Why digital crossovers suck
I like digital crossovers. But i think that the ones one can buy from BSS, Behringer etc all suck. (A) because none of them has a decent way to control the output volume (and I don't consider truncating bits from the digital signal is a decent way) and (B) because they all use a gazillion of op-amps and electrolytic caps in the analogue signal path (it's actually quite amazing how well the BSS models sound despite all this crap!).
In other words: What the world needs from BSS, Behringer et al is a digital crossover that offers (A) a decent volume control for the six analogue output channels and (B) analogue input and output stages that don't put 'lytics and op-amps in the signal path.
I already had a BSS FDS-366. So all I needed was (A) and (B) above. That was my motivation to build Betsy.
12 stepped attenuators…
The FDS-366 works balanced in/balanced out. I intended to keep it this way. And to keep things simple, I bypassed the entire input section of the FDS-366 by feeding the preamp's signal into a 1:2 transformer and from there directly into the 366's A/D converters. Eliminating the output stages was a bit more complex. Here's what I did (with Manfred Huber's help): The six D/A converters put out a balanced signal which first passes six balanced lowpass filter and is then fed into an attenuator. Six channels of balanced signal require no less than 12 attenuators. To keep the imbalancies as low as possible, I chose two 6-deck stepped attenuators from DACT that are driven by one knob via gears. The wiper of the DACTs feed the signals into six differential stages with 12SX7–a special version of the 6SN7 twin triode–and solid state CCSs in the cathodes. Coupling to the power amps is via LL1680 line-out transformers.
Betsy shares the power supply with Anastasia; B+ is LCLC filtered, the heaters are regulated DC.
And how does it sound?
The Betsy/FDS-33 combo sounds a lot (and I mean a lot!) better than the stock FDS-366. The question is only wether the–admittedly big–improvement was/is worth the–considerable–effort and expenses. But that was not the issue when building Betsy…