Light weight bass heads vs. heavier weight bass heads in terms of power

[DrumsAndBass]

For now, the light weight bass heads are around 3-10 pounds. And the heavier ones are 20+ pounds. I've read that the Class D heads are more efficient than A and AB. Most of the Class D heads are the light ones. And there are other features that make the Class D's desirable etc. But do these light weight amps really produce equal power and tone watt for watt as an "older" amp design ? I'm not specifying any companies in particular at this point. What are the trade-offs ? And I'd like to know if the lighter heads are as durable as the heavier ones because I want a long service life without need for any repairs-within reason. Are there other motives for bass gear companies to tout their light weight bass heads ?

[JimmyM]

The tradeoff is that most heavyweight amps have a lot more power past their RMS wattage, often referred to as "peak." Lightweight amps generally don't have much in the tank once you get past their RMS wattage.

[bassybill]

Originally Posted by DrumsAndBass

Are there other motives for bass gear companies to tout their light weight bass heads ?

Surely they're just catering to a market demand from people who like to buy lightweight amps? What other motive could there be?

Sorry - just seemed a bit of an odd question.

[bongomania]

All amps may develop issues at some point; the older style tend to be repairable, while the new ones are designed to be replaced, not repaired. That said, the small size and weight of the new ones will outweigh the repair-vs-replace argument for many people.

[BassmanPaul]

All I can talk about are my own experiences. Yes Class D is a more efficient and cooler running design than either Class A or Class AB. The biggie though is that most are powered via Switch Mode power Supplies. These move the efficiencies of the amplifier's power supply from around 50% into the mid to high ninety %. I own two Class D amplifiers both from Carvin. A light stereo power amp, DCM1000L and an integrated head the BX1500. Both are light, powerful and run cool. I've noticed no difference in operation between the Class D units and the much heavier Class AB units I was using before them. At the end of the last gig the DCM1000L was slightly warm as I turned it off. I switch my amps on after setup and off at tear down.

[jnewmark]

Originally Posted by BassmanPaul

All I can talk about are my own experiences. Yes Class D is a more efficient and cooler running design than either Class A or Class AB. The biggie though is that most are powered via Switch Mode power Supplies. These move the efficiencies of the amplifier's power supply from around 50% into the mid to high ninety %. I own two Class D amplifiers both from Carvin. A light stereo power amp, DCM1000L and an integrated head the BX1500. Both are light, powerful and run cool. I've noticed no difference in operation between the Class D units and the much heavier Class AB units I was using before them. At the end of the last gig the DCM1000L was slightly warm as I turned it off. I switch my amps on after setup and off at tear down.

I also own a BX1500 and knew the power amp was Class D, but I did'nt know that " 12AX7-driven Class A preamps " were part of the equation also.

[BassmanPaul]

Originally Posted by jnewmark

I also own a BX1500 and knew the power amp was Class D, but I did'nt know that " 12AX7-driven Class A preamps " were part of the equation also.

Just about every circuit that uses a 12AX7/ECC83 ARE Class A.

[bobcruz]

Originally Posted by JimmyM

The tradeoff is that most heavyweight amps have a lot more power past their RMS wattage, often referred to as "peak." Lightweight amps generally don't have much in the tank once you get past their RMS wattage.

+1. Nothing in the amplifier design requires it, but I believe most companies are rating their class D amps at peak watts while still rating their older designs at RMS, which might be half the peak watts. I don't buy an amplifier based on how many watts it can produce in a few millisecond burst, but on how many watts it can pound out consistently all night without clipping or overheating. So with the lightweight designs, until I see verified power figures in a Bass Gear Magazine review, I assume usable watts are half what the manufacturer says they are.

[greenboy]

Clues are in what modules are being used in micro-heads, as to how realistic any micro-head manufactuers' numbers resemble a true CONTINUOUS ratings that are referenced to a decent THD.

Power supplies factor into this as well.

With pro power amps, continuous ratings are specified right up until you get into amplifiers designed to produce musical signals above and beyond what the AC wall service can actually provide continuously.

In the bass-oriented sector you rarely see fully referenced specs so the number can be just about anything until you actually get some real referenced test benched stuff outta, say, Bass Gear Magazine.

