Digital amps

[johndenim]

About 15 years ago a bloke at my local P.A store tells me digital amps are going to be the next best thing.

 

Got me wondering, are they?

Apparently, at the time, he showed me an amp that could produce 750w per side at 4R that weighed 1KG and was 2U.

No T tranny, as it was not needed.

 

True?

How good are they?

And why don't we use them as standard?

 

To Add.

Sorry, wrong section.

Mods, please move to sound.

Thanks.

[TomyN]

Hi,

 

pure digital Amps are still expensive and Damping-Factor is still a problem.

On the other hand a lot of amps with switching power supply are on the market, which combine analogue amp designs with the low weight of the switching power supply. In my opinion hose amps are, even if they do not reach the efficiency of a pure digital amp, currently the 'best of both worlds' solution.

 

Tomy

[Doug Siddons]

Digital amps is a misnomer, what we are all striving towards is a 30 k system which weighs nothing fits in the back of a cortina and magically turns everything into sweet pure sound. The term digital amps came about when it was possible to replace the doughnut of a transformer in an amp with a nice shiny silver box which weighed a lot less. :)

[danburns]

I was about to ask what difference making the zeros and ones bigger would make...I think Doug's just answered it for me!

[Simon Lewis]

How good are they?

 

Switch mode power supplies are now commonplace and have done much to reduce amplifier weight. However, the amplifier itself often is still a Class AB, H, G etc., device. These can be very good, but are not too efficient and therefore generate heat - which needs fans and heatsinks to remove.

Class D is a switching amplifier, i.e. some form of pulse width modulation to regulate power delivery. This isn't "digital" per se (the circuit can be analogue or digitally controlled) but it is very efficient, generating little heat, and therefore needing less cooling.

 

Combine the switch mode PSU and the switching amplifier, and you get a lighweight amp that doesn't get too hot and is around 90% efficient.

Have a look at Crest's Pro 9200 or Powersoft amps.

 

The Crest unit supplies around 6500W in an 11kg package, and the specs are pretty reasonable - including a good damping factor at the frequencies that matter...

 

Simon

[KevinE]

The term digital amps came about when it was possible to replace the doughnut of a transformer in an amp with a nice shiny silver box which weighed a lot less

 

I think this is a little misleading, digital amp nowadays really means an amp with class-D output stage which synthesises its analogue output by PW modulating an HF carrier and filtering out the HF. Thus the linear output stage and weighty heatsinks are omitted.

 

A Switch-mode amp simply replaces the heavy mains transformer with a SMPSU and often preserves the analogue output stage, eg Crown Pulse, XTi, Chevin, QSC PLX etc.

 

Of course most class-D amps use both SMPSU and digital output stage as their main selling point is size and weight..eg Crown K2

 

There's no reason to suspect that an amp with lightweight switchmode amp should have any different damping factor than one with mains transformer, a common misconception is that because it has small capacitors it must somehow be weak. SMPSU amps have fully regulated DC busses, so as the current consuption goes up, the control compensates and pumps more power into it straight from the mains. And there's plenty of instananeous power there..try shorting it out!! (joke).

[Doug Siddons]

I think the term digital amp has become a bit like Hoover meaning a high power lightweight amp. There are many debates as to whether true class d is practically possible and of course each manufacturer will use these and other terms to sell products.

 

Just as the analogue digital desk debate causes much consternation, I would like to offer this 2ps worth and say that provided I don't have to lift them, toroidal amplifiers of the same power and manufacturing quality as their "digital" equivalent tend to perform much better in any given situation.

[mervaka]

surely at the end of the day it's a question of ability to respond to a signal and deliver current, so boils down to specific design, regardless of overall concept?

[Sarah Jones]

About 15 years ago a bloke at my local P.A store tells me digital amps are going to be the next best thing.

 

Got me wondering, are they?

Apparently, at the time, he showed me an amp that could produce 750w per side at 4R that weighed 1KG and was 2U.

No T tranny, as it was not needed.

 

True?

How good are they?

And why don't we use them as standard?

 

To Add.

Sorry, wrong section.

Mods, please move to sound.

Thanks.

 

 

Hi John,

 

I have two Peavey DPX amps which are 2U and can produce 750w per side. Can't quite remember the weight but they are very light. They are ideal for what I needed in terms of the compromise between portability and sound. I use them for acoustic music and they have given us fine sound over the years. As one of your other repliers mentioned they do generate more heat than you'd think and we had a problem when one broke down with heatstroke in the final rehearsal the day before a tour. It had just been PAT tested 30 minutes before! We took it to Peavey on our way to the first gig (having phoned them first) and they were superb. They put it on a bench and repaired it on the spot for us. However they did tell us that digital amps can be tricky to repair.

