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In Reply to: RE: First Watt B4 arrives today - setup questions for Tymp I-Ds posted by Davey on April 22, 2017 at 06:40:16
Thanks for all the info guys! If a 1st-order high-pass filter is all one requires for the main speakers, it seems like going with that passive filter for them, with an active, adjustable-level low-pass x/o for the subs or woofers would be an effective, low-cost approach for the op. The B4 does that and more, but at around a grand is perhaps not justifiable, cost-wise. In the case of the Tympani T-IV, the old Dahlquist DQ-LP1, with it's passive 1st-order filter (whose hp filter frequency can be changed by the value of the capacitor installed) and an active 3rd-order low-pass (what the T-IV requires for bi-amping) and level control is just what is called for. If anyone is looking for a DQ-LP1, I just happen to have one (in great shape, with original factory carton and instruction manual) I can let go ;-)---Eric.
Edits: 04/22/17 04/22/17Follow Ups:
Unfortunately, that unit was not designed for this application.
It was designed primarily for sub/main speaker crossover duties where the main speaker already has a native 2nd-order roll-off. Thus, you would achieve a symmetric 3rd-order slope crossover using the electrical 3rd/1st electrical slopes of the Dahlquist unit.
So, yes, in the case of the T-IV it might work effectively, but NOT in the case we're talking about here with the I-D. Two completely different animals with completely different line-level solutions required.
Dave.
Exactly Dave. For the op's Tympani T-1, a symmetrical 1st-order x/o is required for both the high and low pass filters. At the time of it's original manufacture, the T-1 was being distributed by Audio Research, whose PC-1 passive x/o was designed expressly for that application. It created a 1000Hz x/o point, with four level controls, one each for left and right channels/high and low pass outputs.
I would hang onto that Dahlquist unit. That's a nicely conceived unit and could come in handy in the future.
Dave.
Good point Dave. That's why I still have the DQ-LP1! I kept my copy of Frank Van Alstine's plans for his upgrade modification to it. One thing to do is just not use the high-pass inputs---the capacitor is uses for filtering can just as easily be installed on the power amp input jacks, saving an extra set of inter-connects. Then use the active 3rd-order low-pass inputs only. That control has an adjustable frequency range, though not nearly as wide or precise as that of the First Watt B4.
Edits: 04/24/17 04/24/17
Well, it's hardly going to make any difference unless you have interconnects that are a mile long.
Installing the capacitor internal to the DQ-LP1 is preferred as it allows to use the shunting resistor location so you can fine-tune while still using standard value capacitors.
Dave.
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