FDNR Deluxe Active filter

[peranders]

http://www.diyaudio.com/forums/showthread.php?s=&threadid=13497

I have tried to get info about the very special Frequency Dependent Negative Resistor.... filter but noone here seems to have come close to it, except for a very few.

Some day I thought it would be fun to make a killer active filter. I have no personal need for it but I'm more interested in it in a technical sense.

Specifications (only at idea stage):

Input buffer

1 Mono subchannel, 10-50 Hz, 4th order

2 Bass stereo, 50-250 Hz, 4th order

3 Mid stereo 250-3000 Hz, 4th order

4 Treble, 3000 Hz, 4th order

All filter sections fed via an individual Jung Regulator

All highpass filters with simulated inductors as generalized impedance converters

All lowpass filters with FDNR's

All filters with adjustable gain

All filters configurable as 0-4 th order and all kinds, like Bessel, Butterworth etc.

All filter will have place for 2 resistors in parallel and the caps will also have options for different kinds and sizes.

The pcb will look as my pcb's usually look like, with groundplane and all.

The whole filter will be made of holemounted parts except for opamps which will have a SO08 option.

Time schedule if someone is interested in mid 2005.

 

[Luke123]

Peranders

Solutions for you for GIC filters:

1) Electronic Filter Design Handbook by Arthur B.Williams and Fred A.Taylor- ISBN 0-07-070434-1

2) You want to deal with the real thing with no money concern ($1500...? FilterShop from LinearX (www.linearx.com). That is something!

3) Use high quality precision inductors with Sallen-Key filters or MFB topologies. Inductors are hard to get and to some extents more performant than you may think. Electronic inductors have some limits. Trade-offs between the two.

Luke

 

[jackinnj]

http://www.diyaudio.com/forums/showthread.php?s=&threadid=13497

I have tried to get info about the very special Frequency Dependent Negative Resistor.... filter but noone here seems to have come close to it, except for a very few.

You can go to Jim Thompson's website -- S.E.D./Schematics -- and take a look at the stuff on filters -- I modeled the gyrators on Multisim -- just make sure that you pull the output from the correct node!

I think that the problem with making the transformations is that a floating inductor was a little difficult to "realize".

http://www.analog-innovations.com/

 

[peranders]

Guys, I have no problems to design those filters. I just wondered if somebody had come close to them in real life.

 

[BrianL]

There is an old Burr-Brown (now TI) ap-note on FDNRs for
DAC reconstruction filters.

One can use standard RLC topologies and then do a transform
to come up with component values for the FDNR.

 

[peranders]

Please, my question isn't about that. See my post above.

 

[jackinnj]

Please, my question isn't about that. See my post above.

Well, if you wanted to do something really useful you could design an all pass filter with a pga or vga --

 

[peranders]

All pass filter used in combination with what?

OK, I'll continue to think of this highly advanced filter on my own. I'll come back when the idea has left my mind and gone into my Mac.

 

[jackinnj]

all pass filters are used to alter the phase relationship of two signals -- thus you can compensate the time alignment of your drivers.

a pga or vga amplifier allows you to tune the phase without changing many R and C values.

i wasn't kidding. it would advance the state of the art -- you could probably even get it published in Elektor or AudioXpress.

 

[blu_line]

peranders,
I am very interested in such an active cross-over circuit.

A couple of years a go i did build the 40Khz DA filter mentioned in earlier threads and discussions.
Since i could not find info on high pass filters with GIC's i did not persuit the active cross-over. Altough it has been in the back of my mind since then.

Are you willing to share that info ? on high- and low-pass GIC and FDNR sections ?


grtz

Simon

 

[peranders]

I have come to the conclusion that you can't use a FDNR in a HP-filter but you can use GIC as simulated inductors.

 

[blu_line]

I have come to the conclusion that you can't use a FDNR in a HP-filter but you can use GIC as simulated inductors


I know.
But most ionformation i could find is still on low pass filters.


grtz

Simon

 

[peranders]

If you know how a C-L-C-R etc filter looks like you only have to replace the real inductors with GIC's formed as L's.

 

[jackinnj]

as I said at the outset, "realizing" a floating inductor is difficult, but not impossible -- this will work:

 

[peranders]

For LP I plan to use FDNR but in your case, interesting. I haven't seen anything take out the signal the way you do. Any advantages compared to just let the "inductor" go to ground, possibly a more low-ohmish outpout?

 

[peranders]

as I said at the outset, "realizing" a floating inductor is difficult, but not impossible -- this will work:

Have you tested it in real life?

Isn't the two caps a really heavy load for the signal source?

 

[EngelholmAudio]

Some additional requirements from me:

* High pass CO, 3'rd or 4'th order
* Low pass CO, 4'th or higher
Both HP and LP should be fixed, and not configurable. Just messes stuff up!
* Phase shifter, 0 to 180 degrees plus also a switch to alter between 0 and 180. Very useful when tuneing a system to be able to look at the measurement and turn the phase to the exact cancelation.
* Sub sonic CO, between 10 and 25 Hz. Should fit the most of the drivers and amplifiers.
* Gain adjustable from -6 to +6 dB
* Capability to handle a tough load, i.e. to be able to use multiple bass amplifiers (in case multiple bass modules are used)
* Possible to use with the jacket-adapters or what ever they are called. Like this one:

An externally hosted image should be here but it was not working when we last tested it.

 

[stevieblunder]

Hey Guyz,
I'm sure I'm not the only one thinking: this is 2005 and analog filters and slide rules are nifty but not something I'd bother with any more. OK diy is not about being cost effective so have fun, but if you're serious about signal processing you need to find a general purpose DSP and learn to tinker with FIR code instead of op-amps, GICs and gyrators. BTW, Hi-Q analog filters always sound awful; it's just a bad idea.

20 years ago I used to make these nifty electronic crossovers using op-amps, and what we called "bump and roll" filters for the bass, (deliberatey peaked band-PASS sub channel) but if you want phase linear filters for multiple bands of multiple channels, a DSP is just the best way to do it. You could also play with driver timing delays for free. Somebody tell me if I'm wrong but I don't think a truely phase linear filter is even possible with analog filters.

So who has built a DIY DSP? Must be someone in this group?
Cheers,
Steve