I went with the Marchand XM26 crossover because it is the simplest active crossover that I could find. It uses eight tubes total. I’m using new Genalex Gold Lion 12aX7 and 12aT7’s. This system is just as quiet with unbalanced interconnects as it is with balanced interconnects. No need for the added complexity of a balanced unit here.
If you only use one or two pole filters, the signal goes through three triode stages from input to each output. If you need three or four pole filters or require a notch filter, then the signal goes through four triode stages. According to Phil there are only two blocking capacitors in the signal path. I opted for the 0.5dB 24 step attenuators that he offers. They track within 0.01dB of each other so the imaging never shifts when fine tuning settings. It’s a great sounding minimalist design.
At my request, he customized it using HEXFRED diodes for the B+ bridge rectifier. Those provide the best midrange and most open high frequencies of any SS diodes that I have used. He also provided the frequency modules with Bessel filters and changed the circuit to optimize the output stage for a 12aT7 instead of 12aX7 so it can drive full output level into a 10k Ohm load. This was important because I use remote controlled attenuators with a 10k Ohm input impedance at the input of each power amp. This arrangement leaves the DAC’s full line level output connected directly to the crossover all the way through the 15’ interconnects to the mono-block amps located at the speakers. Having the volume control after the crossover and interconnects attenuates both the signal and any possible noise from everything upstream of the amps. It’s so quiet that even with my ears right up to the 107dB H.F. driver and 99dB L.F. driver, I can’t tell if the amps are turned on or off.
Before this a Pass Labs XVR-1 crossover was used in the system. Which is no slouch. In comparison the XM26 beats it in every regard. It sounds more transparent, more like a straight wire. With better low-level detail retrieval, dynamics, imaging and much more realistic bass and tone. Overall, everything sounds more real. I can definitely recommend it for a minimalist active crossover solution.
