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Budget Direct Digital Amps, 4 Way Comparo.

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Have you heard of Direct Digital Amplifiers?  Yes?  No?  What about Power DACs?  They're pretty much the same animal so if you've heard of one then you've heard of the other too.


In a nutshell, a DDA or PWR DAC is a small, integrated style, unit that does away with an actual DAC chip and uses the digital stream (via a pure digital DSP chip) to directly drive a switching (or class D) amp.  It is an interesting idea that was fairly low key until NAD brought out its C390DD.


Now the NAD C390DD is circa $3K aussie and making some serious waves in audio circles, but what DDA or PWR DAC offerings do we have from other manufacturers?  Well, nothing from most of them (the tech has yet to catch on in a big way.), but there are a few budget offerings available.


Wadia have an offering in the 151 PowerDAC mini which until recently retailed at $1200 but can now be had for under $800.



NuForce have two budget offerings in their “Digital Input Ampsâ€, the DDA-100 ($650) and the Dia ($250 to $300).



Chinese company QLS have their QA100 “Full Digital Stereo Amplifierâ€.  RRP $380 purchased direct from QLS and delivered to your door in Oz.



And Hlly, another Chinese company, have their D3 and D5 amps which they (for whatever reason) choose to list with their gainclone amplifiers.  A D5 will cost $380 delivered to your door from China.



And the big question on everyone’s lips is:  “Do they sound good?†

Well, as I have discovered, the answer is “Yes.â€


This all started when I read a snippet of news on John Darkos DAR website announcing the release of the QLS QA100.  How dare he announce news that is this addictive!

Anyway, wether it’s JDs fault or not, :D  over the last 12 months I have managed to collect one example from each manufacturer, a Wadia 151, NuForce DDA-100, QLS QA100 and Hlly D5 so, let’s see how they compare shall we?


I'll start with a pic or three.

post-130663-0-42000700-1365069976_thumb.           post-130663-0-22278500-1365070112_thumb.          post-130663-0-00986600-1365070232_thumb.


From top to bottom, Wadia, NuForce, Hlly and QLS.


In the past I have had a few issues with these DDA units dropping channels and cutting out so I thought I would give them a bit more of a workout than usual so I came up with a test just for them, I called it a Power Delivery test.  I stuck Dire Straits Heavy Fuel on the player and jacked up the volume until something gave in, the results are rather interesting.


The rest of the test system details are as follows.

Source is a Consonance cd120 via digital out through a $20 Crest cable into the amp and then via Lenehan speaker cables to my Lenehan S2s.  The S2s, while easy to drive are not very efficient, 86db*, so they take a bit of grunt to get them to puch the volume up.


Wadia 151.  25W into 8Ohms.  $750-ish.


John Darko has beat me to this one, he has an excellent review of the amp here:


So I won't go into too much detail except to say that this little thing sounds superb, its strengths are clarity and detail but it does an excellent job on everything really.  The only criticism I have is that the bass could be a little deeper but that's being extremely picky.  When it comes to micro detail and sweetness to the ear the Wadia is hands down the winner of the pack, it does seem to be a little low in the power department but as long as you are not into heavy rock or metal that is really not an issue.


On the Heavy Fuel test I maxed out the volume (80 on the screen) and that translated into 97.2db on my SPL meter.  Not bad at all!


NuForce DDA-100.   50W into 8Ohms.   $650-ish


I was expecting good things from NuForce as they have a reputation similar to Wadia and class D amps are their speciality but I'm afraid this amp was a bit of a let down.  Yes it has a good amount of power and it certainly shows no breakup on the highs but it is just a bit too neutral for my taste.  I would call it accurately neutral but bland, it needs a little more zing and a fair bit more soul.  Certainly not a bad piece of kit but just not emotional.

I have had a channel drop out on this amp in the past but in this test, no matter what I did I could not get it to misbehave.

On the Heavy Fuel test I pushed it up to 98db and held it there until my ears gave out, that 98db was reached with a few more numbers left to go, 4 from memory, on the screen.  At this volume level it was pretty hard to handle the NuForce, but the Wadia maxed out was actually OK to listen to. 


Hlly D-5      110W into 8Ohms.    $380.


This puppy has an attitude, it sounds good, nice and strong and clear (not in the Wadias league but more enticing than the NuForce) but a bit agro.  Almost like it was born wanting to sing for Def Leppard.  I have to say I liked the sound of this amp, it wasn't going to be everybodies cup of tea because it was obviously intended for rock and metal music but I have to say it did better than I thought it would on lighter vocals and metallic highs and it kept the edgy sound throughout.  It delivers nice deep and strong bass and has a more focussed attack than any of the other 4.


