Class T-amps

[dave2010]

This post - http://theartofsound.net/forum/showp...66&postcount=9 - referring to a Hlly T-amp 90 got me interested. I'd never heard of class T amps before, so I looked them up - http://en.wikipedia.org/wiki/Class_T_amplifier Seems they're a modification of class-D amps, and typically based around a chip - such as a TA2020.

Then I looked up some reviews, and I found this which refers to several DIY amps - http://www.tnt-audio.com/ampli/tripath_amps_e.html

One amp, the Sonic Impact (model 5066) seemed very cheap, and also quite elegant. However, so far I've not tracked those down. The reviews were a bit curious, as it sounds as though these class T amps have both a wow factor, but are also maybe a bit tiring to listen to. It's not clear how tiring, and how long it is before fatigue sets in. If it's an hour or so, then using these effectively with an alarm radio or similar perhaps doesn't matter, Maybe also the fatigue is less obvious if one is working at the same time - though it might depend on the work.

Looking at the review, mention is also made of Gainclones, so I looked them up too - http://diyaudioprojects.com/Chip/LM3.../LM3886_CA.htm Basically they seem to be amps made using only a very few components - typically ICs. Maybe quite good, and fun for DIYers and projects.

This article - http://www.6moons.com/audioreviews/sonicimpact/t.html - which is specifically about a Sonic Impact amp, maybe indicates some of the fatigue problems - with THD and noise rising as the power rises - see graph.

There's a thread on avforums also which is of interest - http://www.avforums.com/forums/hi-fi...jaw-drops.html

So, now my appetite is slightly whetted. I went to ebay to see what I could find, and these turned up - http://cgi.ebay.co.uk/TA2024-Class-T...item2a05c8622d For £20, if they work then maybe they could be a good buy. There are plenty of others, but these were the cheapest new ones I found. There are some SH ones from around £10, though usually shipping is extra. This one is similar, though probably uses a slightly different chip (TA2020 instead of TA2024) - http://cgi.ebay.co.uk/SA-36-Class-T-...item414e459e3f. You can see more if you search for "class T-amp" on eBay. I think some are probably intended for cars, but there's a lot of evidence that they can drive "real" speakers.

So, are any of these any good? Maybe they are "good value for money", but really sound "****", or maybe they're actually bearable. What do others think? I note that some people have tried making these or modding the amps - could be fun, though the results don't seem to be much better. At these low prices though, could be entertaining.

[The Vinyl Adventure]

I have a temple audio bantam amp.. More expensive that the chinesse jobs but I went for it as I guessed I could send it back if it was crap ... It wasn't crap, in fact, I really like it... Very basic, a little lacking in bass but pleasant to listen to ... Works very well with a stan dac and my dynaudio a42's - it would suprise you how good the sound is I would have thought
Also have a pair of gainclones that a fellow aos memebr built and sold me... They are awesome for the money! Really very suprising the sound quality from them!

[leo]

I once built a TA2020 based amp just for fun, I got a diy amp module from a place called 41hz .com and stuck it in a cheapo metal case, the whole thing was pretty cheap to build and didn't sound bad for what it was

[Ali Tait]

This hlly amp is better than ever now it's run in.Check out DIYAudio for the Class D subforum.Lots of good advice there.Some have posted about my amp,saying it's a little dark and coloured (it uses the TA2022 chip) but I find it very natural and open,very like a valve amp in fact.They do say this chip has a distinct sound compared to the others.I suspect I would find the other types a little too clean and clinical for my tastes,being used to valves as I am.There is a thread on a DIY 2022 module there too.I just bought this particular one as I wanted the power to drive my statics.It sounds so good on my MLTL's that I haven't got round to trying on the statics yet.To put it in perspective,this amp is clearly better than the Musical Fidelity A370 I had.It's that good.

