Justblairs Audio and Electronic's Pages

Already on www.justblair.co.uk we have looked extensively at a brilliant amplifier from Sure Electronics.  The Tripath TA2024 board is a cost effective, high quality amplifier board that in stock form offers value and with a few tweaks can offer serious performance.  It was with great interest that I awaited a sample of the recently released “Big Brother” to this amplifier… The Sure 2*100 watt @ 4ohm TK2050 Class-D Audio Amplifier Board (product code: AA-AB013). Well it’s here in my grubby mitts and today I managed to find some time to give it an initial listen.

Available for $39.99 excluding delivery, this board is a pocket money buy, question is can it deliver decent performance at this measly price?

Introduction

So what’s there be be excited about?   Well lets start with a little history on the Tripath audio chips.

Tripath, a now extinct chip manufacturer made a line of class D amplifier chips.  The D stands for digital, a hint to how the amplification takes place.  Without getting into too much detail here, a voltage is switched at very high frequencies to amplify the sound.  Vary the speed of switching and you get control over the voltage produced.  Their chips were used in a variety of applications by Sony. Blaupunkt, Panasonic, Apple and others in Car amplifiers, Home theatre systems and computers, though not initially in High end Hi-Fi units.

Hi-Fi builders got interested in Tripath chips after a company called Sonic Impact released a very low cost battery powered amplifier that it was discovered was capable of excellent sound.  Modifying the Sonic Impact amplifier then became a bit of an obsession for some hobby audio builders.  Soon other amplifiers based on the TA2024 chip followed, including those described in various articles at Justblair’s Audio and Electronics Pages.

Tripath based amplifiers are often referred to as Class T amplifiers, a name Tripath themselves used to denote the fact that whilst their chips are Class-D, their technology is more advanced than most Class-D designs.

Tripath went out of business in December 07, but there are still loads of their chips sloshing around warehouses.  Sure Electronics have been producing their own amplifier boards based on them.  The latest incarnation uses a combination of the TC2000 Stereo Class-T Audio Controller and two TP2050 50W Stereo Power Stages.  This combines to give a stereo 100w Class-T amplifier.  A good deal more powerful than the single chip Tripath TA2024 amplifier boards that I have tried so far.

Features

So lets take a close look at Sure Electronics latest amplifier design.  Opening the packaging, I was presented with the amplifier board wrapped securely in a expanded polystyrene carton.  Sure certainly look after you with their kits.  The board is sold assembled and also included in the packaging is:

• 2*100 watt @ 4ohm TK2050 Class-D Audio Amplifier Board x1
• Headset jack-to-RCA cable x1
• Banana jack x4
• Bevel washer x8
• Power cord x1
• Auxiliary lead x4

In short all that you need (well no power supply, but for a reasonable price they can add this to your order) to test your amplifier using a personal stereo or laptop.  Looking at the quality of the auxiliary items, they are pretty cheap but functional.  You are probably going to use them for testing, but not all will make their way into a finished design if you are being picky.

Remember this is all for $39.99 excluding delivery.

The amplifier board itself is finished in a very smart matt black solder mask with white writing.  The parts of the board are labelled clearly and it is easy to identify the mix of surface mount and through hole components that Sure Electronics have soldered to the board.  Taking a good hard look at the soldering quality, Sure have advanced their techniques since the TA2024 modules that I purchased previously.  There is hardly any flux residue on the board, and the ultra small smt parts are more neatly placed on the board.  The silkscreen is also slightly clearer.  Whilst none of this is essential to the running amplifier, it’s nice to see that Sure are progressing.

Further signs of improvement are apparent when you look at the electrical design of the board.  I have been e-mailing backwards and forwards with Robert Lee from Sure recently and he was telling me that when designing their new range of amplifiers they looked closely at what the DIY builders (including the articles here at Justblair’s) have been doing with their products and have incorporated some of these (as well as some changes of their own) into their new designs.  Even on a quick inspection of the board I can see a couple of implementations from the modifications I detailed on the TA2024 board.  I can only see this as a positive attitude for the company to take.

Sure’s commitment to the hobbyist extends to the documentation they supply for their product.  The manual available here, gives easy to understand instructions on how to operate the board, but more telling is the inclusion of a near full schematic for the board.  I guess that you have to be proud of your design if you are willing to open up the guts of it to inspection.  For those that feel they can improve on the board, having the schematic is a good thing, these are not always easy to come by.

