Class D audio amp

[walter]

This morning I recieved some E-spam about the TAS5261 class D audio amplifier. I am familiar with class A, AB, and C, but have not heard of D. Apparently it's a single ended digital, high power audio amp. Does anyone know anything about this?

 

[Svart]

Class D is PWM quantizing and MOSFET drive via an RF carrier wave. good stuff. clean and very efficient.

However that part# is only the driver bridge, not the quantizing IC.

 

[SSLtech]

Yup. It's like switch-mode, usually PWM.

Been used in bass amplifiers for a good while, generally considered down-market, got a reputation for unreliability and generally being near-impossible to repair.

It's all about cheap, not about good.

Keith

 

[Svart]

ah I see Keef hasn't been keeping up with the market!

Check out the Zetex stuff Keef, the specs are pretty good and the parts are only getting better. Some of the most high end Audiophool stuff has Class D and you'd never hear the difference.

It's all in the implementation and care in design.

 

[clintrubber]

[quote author="SSLtech"]It's all about cheap, not about good.

Keith[/quote]
Yes, and soon in every theatre, sorry, amp near you (if not already).

Did you think you can buy a 5.1 home-cinema system for some small change and have the manufacturer still adding decent heatsinking etc to the box ? Efficiency has to go up, material costs down and as long as you don't replace the cardboard speakers that came with the set you won't ever find out about the uncoolness of that cool class-D amp.

Don't blame the people making class-D amps, but blame the consumer that wants to have it all - but needs to have it for cheap.

And no !
Class D can be mighty fine though; read this (on the website of a respected amp maker, article by Bruno Putzeys who knows where he's talking about):
http://www.bryston.ca/newsletters/74_files/vol7is4.html

So please don't leave this thread with the idea that class-D is always inferior. There are many tastes in or ways to class-D, just as there are in class A & B.
So then why 'risk it' when you can have a fine A- or AB-amp ? Each class has its pros & cons. I don't want to sound like an ad, but it'd be hard to deny several advantages of class-D (if the sound is still OK of course, a debate we better leave for another time and I rather don't join).

Example: let's say for now that these line arrays are active, so with the power stages & supplies inside. Imagine the difference in weight for stuff like that. Less heatsinking required because of the higher efficiency. And since less power lost the supply can be smaller & therefore lighter.

Regards,

Peter

 

[SSLtech]

Actually, I can buy that.

I should amend my comments to say that most of the ones which I've seen have not been good.

Keith

 

[Svart]

Like I said:

Some of the most high end Audiophool stuff has Class D and you'd never hear the difference.

I've been doing a lot of research on Class D for my own work and some of the really high end HI-FI stuff uses class D.. hint hint.

 

[walter]

Thanks for the feedback. For the last couple years, I have been working with highspeed switching power supplies in audio equipment. The power amps in these seem small for the output. I usually change out assemblies, but sometimes I get to the component level and learn something new.

 

[Gus]

The acoustic image bass amp I heard sounded good.

 

[Boswell]

Try this link:
http://minidisc.org/classd_amp.html

 

[Rochey]

[quote author="walter"]This morning I recieved some E-spam about the TAS5261 class D audio amplifier. [/quote]

How rude :wink:
If you don't like getting emails from TI, you can simply opt out in your my.ti.com profile.

However, I actually enjoy getting those emails once in a while - it really fires of some potential ideas for products... even when they are competitors products :green:

 

[Mendelt]

[quote author="Svart"]Like I said:
I've been doing a lot of research on Class D for my own work and some of the really high end HI-FI stuff uses class D.. hint hint.[/quote]

I've heard a couple of class-D amps.
Some of them are completely crap. My mp3 player has a class-D amp chip to be able to drive a headphone output from a 1.5V battery and it sounds horrible. Most car-audio is class D too.

But there are some really good class D amps too. And they're certainly not audiophile foolery. I heard a UCD amp (bruno putzeys was involved with that one if i'm not mistaken) and it was the closest i heard to the 'wire-with-gain' amp that i heard untill now. The diyaudio forums has an active class-d community. They're building amps from class-d modules (like the ucd ones) and there are even some people DIYing complete class D amps.

