Behringer 904B VC High Pass Filter

Nice thin wispy sounds

The Behringer System 55 904B High-pass Filter compliments the 904A low-pass cousin. I can't say I use this filter as much as the 904A; like all high pass filters, there is no resonant effect (no ladder network possible) that make this as spectacular as a low pass filter, however, it is subtle and pleasing. Both the 904A and 904B should have separate attenuators in-line with the CV inputs and I typically use a 995 or CP35 attenuator to accomplish this.

For my system a voice section usually comprises of 3 oscillators, mixed, and then these patch through a 904A then a 904B before exiting through a 902 VCA. There are two 911 envelope generators to use between these 3 modules... one is connected through an attenuator to the 904A and the also through another attenuator to the 904B. The other 911 patches to the VCA. In this way, I can remove either or both filters from the audio track by simply turning up the filter's "fixed control voltage" knob and the patches remain static.

Not every voice channel in my system requires a 904B filter but it's nice to have on at least one channel.

I like the sound of this filter better when driven by a control voltage from my keyboard... another good location for an in-line attenuator.

Like all of these modules the build quality is there. I really have no complaints.

Spot on

A lot of people will, probably and rightly, judge Behringers new system 55 on the most defining module of them all, the 904 low pass filter. After playing with it for some days now - and to be honest, already after hearing it for a minute - I can say it sounds wonderful. My references are the lpf's in the Grandmother and Mother 32. The 904 is a bit more agressive, well made, and reacts wonderfully. One negative: it loses a lot of bottom end when regeneration (resonance) is turned up. But I understood this was the case with the original. (so it's actually a kind of compliment). Anyway: with the system 55 modules on the market thus far, you're already able to reproduce (what must have been) the typical Moog modular sound. Close your eyes and you're there.

I'm still a bit ambivalent about the copying of authethic gear. But a real system 55 is so far out of reach for the most of us, that I can justify this. Behringer did an impressive job. Even when you don't want to build the whole system, the 904 would be a good addition to your rig.