But there is a background story to this one, the amp on Hlly's website is listed as 80W per channel so this one is either the updated version or an experimental one.  When it arrived and I went over the invoice it stated the value as $30 and that it was a pre-production model for demonstration use only.  I decided to fire off an email and ask what the go was but the website I bought it from has ceased to be (bye, bye HiEndKing), it has a completely different power supply to the 80W unit shown on the website, that unit has a torroidal transformer and this one has what I am guessing is a switching power supply with a similar design to the other units.


I am hoping that this unit is a prototype because on the Heavy Fuel test it started to cut out and cut back in at a mere 86.4db, there is no volume display so I don't know how far along the "dial" this was but it was reached very quickly.  A very disappointing result!  There is no way I could possibly recommend this amp if there is something obviously wrong with it.


QLS QA100   60W into 8Ohms.    $380.


I've had this one the longest, long enough that I covered it in my "Addicts Guide" thread back when I was using my Osborn Eclipse speakers.  I liked it then and I have to say it sounds a bit more capable through the S2s, the Eclipse were a fussy speaker in the highs where the QA100 showed a little bit of standard class D behaviour but the S2s are not so fussy and that class D behaviour is completely absent from the QA100 I am listening to now.  It doesn't have the clarity of the Wadia but it does have far more soul and body than the NuForce and it has a nice deep but smooth bass that beats out both of them.

There is also one little handy function it has which is that it remembers the volume settings of each of the imputs, I found that very useful when moving from music to TV.


The Heavy Fuel test produced a 98db result very quickly with more room on the dial to go, it did get a little tinny above about 92db but that's fairly normal.


So from loser to winner we have:


4.  Hlly D5    Can't get to 87db!  And you call yourself a rock amplifier!  Hang your head in shame!


3.  NuForce DDA-100   Not a bad amp, but just not anything special.  The base model Camry of the PWR DAC world.


2.  Wadia 151  (For those of us that like rock.) or QLS QA100 (For those of us that like vocals, Norah, Dianna, Peggy, etc.)


1.  Wadia 151  (For those of us that like vocals, Norah, Dianna, Peggy, etc.) or QLS QA100 (For those of us that like rock.)


If I was rating things purely on a value scale I would have the Wadia 2nd and the QLS 1st but really, it depends almost completely on your intended musical target range.


If you are after a small form factor and good quality sound the Wadia and QLS units will not disappoint, the NuForce amp may be what you are after if neutral is your thing but on the subject of the Hlly, I would wait for the next model before I tried again.


Remember the * next to the 86db way back above the Wadia section?  Well it was there to remind me of the reason I started this whole thing.  Everyone is talking about the Usher S520 as being a kick arse bookshelf speaker at a rock bottom price but it (like the S2s) has a low efficiency and so needs an amp that can deliver some grunt to make it get up and really sing at volume.  The Redgum SG5500 is a popular choice but is now only available second hand and if you want a cheap amp with grunt then your choices are pretty limited, hence my investigation of the Hlly, NuForce and QLS amps above.


At $380 bucks the QA100 still breaks the '50% budget on speakers and 30% budget on amp' rule but it is the cheapest candidate I can find that I think will really work.  I'll have to investigate the matter further when my S520s arrive.


Cheers folks!


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Thanks for the review cafad! What do you think of the QA100 paired with the Johnblue JB3 for a desktop setup? How much of a step down would the nuforce Dia be from these amps?

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Glad you liked it fangdangled.  I haven't heard the nuforce Dia but I would be guessing a fairly similar sonic signature to the DDA-100 at a lower power rating.  That little JB3 looks like a nice speaker I can't see the QA100 having any trouble powering it (unless it hides a truly scary impedance curve but I don't imagine that is likely, not with its intended market being smaller amps). 


If you decide to go down that road let us know how they sound as a set.

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Thanks Cafad - I have a Wadia 151. I think it is highly underrated in Australia. Maybe the price drop will help.

I just like the small footprint, the looks, the ipod dock etc and that is why I bought it (before the recent reviews)

Since I used it with an old set of AR 18S I just cannot sell it. 

Mr Darko's review is also excellent, thanks for the link.

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Cafad. What a tremendous post. Truly.


You should team up with Cafad and then he'll have a job!

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I agree - great write up.

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Great reviews. Your dedication in the pursuit of this hobby is commendable.

