Booth Audio Model 1001 electronic 12db 2 way stereo crossover in excellent condition. It is all discrete transistors/JFETs, no opamps! The Booth Company used first rate components as you can see in the photos. It has unity gain for the high pass section and 10 db of gain for the low pass section with level control for the low pass, high quality RCA jacks, damping on the inside of the cover to reduce induced noise. Very nice workmanship. I have the original manual that describes the crossover in detail.
Booth Audio was a company founded with ex-Threshold employees. They made this high quality electronic crossover designed for either subwoofer (100 Hz) or any other frequency. Right now it is setup for a crossover point of 2200 Hz. I can set it up for any value you need from 100 to 3000 HZ as long as I have the caps needed or if you can solder, you can play with the values to get the right crossover.
When I bought this unit it was setup for a 100 hz. I emailed Roger Artman, one of the ex-Threshold employees and he sent the emails below. I initially set it up as described below for 1500 Hz, but found 2200 Hz was better. I have since sold the speakers and am not using this crossover. I will sell it with the original caps as well as the ones in it.
"... You will notice there are 8 pairs of polystyrene capacitors (16 total) on the crossover board. Each cap value is 10,000 pF (0.01 uF) and is in parallel with its "mate" giving each section a summed value of 0.02 uF. Near each section of these paired caps is a single, black 73K2 resistor (73.2kOhms). Each cap section and its corresponding resistor form a single pole in the crossover network. These particular RC values give you high and low pass 12 dB/Octave Butterworth filters that crossover just a bit above 100 Hz. Perhaps the easiest way to change the crossover point to 1.5KHz would be to change the capacitor values only. Each of the 8 capacitor sections should have values as close to 1450 pF as possible for a crossover at 1.5kHz. As you've probably figured, you don't need to replace all 16 caps if you're willing to settle for a crossover value a little above or below your intended crossover frequency value. For example, a single 1500 pF cap (a common value) in each of the 8 sections will give you a crossover frequency of 1.45kHz. In order to calculate resistor, capacitor or frequency values, you simply need to divide 2 of the three values into 159155. (Just remember that C will always be in uF using this particular constant! So, if C = 1.450 X 10^-6 using 159155, C is 1.450 pF and not 1.45 uF.) Mouser or DigiKey will have all the common film cap values. It doesn't hurt to buy more than you need and hand select the values closest to the value you need if you have a cap meter. Hope all this helps!
"... To address your questions, I should start by saying that I wrote the manual and that the design was by Eric Lauchli when we were at CODA and Continuum, "back in the day". (Before then, he worked directly with Nelson Pass when Eric and I worked at Threshold. Eric is the most brilliant analog designer I've had the good fortune to work with!) I don't recall the crossover circuit in any detail, but I'm sure it bears a resemblance to the schematic you included, simply because both are minimalist, FET designs. Additionally, my writing in the manual that the filter types were Bessel was simply incorrect. Upon reflection, I am certain that they are Butterworth as I do recall Eric saying the crossover was maximally flat through the pass band. As you, are no doubt aware, .7 is the Q of Butterworth filters. (Personally, I'd leave the crossover as it was designed; it's is the most seamless and transparent analog crossover I've heard and Chuck Booth shares that opinion.) Should you decide to experiment with different filter types to alter the Q, remember that JFETs are sensitive creatures!