gyrator question

[Mike Burgundy]

Okay, gyrators in all their ever so slightly different forms all do a great job of acting just like a coil hooked up to mass. Great for LC filters.
Does anyone know of a gyrator-type circuit that can be used in a more in-line fashion (meaning one end *doesn't* go to ground buit back into the circuit - have a look at some Pultec EQ's to get the idea)?
I know this is probably a fairly futile exercise, but the LA2Alight got me thinking about a minibooster-driven Pultec type EQ...although I should just build a straight-forward gyrator cicuit

[R.G.]

Gyrators do come in two forms - the grounded variety and the floating variety. Floating inductor gyrators are more complicated, as you would expect, but are fairly well known. You need about three or four opamps to synthesize a floating inductor.

Try a web search on "floating gyrator"

[Mike Burgundy]

Thanks!
Tried several variations and ended up with theory on how to implement this on a CMOS chip for VHF circuits (consisting *entirely* of MOSFETs and Focusrite commercials, but nothing that really cuts the mustard. I'll have a look in the university's ET library one of these days, see what they might have (they also had the old RCA tube manual, so who knows what gems might turn up)

[Rob Strand]

There's a number of floating gyrators circuits.  Look-up the ones by Mr. Antoniou.

[puretube]

:?:

[Nasse]

:shock: CMOS inverters were amazingly popular in experiments in mid 70´s I believe, I have not seen any schems what Puretube is interested about, but in some literature or old magazine articles there has been words pointing for something like that. I have a small electronics mag article about using cmos inverters in audio applications but I have lost it, I hope not totally but there is a hope I will find in the attic of my woodshed when the summer holiday arrives.

In those days opamps were very expensive, and those available were poor quality. CMOS logig chips were as cheap as today, and experimenting with these was cheap

No gyrator in that mag article I lost, but there was some example circuits like unity gain amplifier, sum and difference amp (unity gain) and Baxandall tone control. I quess anybody fiddled with tube sound fuzz like circuit can recreate those very easily. That Baxandall tone control I miss most, but it was just similar as one based upon opamp feedback, I believe you can make one working just by choosing large value pots like 470 k and small cap values (you know it is high impedance) and dont except as much cut/boost range because of the limited gain

There was "gyrator" suggested in that old mag article anyhow, but not in same meaning what Puretube asks. It was just for power supply for inverters. Example circuit was just done with small signal silicon transistor
and few caps and resistors

[puretube]

:?:

[Nasse]

Could you just try using normal single inverter stage, if input and feedback resistors are about equal I know gain is around 1 (depends supply voltage and actual chips)

In "Hi-Fi" applications you need to keep signal voltage level at certain limits, dont know if it can take 200 mV or less

[puretube]

thanx, Nasse: think I gotta go thru some old magazines for this special purpose (or go breadboard)...

anyone else?

[Paul Perry (Frostwave)]

http://www.kmitl.ac.th/msplab/Journal/journal1.html

article 4 here might help, I havn't read it, my download speed too slow..

[gez]

You might be able to use a 4007 chip PT.  Use one MOSFET as a source follower for the Gyrator and use the rest of the chip for audio?  I should think that it wouldn't be as good as a transistor Gyrator but who knows?

[puretube]

thanx for the tips, guys...

Paul: those Thai articles are very interesting, but very indepth...

(still looking for clues)

:?:

[puretube]

...so I went to the attic and searched my dusty archives,


free information sucks...

[gez]

Not exactly gyrator, but bandpass - so the intended function I got in my mind will be fulfilled.

I've used spare inverters for filtering/tone shaping in a few circuits using mulitiple feedback and Twin-T filters.  They work (good enough for distortion circuits) but not as efficiently as op-amp filters.  Part of the reason is poor gain, the other is the high output resistance being in series with any resistance that sets filter frequency (plus can interact with gate capacitance).  

This can be compensated for by jiggling component values OR buffering the output of the inverter with, say, a JFET and running the feedback network (or part of it if it's going to bugger up biasing) from the source of the FET.  If you run the chip from a 5V regulator, the buffer can be run from a higher voltage, which helps avoid clipping.  Using buffering, I've managed to get results as good as (or better!) than conventional circuits.

2 or 3 of them will go into a circuit, which otherwise would have left 2 or 3 inverters unused...

That's one of the reasons why I love these chips! (despite their limitations)