Paralleling the two stereo outputs of a TA2024 power amp to form one mono output - Page 1
Forum section: electronics / projects

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 05:28:48 pm
content: I bought a TA2024 amp from eBay for my boombox project. At the time I didn't realise that it can't be bridged, so I am now looking to put the outputs in parallel. I only have one speaker which is rated at 30W nominal so this should be fine.I foundthisthread on diyaudio.com which seemed to refer to putting multiple chips in parallel. Ideally I would like just to use the board I have. It also says that in the LM3886 datasheet there is an outline of a "parallel mode" but I can't find one. I'm about to make a Farnell order soon so I will need to know what power resistors to order if this is possible.Thanks!

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 06:34:13 pm
content: The size of the sharing (output) resistors necessary will depend largely on the output power (up to 30W I guess, in your case) and the accuracy and precision of the amp. The lower the voltage differential across channels, the lower your sharing resistor could be. What you need could range from, say, 0.05 ohms to 0.50 ohms. The larger the sharing resistors, the less current between channels that will be induced by the voltage differential, but obviously at the cost of a lower efficiency (and damping factor - but that's a different can of worms - some people think damping factor is important and some do not).

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 06:42:57 pm
content: I assume the voltage differential is simply a matter of the amp's accuracy - the left and right channels are combined using two 10k resistors and although the mono input currently only goes to the right channel, it's easy enough to hook it up to both. I'm not too familiar with audio – what should I be looking for in the datasheet (here)? From the other forum that I linked to I'm estimating that around 0.2 ohms should be about right for the sharing resistors.Thanks for the info; as I said I don't have much experience with audio so extra info is always helpful. I looked at the datasheet to see the block diagram and I see what you mean!Thanks!EDIT: Yes, the output power is about 30W although in practice maybe a bit less; the TA2024 is rated for 10% THD+N at 15W (x2). I'm no audio nut but that doesn't sound too good.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 07:07:21 pm
content: 0.2 ohms would likely do the job easily and even 0.1 could possibly be fine. Personally I might play around with the chip a bit and measure the differences in gain/offset voltages under varying circumstances. That's something I tend to do since I don't do volume production of anything. So I like to verify how my specific chip works, just make sure there's not a large output voltage differential, and use that information when calculating the sharing resistor values.Basically you just want the maximum power transfer between amps/channels due to that differential to be minimal compared to both the power handling of the chip(s) (so you don't burn them up or run them into protection such that they shut down) and also the typical output power (mainly for efficiency).

author: edavid
author_rank: Super Contributor
timestamp: April 23, 2014, 07:10:23 pm
content: I'm not sure if the other people posting realize that this is a class D (class T, whatever) amp.Tripath is so vague about the way their chips work, that it's hard to say what will happen. You may just have to try it and see if it blows up.It also may not work well without some additional filter inductance, since cheap eBay boards usually skimp on that.Have you tried hooking up just one channel to see if it's loud enough?

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 07:15:50 pm
content: Quote from: edavid on April 23, 2014, 07:10:23 pmI do realize that it's Tripath; I've got some experience with it but far from a ton. I usually deal with simpler Class AB stuff yes.It is possible that the output filter will need to be modified, but I'm going to say that is unlikely. It should be fine and comparable to running 16 ohm speakers on a single amp. Most people don't run 8 ohm speakers but it's rare to find an amp that won't. Tripath IS more sensitive to output impedance than some other Class D amps, though. Personally I prefer Philips/Hypex UcD.Edit: Now, if you also mean that it COULD be modified INSTEAD of using a resistor, that I am not really sure of. I suppose you could probably increase it somewhat, but if that's a better option, I am not sure offhand.Quote from: microbug on April 23, 2014, 06:42:57 pmI don't know what the purpose of this project is, but if it is something in which you desire good quality, you want to aim for definitely under 1% THD, and ideally more like 0.1%. High-end audio gear is often much lower than even 0.1% (sometimes by another order of magnitude!), but it's not THAT important at those levels. 10%, though, is absolutely terrible. Tripath chips are not going to compete with high-end Class AB amps on THD, in my opinion, though they are plenty good when the circuit is properly designed. They can be prone to more offset voltage than some other amps, though.

