Class D amps ...

Check out the Peavey DPC 1400X-

http://www.peavey.com/products/shop...details&item=00350750&wc=2A2C2&fam=2C&tcode=2

I love mine. There are a lot of other amps that use similar technology (switching) and are catagorized in various "classes" (ie; H class?). I'm not really familiar with these different "classes" and what they mean. Maybe someone could step in here with a little more knowledge about the digital switching amps?

 

Here ya go, an excerpt from TalkBass TechTalk:

Due to the nature of loudspeakers, amplifiers have to be designed so that a loudspeaker can move in (negative) and out (positive) the cabinet. In practise, this means separating the amplifier in two halves: one for each half of this movement. A problem occurs when the two halves have to take over from each other. At near-zero current, both tubes and transistors are non-linear. It means they will not reproduce the signal well (aka "crossover distortion"). This problem returns every half cycle of the waveform, as a waveform crosses zero twice each cycle.

Another problem occurs when the output devices of the amplifier are not fully "on". Because a music signal is of a constantly changing amplitude, this is practically always the case. The connected load of the amplifier receives part of the output voltage, while the output section gets the remainder of the supply voltage. This remainder is converted to waste heat. When an amplifier is working somewhat below its maximum power, more heat than output power is produced, even if the amplifier is theoretically ideal.

There are several ways to address these problems. They're called "classes". Not every amplifier class is suited for audio (there are more purposes for amplifiers). Only those who are, are listed below.

· Class A: Maximum current flows through the output stage at all times. This way the near-zero current is avoided, and thereby crossover distortion eliminated. An unavoidable side-effect is, when no signal is present, power consumption is at maximum, and the amplifier will run hot when no sound is produced. Better still, the amplifier will cool down when operating at moderate to high output power.

· Class B: The opposite of class A. No current flows through the output stage when in rest. Stand-by power consumption is nearly non-existent, but crossover distortion is eminent, be it acceptible for some applications (like speech or sirens).

· Class AB: The best of both worlds. A small stand-by current keeps the crossover distortion at a low level, and when silent, power consumption is only a fraction of the maximum power. Nearly all conventional power amps are class AB.

· Class D: As mentioned above, heat is produced when an amplifier output device is not fully "on". Class D amplifiers use digital technology to rapidly and constantly switch the output devices on and off, effectively avoiding the "in-between" state. By filtering (averaging) the switching frequency out of the output, the intended amplified signal appears on the output. This class is a.k.a. switching amplifiers. It won't be before long when every amplifier uses class D topology ('cept for them good-ol' tube amps, but then again, ya never know). When combined with a switching power supply, instead of a conventional heavy mains transformer, weight, mains power and cooling requirements can be drastically reduced.

· Class G: This topology uses two sets of output transistors and two supply voltages. One set controls low-to-medium power signals, keeping power consumption and heat at a moderate level. When high power is needed (during signal peaks), the second transistor set takes over and provides the higher voltages, fed by the higer supply voltage. As soon as the peak is over, the first set gets back to work.

· Class H: Much like class G, this system uses two stages. Only now the supply voltage is temporarily increased (switched) to deal with the peaks. The advantage is: you only need one set of (expensive) output transistors, and the switching can be done by much cheaper electronic switches.

 

Stewart makes various class D amps.
Peavey also has the DPC1000 and DPC750, and the DECA series. I personally have a DPC1000 and I love it!
Soundtech also makes a couple of Class D amps.

 

To the above-

I quick read-up on a few manufacturer's wesites revealed the following:

Stewart- Class H technology
QSC (PLX and up)- Class H technology

I'm guessing that the classes (D, G, & H) are often confused. Before I purchased my Peavey DPC 1400X the folks over at Bass NW almost had me sold on Stewart. Since $$$ wasn't an issue in my purchase, I went with the superior system which was the true class D amp.

Thanks to an "amp guru" at my local Mom-N-Pop shop I found out the following: Apperently it's a more stable system (class D) under fluctuating line voltage levels due to the fact that it's draw is constant under any load. Class G & H amps temporarily increase their draw under heavier loads (signal peaks, etc...).

There are probably a few things I'm missing but generally speaking the class D amp is better (and costs more too!). Hopefully this helps out the original poster a bit. Anybody else that has more knowledge then myself, feel free to correct me if I've posted innaccurate data.

 

I just snagged a Peavey DCM1000 on e-bay for $300 to replace my Stewart World 600. While it doesn't bridge into 4ohms (my Epi 2x12 is 4ohms), I can equal the Stewart's 600W out of it when driving a single channel, PLUS I can get the full 1000W if I add a second cab, which could happen in the future, as I may be playing some pretty loud funk/reggae gigs.

I've heard one too many horror stories about bridged Stewarts shutting down. I'll deal with the fan noise in exchange for that rock-solid Peavey reliability. Stewarts just seem very dodgy to me, particularly when they're actually pushing their advertised wattage

I'll post a report on the DCM1000 when it arrives.

 

NYC-

I've heard of some others from across the pond over in the UK. I can't recall the name. Does anybody else know of these amps?

 

Smartlight SL600 and 1200
www.sospubs.co.uk/sos/feb00/articles/smartlight.htm

 

Oooo,

nice! yet another single space, lightweight poweramp!