[greenboy]

Originally Posted by bobcruz

Nothing in the amplifier design requires it, but I believe most companies are rating their class D amps at peak watts while still rating their older designs at RMS

Not my experience. Until you get beyond what a wall service can provide continuously, pro power amps seem to be referenced with continuous ratings, regardless of class, more often than not. But I haven't looked at the Crown XLS Drivecore specs in detail yet to see if that is true there.

When you get beyond what an AC receptacle can supply continuously is when you begin to have to reference products with duty cycles, power draw tables, and voltage and burst/duration figures. This is not evasive - it's necessary in the case of multi-Kwatt amps.

[fdeck]

I've measured the outputs of several bass amps of both classes. In almost all cases, I had to be somewhat generous in interpreting the manufacturer's power ratings, for instance by assuming a 10% THD criterion for the maximum output. I have not seen evidence for any bass amp having a magical reserve of power above its ratings. Some amps may sound louder than others, and this can have a lot to do with factors such as voicing and distortion.

[greenboy]

Originally Posted by fdeck

I have not seen evidence for any bass amp having a magical reserve of power above its ratings.

Surely that loud magical armageddon sound that happens right when stuff is blowing in the output section qualifies as a "burst mode" ; }

[seamonkey]

Originally Posted by DrumsAndBass

For now, the light weight bass heads are around 3-10 pounds. And the heavier ones are 20+ pounds. I've read that the Class D heads are more efficient than A and AB. Most of the Class D heads are the light ones. And there are other features that make the Class D's desirable etc. But do these light weight amps really produce equal power and tone watt for watt as an "older" amp design ? I'm not specifying any companies in particular at this point. What are the trade-offs ? And I'd like to know if the lighter heads are as durable as the heavier ones because I want a long service life without need for any repairs-within reason. Are there other motives for bass gear companies to tout their light weight bass heads ?

No, lightweight amps are actually more powerful. Class-D watts are louder, because you get more of them.

A 15A standard circuit can provide 1800W at most. 80% continuous or 1440W

A class AB amplifier with a big heavy transformer power supply is 50% efficient or 720W for audio power and 750 watts wasted to heat. Don't forget fans to keep it cool.

Class-D with SMPS and PFC is 90% efficient easy. That's 1300W available continuously for the audio.

Capaciitors and light weight and builders of class-d SMPS know to use appropriate amount in the power supplies so they can beat any old style power supply. You can use smaller capacitors because your filtering high frequencies. Not 120hz. That's nuts to filter. That's why even wall warts are now SMPS. And that's why even hearing aids are class-d - less draw and longer lasting batteries.

/exaggerate due to some exaggeration of weight as some magical energy store.

[musicon197]

Last weekend I supplied my GB shuttle 6 pushing a 2x15 cab for a surf Fest in Atlanta running continuously from noon to 10pm, used by 9 of 10 bands. It was outdoors, all power to the stage was supplied by two gas generators and it ran beautifully all day with the only exception being one bass player three bands in turning the gain on the preamp too high for more stage volume, at which point the internal limiter kicked in a couple of times. I dialed him back in lowering the preamp gain, raising the eq slightly and raised the main volume to give him the level he was looking for as they played and there was no other issue the rest of the day. 3.75 lbs class d, this amp is fantastic. The one band that used their own was an old fender bassman that actually was the amp used at this festival in past years, much loved in the surf community, and the shuttle 6 held it's own all day in volume and tone amongst a wall of Fender piggy backed amps. It's not easy for non-fender gear to get love amongst traditional surf enthusiasts, though I got a lot of complements that day.

[JimmyM]

Originally Posted by fdeck

I've measured the outputs of several bass amps of both classes. In almost all cases, I had to be somewhat generous in interpreting the manufacturer's power ratings, for instance by assuming a 10% THD criterion for the maximum output.

I was referring to peak power. Most amps have double their RMS rating. Sure, it's distorted heavily, but it's there. Micros are an exception, according to Bass Gear Mag, as most of them tap out shortly after they hit their peaks.

