Hi Jose,
Regarding the spike, it's a mix of misunderstanding by designers, and trying to justify the extra cost and size to customers once you have comiited to that. In a few niche situations it might be desirable I guess, but mainly all the big impedance increase does is cause the amplifier to be unable to deliver power to the speaker / attenuator. It causes a flabby, quiet, loose dip in tone over just the first few frets of low E on a guitar, which isn't really very useful for anyone.
It's a tough truth to accept, but 95% of electronics designers in the audio sector, and I mean some -big- names, have alomst no idea what they are doing and just copy what they see. I've had my hands on some spectacularly dumb designs. One 100w tube amp, which I shall not identify, has a phase reverse switch which literally flips + and - on the speakers. This is fine if you are connected to only a speaker, but if you use an attenuator and some kind of direct recording box this means + is now connected to earth via the recording gear and so you can say goodbye to that amps output transformer! This is a real thing. Its horrific. (I actually stopped making direct recording devices when I foudn this because I didn't want to be responsible for killing an amp until I could redesign my units to have floating inputs.)
Equally, of course, the infamous Marshall Power Brake which can go into self resonance, feed back into your amp and also fry it whilst turning into a lightning generator.
Apologies! The current units only use one inductor. Some of my old ones used more so it's a habit to pluralise. I have the inductors custom made to my spec by the same factory makes Bang & Olufssen parts so they're kind of a trade secret.... But I will say it's the core material that -really- matters. Thats where the real tone is. Regular ferrite saturates in a way sounds feeble, and iron sounds good but is big, bulky and then clips hard if you hit the limit. Air gaps are saturation-free and clean, but this needs an inductor the size of your fist and pure clean isn't great. Ours have a secret high density ferrite mix
Beyond that you want good thick copper wire. Diddy little inductors aren't really going to sound good with a big amp through them hitting stauration too soon.
Ultimately the tone isn't mere electronics, it's physics. And that's much harder. But I'm a crazy PhD person who dreams of rocket and staellite electronics and sending something into space, so I'm one of the oddballs who likes horrible maths. Speakers and attenuators are all absolutely strange things. Do you know (for example) that the saturation and inductance of the inductor vary depending on the proximity to the case walls? Steel cases increase inductance whilst reducing saturatiuon capacity. Aluminium damps the inductance so you have to overwind to compenate. Physics is fun.
I had a quick look on my home computer for a gut shot just now, it's not really a secret per-se, and I couldn't find an up-to-date one, but this is an older HB125i. It's a far simpler unit to the HB130, but the inductor floating in the middle is near enough the same and I still use point-to-point wires throughout, only Arcol resistors (I honestly think they sound far superior to ceramic and chinese made ones, you can 100% hear the difference in a blind test, but for the life of me I can't actually identify why! At some point I want to dremel a few in half and do some inductance test on them...) also nicer, thicker triple-rated wires for the flexi ones these days.
Sorry for the long waffle. Hope you get some interesting thoughts from it!
- Sean