 

I had a good look at the smart light amps
Things look very good and the guys are very approachable on the phone...
Only problem is that the SL600 & SL1200 (£599) only run down to 8ohm bridged
Most people (myself included) want to run power amps at 4ohm bridged if possible.

The smartlight SL2000 (£999) will run at 4ohm but its about twice the cost of the SL1200.
Its a shame as I wanted to power my Goliath 6x10 4 ohm cab off the bridged section of the SL1200.

Not many other options I can find in the UK for single unit power amps putting out 1000w +

Dave

Anybbody know of any options other than the Peavey ditital power amp in the UK

 

I have a Laney B1 - 1500 W bridged , 750 W bi-amped at 4 Ohms. It's a class T amplifier which I don't fully understand but it sounds fantastic and it's very light. Got mine for £559 from a London shop.

An awesome amplifier and well worth demo'ing if you can find one in a shop.

 

My understanding is that while PWM changes the duty cycle of a fixed frequency wave, class T changes the frequency as well. Like all patent holders, Tripath claims it solves world hunger and peace in the middle east, but honestly I suspect the biggest benefits are in bumping the PWM frequency up closer to the Mhz range than your traditional class D home audio "subwoofer amp".

http://www.tripath.com/downloads/an1.pdf

 

The Stewart thermal shutdown problem is way way overblown. It doesn't apply to all of their amps, but only to the ones that don't have fans. Also, it applies to mono-bridging into the minimum load. Adding a fan to the rack usually solves a shutdown problem when it does occur.

I play in fairly loud bands and don't go through the PA, so I got a Stewart World 2.1 (has a fan). It's the coolest amp I've ever had in my rack... and I mean that literally! A couple weekends ago I played an outdoor gig in humid 95 degree weather, and my Stew delivered massive clean throbbin' lows: it remained cool to the touch, quite unlike my SVP-Pro preamp!

Oh: I'm not trying to sell Stewart over any other brand, there are other good lightweight amps out there. I'm just clarifying the quoted statement.

 

I have 3 Stewart power amps and have never had one shut down. 2 of my amps are the older PA-1000
which do not have cooling fans. If I play a loud gig in a hot location I use my World 1.6 which does have a built in fan.

I have some friends who have had Stewart power amps shut down on high temp. They use the amps bridged into a 4 ohm load. My big cab is an 8 ohm Eden so my amps do not see that load.

Chuck

 

I don't know that it's overblown. If an amp thermals out regularly while doing something it's specified to do, then that's a problem. It'd be one thing if they specified it as an 8-ohm minimum amp. But the power ratings are so much higher bridged for these amps, they'd loose their competitive advantage.

I have bought 4 used Stewart amps. 3 of them were broken when I got them -- this is a totally separate issue (power supply fried) from the thermal problems they have. Fixing this is expensive and takes 3-6 weeks, as the amps have to go back to the Stewart factory.

I've never had such consistent trouble with any other brands. I know there are lots of satisfied customers out there, but I wanted to relay my experience as well.

 

but lets be realistic,

seems like most of these "used" stewarts that people pick up are prolly be sold because the previous owner obviously DID NOT take good care of 'em.

seems like most of the guys here, who bought the Stew's brand new, understand that with a little common sense, a person can take good care of their investment by using the stew's in a well ventilated rack space, using only enough power in the situations called for, etc.

IMHO, i dunno why ANYONE would need to blast 1200 watts at all. but for some odd reason, people are cranking them up soooo farkin' high, causing them to overheat and shutdown, and ruining a great piece of bass gear. its obvious the Stewart 1Urack's get hot, and that they dont have a fan. sooo, i say lets use our noodles, yea?

if you need the piece of mind a variable fan gives you, then Soundtech, Peavey, and now Smartlight, all offer you that option with a slightly heavier box.

 

Class D amps first made their appearance in the audio world a number of years ago for powering subwoofer cabinets because the earlier designs lacked enough high frequency response to get a good full range signal. The reason for this was that the semiconductors available could not switch at a high enough frequency to increase the audio passband to an acceptable level. There were also other filter design and circuit feedback challenges which limited the upper passband and further contributed to the poor full range performance.

The EA circuity uses modern components in a well proven proprietary design which gives a useable frequency response up to about 20Khz. Actually, we can increase the audio passband to 50KHz if desired, but this offers no performance improvement to the bass player in a MI application. The circuitry runs at about 90% efficiency and even full power sine wave signals won't trip off the amp on overtemperature.

We also did some serious audio tweeking to get the iAmp800 to sound more like a tube amplifier, and reports from the field have indicated we have succeeded. On the other hand, the iAmp200 (used in the Wizzy combo) has a more crisp sound than the iAmp800 and better contributes to the awesome punch we wanted to achieve from a small lightweight combo system.

A lot of time was spent getting the Class D amps to sound gorgeous and we encourage anyone interested to do an A/B listening test comparison with any other linear amp product on the market. While all amps have inheriently a different sound, you will find the EA sound to be open, transparent, and fast, and perfectly suited for the professional player who wants no unwanted coloration. We at EA are convinced that Class D technology is the only option to reduce the size and weight of high performance MI gear, and we will continue to push the technology.

Gary Gibilisco, Euphonic Audio, Inc.

 

I want it, but I don't want it $1400 bad.