Someone recently said the ME850 would be superior to all the class D amps. I believe the specific adjective used was mediocre. Thoughts?

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Thanks guys.  I have 4 pages of scribbled notes, one on each amp, but when it came time to do the actual write up I was pretty tired so I just stuck to the basics.  If anyone has any questions I've got a fair amount of info to refer back to.


Thanks for the thought pchan, how is the superannuation package for a reviewer starting out JD?  Can you claim travel to and from audio shows as a tax deduction?  What about accommodation?


I can't say I've heard any ME gear audiobugged, was a price range mentioned?  Some of the class D amps available are very good but they are also very "well endowed" when it comes to their RRP.

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Cafad. What a tremendous post. Truly.






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The S520s arrived yesterday, I hope they enjoyed the scenery on the way because they certainly took their time in getting here but, now that they are here I can move forward.  Very nice looking speakers, even Toms pics of them do not do them justice.

They sound good too, I plugged them into the system without any other mods and they absolutely loved 180 watts of clean power.  I decided to get a bit more realistic after watching some TV and I'm now running them in with the Xindak A08 (trying to kill two birds with one stone, the Xindak is one of those amps that I am hoping improves with time).  Once they're run in for 100 hours or so I'll start swapping in direct digital amps and see what works best.

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I'm listening to a Xindak A08 and S520 set up at the moment.


My Cary pre is in the hospital for a broken tube socket.


I'm amazed at how easy to listen to this combination is. There's obviously a huge difference between these and my main system but for the price the Class D Chinese amp and the Ushers are stunning.


Of course I'm getting close to 60 so my top end hearing is sadly lacking so I can't hear any major problem with the Xindak.

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Great review thanks Cafad. Excellent writing style too.


If any design team can nail this design  genre it would be Wadia with their long legacy of brilliant filtering innovations.


It would be nice to put the Wadia 151 with a speaker with >93dB sensitivity. Do you now anyone with some Zu's?

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Actually I do, I may have to send it Damos way once I'm done.


A. Dent:  The Usher/Xindak combo does sound pretty good.  I'll put off the critical listening until later in the week though, otherwise I may have to change my mind once they're run in.

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Well I have to say that the Usher/Xindak combo sounds very good, but be careful as to how you go about it.  I found using the Xindak's internal DAC gave a 5db softer sound but it mostly avoided the typical class D brightness and glare.  Feeding the A08 an analog signal via Bunnings ICs sounded terrible, tons of glare and brightness, harder metallic sounds and just generally making my teeth hurt while listening.  Swapping the Antsig (Bunnings, $28 for two) for Ribbonflex ICs made a profound difference  (certainly the first time I have managed to to hear a definite difference using an integrated amp) 90% of the glare was gone and it was a very agreeable amp to listen to.  Plenty of power and punch, vocals were good if edgy on occassion and the highs seem to ring out a bit too far but I could live with it.  Then, after wondering why I tried a pair of $600 plus ICs with sub $400 speakers I swapped the ribbonflex for LBP Papakaio ICs and they were almost as good (a bit more brittle but considering the price difference they were pretty close).  It seems that the Xindak A08 might just be hiding a secret, it does not like stranded ICs!


So far I've tried the QA100 and the Hlly D5 with the Usher S520s and they both sound great.  I think I'd actually prefer the Hlly D5 if it was a fully functional piece of kit, great edgy sound but again it died above 86db, but as it was the Qa100 does a great job, a smoother presentation than the Xindak but with less power available for that shear punch the Xindak manages to push into the foreground.  I would have gone further tonight but I was a touch distracted by taking apart the Hlly D5 and trying to figure out what was wrong with it (any DIY'ers out there care to speculate, I've got a soldering iron now so suggest away!).


The general sound of the Ushers is awesome, a great midrange that really lets the vocals roam around the room, nice highs without any breakup (in fact they seem to act to curb the typical class d sound quite a bit, almost as if they were designed with an "anti-glare" function), the only quibble I have is that they just don't have the bass depth for rock music.  Still, I knew that going in so I shouldn't be holding that against them.  They really are a great little speaker, and I have found that they respond well to a 3kg weight placed on top of them.


I hope to get to the Wadia and the Nuforce tomorrow night.

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Hi Cafad


I've been listening to my Xindak S520 combo exclusively since my Carys have been out of action.


I'm using my AP2/PP into the internal DAC and the sound is pretty good apart from the (about) 5dB drop in volume. (why would this happen?)