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 07:17:44 pm
content: I am well aware that this is a Class-D (Class-T is marketing bullshit) amp.I will order the appropriate power resistors for testing the amp (my speaker is 4 ohms). Offset voltage is rated between 50 and 150 mV.I have hooked it up and while it's fairly loud, it would be nice to have a little more volume given that I specifically bought a 30W speaker. I will probably need to add some extra parts to make it up to Farnell's free postage (Add £3 to your order and get next postage worth £3.95 free) so I'll investigate some better inductors and replace the undoubtedly fake Nichicon caps (and the pile-of-crap "HuaHong") with genuine ones. I was considering doing this anyway, given the likelihood that a board costing £6.28 incl. shipping wouldn't be using high-spec parts.

author: retrolefty
author_rank: Super Contributor
timestamp: April 23, 2014, 07:19:42 pm
content: Not sure my audio amp theory is too rusty or not, but I don't think you will gain any increase in output power even paralleling the amp channels unless you also decrease the load impedance of the speaker load. The paralleling of the channel outputs doesn't increase the voltage swing, but could increase the total current drive available.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 07:23:28 pm
content: Quote from: microbug on April 23, 2014, 07:17:44 pmFYI, there is MUCH more to a speaker than just the size and power you run through it. One extremely important rating is the sensitivity or efficiency (they are not the exact same thing but they are extremely similar and directly proportional) which basically tells you how much sound to expect from a given power. But this can be measured in various types of boxes or can be free-air or on an open baffle mount, etc. Best to look at the frequency response graph and make sure it meets your expectations. Also keep in mind sensitivity is often specified as either at 1W/1m (measured 1 meter away with 1 watt running to the speaker) or 2.83V/1m (which is 1 watt at 8 ohms, but keep in mind your driver has varying impedance throughout its frequency range so it won't be exactly 1 watt and will vary with frequency). Depending on what you're doing with the data, it can be more convenient to look at 1W or 2.83V ratings. Crossover design, for example, will use the 2.83V/1m method. You, however, will probably want 1W/1m measurements.The box design you use also makes a HUGE difference in frequency response, sensitivity, output power handling, AND sound quality.There is also a thing in speaker design called Hoffman's Iron Law. (If you know the audio brand KLH (which is junk now but they used to be good and they discovered new technology), Hoffman was the H.) The simplest explanation is: enclosure volume, system efficiency, bass extension - you must give at least one of these things up.I've built way more speakers (systems, not raw drivers) than amps, heh.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 07:25:00 pm
content: Quote from: retrolefty on April 23, 2014, 07:19:42 pmYes, this is correct, but it has other potential benefits like lower distortion and slightly better temperature characteristics inside the amp. I say "slightly" because both channels are in one chip so you won't gain that much uniformity or lose that much thermal resistance, but if it were separate chips it would affect that even more. Obviously the distortion matters far more, but temperature fluctuations can affect the voltage differential between channels somewhat, so it's good to have that under control even more so if you're paralleling amps.Whether OP needs them to be parallel or not, I am not sure. Would need more info about the system as a whole, like which speaker it is in specific. But keep in mind, as discussed earlier in the thread, Tripath gives some of their power ratings at 10% THD, which is terrible and really an unacceptable way for them to rate power.

author: edavid
author_rank: Super Contributor
timestamp: April 23, 2014, 07:35:32 pm
content: Quote from: Holograph on April 23, 2014, 07:15:50 pmWell, I'm just wondering if there will be shoot-through current from one output to the other.

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 07:40:29 pm
content: Since you asked:The speaker is a Pioneer TS-G1021i 10cm dual-cone speaker. Specs:Maximum input power: 180 WNominal input power: 30 WImpedance: 4 OhmsFrequency response: 45 - 26,000 HzSensitivity (1W/1m): 88 dBWoofer size: 10 cmWoofer material: IMPP coneCut-out Hole: 106,0 mmMounting Depth: 43,0 mmAmplifier isthis one.Mounting in a large tic-tac box with the amp, Li-Poly battery and various other bits & bobs. See the pictures!