[bplayer1]

Originally Posted by musicon197

Last weekend I supplied my GB shuttle 6 pushing a 2x15 cab for a surf Fest in Atlanta running continuously from noon to 10pm, used by 9 of 10 bands. It was outdoors, all power to the stage was supplied by two gas generators and it ran beautifully all day with the only exception being one bass player three bands in turning the gain on the preamp too high for more stage volume, at which point the internal limiter kicked in a couple of times. I dialed him back in lowering the preamp gain, raising the eq slightly and raised the main volume to give him the level he was looking for as they played and there was no other issue the rest of the day. 3.75 lbs class d, this amp is fantastic. The one band that used their own was an old fender bassman that actually was the amp used at this festival in past years, much loved in the surf community, and the shuttle 6 held it's own all day in volume and tone amongst a wall of Fender piggy backed amps. It's not easy for non-fender gear to get love amongst traditional surf enthusiasts, though I got a lot of complements that day.

My rig for the past couple of years has been an Eden Navigator, QSC 3102, and 2 Accugroove 112L cabs. I just bought a Genz Benz Shuttlemax 9.2 to use back in forth at another practice place. I use it and 1 AG 112 cab and I'm shocked at just how good this thing sounds, how loud it is, and after two hours of constant use at rockin volume it was cold. No hint of any heat and very stable. I bought as a light weight backup but now I wounder if I will use the old rig anymore. It's so versatile and lite! Most of my studio gear runs warm to very hot so it's refreshing to have something so lite, and loud run so cool!

[Windreaper]

Originally Posted by fdeck

I have not seen evidence for any bass amp having a magical reserve of power above its ratings.

Dynamic headroom? Not a particularly useful or informative spec, if you ask me, but still...

[jsbarber]

Here's some info from Wikipedia on Amplifier Design Classes. More detail on each class is also available: Electronic amplifier - Wikipedia, the free encyclopedia

On this topic, I recall some discussions here on TB, around 5 or 6 years ago. One of our highly respected manufacturers of bass gear opined that the switching designs did not deliver when you played long low notes (low B). They couldn't provided sustained power on these low notes. I noticed that those opinions were deleted sometime later, and wasn't sure why. It may have been that the amplifiers improved, or some other reason. But at that time people seemed to conclude that there were some shortcomings of the switching designs, in this regard.


Power amplifier classes

Angle of flow or conduction angle

Power amplifier circuits (output stages) are classified as A, B, AB and C for analog designs, and class D and E for switching designs based upon the conduction angle or angle of flow, Θ, of the input signal through the (or each) output amplifying device, that is, the portion of the input signal cycle during which the amplifying device conducts. The image of the conduction angle is derived from amplifying a sinusoidal signal. (If the device is always on, Θ = 360°.) The angle of flow is closely related to the amplifier power efficiency. The various classes are introduced below, followed by more detailed discussion under individual headings later on.

Class A

100% of the input signal is used (conduction angle Θ = 360° or 2π); i.e., the active element remains conducting[6] (works in its "linear" range) all of the time. Where efficiency is not a consideration, most small signal linear amplifiers are designed as class A. Class-A amplifiers are typically more linear and less complex than other types, but are very inefficient. This type of amplifier is most commonly used in small-signal stages or for low-power applications (such as driving headphones). Subclass A2 is sometimes used to refer to vacuum-tube class-A stages where the grid is allowed to be driven slightly positive on signal peaks, resulting in slightly more power than normal class A (A1; where the grid is always negative[7]), but incurring more distortion.

Class B

50% of the input signal is used (Θ = 180° or π; i.e., the active element works in its linear range half of the time and is more or less turned off for the other half). In most class B, there are two output devices (or sets of output devices), each of which conducts alternately (push–pull) for exactly 180° (or half cycle) of the input signal; selective RF amplifiers can also be implemented using a single active element.

These amplifiers are subject to crossover distortion if the transition from one active element to the other is not perfect, as when two complementary transistors (i.e., one PNP, one NPN) are connected as two emitter followers with their base and emitter terminals in common, requiring the base voltage to slew across the region where both devices are turned off.[8]

Class AB

Here the two active elements conduct more than half of the time as a means to reduce the cross-over distortions of class-B amplifiers. In the example of the complementary emitter followers a bias network allows for more or less quiescent current thus providing an operating point somewhere between class A and class B. Sometimes a figure is added (e.g., AB1 or AB2) for vacuum-tube stages where the grid voltage is always negative with respect to the cathode (class AB1) or may be slightly positive (hence drawing grid current, adding more distortion, but giving slightly higher output power) on signal peaks (class AB2). Solid-state class-AB amplifier circuits are one of the most popular amplifier topologies used today.

