  You can hear a re-built set of classic speakers.

Cheers.

Steve

[DMurphy]

Well, I'm not that far away--Washington, D.C.  And I've spent a lot of time in Pittsburgh, although that was back when you could barely see the sun set because of the United States Steel plant emissions.  I hear they've cleaned up the place.