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 23, 2014, 07:45:24 pm
content: Quote from: retrolefty on April 23, 2014, 07:19:42 pmIndeed, this is correct.The TA2024 is happy to work into 4 ohms, so putting them in parallel - if that were even remotely a good idea - would gain nothing. Forget about it...Putting a pair of LM3886s in parallel is another thing altogether. Very easy, and it works, especially if you then go on to bridge the combination (as in a bridged setup, each half "sees" half the impedance). I've done it myself. But there is no "voodoo" with these class B amps.The TA2024 uses bridged outputs, so each hot and cold output would need to be connected together. Get that wrong and they fight. To be honest, as the switching scheme isn't discussed in the datasheet - so we don't know the phasing of the PWM relative to each half - you might end up with a fight at HF anyway.BTW, the THD+N is much better than 10%. It's common for chip manufacturers to quote the power output at 10% THD, but below these powers it improves dramatically. There is a graph on page 1 of the datasheet.Are you are aware that loudspeaker power ratings - unless quoted as "continuous average sine wave power" - are wild guesses, based on an optimistic view of the peak to mean ratio of typical programme material. So the 30 watt rating of your loudspeaker (at unspecified impedance and unspecified frequencies) is pretty meaningless. Feeding it with a 15 watt amp could be described as "sensible engineering".Are you are also aware that the difference between 15 watts and 30 watts is only 3dB? The human hearing system can only just about hear a change of 1dB, providing you have a reference, and 3dB is actually a tiny change.If you want to do something meaningful with a stereo IC, use the other half to drive a tweeter. Design a low-level crossover to split the HF and LF at line level. Hey presto - you have an active loudspeaker - very common in professional setups. The power loss in a passive crossover can easily exceed the 3dB you're worrying about if you properly equalise for "baffle-step" and other things...

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 07:46:45 pm
content: Okay, that's a decent enough speaker. I don't know if you noticed but I've modified my post explaining speakers a few times since I wrote it to add further info, should it interest you.The sensitivity is not super great, but you won't get great sensitivity at that size of driver (driver = "raw speaker," as opposed to a complete speaker system), so that is to be expected. The polypropylene cone will be relatively weather resistant.And yes, you will definitely want to parallel the amps since it's a 4 ohm speaker and not 8 ohm. For some reason I had the idea that you had said 8 ohm, but I reread your posts and apparently that's just something I made up in my own headIs the box ported, or are you sealing it up for mobile/outdoor usage? If you port it and you tune the port reasonably well, you should get a few extra decibels of sensitivity in the bass and lower midrange. Well, for most speakers, anyway. Some speakers are designed only for sealed usage and don't do well with a port (the Qts rating can be used to roughly judge whether to port a speaker or not), but car door speakers are not designed like that.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 07:48:33 pm
content: Quote from: Mark Hennessy on April 23, 2014, 07:45:24 pmI'm going to say you're wrong to assume that he'll simply be happy with half the wattage of his original idea. 3dB is not often considered a LOT, but it is not insignificant at all. He specifically said he was unhappy with it. Your idea of changing his expectations is not your decision; you should stick to answers to what HE wants (assuming it is possible, which it is), not what you want.Plenty of people have done this with Tripath chips. It can work - he just has to be careful about more things. Is it the BEST solution? No. I'm not a huge fan of Tripath in general. But he already has it, and this has already been done by others as mentioned in his original link and in other places.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 23, 2014, 07:56:11 pm
content: Quote from: microbug on April 23, 2014, 07:40:29 pmLike I said: meaningless.How big do you think that voice coil is? 25mm at best? Give me a 30 watt amplifier, and I'll destroy that within an hour.And a frequency response with no limits is also meaningless. It might well make noise at 45Hz, but it could be 20 or 30 dB down relative to 200Hz. If they'd said 45Hz to 26kHz +/-3dB, that might actually convey something.Don't let me put you off - I'm sure the thing will make a nice noise (I presume you've got the T-S parameters and have designed a box for it with the correct materials and tuning frequency?), but worrying about getting another 3dB from the amplifier is utterly immaterial. Not to mention impossible from a 12 volt battery without a step-up DC-DC converter. To get 30 watts into 4 ohms (nominal, as impedance varies enormously with frequency), you need 11 volts RMS. That's 31 volts peak to peak. See where I'm going?

