The ART was fun and better sounding than I expected but really, not that good. Most of its success I would attribute to the bi-amping.

Steve Brown sent me this link and another but formulas give me shingles.

I'm anxious to hear the new crossover but even more anxious to have both amplifiers running.

The trick is getting the tweeter's response curve right. The proper top-octave compensation is 6dB/octave, but you don't want it to start until above 4kHz and crossover is below 2kHz, so you have over an octave that should be flat before starting the 6dB/octave rising region. The way I do that is to make the load impedance a little bit high on the high-pass filter in the tweeter circuit. That causes it to be slightly underdamped, which causes it to peak around the crossover frequency. Then, when a 6dB/octave top-octave filter is added after that, the first octave becomes flat, followed by the region of rising response.

My suggestion for making a passive line-level crossover would be to do the exact same thing, but at high impedance levels appropriate for the preamp. Instead of using circuits designed for 8Ω, make them 800Ω instead.

Here are some circuits that would work:

Woofer circuit:
o-----150mH--------50mH-----------o
| |
| |
in 0.2uF 820Ω out
| |
| |
o---------------------------------o

Tweeter circuit: ----0.0047uF---
| |
o---0.08uF-------0.22uF---------1.68KΩ-----------o
| | |
| | |
in 60mH 1.68KΩ 820Ω out
| | |
| | |
o------------------------------------------------o

You'll notice the inductance values are very large. Fortunately, they do not need to have much current capacity so they can be made with small guage wire. Don't look for speaker crossover coils, instead, use small signal chokes. Unfortunately, most of these have cores that aren't that great for fidelity. They won't get anywhere close to saturation, so maybe that's OK, but I'm not sure I'd want a ferrite core coil in the crossover circuit. Maybe you can find better low-hysterisis coils.

Another possibility worth looking at is Steve Bench's 6DJ8 Tube Crossover. Circuit boards are available, making assembly easy and keeping it clean. I made a Spice model to help me find components that would provide the proper top-octave compensation, having the initial flat shelf and then 6dB/octave augmentation above 4kHz. Use this circuit with crossover splitter values of 1.3kHz 3rd order low-pass for the woofer and 1.6kHz 3rd order high-pass for the tweeter.

I can't read the teeny writing in the Bench schematic GIF, is it possible to post or e-mail just the schematic to be enlarged? I saved it to My Pictures but my photo editor won't read it.

What I can see doesn't look too bad to build, point-to-point. don't know about a power supply, tho'.

I'll open up the tube crossover schematic in OrCad, size it larger, screen print and E-Mail it to you. You might also want to download the OrCad (PSpice) demo distribution and the 6DJ8 crossover model because those are the source files.

http://marchandelec.com/xm46.html

he'll sell the populated boards alone.

http://marchandelec.com/ftp/xm46man.pdf

Bottlehead PT-1 preamplifier power transformer

Our search for a cost effective, quiet power transformer for our Seduction phono preamp led us to having our own custom model made. With a large core and both electrostatic and magnetic shielding this transformer radiates less than 2/3 of the electromagnetic field of off the shelf models, making it a great choice where space is limited and the power supply sits close to the amp circuit. It turned out so good that we decided to offer it by itself. Super for line stages, phono preamps, mic preamps, active crossovers, any low level application.

Specs are

120V primary

250V CT @ 20mADC secondary

6.3VAC @ 1.2 A rms secondary

Made in the USA with channel frame construction, 2-1/2" mounting centers and solder terminals so you can use your favorite wire to hook it up. This transformer now ships with our current Seduction phono preamp kits and is essentially a drop-in replacement for the original Seduction power transformer, requiring only a little additional wire for installation. Intended for mounting on the underside of a chassis. The installation of this trans and the recommended Hammond die cast box over the Seduction preamp circuitry will yield a dead quiet tube phono preamp. This super quiet transformer can be useful in Foreplay mod projects too, by drilling new mounting holes and converting to a full wave rectifier. Price is $40 plus shipping.

PT-1 preamplifier power transformer, plus UPS to US address