Equalizer which design should I use..?

[überfuzz]

I'm about to design an eq and I just found TSC 1.3, thanks soundgugruman. There are some standard eq:s in the software. However, I always wanted to try and build an eq with more band sweeps, something like 4 or 5. Is there anyone here that can show me how or point me in the right direction?

[Steve Conner]

Multi-band EQs are all solid-state or hybrid. RG explains how they work here.

Simple, Easy Parametric and Graphic EQ's, Plus Peaks and Notches

The Mesa and Ampeg graphic EQs are classics, but they use a lot of inductors. The modern approach with gyrators or state-variable filters is much easier.

[R.G.]

In National Semiconductor's Audio Handbook from about 1973, they talk about Baxandall style bass/treble tone control design, and then adding a mids control, and show how it's done. They then note that there is a temptation to add more tone control bands, but that it should be firmly resisted, on grounds that the bands overlap and interact too much to be useful. The problem you get into is that simple EQs only one active/amplifying device can't be made sufficiently independent from channel to channel.

They recommend going to an amplifier-per-band setup, and then launch into a variant of the constant-Q graphic EQ design. RANE has some online stuff on designing a constant-Q multiband. The filters for a constant-Q can be biquad, state variable, etc. You can also go to the LC boost-cut style which is not constant-Q, but only requires one amplifier for as many bands as you like. The problem then becomes that you need inductors, or one amplifier per "inductor" to fake the inductor by gyration.

[Gtr_tech]

I don't like the inductor based stuff. It works, but adds noise via hum pickup. Its real easy to design active filters with op amps for tone controls that really do something. Deriving a dual rail supply may not be so easy. With older designs, yer only option is to single supply them with a 30v ran off the bias tap....which I personally don't like or do. I don't want anything hanging off the bias tap that can pull down the bias supply in the event of a short. Carvin did this the right way back in the 80s on the X amps. There was a seperate xfmr winding for the low V stuff. I do have an early X60 1-12 combo that does it the "wrong" way via the bias tap, and it makes me nervous everytime I use it.