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:01:56 pm
content: Thanks for the big response – knowing this forum I wouldn't expect any less but nevertheless it still took me a few minutes to read all the responses. I did know that the THD+N was better than 10% at lower power: 0.1% @ 11W with a 4 ohm speaker.It now seems that my options are either to:– Put the two outputs in parallel and drive the speaker with both to get a fairly small gain in volume;– Buy a tweeter (or two) and use the second output to drive it (them) separately. Having just looked briefly on the same website I bought my current speaker from, they appear to be rather expensive; my budget is max £15, maybe stretchable to £20. Any better sources? Also, how much would a tweeter improve the sound quality – if it would make a comparatively big difference I'll go with it.I am going to take a stab in the dark and guess that 'porting' is drilling holes to allow air to escape so the speaker can function properly. If that is the case, I was not planning on doing it but then again I didn't know about it. I will be using this outdoors but only in mild weather and I wouldn't leave it out in the rain. How does one tune a hole (or am I barking up the wrong tree?).EDIT: having just seen Mark's latest post, I'll go with the tweeter. And no, the box is just a plastic thing I saved for some project a while back, and I found a use for it – how much of a difference will the box make? Yes, I see where you're going!EDIT 2: the lack of information / data sheet regarding the speaker is also annoying but having looked at similar ones when selecting it, it is fairly typical.

author: fcb
author_rank: Super Contributor
timestamp: April 23, 2014, 08:02:06 pm
content: Quote from: Holograph on April 23, 2014, 06:34:13 pmWrong. Most bridge amplifiers use single rails - that's one of the beauties of bridge configuration.But back onto the TA2024 parallel issue.You won't get any increase in power (theoretically) as you aren't increasing the voltage swing across the speaker - you'd only benefit if the TA2024 can't supply the current required for the voltage swing (not likely to be a problem as you are using 8ohm speakers).I'd also be surprised if the Class D (because that's what the are) enjoyed being paralleled, feedback design being non-trivial. Try it and have a go, but you will probably need larger ballast resistors than suggested.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 08:03:11 pm
content: Quote from: Mark Hennessy on April 23, 2014, 07:56:11 pmIt's certainly not a good list of specs - car speakers are often not listed with full T/S parameters, unfortunately. In fact, almost none are given, typically. But meaningless? Not totally.The voice coil size matters and the main thing that affects is the highpass filter used (I do recommend a highpass filter, though it's technically not 100% necessary if you're careful enough). As a side note, if you do port the box, you MUST use a highpass filter, and it must be at the port tuning frequency or higher (with beefy speakers you can sometimes go under the port tuning frequency by a little but not here).As for the 26kHz, I'll give that one a laugh. It might make sound there but it's going to be rollercoaster in the midrange and up since it's an inexpensive coaxial speaker.Quote from: fcb on April 23, 2014, 08:02:06 pmAh. Guess it's just been the specific amps I've used that have happened to be like that. But since I've used various amps from various brands I took it to MEAN that. My bad. Thinking about it from the electronics perspective - and not what I've actually seen advertised - what you say does make sense. I've removed the offending statement from my previous post.

