| Electronics > Projects, Designs, and Technical Stuff |
| Guitar amplifier - Current-drive & Soft-clipping, combining both |
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| magic:
What a silly argument :scared: If you want to produce the effect of a speaker driven from hig source impedance, driving the speaker from high impedance is actually the easiest way of getting there. Emulating it in the preamp means complex opamp filters or DSP and it only works right if you get your model right. And in audio, convincing your users that you got it right could easily become a task of its own, even harder than getting it right in the first place. Even Douglas Self would readily admit it, gritting his teeth :-DD |
| magic:
There is indeed some errors in your article. I have to nitpick: neither current, nor force, nor power going into the speaker should be kept constant with frequency for accurate reproduction. It's a common myth, it's wrong. And possibly neither voltage, to the horror of all the damping factor fanboys. The impedance peak at low frequencies is caused by mechanical resonance. It means that once the cone has been put into vibration at the right frequency, it keeps vibrating at that frequency with very low energy input. That's why its impedance increases (no current wants to go into it) and that's why power into the speaker decreases. And this is the right thing to happen, in a HiFi application. Trying to push constant power at resonant frequency will cause bass boost. That being said, you aren't doing HiFi and if you want to emulate a tube amp you gotta do like tube amps do. OTOH, the rise of impedance at high frequency is caused by parasitic inductance of the voice coil. It also causes lower power to be delivered into the speaker and this time it results in legitimate treble rolloff. Current drive actually makes more sense in such conditions. I'm not entirely convinced by that emitter degeneration trick. And even less if they only increased it from 0.22Ω to 0.47Ω. Problem is, any loss on emitter resistors is almost perfectly compensated out by the opamp. The better the opamp (more open loop gain, higher gain bandwidth product) the less difference those resistors make. I would rather be looking into combining soft clipping feedback networks with the constant current circuit from your article. Or go into the "low overall feedback" rabbit hole, which eliminates the problem of global feedback "correcting" output stage sag. Also, your design oscillates like mad ;) |
| 2N3055:
@magic, Who are you arguing with and about what ? |
| magic:
First with the idea of emulating tube output stage frequency response in small signal circuitry, later with the article linked in the OP. |
| 2N3055:
--- Quote from: magic on September 22, 2019, 01:35:02 pm ---First with the idea of emulating tube output stage frequency response in small signal circuitry, later with the article linked in the OP. --- End quote --- Aha, OK thanks! |
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