well it makes sense to me ... when a musical instrument produces sound waves they air is compressed towards the listener but not sucked out
There is no air push-pull in sound emission ... only air pushed towards the listener
The pressure increases from the atmospheric pressure (no sound) to a positive value above it ... and back to the atmospheric pressure (no sound) ... but it never goes below the atmospheric pressure That is called vacuum i think I guess you can see (and measure) it with a microphone ... the mic signal never goes below zero
Instead a push pull amplifier moves the woofer's cone forth and back ...
there should be a diode maybe in series with woofer so to get only a forward displacement of the cone ?
i wonder how that would sound 🙄
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Nelson Pass words cheap talk ? 😱
his papers is what i read with the utmost interest ... i think they are a gift to everyone interested in audio reproduction
Do you mean that is wrong ? come on .... say something debatable
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Pass LabsSingle-Ended Class A - Pass Labs
it is perfectly clear to me ... and they are the basics to me To understand the real nature of the phenomena
On the basis of Mr Pass words and as a compromise ... i would think to a single ended front end followed by a classic push pull ... to have both "nice" sound and power
And this reflects also the popularity of hybrid solution ... tubes followed by solid state amp.
Also the BOZ would be perfect of course
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At best, a really good, reverberating fart, what you might call a duvet-lifter, when expressed with deliberate gusto, might have a peak pressure of 1% of one atmosphere (0.147 psi), which it sustains for only a fraction of a second.
A vibrating item rarefies as well as compresses air when producing sound, but, it is accepted that often the leading transient is in one direction only, and it has been argued that the phase of this is audible - I seem to remember it being discussed in the 80s.
It sounds like a blown amplifier... 😛
I can talk or whistle while I breath in. That would be "pull" not push 😀
Indeed, it's all about compression and rarefaction.
Sound waves are an oscillating pressure pattern superimposed on atmospheric pressure. The low end pressures are indeed below atmospheric as evidenced by a loudspeaker cone...when the cone recedes the pressure wave is below atmospheric pressure but obviously still a positive pressure.
do you mean that the sound wave generated by a musical instrument is identical to the sound wave generated by a transducer ? that would be in the ideal case of course
But reality is often far from ideal ...
i think that the answer, as always, is in measuring the relative/gauge pressure produced by the musical instrument in time ... i am pretty sure it will never be negative but only positive or null
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You're wrong. Sound is compression and rarefaction of air. Virtually every sound you hear exhibits this phenomenon.
Most amplifiers have this topology already.
You could try it. Then you'd realize it's not a good idea.
I don't think the Pass does what you think it does.
Stability and safety features are important and are incorporated in many designs.
I remember looking at complex designs and thinking "What's this? What does that do?" Then I studied and prototyped and tested. Now I'm designing my own safety and protection circuits.
That's a good learning experience. I did this when I was 15 or 16 and starting to learn about transistor amplifiers.
You violated the Nyquist stability criteria most likely. In other words, you made it oscillate. There's a topic for you to study.
Walt Jung's IC Op Amp Cookbook and IC Op Amps for Audio Applications explain this in great detail. The principles apply directly to discrete amplifier design.
I recommend you learn how to build good op amp audio circuits first. There's way less moving parts and you can learn electronic principles that allow you to move on.
Then the gauge pressure goes negative ... i trust you. Never seen measurements to be honest.
thanks This is an important confirmation I also read that is the Vas that contributes more to the sound. So if the Vas is single ended the sound could be more musical maybe ?
i trust you ... no reason to doubt 🙂
well the Pass Aleph series and the diy BOZ are indeed single ended. I think he felt the need to give a theorical basis to his design choices ?
I see the schematic ... they are single ended no feedback
I understand that his last commercial units are different but i do not know for sure.
stability is very difficult to understand. Safety less difficult.
I know that an unstable unit can catch fire for instance. Safety can be solved with some kind of life-saving circuit ... my power strips have all a magnetothermic breaker plus the one in the house of course
yes, i made an awful mistake. One thing is to recap or replace some bjts ... another modifying the design. Now i know. I should start with a LTSpice manual i guess. I even do not know if stability can be checked with sim.
That would be very nice indeed. And then, much less important, PSRR ... but this can wait. Stability first.
thank you very much indeed for the very kind and valuable advice.
In the end i see any amp as a discrete op-amp just more complex one for another and with different requirements in terms of gain, power ecc. ecc.
It is a very fascinating issue.
I do not know if an audio design can be scaled up or down. Taking for instance a very good design working for a preamp stage increasing the V supply and the power of the devices maybe i could end with an equally nice power amp. If more current is needed i should just put more bjts in parallel ...
I really would like to know how popular is LTSpice among audio designers ... do they really use it or not ?
My feeling is that it is a very powerful tool at least for a very preliminary design
Thanks a lot again
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No, gauge pressure uses the local barometric pressure as it's reference essentially a "DC" reference. The absolute pressure can not go below 0 (a vacuum) but an ordinary sound wave is a +- variation on top of the barometric pressure. Due to the vacuum limit on rarefaction the loudest normal (not shock) wave is ~194dB IIRC and at very high SPL air is non-linear.
Thank you very much indeed. I was clearly very wrong. It can go also below the barometric pressure. So soundwave propagation is indeed a air push-pull phenomena
While it was evident for a speaker driver not so for the soundwave coming from a musical instrument. Or voice ... 😱
If you try a diode, I recommend doing it in a signal cct rather than on the O/P of a power amp.