How true? Class D amps can't sustain their maximum spec'd power

[RayDunzl]

I am not sure why "headroom for transients" is such a big deal.

Because folks don't understand that the "transients" don't request any more power (as in voltage) than any other part of the signal that reaches full-scale, particularly in a digital (and therefore hard-limited) signal.

 

[Doodski]

Because folks don't understand that the "transients" don't request any more power (as in voltage) than any other part of the signal that reaches full-scale, particularly in a digital (and therefore hard-limited) signal.

Musical waveforms are all transients and the total wattage is the headroom with a PWM power supply with class D output stage and even a tightly regulated linear supply.

 

[DonH56]

QSC class D amps have 3 dB of headroom and are not expensive so it can be done. I understand what you are saying but what I am saying is it is way cheaper to design in 2to 3 db of headroom as compared to 2 to 3 db more continuos power.

My last post on this, I hope, as this is clearly something we will never agree upon.

I do not know what QSC's circuit looks like.

Creating 3 dB headroom means the output components have to support 40% more voltage and all that comes along with that, but does not require additional heat sinking, output devices, and all that jazz. The transformer/power supply has to supply that much more voltage, natch. I agree it is cheaper to design for more headroom than continuous power, but disagree on whether or how much that is a desirable goal or even a significant criteria in amplifier choice, especially given the amount of power class D (or most any AB these days) already provide. I can readily purchase an amplifier with continuous power meeting my needs; perhaps that is not practical for you or others who depend upon extra headroom for transient peaks. But remember 3 dB is not a very large increase in volume, so chances are if you need more than that if you really are underpowered.

 

[MakeMineVinyl]

I've never measured my vacuum tube 2 1/2 watt amplifier for transient power, but I bet it would be awesome. I know it plays for something like 15 seconds after I cut plate power.

 

[Doodski]

I've never measured my vacuum tube 2 1/2 watt amplifier for transient power, but I bet it would be awesome. I know it plays for something like 15 seconds after I cut plate power.

What is the slew rate or the bandwidth of a tube amp like your amp? I'm not familiar with the general operational parameters of tube gear and so I am asking.

 

[MakeMineVinyl]

What is the slew rate or the bandwidth of a tube amp like your amp? I'm not familiar with the general operational parameters of tube gear and so I am asking.

I have never measured the slew rate, but the power bandwidth is below. It is -3db at around 30kHz and a little bit more than 1db at 20kHz. Remarkably its only down a bit more than 1db at 10Hz, although in my system this amplifier only amplifies above 500Hz. Truthfully, I've never attempted to measure transient power, but the output is realistically limited by the driver tube. The amplifier cannot be driven into hard clipping; the waveform just gets rounder and rounder no matter how hard its driven. Again, this is more to do with the driver tube. The amplifier, which I heavily modified, has a voltage gain of only about 2db (all the voltage gain is in the preamp, which is also vacuum tube).

 

[Doodski]

I've never measured my vacuum tube 2 1/2 watt amplifier

Is that a RMS or peak power rating?

 

[MakeMineVinyl]

Is that a RMS or peak power rating?

RMS, steady state. No thermal problems here, cuz its already hot.

 

[Doodski]

RMS, steady state. No thermal problems here, cuz its already hot.

With all that power on tap and what I can only guess is a active system what speakers are you using?

 

[MakeMineVinyl]

With all that power on tap and what I can only guess is a active system what speakers are you using?

Its an active system and this amplifier is driving a compression driver/horn with 107db 1 watt sensitivity. I wouldn't want to be in the room with even 1 watt above 500Hz. I use an awe inspiring, mind bending 40 watts for the LF below 500Hz. The subs (two 18' per side, operating in stereo) are driven by 500 watts per side from a class A/B SS amp. An upcoming project is to replace this amp with a Hypex NC502 OEM module for the same power.

 

[Doodski]

Its an active system and this amplifier is driving a compression driver/horn with 107db 1 watt sensitivity. I wouldn't want to be in the room with even 1 watt above 500Hz.

Wowzerzz.. Max efficiency. Is this esoteric gear or off the shelf parts?

 

[MakeMineVinyl]

Wowzerzz.. Max efficiency. Is this esoteric gear or off the shelf parts?

No, its a modified Altec horn system. I used to work for them back in the day.

 

[Doodski]

No, its a modified Altec horn system. I used to work for them back in the day.

Ahh. I operated a Altec horn for some years with tangerine diaphragms. I had no idea they get that efficient. I used a 100W/ch SAE power amp on the horns with no blocking caps on the mids or tweets. A hybrid system of a KEF woofer in a transmission line cabinet and 107.2 matched tweets.

 

[Doodski]

No, its a modified Altec horn system. I used to work for them back in the day.

Are you using the extra large Altec horns or the medium size about .5 meter deep?

 

[MakeMineVinyl]

Are you using the extra large Altec horns or the medium size about .5 meter deep?

The medium size. The multi-cells are too insane even for me.

 

[MakeMineVinyl]

Ahh. I operated a Altec horn for some years with tangerine diaphragms. I had no idea they get that efficient. I used a 100W/ch SAE power amp on the horns with no blocking caps on the mids or tweets. A hybrid system of a KEF woofer in a transmission line cabinet and 107.2 matched tweets.

I was at Altec around the time when those Tangerine phase plugs were developed. I bought a pair of drivers with them and hated them so much that I sold them to another employee in a week. The radial phase plugs sound so much better to me. The Tangerine ones do have more HF output and that, along with the Mantaray horns, were better for auditoriums and theaters but they sounded horrible to me.

 

[Doodski]

The medium size. The multi-cells are too insane even for me.

Yeah the full size Altec horns are large'ish. I traded a set of full size metallic green Altec horns for a mid sized flat black Altec horn assembly and used them on top of the speaker cabinets at about 4 feet in height at the horn throat with the tweets right below. It sounded snappy, dynamic and clean.

 

[mhardy6647]

The multicellular Altec horns are where things get real -- I can't afford a pair, though.
I still love Gary Kaufman's A5s... some of the best loudspeakers I've heard that aren't (weren't) insanely expensive.

 

[Doodski]

I was at Altec around the time when those Tangerine phase plugs were developed. I bought a pair of drivers with them and hated them so much that I sold them to another employee in a week. The radial phase plugs sound so much better to me. The Tangerine ones do have more HF output and that, along with the Mantaray horns, were better for auditoriums and theaters but they sounded horrible to me.

I use the parametric for top end sizzle and midrange tightness. So bright horns are good for my ears.

 

[Doodski]

The multicellular Altec horns are where things get real -- I can't afford a pair, though.
I still love Gary Kaufman's A5s... some of the best loudspeakers I've heard that aren't (weren't) insanely expensive.



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I still see AL Voice of the Theatre and other models coming up @ Canuck Audio Mart. (The US Audio Mart Canadian equivalent.)