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:09:01 pm
content: I knew there was lots to consider but never realised quite how much!– @fcb - my speaker is 4 ohm, not 8.– When you refer to a high pass filter, do you mean for a hypothetical tweeter, for the mid/high range cone or for the whole speaker?– I looked up porting; I'll have a closer look later but I don't know if I'll have enough room in the enclosure judging by the photos I saw (first glance, could be completely wrong).– Although it may not be a problem in the short term, I will probably install some better components in the output filter of the amp since I don't completely trust that the phoney caps currently there won't explode in my face.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 08:14:24 pm
content: Quote from: microbug on April 23, 2014, 08:09:01 pmIn this specific case, the highpass filter I am referring to may also be called a "subsonic" filter, though that term is more appropriate with subwoofers. It cuts out the stuff your speaker won't be able to play because of the speaker's natural frequency response (or in the cases of beefy subwoofers, the limits of our hearing - which is technically the more accurate definition of a subsonic filter).In most audio, most of your power is going to be in the bass frequencies. There's a great graph on sound.westhost.com (which is an EXCELLENT site that I learned a LOT from several years back) that gives an estimation of this.http://sound.westhost.com/tweeters.htm-- first chart. The way you read it is that at any given frequency, find the power level in % in the graph, and that - on average - is how much of the signal's power is contained in that frequency and below. You can see that it's biased towards bass. That means we need to cut some of that bass out so that we can run enough power in the midrange and treble while not exceeding the speaker's power or excursion limits. This is the highpass filter. With that speaker you will probably want it around 80Hz but you can play with the value a bit depending on what types of material you listen to and stuff.As a side note, that graph also explains why biamping speakers (running the woofer on one amp and the tweeter/mid on another) doesn't really add much power handling. Your limit is nearly always your woofer, so unless a speaker has multiple woofers that can be run with multiple amps, you aren't going to be able to gain much output capability.With a ported speaker you typically get more efficiency (most speakers work better ported but not all) but you get a suspension unwinding effect below the port tuning frequency (you tune the port by its diameter and length but it varies per speaker and with box size). This means that it's very easy to hit the excursion limit (Xmax for linear excursion (it'll add way more distortion above that value) or Xmech for actual physical clearance) below that frequency, which can destroy the driver just like running too much power and melting the voice coil can.I'd normally recommend software like WinISD or Unibox to calculate the box, though it's going to be difficult if your driver doesn't have Thiele-Small (T/S) parameters available. Hopefully Pioneer gives some information about choosing the right enclosure for it. But they might not, since most people are just going to put that in a car door and be done with it.One thing I had meant to explain in an earlier post but forgot (Mark's reply after this one reminded me). It is more efficient to get your sound from surface area** (edit: fixed typo) than stroke. Meaning larger speakers are typically more sensitive. The reason is mainly because as you increase excursion/stroke capability, you need to add more tolerance in the gap so the coil doesn't rub up against it. But the more tolerance you add, the weaker the magnetic forces become, lowering sensitivity. Also, as power handling increases, voice coil size and weight increases, which hurts high-frequency reproduction (which is a major deal with a coaxial speaker like this). But if you go with a larger speaker with similar Mms (moving mass - another T/S param) and Cms (compliance of the meahcnical suspension) but larger Sd (surface displacement of the cone - yet another T/S param) you will get more sensitivity and thus more volume.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:18:11 pm
content: Quote from: Holograph on April 23, 2014, 07:48:33 pmIt's not fair to accuse me of "changing his expectations" simply because I've pointed out the stark reality that his expectations are not achievable with the chip he has. According to the datasheet, 15 watts into 4 ohms is as good as it gets. Don't shoot the messenger.And exactly how is 3dB a "LOT", especially without a reference? If it's not loud enough for him currently, he'll need rather more than 3dB, which is a barely noticeable change in reality. Hence my suggestion of a boost converter (and a different chip). Or a more efficient loudspeaker, if that's an option at this stage (probably not).

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:28:49 pm
content: If I were trying to make a professional speaker system I'm sure I could do much better, but I'm making a Bluetooth boombox to listen to tunes in my room & the garden – it doesn't need to be studio quality and I don't have studio money. It's plenty loud as it is, I was only thinking that given that there's an unused output I might as well hook it up, but since it will barely make a difference I won't bother going down that route.The TA2024 datasheet says it will take between 8.5V and 13.2V. My battery, being a 3S Li-Poly, will vary between 12.8V (fully charged), 11.1 (nominal) and 9V (depleted). Given the comments that paralleling will make little difference, I suppose it would make more of a difference to buy one of the many cheap adjustable boost converter boards from eBay and set it to 13V (and put in a low battery light - without the volume difference I wouldn't notice and depleting an Li-Poly too far can destroy the battery).Given my budget I think I'll just work with what I have – I'll keep the amp & speaker, fix the rubbish output filter components on the amp and possibly buy a tweeter. I have space restrictions though; I just measured: 3cm max mounted surface diameter if the tweeter is on the front, 44.6mm if it's on the bottom (perpendicular to the ground if you lie down the box flat, but since I have ordered raised feet it will face the ground slightly. Will a tweeter be viable?EDIT: Just realised I could have the tweeter on the top of the box. Max diameter would be about 48mm.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 08:29:52 pm
content: Quote from: Mark Hennessy on April 23, 2014, 08:18:11 pmI'm just saying he should try to use the whole chip before deciding, since he already has the thing. If he's REALLY not impressed with it then yes, a beefier amp or speaker is likely necessary. But I wouldn't say "Use only half your chip, or buy a better speaker." I don't think those are the only two valid options here.I didn't call 3dB a lot - I said it was not a lot, but also not insignificant.

