High power amp for low power needs - better result?

Status
Not open for further replies.
martinsson said:
A seemingly stupid answer: current 😉
Click to expand...
So why are we not talking about current amplifiers with DF=~=0?
😉
Where 99,99% of the market seems to be all about voltage amplifiers?
Voltage is not the "thing" that moves the cones.

Instead of putting a voltage upon the terminals of a Loudspeaker, and asking it: "Please, please, would you be kind enough to move your .... cone",
Why not simply shove the current down its throat,
with a modulated current source (current amplifier) of almost infinite output impedance?
In this "Other side of the mirror" World, back-EMF is only just an interesting side effect.
 
Last edited:
I'd decide to go with a more clean sounding and less current design;-)

Never I would use a complementary-parts-pp-design. Horrible.

And: Clamp all cones, the 25 kg subwoofer-cones too;-) If not, NEVER you will get a clean tone! NEVER you will get "control" over any driver;-)
 
Current drive is a interesting topic for sure, unfortunately the speaker world, and indeed the entire commercial audio world for that matter, have centered on voltage drive, even the likes of lab.gruppen, QSC, Crown and all other professional audio amplifier manufacturers.

One sometimes wonder why that is, when used as "straight to driver" amplification (no passive crossovers) it may work just fine, I do not know about the efficiency though, amplifier wise I mean, and especially for amps in the "several kW/ch" range.

Now... back on topic 😉

I realize I keep getting the same answer no maybe it is time to stop asking and say thank you to all who has contributed to my question.

My conclusion is that there will most likely not be any noticeable difference in SQ between FP6400 and IP450 when driving ROAR15 sub woofers equipped with B&C15SW115 at a level of >10W.

I'm a tad disappointed to be honest, as it strikes against my gut feeling that there would be a difference, but that's called learning, and I'm grateful none the less.
 
A high power amplifier run at low power is likely to be unstressed, which perhaps gives a better long-term prognosis - less likely to drift out of bias, less likely to suffer component failures, but is this worth it? So long as the amp handles the biggest transients in your signal it is powerful enough.

Size an amp so it doesn't clip, definitely, but no need to go further.

A very overpowered amp absolutely must have power-on and power-off muting or else the switch on and switch off thumps will blow out your speakers.

A very overpowered amp, if accidentally set to high output levels will blow out your speakers faster than you can react to stop it.

A very overpowered amp even with speaker protection may blow out your speakers on a fault (remember everything is designed for matching speaker power handling).


Of course you can over-rate your speakers too, that's then a system capable of continuous high power.
 
martinsson said:
Lets look at it from the other perspective, -What factors (or design criterias) of an amplifier influnces the loose term "cone control"? and perhaps related (not sure) -when does a load in terms of back emf (reactive current and voltage) become a problem for the amp and why?
Click to expand...
Output impedance, often given as DF in adverts. Anything better than around 20 is good enough. Ignore almost everything you read on audio websites about 'back emf'.

As others have said, the higher the amp power the more likely it is that compromises have been made in other matters. For example, bigger transistors tend to be slower and so harder to keep the loop stable.
 
A high power amplifier will exhibit high distortion even at light load. All the time.

What causes a cone to move?
Click to expand...

An electromagnetic (force) field. Not "back", just plain EMF.

Never I would use a complementary-parts-pp-design. Horrible.
Click to expand...

Yes. It treats music signals horribly.
 
Mark Tillotson said:
A very overpowered amp absolutely must have power-on and power-off muting or else the switch on and switch off thumps will blow out your speakers.
Click to expand...

Absolutely must?

At some stage i had a couple of monoblocks which could raise 700W/4ohms and 1200W/2ohm and in an attempt to preserve sound quality had no muting relays at output. Listened to them on a pair of stand mount Sonus Fabers which could definitely not take more than a 100W even for a very limited time. Never had the slightest problem. Hardly any power on thumps either.
 
DF96 said:
Output impedance, often given as DF in adverts. Anything better than around 20 is good enough. Ignore almost everything you read on audio websites about 'back emf'.
.
Click to expand...

Absolutely true, 20 is plenty. But the DF for small and large signal conditions are not necessarily the same. You can have a DF of 1000 that falls to 5 or less under the right (wrong) conditions. Poor amplifiers will do exactly this and that’s why the bass sounds muddy. It can happen at clipping for sure, but more often your output followers simply run out of gain in your typical price-point amplifier.