Design

Inputs

Getting in to the nitty gritty now, lets have a look at what Sure have designed into this board.  A visual inspection of the board offers some well thought out features.

Starting at the inputs, Sure Electronics have supplied two sets of inputs for the amplifier, RCA and terminal block.  The RCA inputs are low quality flimsy units, perfectly fine for testing purposes, but if you intend building this into a case, I would budget a little for heavier duty case mounted RCA connectors.  I would consider the tinned lightweight RCA sockets are ideal though for testing the amplifier board, Sure thoughtfully supplied a RCA to mini Jack for this purpose.

The terminal blocks on the other hand are far more likely to be used when your amplifier board makes it to its final destination.  As terminal blocks go, these are solid enough.  They can also be removed fairly easily if you decide to hard wire inputs to this amplifier board.

Talking of terminal blocks, Sure must have a good supply of these that they are trying to dispose of, they have supplied power inputs on both sides of the board, this allows you to very neatly daisy chain a few boards together within the amplifier case.  The power inputs are also doubled up, with two terminals available on each side for the ground and positive (VCC).  Although probably not strictly necessary, I noticed a bit of a difference when I beefed up the power lines to the TA2024 based module.  Having two terminals per power line allows you to double up the number of wires to your power supply.

On the CH2 side of the board, sure has supplied a mute circuit to the amplifier board as well.  When the 5v supply (also found on the board via the lm317 regulator circuit) is connected to mute, the amp should switch off.  I have not tested this yet, but I cant see why it would not work.

Sure also have supplied an additional DC input in the form of a 5mm power jack.  This allows you to very quickly connect the power to the unit via the supplied cable (They  really do think of everything!).  Again, once the amplifier is in its final casework, you will want to use the more secure terminal blocks, but the 5mm socket is a real boon during the testing phase.

I also should point out that Sure have supplied Diodes on the positive inputs of the board.  This is here for both beginners and more experienced yet dozy builders.  They protect the circuit against reverse polarity connection of the power supply.  I am embarrassed to tell you that I (having tried this out strictly in the pursuit of a thorough test you understand) that these protection diodes work as intended!

Outputs

Heading to the other end of the board, Sure have supplied two methods of connecting up your soundbar speakers to this board. More terminal blocks (That is 17 separate terminals in and out) allow connection to the bridged outputs.  Also included in the design is a series of holes that match with the speaker binding posts supplied.  Again this thoughtful addition makes testing the boards very easy.  It took me less than 5 minutes to wire up the power, signal input and speakers to the board.  Another two to reverse the polarity of the power to the correct orientation.. And I had sound out of the board without so much as looking at my soldering iron.

Looking Closely at the Circuit

As I mentioned earlier, Sure have made it easy for the owners of their amplifiers to examine the circuit they have designed.  The PCB (Printed Circuit Board) is clearly marked with components easy to match against the schematic supplied in the manual.

Looking at the signal level input of the amplifier first of all, the signal comes in via RCA or terminal block. The signal line then travels through two capacitors C16 and C17 (on CH1).  C17 is a 1uf ceramic capacitor, not usually the best type of capacitor to place in the signal line. I can only assume that Sure opted for this as higher quality polypropylene or even polyester capacitors tend to be fairly large physically (making the board less compact) or were two pricey to get this amplifier into the measly $39.99 price tag of this board.

Sure though has taken steps to mitigate the problems caused using ceramic capacitors by paralleling the 1uf capacitor with a 0.22 MKP (Polypropylene) capacitor.  Paralleling lower grade capacitors with higher quality lower values is a little trick that can be used to smooth out the response/tone of the poorer sounding capacitors.   Regardless of this, this is one area that I will be looking at improving on the amplifier.  1.22uf in the signal line works as a high pass filter, blocking out some of the bass reaching the amplifier.  On the previous TA2024 board I tested, upping the value of the capacitor and swapping to Polypropylene components made a big difference to the sound quality.

The input capacitors serve two purposes.  A low pass filter prevents any DC signal entering the amplifier and being amplified.  DC (Direct Current) in large doses is not very good for your speakers as it forces the cones out or in.  More so as it passes through the voice coils of the speaker it heats them unnecessarily.  In large doses it can burn out the speaker.  More importantly for this type of amplifier, the inputs to the TC2000 controller require a bit of bias.  That is they need the signal input voltage to be raised above the level of ground by a few volts, its the way they are designed.  This voltage would travel back to your source equipment potentially damaging it with out the capacitors there to block it.