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:37:08 pm
content: I'm going to guess that a boost converter putting the input voltage to the TA2024 at 13V will make more of a difference than paralleling the inputs since it will actually increase the voltage swings. If not, at least it will make the volume more stable while the battery is discharged.I am not "REALLY" unimpressed with the speaker by any means, I just thought I might as well get the most out of the chip. However, it seems adding a tweeter would probably be a better option if that's my goal.

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 08:41:03 pm
content: Quote from: microbug on April 23, 2014, 08:37:08 pmThe boost converter set at 13V will likely increase your available output power (possibly up to 17% if the internal circuitry in the chip doesn't limit that, but probably not quite that much in reality), but its main advantage will be that the voltage drop won't happen until the battery is depleted. Without this, your available power would decrease with voltage, which could cause a rise in distortion which may be audible.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:42:37 pm
content: Quote from: microbug on April 23, 2014, 08:09:01 pmLoudspeakers have a number of parameters that describe how the unit behaves around the resonant frequency, and these parameters can help a designer to choose the best enclosure for it. Some drivers work well in a sealed box of a particular frequency; others are more suited to a ported enclosure - which is a box that is sealed apart from an opening. The opening might be a slot, a simple round or square hole, or a hole with a tube behind it. Whatever it is, the air in the opening resonates at a chosen frequency (determined by the dimensions) to augment the output from the bass driver itself. Sealed boxes are pretty easy to get right - with ported enclosures, there are lots of ways to screw up the tuning!To get a feel for this, have a play with WinISD, which will simulate the behaviour of a driver in a box. I have some examples of this on my website:http://www.markhennessy.co.uk/audax/background.htmIt's my experience that car loudspeakers aren't especially suited to either - because the manufacturer has no idea or control over how the units will be mounted (in doors, in the dash, on the rear parcel shelf), they design them so that they hopefully won't suffer mechanical damage when over-driven - in other words the suspension is very stiff, giving a high resonant frequency and a high "Q" for the size (compared to a driver that you'd use for hi-fi in a known enclosure). Essentially they are designed with open-baffle use in mind. As a consequence, the bass output is quite limited - but luckily car head-units have tone controls, and people aren't afraid to use them! Contrast that with the hi-fi crowd, where tone controls are a big no-no...It's quite easy to measure the key parameters - called T-S after Theile and Small:http://en.wikipedia.org/wiki/Thiele/Small- to do so, you need an audio oscillator, an AC voltmeter, and the ability to make a box of known volume. An audio amp and a low value resistor is also needed. Even when the manufacturer supplies the measurements, you do need to double-check them anyway.Regarding making an active system, I hadn't seen your loudspeaker when I wrote that, so didn't know it was a two-way coaxial job. Probably not worth doing now...The mention of a high-pass (or subsonic) filter is about trying to conserve energy - no point shoving in loads at 50Hz if the drive unit is 20dB down at that point, all that will do is heat up the voice coil needlessly and perhaps cause distortion and other problems - especially if the box is not sealed. So a 12dB/oct filter - just a single op-amp - will be useful. I did that in a small project ages ago:http://www.markhennessy.co.uk/activespeaker/index.htm

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:48:03 pm
content: I was thinking along the same lines (although I didn't realise that a lower voltage could cause distortion). I will definitely need to add some sort of warning system for a low battery though; a red light would probably suffice since the capacity of my battery is 2.2Ah – I'll notice long before any damage is done.I'll have a look at porting tomorrow, but my gut instinct is that once I've cut a hole I can't go back. I'm guessing by "audio oscillator" you mean an ability to generate waveforms of a given frequency; I have an AD9850 module (pending eventually putting with a precision op-amp amplifier) which can do that. I'll look the examples on your website tomorrow as well (it's 9:47PM here for all you Yankees!).