[Vincent Kars]

A couple of years ago the T-amp was hot. It was based on the Tripath's design.
It is still on sale: http://www.trendsaudio.com/index.php...d=37&Itemid=28

[UV101]

Not quite a T class but I recently purchased a couple of chip amps for m rear channels. Coupled to a 225va transformer, I tested on my main fronts 1st and was blown away! Not quite my Restek but then they cost about a 20th of the price!!!! These are awesome VFM!

[john blackburn]

If you don't need much power give the LM1875s a look at, cheap to build and a nice sound.

John

[dave2010]

It occurs to me that interest in this type of amp is for one of two reasons.

1. The need for a small, neat, cheap amp of reasonable quality

or

2. The desire for a high quality amp implemented relatively cheaply.

Some people might also add in

3. The desire/need for a cool running efficient amp, which uses relatively little electrical power.

Although I like the idea of using little power, here I'm discounting this as a dominant factor for most of us.

The first case probably applies for subsidiary systems. In my case that might apply to systems for use in the kitchen or bedrooms. Fewer, smaller and unobtrusive boxes would be desirable. Different people might have views about what is cheap, but in my case I'd probably put it at £50 or less - others may have a higher threshold, while for some £50 might be considered expensive.

The second case is where the quality is the dominant factor, so prices could be significantly higher, but would only be worth paying if the quality is similar to, or substantially better than, other amplifiers in the same price range. Larger size would not be a problem for this application.

I don't know what the differernce is between the so-called "class-T" amps and class D amps, except that the T amps are following designs originally from Tripath, and based on a (mostly) one chip design.

I note that it's now quite common for some equipment to have essentially class D amps embedded. Examples would be the new range of iMac computers, and multi-channel surround sound systems. A clue in the latter case would be the power output of the total system. In my own case I have a surround sound system (Sony, fairly cheap) which has a claimed power output of over 1000 Watts into 6 channels.

It occurs to me that I could get an impression of the sound of such digital amps by feeding the signals from my audio kit into the surround sound system, and attaching the speakers from my audio system to that.

Would that be a reasonable thing to do? If you've been following, you'd notice that here I'm operating in my mode 2 - prioritising quality over other factors. My decision as to whether to pursue this further would then depend on how I liked the sound from the surround sound system used as an amp. Of course it is also possible that even with such digital switching amps that there could be differences in quality, and that some are audibly better than others, though at first glance it's a bit hard to see why that should be the case. Even the poor DC offset control of some cheap class-T amps shouldn't make too much difference most of the time [I can't see why the DC offset can't be blocked easily by a capacitor, but what do I know?], though would be undesirable in a really high quality system.

For my own decision, if I liked the sound through the surround system, I might then go and look for a decent digital amp, and could then be prepared to spend £00s, but if I didn't find it to my liking I'd be more inclined to spend less, maybe even buying one of the cheap Chinese amps, and then be prepared to spend rather more on a more conventional amp for my main system when I get round to upgrading it.

Would that be a sensible way to go?

[Ali Tait]

The cheap to run bit was exactly why I bought this,the great sound I didn't expect! This was to be used for playing tv and films when I get the direct-coupled amp,as I didn't want it to get such heavy useage,bad for valve longevity,and also the fact that power consumption will be 500w+! Expensive when running several hours every day,hence the Tripath amp.It does sound way better than I expected,and very like a good PP valve amp.

[Vincent Kars]

I'm not very good in electronics but what I understand is that T uses pulse width modulation and Class D amplitude modulation.
Class D is not digital, it uses a oscillator to amplify, in essence it is AM, (amplitude modulation) well known from AM radio. http://www.hypex.nl/docs/allamps%20hypex%20layout.pdf
Both are pretty frugal, Class D > 90%
This is probably the reason why D is implemented in all kind of portable devices.

Would that be a reasonable thing to do?

Yes, maybe it is not the best possible Class D implementation but as a 'proof of concept' a very interesting experiment.
I drive my Apogee's with 2 Class D mono blocks, UCD 400 with HxR regulators: http://www.hexateq.com/