"Bench" TS in Tone Stack Calculator

[Gtr_tech]

The inductor values don't state the unit of measure. I'm going to assume that they're in MH. Sound close? I doubt they'd need to be any larger for the audio band they need to cover.

Gonna play with this and see how it sounds....but I'd like a confirmation on those coils first. Steven Bench seems to have dropped off the earth....

[jrfrond]

It's safe to say that anything in the audio band will be in millihenries.

[Lauri]

The inductors are 20H and 6H

L-C Based Tone Stack

[Gtr_tech]

Oof....ok then. I doubt good quality shielded inductors are even available in that high a value. Back to op amps then.....

[Steve Conner]

I believe Steve Bench used some little audio transformers as his inductors.

[Gtr_tech]

Yea he did.....which *would* work but hum pickup inside an amp chassis would get pretty obnoxious.

[teemuk]

You can always replace conventional inductors with gyrator circuits.

[imaradiostar]

If you wanted to keep with the tube aesthetic (no op-amps) it's possible to make a gyrator with a high-voltage mosfet. Haven't tried it, have simulated it and it worked fine.

jamie

[Steve Conner]

Yes, that should work fine, and a high voltage BJT like the MPSA42 might even work too. I suppose you could even make a gyrator with a tube cathode follower. But bear in mind that the higher the gm of the device, the closer the gain of the follower will be to unity and the better the gyrator will work. The FET and BJT will wipe the floor with a tube in this respect. Having said that, the poor performance of a tube gyrator might well add some sort of "mojo" to the sound.

The only downside of gyrators is that only one end of your virtual inductor is accessible, the other end is tied to ground. I can't remember if this is a problem in the Bench circuit. There is a gyrator circuit with both ends floating, but it needs two op-amps and I've never seen a discrete version.

Audio transformers are available with little mu-metal shielding cans. I used a pair in the input stage of a tube stereo amp I built. I had to place them carefully inside the chassis to minimize hum, but I got it inaudible in the end.