Also on the input circuit is a 22k surface mount resistor that working with the input capacitors works as a low pass filter.  Sure used this design on previous models as well, much to the detriment to the sound quality of the TA2024 offering.  I can see why they would do this.  One it rolls off and removes the inaudible frequencies at the very high end.  This removes Radio frequencies that enter the signal line reducing the overall noise levels of the amplifier.  The previous amp I tried sounded better even accepting that measured noise was probably higher (though inaudible to human ears).

Sure also have included a nice touch with a four way set of selector switches.  These allow you to adjust the gain of the 2*100W Tripath board to suit your input.

The manual explains the gain adjustment which works by paralleling 22K resistors R18, R19 with R11 on Channel 1.  This allows you to tailor the gain (how much it amplifies the sound) according to the input you choose to use with the amplifier board.  For instance having all switched set to on offers the lowest gain, suitable for use with headphone outputs on devices such as I-pods and similar devices.  All off would suit lower line levels such as a pre-amplifier connected to a traditional CD player.  You can play with these settings to get the most suitable levels for your use.

Next in the signal line chain is a circuit that raises the input line voltage to a level acceptable to the TC2000 Class-T Audio Controller IC.  R5, R6, R8 and C15 make up a bias circuit.  Here is an innovation from Sure over the previous amplifier board I tested and modified.  R5 is a variable resistor that allows the bias to be adjusted.  The level of bias has a direct effect on the DC offset of the board.  DC offset is a measure of how much Direct Current comes from the amplifiers output stages.  Whilst a little DC is almost inevitable in this design, and 100mv or so is not a major issue, using a variable resistor (sometimes called a trim pot) here allows fine control over how much DC the amplifier puts out.  Sure don’t recommend adjusting these pots, but you may need to.

The issue is that Sure adjust the DC output of the amplifier at the factory using a 24V power supply.  Indeed when I measured DC offset on my sample, It was near perfect at this power supply value, giving 9mv and 0.3mv DC values on the two channels.  However, just as I noted on the TA2024 IC based amplifier, changes in the power supply require different adjustments to the variable resistor.  This amplifier board can operate between 10v-36v.  I tested the board using a 14v power supply and the DC offset values were 77mv and 70mv on each channel.  Playing with the included variable resistors it was easy to adjust this DC back to 0v.  One of the modifications that I performed on my Tripath 2024 amplifiers was to add a precision variable resistor at the equivalent position in the circuit.  Sure uses a fixed set of resistors here and DC offsets were unpredictable at best between boards.  I said before that they have clearly learned and improved in this design.

The Power Line.

I have mentioned already that Sure have supplied a pair of terminals per voltage line on each side of the board.  After the protection diodes the boards have a total of 6 330uf electrolytic capacitors on the power line, three per side of the board.  These are marked as VZH 330 50V on the bare metal cases.  I did a search of the web to get some idea on their origin, they are made by Lelon and are described in their datasheet as Ultra low impedance capacitors.  Low impedance capaitors are the order of the day for this design.  They are there to filter out AC from the power lines and also to deliver quick bursts of power during loud transients in your music.  Again here Sure have executed the trick of paralleling polypropylene capacitors of lower values in the power circuit.  Polypropylene capacitors discharge more quickly than  electrolytic varieties, acting to improve the performance of the capacitor bank to quick changes in current supply.

Looking to the underside of the board Sure have routed the power through wide traces.  Interestingly they have also added a couple of solder traces to each of the power line traces presumably to reduce trace resistance.

There are two main power lines on the underside of the board, the ones I have marked yellow simply performs the duty of routing the voltage between the two sets of terminals.  As wide as it is, I would probably prefer not to use this line to transfer power in daisy chained boards at least not for more than two boards at a push.

The power line marked red comes after the protection diodes and routes power to the boards components.  Personally I would sacrifice the straight through power line capabilities of the board for a more direct supply of power to the amplifier stages, but I can appreciate that in a case, this will simplify the wiring spaghetti to multiple boards.

5V Regulator

Sure have provided a lm317 based 5 volt line on this board.  It is required for the Tripath circuitry, but there is a 5v output on one side of the board.  There are cheaper ways to regulate down to the 5v required and although I have not checked the datasheets carefully I will be surprised if the current requirements of the IC’s are anywhere close to what this regulator is capable of supplying.  As it happens I have a relay operated volume control sitting in a box that I have not used yet.  I bet that I can power it from this control.

