filter

[al_p]

hey

i was hoping some of you could give me some ideas on this. i'd like to build a nice simple analog filter. my design requirements would be a stereo unit [matching not super critical but would be cool to get it close]with 1 set of controls. basically the MCDSP F2 hi and low pass filters. so the controls would be Fc, and Res for each filter and if it's not a huge undertaking slope would be cool but not essential. i mostly would use 24dB/8. the unit would be balanced +4dB ins and out and be able to drive MCI and studer inputs.

i've been looking at some DIY synth module kits, but don't know where to go from there in terms of interfacing it properly to get the balanced +4 I/O. like i have no idea about the input and output impedance of the filter circuit/possible line amp/TXs.

a TX balanced design would be welcome as would any suggestions for juicy wasteful discrete line amp suggestions [JFPs?]. continuing research. thank you guys.

PS. i know we all know this, but the search function is brutal.

 

[PRR]

> hey.... basically the MCDSP F2 hi and low pass filters.

I love guessing games. WTF is a MCDSP F2?

My guess is you mean something from McDSP, and something not in their current products. Am I close?

> Fc, and Res for each filter and if it's not a huge undertaking slope would be cool but not essential. i mostly would use 24dB/8.

Stereo tracking 24dB/8ve filters are very nasty in analog. You need an 8-gang variable-something: chokes, caps, or resistors with opamps and caps. Or for low-pass there is the Moog VCF (and pretenders)... never seen it done as a high-pass, and is noted for "color". Or you can stack eight VCAs inside bi-quad or phase-shift filters, I guess that is how you could do analog 24dB/8ve hi- or lo-pass without an 8-gang choke.

If you can find a Moog-system analog filter that makes you happy, the "balanced +4dB ins and out" is trivial. Hang a 10K:10K transformer on the input, a good 600:600 transformer on the output. Moog-system gear is 100K input and 1K output up to 10V peak, which is close enough to +18dBm in 600.

> the search function is brutal.

I'm guessing this remark means "the Search can remove suspension bolts from a 1987 ElCamino with its bare hands."