The higher quality class-D amps are surprisingly similar in layout to normal class-B amps. The biggest difference with normal amplifiers is that they introduce a deliberate 180deg phase shift in the feedback-loop at the desired switching frequency so the amplifier starts oscillating, because the output is limited by the power rails you'll get a square wave output. Instead of using an opamp as an input buffer you can use a comparator so to pwm the oscillation.

These amps are not much more complicated than a class a or b amp. So they're it's not that difficult to repair them. And theyre not inherently unreliable. Some older class-d amps had problems where both output-fets conducted at the same time in the crossover region effectively shorting the power rails for short periods. So they blew up after some time. But most modern class-D amps are as reliable as any other amp.

 

[Mlewis]

i heard that these were class D amps.

http://www.lipinskisound.com/l301.aspx

So the storey goes, Lipinki's design goals were to match if not excede the performance of what everybody seemed to be powering the L-707s with, ie. the Pass Labs X250. Given the rave reviews of the speakers, subs and mic pres, i'm inclined to beleive they're not to be sniffed at.

 

[Mendelt]

[quote author="Mlewis"]i heard that these were class D amps.
[/quote]

http://ralaudio.com/lipinski-l301-threeinone-speaker-amplifier-p-86.html

Yup, looks like class-D... big inductors for filtering the switching frequency from the outputs.

 

[Mlewis]

i have to say... I'm not sure if that actually is a pic of the L-301 guts. It looks suspiciosly identical to the pic on the lipinski site for their S-1000 sub amp

http://www.lipinskistore.com/store/product_info.php/products_id/36?osCsid=e9a0af516a07f5e3ffb2599956c78bfd

(exact same angle, cable knots etc just with the background photoshopped out) which makes me wonder if R.A.L. Audio have fudged the pic. i'm pretty sure they would look similar naked though so your coments still apply i'm sure.

 

[rotation]

This week i bought the Hypex UCD 180ST modules. Paid 50 euros for each.
I tried them and they sound good to me, better than any of power op amps i heard. But problem is that almost all components are smd including op amp at the input. Btw, Hypex is claiming it is possible to change and experiment with op amp and in/out capacitors, that's why i bought modules. But as i said, they are smd and very difficult to change them. That's the only bad thing i can say.

 

[Svart]

I saw those some time ago but they are difficult to get here in the states, at least I can't find anyone who has them to sell. I'd like to see if they use off the shelf ICs or custom programming.

Also from what I can tell they are also only running half bridge (180deg), not full bridge even though they say they are in their literature. the 180 model only has a pair of heatsinked parts it looks like from the tiny picture. I think will affect the distortion charachter but they claim >=1% with +-45v rails.

EDIT: I see that their basic design is the same between all modules, the voltage rails are just higher.

Can you take a closeup picture?

 

[bobkatz]

[quote author="SSLtech"]Yup. It's like switch-mode, usually PWM.

Been used in bass amplifiers for a good while, generally considered down-market, got a reputation for unreliability and generally being near-impossible to repair.

It's all about cheap, not about good.

Keith[/quote]

Not necessarily, Keith. These amps have come a LONG way in their development. You would not believe their tonality, with the proper board layout (critical) and good power supply design, not necessarily a switcher, either. Sonically, the Bel Canto EVO is very nice. I've just received a pair of Class D Lipinski amps and I'm wiring up my speaker cable as they are "power biamped" in each channel. I'll let you know how they sound compared to my $6000 Class A Pass X250!

Bruno Petsys knows where all the class D bodies are buried and he makes excellent-sounding Class D amps.

 

[bobkatz]

[quote author="Mlewis"]i have to say... I'm not sure if that actually is a pic of the L-301 guts. It looks suspiciosly identical to the pic on the lipinski site for their S-1000 sub amp

http://www.lipinskistore.com/store/product_info.php/products_id/36?osCsid=e9a0af516a07f5e3ffb2599956c78bfd

(exact same angle, cable knots etc just with the background photoshopped out) which makes me wonder if R.A.L. Audio have fudged the pic. i'm pretty sure they would look similar naked though so your coments still apply i'm sure.[/quote]

Lipinski is using a standard module (I don't know the manufacturer) so it may not be a coincidence!

 

[Svart]

and good power supply design, not necessarily a switcher, either

Yes it's very common to use rectified and smoothed but not regulated rails too.