Of course the intended use for the 5v output is to control the mute feature of the amplifier.  Add a switch to this and the mute terminal and you can place the amplifier board into a low current consuming standby.  Sure’s Schematic shows that the TC2000’s mute pin is attached to a LED indicator as well.  Handy for testing, this could be removed and a wire soldered in to a case mounted LED as well if you wanted the feature.

Again the use of a decent regulator here demonstrates that Sure are serious with this design.  The LM317 circuit they have used could be improved upon with the addition of a capacitor between ground and Vadj but this would most likely be overkill.

Cooling

The amplifier is supplied with an aluminium heat sink, and in testing it was obvious that it is required.  It does get hot, though not dangerously so..  My highly accurate fingertip thermometer would estimate the running temperature to be around the 50’s.  I can hold a fingertip to the heat sink continually (that’s how I guess) and though its slightly uncomfortable, no damage was done.  I would think though you will have to consider heat dispersion when making a case choice for this board.  This was using a 24v supply.  The board can operate up to 34v.  More cooling, possibly forced airflow (e.g. a fan) might be necessary if you are operating at the top of its voltage range.

The heat sink is of the type you find on PC motherboards for cooling Northbridge processors.  initial appearances is that is held in with plastic push pins.  Further inspection revealed however that Sure have used some heat conducting cement to bond it to the chips.  I did not try hard to dislodge the sink for fear of damaging the chips underneath.  It may be possible with some solvent if you wanted to apply a more substantial heat sink. Zalman do some much bigger heat sinks of this type (pictured) designed for passive cooled PC’s.  One of these might be a worthwhile addition for the paranoid! (I have not checked dimensions, but it looks about right)

Outputs

Looking to the outputs of the circuit, Sure have opted for surface mount inductors and Polypropylene capacitors for the output filter.  Class-D (Class-T if you prefer) generally require a low pass filter on the output to remove high frequencies generated in the amplification process.  It’s hard to judge the quality of the inductors on sight, but Polypropylene capacitors normally offer superior sound quality.

The 100W claimed output for the amplifier board is accomplished by bridging 2 50W stereo channels to make 100W.  The board holds two TK2050 power amplifier chips to give stereo.  Don’t be tempted to bridge these outputs for 200W, this can’t be done.  Also care should be taken to isolate the negative outputs from each other.  They are not common to earth and the amplifier will most likely be damaged if you connect them.

Design Conclusion

All in all Sure have taken some care over their design for this amplifier.  The board is a decent size and appears well laid out.  Its certainly a flexible board design.

Over previous boards, Sure have designed this amplifier board to be flexible, offering a setting for gain and adjustable DC offsets gives the board added compatibility with a range of sources and power supplies.

Superior components have been used in various places in the design though one or two compromises have been made to cost.  The hobbyist is going to find one or two areas they can perhaps improve the sound of the board.

Listening

For the listening test I plugged in the Sure Electronics 2*100W amplifier board using the supplied connectors.  I used a Sure TA2024 Amplifier Board as my reference.  Sure recommended a 24v power supply that they also stock to drive this board.  I am always happy to take recommendations on board so used the Meanwell 24v 10A SMPS power supply.  A DDDAC1543 was used as the source and a Kookaburra digital volume controller performed the pre-amp duties.

The first track that I played was Aye Fond Kiss, sung by Eddie Reader.  This is a beautiful ballad, and the 2*100W instantly sounded fantastic.  The track has a very strong female vocal.  If you are familiar with the Tripath sound, the Sure board has it in abundance.  For those that have not had the pleasure of listening to a Class-T amplifier before, the first thing that you notice is the expansive and very accurate sound stage that these chips produce.  Instruments sound rooted in the their places and are spaced well both from left to right, but also from front to rear.

The midrange clarity is probably the strongest point of the Sure 2*100W board.  Eddie Readers voice sounded very powerful and yet delicate.  Detail is very delicately presented, string plucks have a crispness to them that is distinct but at the same time not wearing or harsh.  The sound in the midrange is what is often described as airy.  I think it is the excellent separation of the instruments in the recording that gives the sense of space around the performers.