Still, the best SQ with this combo is from the matching Xindak CD player (also bought cheap on eBay) via Chord Chameleon XLR ICs. I've tried 8 different ICs and the Chord XLRs are clearly the best.


I'm still stunned by the quality of this cheap combo and honestly do not hear any glare the way I have it set up.


Thanks for the effort you have put into this thread. Your writing style is compelling. Keep it up.



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Thanks for the kind words Andrew, I certainly intend to stick with the hobby for a while yet.


As to the drop in volume between the internal DAC and an external line level signal I imagine it is due to the internal DAC not needing to boost its output up to line level so when you use the internal DAC the power amp section is getting a signal that is weaker than line level and it gets the same amount of amplification as the line level signal via the power stage so it comes out weaker overall as well.


I wonder if this ability to "work with" class D amps is typical of the entire Usher line, anyone know?

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I wonder if this ability to "work with" class D amps is typical of the entire Usher line, anyone know?





I've been coveting a pair of BE-10s

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Most of the Class D amps I have heard seem to have quite poor image depth.The soundstage seems to be spread out around the speakers with not much going on in between .

The Xindak seems quite good for image depth.I was surprised because I have heard the ICE amps in other  products and they never sounded right in this regard.So Xindak appear to have done a great job with the A 08.

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I did get to the Wadia and the NuForce, but there were no exciting moments to be had.  The Wadia continued on its excellent way sounding nice and clear with less bass than when heard on the S2s (as I said, no surprises there) and the NuForce was also a carbon copy of the S2 performance with a bit less bass (and only a very little amount of glare).


If anything I think the winner of this exercise is the Xindak A08.  I know, technically it didn't even enter but its performance on the S520s is so unexpectedly good that it stands out in the mind.  It is true that there isn't a lot of bass to be had from the Ushers but the Xindak manages to counter this somewhat by using its power to push up the level of impact and presence of the music.  I suppose it does sort of count as a digital amp since it has digital inputs but its RRP is usually around $2K so I doubt too many people will be buying one of those to pair with S520s.  However if you can snag one over ebay (as I did) for about $800 then that is a whole different ball game.


From the original starters the ranking remains the same.  I'll keep trying to "fix" the Hlly D5 (no luck yet!) but as I said earlier it's better to wait for a new model, unless you're a DIY'er looking for a challenge.


I hope I've given some S520 owners some options to mull over and maybe an upgrade or two to think about.


Cheers folks!

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There does seem to be excellent synergy between the S520s and the Xindak. Almost fluky really.


I tried the Xindak on my Tannoys and it was totally unlistenable due to the glare. Fellow SNAer, SuperThumb, was over for a listen to the Tannoys and the only amp I had working was the Xindak. I think I may have permanently put him off both Tannoys and Class D amps because the combination was so bad.  


Luckily I have my Cary pre back from the repairer and I can now use the Tannoys again.


If people are contemplating one of these Class D amps they are going to need to try it in their system first because there could easily be a horrible mismatch.


Thanks again, Cafad, for your interesting thread. I was reluctant to try a Class D amp before you started but now I'm convinced they have a bright future.

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I'm a Class D / Digital convert. I own a Nuforce, a Denon PMA50 and a QLS QA100 (the QLS just arrived). What these "pure digital" amps give you is an incredibly clean sound.


I'd agree with the assessment here that the QLS has more soul or groove or whatever than Nuforce. There are still ways that Nuforce sounds better - if you want TOTAL cleanliness basically! The Denon is great too, but not as clean as either of these.


For sure the QLS QA100 seems like a crazy bargain in terms of power and digital goodness for your pound or dollar!


Oh yeah, and the chunky metal volume control on the QA100 - and something about the digital stepping of that volume control - is better than any of the volume controls on any other Class D amp on the market (Nuforce / Denon / NAD). So if it's all about the volume knob - go QLS!

Edited by Justin Keery

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Thought I would re-ignite this topic to see if there are any new contenders on the scene for a sub $300 digital amp. Anyone have any experience of these amps of late?

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Well there are a fair number of options available in the sub $300 market but you have to move down a notch from the four amps I was looking at originally as none of them were under $300 back when I started.


There is the SMSL Q5 which I have heard but wasn't a great fan of.  It sounded a bit thick to me, as if it was trying to sound like a larger, more expensive, class A amp but in doing so it was masking the clear top end that T chips usually do so well.



And this I.AM.D offering which I have not heard but found easily.  



Or this puppy from FX Audio.



Honestly though, I would fork out a bit extra and aim for the new offering from QLS if it was me.


It looks good, but it is going to be about triple your $300 budget.


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