Negative impedance converter reactance

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
ilya
Posts: 67
Joined: Tue Dec 29, 2009 3:10 pm
Location: Russia
Contact:

Negative impedance converter reactance

Post by ilya » Sun Sep 02, 2018 4:02 pm

I'm trying to achieve a specific resistance curve and to do that I need to connect a negative resistor in parallel to the variable resistor in the circuit. I'm testing the standard NIC circuit (see attachement) which works mostly as expected. But at some settings of the variable resistor it looks like this circuit has some sort of reactive component that screws the functionality. I can't see where this component may be coming. Any ideas? This reactive component becomes way less if I change the 10K resistors around the op-amp to 1Meg ones, but still it puzzles me...
Attachments
negimp.jpg

User avatar
JR.
Posts: 2410
Joined: Sat May 24, 2008 7:21 pm

Re: Negative impedance converter reactance

Post by JR. » Sun Sep 02, 2018 11:47 pm

It's difficult to evaluate without seeing more of the circuit.

JR

ilya
Posts: 67
Joined: Tue Dec 29, 2009 3:10 pm
Location: Russia
Contact:

Re: Negative impedance converter reactance

Post by ilya » Mon Sep 03, 2018 1:55 am

Sorry, got distracted by kids and forgot to upload the other part. The first snippet goes in parallel with each potentiometer.
Attachments
negimp2.jpg

User avatar
JR.
Posts: 2410
Joined: Sat May 24, 2008 7:21 pm

Re: Negative impedance converter reactance

Post by JR. » Mon Sep 03, 2018 10:17 am

are all those NR1 and NR2 nodes just measurement nodes and too be ignored?

what exactly does that circuit connect to, a variable resistor in some larger circuit?

1M is kind of high impedance for a 5532 and I can't see what it is connected to.

JR

ilya
Posts: 67
Joined: Tue Dec 29, 2009 3:10 pm
Location: Russia
Contact:

Re: Negative impedance converter reactance

Post by ilya » Mon Sep 03, 2018 10:41 am

NR1 and NR2 nodes are where the circuit from the first post (NIC) connects. There are two identical NICs, one with NR1 terminals, another with NR2 terminals.So they connect in parallel to R33 and R34 and are there to mimick the -11K resistance.

User avatar
JR.
Posts: 2410
Joined: Sat May 24, 2008 7:21 pm

Re: Negative impedance converter reactance

Post by JR. » Mon Sep 03, 2018 12:31 pm

I am guilty of performing "stupid op amp tricks" in the past. 8-) What are you trying to accomplish other than negative resistance?

Negative impedance involves positive feedback that can easily become unstable.

JR

ilya
Posts: 67
Joined: Tue Dec 29, 2009 3:10 pm
Location: Russia
Contact:

Re: Negative impedance converter reactance

Post by ilya » Mon Sep 03, 2018 12:35 pm

Well, the whole point of this exercise is to get rid of an awkward dual rev log 100k pot and replace it with somewhat more friendly dual 10k linear one.

User avatar
JR.
Posts: 2410
Joined: Sat May 24, 2008 7:21 pm

Re: Negative impedance converter reactance

Post by JR. » Mon Sep 03, 2018 2:46 pm

By using even more awkward active circuitry? :lol:

Sorry, does not seem like a good use of time and effort. Active NIC will add noise and perhaps instability if involved in other circuit's feedback networks.

For production volume custom tapers are not that expensive, but you need to deal with high quantities.

You can bend tapers with slugging resistors but I don't even like that (20% bulk resistance tolerance of pots makes slugging unreliable for production).

OK again, where does this awkward pot go in what circuit?

JR

ilya
Posts: 67
Joined: Tue Dec 29, 2009 3:10 pm
Location: Russia
Contact:

Re: Negative impedance converter reactance

Post by ilya » Mon Sep 03, 2018 2:49 pm

I'm not ready for production quantities...

This resistor sets the frequency in the bridged-t equalizer.

User avatar
JR.
Posts: 2410
Joined: Sat May 24, 2008 7:21 pm

Re: Negative impedance converter reactance

Post by JR. » Mon Sep 03, 2018 5:16 pm

ilya wrote:
Mon Sep 03, 2018 2:49 pm
I'm not ready for production quantities...

This resistor sets the frequency in the bridged-t equalizer.
So if I google "the bridged-t equalizer" I'll get your schematic?

I'm tapping out now..

JR

Post Reply