 

They work well for me but the downside is the potential difficulty if things go wrong.

 

Hope this helps,

Sarah

[ian hatch]

Hi all

Just a slight spin off from the original op.

Do 'D' class amps need less power to run them?

The reason for asking is, as a lot of people know, when you have to do pub/club gigs, the amount power available is normanly very limited, so any piece of kit that needs less power is all good to me.

 

Ian

[ACIDMAN]

Please do not confuse " D CLASS" with anything digital ! Class D was merely the next letter after C in amp classification, nothing to do with D for DIGITAL ! In the same way that " class A" does not mean ANALOGUE.

If it were digital they would use Pulse Code Modulation and they don't.

The D class amps use a more efficient form of power supply. Where a torroidal transformer uses power All the way through the sine wave a switch mode CHOPS it up,rectifys and filters the current to produce a higher current.

Where most torroidal amps are only about 60% efficient (as a lot of the power is dissipated in heat), a switch mode amp can be up to 90% efficient and produce less heat.

Oooh and weigh a LOT LESS ! Hope this helps !!!

[mackerr]

Please do not confuse " D CLASS" with anything digital ! Class D was merely the next letter after C in amp classification, nothing to do with D for DIGITAL ! In the same way that " class A" does not mean ANALOGUE.

If it were digital they would use Pulse Code Modulation and they don't.

The D class amps use a more efficient form of power supply. Where a torroidal transformer uses power All the way through the sine wave a switch mode CHOPS it up,rectifys and filters the current to produce a higher current.

Where most torroidal amps are only about 60% efficient (as a lot of the power is dissipated in heat), a switch mode amp can be up to 90% efficient and produce less heat.

Oooh and weigh a LOT LESS ! Hope this helps !!!

 

While Wikipedia is not the end all and be all of information, I think they have it right with regards to Class D amplifiers, which use "pulse width modulation" in tandem with a low pass filter.

 

It is not about switching power supplies, which can be used with any amplifier topology.

 

Mac

[Simon Lewis]

Do 'D' class amps need less power to run them?

 

Yes, they are usually more efficient, thus drawing less mains power for the same audio output.

 

A concurrent post has been automatically merged from this point on.

 

Please do not confuse " D CLASS" with anything digital ! Class D was merely the next letter after C in amp classification, nothing to do with D for DIGITAL ! In the same way that " class A" does not mean ANALOGUE.

If it were digital they would use Pulse Code Modulation and they don't.

The D class amps use a more efficient form of power supply. Where a torroidal transformer uses power All the way through the sine wave a switch mode CHOPS it up,rectifys and filters the current to produce a higher current.

Where most torroidal amps are only about 60% efficient (as a lot of the power is dissipated in heat), a switch mode amp can be up to 90% efficient and produce less heat.

Oooh and weigh a LOT LESS ! Hope this helps !!!

 

Acidman,

 

Sorry, but you seem to be confusing the switch mode PSU with the switching amplifier circuit. Switch mode power supplies (which you allude to) can be used with any amplifier topology to provide the +/- voltage rails. Such a power supply can be used to power other non audio devices.

 

Class D topology is a switching output stage, and the amplifier could be fed from a linear power supply with a conventional transformer. It just makes sense in most cases to combine the low weight switching PSU with the class D amplifier.

 

Have a look at the generic class D circuit on page 149 of Ben Duncan's book, High perfomance audio power amplifiers for music performance and reproduction.

 

Simon

[ACIDMAN]

Sorry Simon ! Not afraid to admit I'm wrong !!

[Chris L]

Hey

 

I don't know if anyone's done it commercially for pro audio yet, but I do know of a few places where Class T amplifiers are used. This is a new (well, practically) type of "digital" amplifier (ie the power transistor(s) are fully on or off at all times) which uses delta sigma modulation or pulse position modulation with a low pass filter. In theory they should be more efficient and lighter than a Class D amplifer as they allow the power transistor(s) to have a lower peak to RMS rating ratio (RMS / Peak). This in turn means it will give out slightly less heat, so smaller (lighter) heatsinks can be used. Also, it loads the PSU more "evenly", allowing smaller inductor/capacitor values to be used with a higher power factor.

 

Does anyone know of a class T amplifier in the pro-audio market?

 

Chris