I plugging in the original TA2024 amplifier board that I am already familiar with gave me a little surprise. Sure’s TA2024 board to my ears was always good.  However in comparison to their new offerings it was clear that improvements have been made.  I am sure that having the additional power makes a difference.  I am using Mission 753 speakers in my current setup.  They are easy to drive, even with the mere 15w TA2024 Tripath chip.  However with the bridged TK2050 powered output stages it was clear that the beefier amplifier was directing the 4 8’ drivers of the mission speakers with more ease and greater speed.

It is also clear that straight out of the box, the top end on the newer amplifiers is less muffled than the unmodified TA2024 boards.  Although to my tastes the TK2050 boards are a little quiet in the high frequency ranges, I found the detail to be clear.

I tested the amplifier boards side by side next with Renauld Garcia Fons latest album “La Linear de Sur”. Renauld Garcia Fons is a double bass supremo and I find his compositions relaxing to listen to with great dynamic range.  Again the mid range is where the TK2050 based amplifier was really excelling.  Percussion also came across very well from the board.  I did however detect that the lowest notes from the double bass were not as pronounced as they ought to be in the recording.  I am using Mission 753 speakers however.  Despite their size and multiple drivers they are not the bassiest of speakers around.  So perhaps with other speakers this loss of sound in the lowest frequencies will not be so pronounced.

The input filter to the board does have a mere 1.22uf capacitor in the signal line which creates a high pass filter.  In the previous offering from Sure I found that raising the capacitance on the input made a worthwhile improvement to the board.  I am fairly confident that using a 2.2uf or even higher value will redress the balance between the bass and the stunning mid range this amplifier board produces.

Finally I listened to The Bare Naked Ladies track “Tonight is the Night”.  A whimsical recording this track has very strong male vocals and an orchestral feel to the arrangement.  It was again in the low down frequencies that the instruments of the band felt slightly unbalanced.  Kettle drums were very punchy, but lacked the final lowest frequencies that makes their sound so distinctive.

Lets put this into its proper place.

Listening Conclusions

This amplifier from Sure Electronics is going to surprise those that bought one of its less powerful predecessors.  I thought that I knew the sound from Tripath Class-T ampliifers.  Excellent Imaging, clean detailed playback and wide airy soundstages was what I was hoping for from this new product.

Well the Sure 2*100W Tripath TK2050 amplifier board supplies all this and is not going to disappoint a Tripath Fan.  Where it will really stun you is in the midrange power.  To get such forceful yet detailed presentation in the midrange is jaw dropping.

The minor drawback to the amplifier board (at least in unmodified form) is that the bias is slightly too much in favour of the midrange.  I am almost 100% certain that this can be easily remedied with only one or two quality parts and some decent run in time.  Speaker choice itself may make this low end roll off un-noticeable.  It takes fairly critical listening to detect  it as is.

Power wise, the 100W units are capable of really seizing your speaker cones and controlling them incredibly closely,  This gives speed and detail in the mid to low range that is beautiful yet exhilarating.  These amplifier boards Sure do entertain (dreadful pun!).  I would think that this will make this board suitable for controlling a wide range of speaker designs, I would love to try it out with some transmission line enclosures.

The real surprise with these boards is just how much high performance audio you get for your money.  At 39.99USD these amplifier boards have to be the bargain of the centaury.  The build quality is excellent, the circuit design is intelligent and to finish it off, Sure have thoughtfully included pretty much all accessories required to test your new pride and joy.  At this money, why just buy one.  Bi-Amp your speakers for a fraction of the cost of even a mid range stereo amplifier!

Pros

• A novice builder can plug this together with only a power supply and a screwdriver and be up and running
• Flexible Design, lots of possible configurations
• Price.. My goodness this is an affordable amplifier, pound per watt its outstanding
• Power, even more demanding speakers are going to love this amplifier
• A little room has been left for that all important tweaking that make this hobby fun
• Sound, Sound, Sound.   the quality is not going to disappoint all but the most critical listener

Cons

• Slightly too strong on the midrange, though this can be tailored I am certain
• Supplied accessories are of testing quality, though their inclusion is generous on Sure’s behalf.

Expect to see some modifications for these boards.  I need to give them some decent play time first though to get them performing at their best in stock form.

The first target will be that filter on the signal inputs.  Some more volume in the low end will be the first goal.  Once that is done I will re-evaluate the higher frequencies to see if a modification is even required here.  I am pretty excited as to what further performance remains to be unlocked.

Watch this space!