Sourcing or making my own inductor

[bjosephs]

Hi all,


I want to make a reactive load for my amp similar to this article by Randall Aiken but it requires a large value inductor with a low DCR. Fortunately I’m targeting a nominal load of 8 ohms so I get to cut the L in half but 25mH still seems to be hard to come by. Erse Audio has one but there’s a 10 pc min and parts express has those and all similar products marked as back ordered. Is there another source that someone could point me too? If not, perhaps someone here can help me piece together the parts to wind my own? It looks like this is a very deep area of science/art so I’m not expecting to “design” this but if I get a spool of 16awg magnetic wire, a decent LCR meter, and someone directs me to the right kind of core could I get this done?


Brian

 

[dmp]

Couldn't you use the coil from a speaker?

 

[bjosephs]

Couldn't you use the coil from a speaker?

Maybe? I don’t have any around that I could dissect. Can the coil of a speaker be removed in a way that preserves it’s mechanical and electrical attributes? Isn’t the moving portion part of the core?

Edit: Weber seems to make an attenuator/load box that uses a “motor assembly” as the reactive element. I’m not sure how to remove such a thing from a speaker safely nor am I sure it’s an easier (cost/effort) way to achieve my needs.

 

[capacitor]

If you're able to get a sacrificial 8 ohm speaker, maybe this would help.

I had a Weber MiniMass, and it worked pretty well in my experience. So, I thought I'd give a DIY version a try. I took an otherwise useless 8" 25w/8 ohm speaker and removed the cone, keeping the spider intact. Then I cut the basket away (just to make it smaller), leaving the magnet assembly & voice coil/spider plus the wires intact.

I didn't box it up, just let it sit on the bench, and wired up a simple direct output/voltage divider using a resistor & pot. I used the "slave" (sorry) output from a Boogie MkII schematic.

I found there was a lot of high end feedback between the guitar & device, when even moderately cranked. I'm sure part of this was it needing to be isolated in a box.

I think that these devices need good physical damping, since the cone is gone; maybe some type of heavy, flexible/rubberized paint, applied to the spider.

 

[bjosephs]

If you're able to get a sacrificial 8 ohm speaker, maybe this would help.

I actually found a proper inductor from a European hifi shop. ~27mH at a few amps if I recall.

I made a prototype and I also get a lot of feedback. It does sound more realistic. I’m actually using it as an attenuator by inserting a fraction of an ohm in the ground path and splitting off to a cab. Works ok but my high wattage pot isn’t so great.

 

[guitarmike2107]

Hi Brian, did you manage to sort this, I have made my own inductors for this, I have M6 core here too, so if you want to wind one I can give you some pointers.

 

[bjosephs]

Hi Brian

Yes, I purchased a suitable inductor from Willy’s hifi. It’s a bit lower than the advertised target but in spec at 28mH.