Back EMF is often blamed for a multitude of sins, but it’s one thing you really can’t blame. Back EMF in a motor is modeled as a voltage source in the opposite polarity as the applied power source. Hence, “back” EMF (electromotive force, aka voltage). It tends to cause the current drawn to come DOWN, not up.
 
wg_ski said:
Hence, “back” EMF (electromotive force, aka voltage). It tends to cause the current drawn to come DOWN, not up.
Click to expand...
Hmmmm .... True.

But it would also be fair to state that the loudspeaker, as a whole, is a complex impedance, not necessarily just inductive. And on top of that, with the intertia of its moving masses and coils submerged in magnetic assembly, it actually works (at times) as a true generator.
Therefore, depending on the not-just-simple-sinus complexity of a real music signal, there may exist music signal sequences that actually "trigger" a current draw of a much higher value, that what would be intuitively imaginable at a brief glance. Up to five times higher in peaks than what you would get / expect on a pure resistance dummy load.
 
Last edited:
A 400w 8 ohm, 750w 4ohm amp would be what I would like to build. I want the amp to loaf. This is just an opinion.😉
 
Given the two amplifiers I initially asked about, the Labgruppen IP450 (the small one) and the Labgruppen FP6400 (the monster), and that the question related to low to moderate power levels (>10W) into what i believe to be a "tricky" (highly reactive) load (15" 3,4Kw program capacity transducer in a higher order series tuned quarter wave design), and which of these would manage the load best, giving a better experience listening wise.

How well these amplifiers will handle the reactive part of this I now understand pertains to output impedance, (a.k.a DF), where a value above 20 is voiced to be sufficient, how would one go about seeing this in the specs for the above mentioned amplifiers, or can it be derived at by any other published specs if not published as a stand alone specification.

I also want to mention that I subscribe to the what is mentioned in this post by zjjwwa:
But it would also be fair to state that the loudspeaker, as a whole, is a complex impedance, not necessarily just inductive. And on top of that, with the intertia of its moving masses and coils submerged in magnetic assembly, it actually works (at times) as a true generator.
Therefore, depending on the not-just-simple-sinus complexity of a real music signal, there may exist music signal sequences that actually "trigger" a current draw of a much higher value, that what would be intuitively imaginable at a brief glance. Up to five times higher in peaks than what you would get / expect on a pure resistance dummy load.
Click to expand...
I believe the dummy load way to approach load and power characteristics in amplifiers is way to simplified for an accurate description of the amplifiers behavior at music playback.
 
Last edited:
Most amplifier advertising mentions DF. If not, simply divide the output impedance into the nominal speaker impedance (typically, 4 or 8 ohms). In reality almost any 'normal' solid-state amplifier will have high DF; exceptions may be a few DIY or 'high end' amps designed using something other than engineering, and of course current drive amps but there are few of those.
 
Output impedance as per their respective datasheets :
Labgruppen IP450 : 30 mOhm
Labgruppen FP6400 : 60 mOhm

So is DF then calculated as 30/8 = 3,75? (The only way I could arrive at a reasonable result).
Seems a bit low in that case (7,5 for the FP6400).
Both examples for a nominal 8Ohm load.
 
martinsson said:
Output impedance as per their respective datasheets :
Labgruppen IP450 : 30 mOhm
Labgruppen FP6400 : 60 mOhm

So is DF then calculated as 30/8 = 3,75? (The only way I could arrive at a reasonable result).
Seems a bit low in that case (7,5 for the FP6400).
Both examples for a nominal 8Ohm load.
Click to expand...
I presume that the "m" stands for "mili" or "0.001". Hence:
8/0.030 = 267,
8/0.060 = 133 (imho).
 
Krisfr said:
A 400w 8 ohm, 750w 4ohm amp would be what I would like to build. I want the amp to loaf. This is just an opinion.😉
Click to expand...

Like this?
 

Attachments

  • Untitled.png
    Untitled.png
    172.4 KB · Views: 247
bimo said:
It is symmetries topology.
Click to expand...


Rail Voltages? How many output devices? BJT or FET? Complementary? Sometimes I think you are big teaser😀😀😀😀😀 ... But it is okay, Thanks for the hints and at least making me think that the approach is a good one. Time will tell. And for Dadod sharing so much, He is Phenomenal.
 
Status
Not open for further replies.
Back
Top