Passive EQ?

[EAdanikDG]

I've seen on the specs for the Aguilar DB750 that it has a passive EQ. How does this work? I thought that frequencies could only be cut passively. Is there any advantage over active controls? Did they only do this so their DB751 would be a better amp? Thanks.

[bongomania]

Passive EQ is cut-only, with the exception that there may be resonant peaks at some settings. The advantage is chiefly the tonal quality of the inductors and other premium passive components that are used in "boutique" examples like in the Aggie head. The components have a different sound than a typical active EQ. Additionally, the shape and interactivity of the EQ profile from a passive setup is different from most active EQ's, and some people really like the way that works, with kind of an organic, intuitive shaping rather than "boost 500 Hz by 3 dB".

[TRU]

Found an excellent page about passive eq...

http://home.online.no/~jaeioluf/sound/eqpassiv.htm

[EAdanikDG]

Thanks, I think I get it now. It seems there would be less db that you can boost and the manufacturer wouldn't really be able to just centre the controls at any frequency. Sounds interesting though.

[TRU]

Basically how I see it:
- continuously variable center frequency not possible
- no extremely steep eq "curves" (typically 6dB/octave for boost/cut if I remember my electronics correctly)
-> this can be perceived as "natural" sounding. It can also sound "lame" to others.
- boost/cut itself can be quite extreme, but can only affect wide range of frequencies as by the previous point

Please correct me if this is wrong

[bongomania]

Hmmm... not necessarily on those first two points. The center frequency can be made continuously variable with passive EQ, but whether it is that way on any one amp is up to the designer. The amount of cut can be a lot more than 6 dB, but there is no boost (aside from some minor technical exceptions).