Class C

Less than 50% of the input signal is used (conduction angle Θ < 180°). The advantage is potentially high efficiency, but a disadvantage is high distortion.

Class D

These use switching to achieve a very high power efficiency (more than 90% in modern designs). By allowing each output device to be either fully on or off, losses are minimized. The analog output is created by pulse-width modulation; i.e., the active element is switched on for shorter or longer intervals instead of modifying its resistance. There are more complicated switching schemes like sigma-delta modulation, to improve some performance aspects like lower distortions or better efficiency.

Additional classes
There are several other amplifier classes, although they are mainly variations of the previous classes. For example, class-G and class-H amplifiers are marked by variation of the supply rails (in discrete steps or in a continuous fashion, respectively) following the input signal. Wasted heat on the output devices can be reduced as excess voltage is kept to a minimum. The amplifier that is fed with these rails itself can be of any class. These kinds of amplifiers are more complex, and are mainly used for specialized applications, such as very high-power units. Also, class-E and class-F amplifiers are commonly described in literature for radio-frequency applications where efficiency of the traditional classes is important, yet several aspects deviate substantially from their ideal values. These classes use harmonic tuning of their output networks to achieve higher efficiency and can be considered a subset of class C due to their conduction-angle characteristics.

The classes can be most easily understood using the diagrams in each section below. For the sake of illustration, a bipolar junction transistor is shown as the amplifying device, but in practice this could be a MOSFET or vacuum-tube device. In an analog amplifier (the most common kind), the signal is applied to the input terminal of the device (base, gate or grid), and this causes a proportional output drive current to flow out of the output terminal. The output drive current comes from the power supply.

[agedhorse]

Originally Posted by JimmyM

I was referring to peak power. Most amps have double their RMS rating. Sure, it's distorted heavily, but it's there. Micros are an exception, according to Bass Gear Mag, as most of them tap out shortly after they hit their peaks.

Hold on a minute Jimmy, there's some (common) mix-ups of terminology going on (not just by you... and i'm not pickin' on you unless you are buying the drinks )

There are several ways to express power and several ways to express exactly the same power level using different units of measurement.

"RMS" power is any power measurement that uses the true RMS (or DC heating equivelant) voltage and/or current in the calculation. The waveform is based on a sine wave shape. The equaltion is P=(Vrms**2)/R or any of the Ohm's Law derivitaves of course.

"RMS" power may be measured or used as continuous (meaningless for musical amp reproduction since the waveforms are not continuous sine waves) or based on a duty cycle. For example, both safety testing (many) and all FCC emission measurements must be made at 1/8-power which can be either 1/8-level or 1/8-duty cycle. (generally 1/8-level is what's used but both are valid). When designing power supply capacities, especially in very large amps, using duty cycle derating is of valid and practical benefit to the customer because of the weight and size savings for capacity that will never be used in practice. Duty cycle management is also used to limit the maximum AC current draw which may be a condition of things like UL or CSA acceptance... products like PowerSoft, QSC PL-380, the big Crown I-techs, etc. all use this because continuous power numbers do not have any value for our applications but carry the potential penalty of a breaker opening during a gig where something gets pushed (much) harder than intended... usually due to an "accident" or lapse of good judgement.

"Peak" power, when talking about a sine wave shaped waveform is exactly 2x the "RMS" value. It's purely a math difference... The peak voltage is 1.414x the RMS voltage for a sine wave, so when you square the 1.414 term in the power calculation equation, you get 2, and that's the difference. The waveform is the same, the expression of measurement is different.

Dynamic power, this can be expressed as based on either the RMS or peak voltage, but includes signal dynamics or duty cycle effects in the equation. Effectively, it CAN be a really good indication of how an amp might feel under typical dynamic playing conditions. Unfortunately, there's no real standard (that applies to bass) and many manufacturers have also taken these concepts and terminologies and bastatrdized their meanings to where they are worthless without the qualifying conditions.

[DrumsAndBass]

Are lightweight amps up to the challenge of amplifying a whole band ? Can they be used for large scale applications? The heavyweight amps can do that. Is the Class D amp technology so great that Class AB bass heads -for example- can just be left in the vehicle as backups ?