sourcing audio inductors in 2022 (for equalizers)

[Admiral-dk]

Not to ruin it for those with a Religious relationship with Inductors - but I see that most 'Pro Audio Gear' I service, has switched to using Gyrators instead for the last two decades (or more) ....
They are cheap, very reliable + it's very easy to adjust/construct to the value required
They are unaffected by Magnetic disturbances
You don't have to fight the Hysteresis Curve of the B-Field => much less distortion (as long as the supply voltage is high enough).

Only drawback - One end has to be 'connected to Ground'

Per

 

[abbey road d enfer]

Only drawback - One end has to be 'connected to Ground'

Not necessarily.
Electronics giant Bob Pease designed this.

 

[Bo Deadly]

Not necessarily.
Electronics giant Bob Pease designed this.

Very cool.

But in practice I'm not sure I would want to run signal through 2M of series resistance. Maybe with the right amps the impedance could be dropped to 100k or so.

 

[abbey road d enfer]

Very cool.

But in practice I'm not sure I would want to run signal through 2M of series resistance. Maybe with the right amps the impedance could be dropped to 100k or so.

The signal does not goes through 2 Meg. It runs through the 470r, where it meets an active node.
You don't worry when signal goes to a xfmr's primary and stops there, with only a few pF of parasitic capacitance, do you?
The 1Meg value is just one of the many possibilities; the nominal simulated inductance is C.R.r.
1k and 470k would give the same result, except the parasitic parallel resistance halves and the parasitic series resistance doubles, which lowers the Q.
The only drawback is that, because of the not infinite GBW of opamps, performance deteriorates at HF, but there is no issue in the audio spectrum, particularly at low frequencies, where physical inductors become bulky, costly and performance limited.

 

[Bo Deadly]

The signal does not goes through 2 Meg. It runs through the 470r, where it meets an active node.
You don't worry when signal goes to a xfmr's primary and stops there, with only a few pF of parasitic capacitance, do you?

Seems to me the only reason for using this "floating gyrator" would be to simulate a series inductor like the high boost of an EQP1 in which case there's no way to pass signal from A to B without going through the 1M. And from a noise perspective, it also seems to me that those 1M on the amp inputs are going to dominate the noise contribution (so 2M?). This would be easily confirmed with a .noise analysis in LTSpice.

The 1Meg value is just one of the many possibilities; the nominal simulated inductance is C.R.r.

1k and 470k would give the same result, except the parasitic parallel resistance halves and the parasitic series resistance doubles, which lowers the Q.

Ahh, so the parallel resistance is a "drag".

The only drawback is that, because of the not infinite GBW of opamps, performance deteriorates at HF, but there is no issue in the audio spectrum, particularly at low frequencies, where physical inductors become bulky, costly and performance limited.

Definitely very interesting. Fiddling with this is going on my E bucket list.

 

[cardboard]

It is very easy to wind an inductor to come up with a desired value, and very difficult to wind an inductor that sounds great.

...

Other than that it means buying broken EQs that have a good inductor of the value you need.

I turned to buying tone generator boards of old cheezy shitty organs. There is always at least 12 coils on them, in a rather useful range and with the right core material (for below say 100 kHz, not above).
Indeed, quality may vary and should be listened to, but innards or old transistor organs are cheap.

mart

hoping for user ‚inductor‘ to leave a like, but no, it is:

 

[abbey road d enfer]

Seems to me the only reason for using this "floating gyrator" would be to simulate a series inductor like the high boost of an EQP1 in which case there's no way to pass signal from A to B without going through the 1M.

You don't understand how this circuit works. Just like a transformer transfers the energy at the primary into the secondary, which in turn reacts with the primary, the Pease circuit transfers the stimulus at node A into a stimulus at node B, and vice-versa.

And from a noise perspective, it also seems to me that those 1M on the amp inputs are going to dominate the noise contribution (so 2M?). This would be easily confirmed with a .noise analysis in LTSpice.

The added noise has nothing to do with the 1Meg resistors, because the main portion of the signal does not pass through them. It passes through the 470r's.
Of course, being an active circuit, there is noise added. The noise contribution of the 1Meg resistors is tamed by the 17nF capacitor, so the noise spectrum is shifted towards bass.

Ahh, so the parallel resistance is a "drag".

Remember that real inductors have it also (air core ones less so), in a more pernicious way because it's frequency and level dependant.

Definitely very interesting. Fiddling with this is going on my E bucket list.

Knock yourself out, and report!

 

[Matt Syson]

The distortion with increasing signal level and hysteresis of a real inductor presumably add to the 'charm' of an Eq unit and of course the distortions produced are 'filtered' by it's own circuit. A gyrator would stay 'clean' (distortion free) unless any point gets close to the signal voltage handling of the amplifiers at which point they would presumably clip. Implementing a variable 'gyrator filter could be make more interesting sonically by using a VCA which can produce distortion if accidentally or deliberately trimmed FOR distortion. (warmth control)

 

[Admiral-dk]

Thank you Very Much Abbey Road

Electronics Giant Bob Pease

Couldn't agree more and another Gem from him I haven't seen before - definitely one to 'Fool Around With' in the simulations

Best wishes

Per

 

[zzzzz]

to chime in on a dead thread, myself and a friend were able to determine based on visual inspection of many Auditronics units that they were likely using toroids made by Triad.