author: Holograph
author_rank: Regular Contributor
timestamp: April 23, 2014, 08:51:58 pm
content: Quote from: microbug on April 23, 2014, 08:48:03 pmWhat I meant by that is if you've got your gain set such that you're getting output voltage peaks of 11v, but then your battery voltage decreases to 10vand you don't change your gain, you're now clipping the amp to 10v (or less), raising distortion significantly. If you put the boost converter in to make sure your battery voltage only drops when the battery runs out of charge, then you won't have this issue.For the port, you can of course cover a hole - it just might not look as good when you're doneThey make ports that are variable length so you can play around with it and then you just glue the 2 pieces together when you decide on a length.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:56:34 pm
content: Quote from: Holograph on April 23, 2014, 08:41:03 pmSay you get an extra 10% power. That's 0.5dB. Think you'd hear that? I certainly wouldn't!By all means try it - after all, it's easy enough to power the amp from a variable bench power supply - and certainly regard it as a future retro-fit option, but in my opinion it's simply not worth the extra complexity and hassle. KISS.I first got this lesson aged 16 or 17. I wanted a louder car stereo, and back then, cheap high power amplifiers simply didn't exist. So I designed a bridged amplifier, and invented a topology that gave almost rail-to-rail operation - normally, you're lucky if you can get within 2-3 volts of the rail, especially into low impedances. Anyway, this thing did work quite well, and was very nearly completely debugged, but I'd run into a problem - perhaps I would have solved it if I'd stuck at it, but at that point I decided to so the dB calculations. At this point, I realised that for the sake of gaining an extra 1.5 or 2dB, I'd be better off abandoning my crazy design, and instead I used a pair of TDA2005s in bridged mode. In fact, I now had extra room in the box as my design was largely discrete, so was able to fit 4 channels of amplification instead of just 2. Result! It was a great amp, and I still have it somewhere in the attic...

author: microbug
author_rank: Frequent Contributor
timestamp: April 23, 2014, 08:59:47 pm
content: OK – I'm not expecting any noticeable difference but I imagine it would be better just in terms of stability and noise, as previously discussed. I won't bother testing the amp on 13V to check for a sound difference.

author: dannyf
author_rank: Super Contributor
timestamp: April 24, 2014, 11:05:10 am
content: QuoteThe output stage in that chip is a full bridge itself. So paralleling it really isn't a great idea.If your goal is to parallel it (to what end?), I guess you have no choice.If your goal is to increase power output, there are other ways to do it, without paralleling it.If your goal is to decrease distortion, there are other ways to do it as well, without paralleling it.You just need to know what you want to do.

author: Anks
author_rank: Frequent Contributor
timestamp: April 24, 2014, 12:57:36 pm
content: Do you think 50 TA2024 will power these or am I better fixing the crown K2 next to them?On a more serious note these chips are pretty crappy and as previously mentioned are already a bridge arrangement. You could try paralleling them and giving them a bit more voltage to throw around or lowering the impedance of the load but not worth the effort really and most likely wont last long.

author: microbug
author_rank: Frequent Contributor
timestamp: April 24, 2014, 02:31:41 pm
content: If the TA2024 is "crappy", what would be a better amplifier? I would like it to be efficient (class D) as this is battery powered.

author: microbug
author_rank: Frequent Contributor
timestamp: April 24, 2014, 03:51:32 pm
content: OK, I found a tweeter:http://www.electromarket.co.uk/speakers-audio-equipment/parts-components/tweeters/cca0387Thoughts?

author: Anks
author_rank: Frequent Contributor
timestamp: April 24, 2014, 05:13:01 pm
content: Quote from: microbug on April 24, 2014, 03:51:32 pmI would sign up to Speakerplans forum and look what people do there. There are lots of people there that make battery powered systems but if your just going for it works albeit a bit crap then the TA2024 build it yourself way will probably teach you something. Depends what your going for.

author: Holograph
author_rank: Regular Contributor
timestamp: April 24, 2014, 05:57:58 pm
content: Quote from: microbug on April 24, 2014, 02:31:41 pmIf it's doing the job well enough now, then just keep it. No, it's not the best chip, but you already have it and you might as well get your money's worth. If you end up killing it at some point, oh well. If you end up upgrading later, fine.I have my own standards in audio, but I try not to spend other people's money too much. I myself am really into audio and use mostly higher-end stuff. But If you're reasonably happy with the setup and can't afford anything significantly better anyway, then don't listen to people saying the amp chip is crappy. This is your project, not ours.There are lots of sources you could check out such as DIYAudio, DIYMobileAudio (more about car audio but that community is generally more knowledgeable than any other car audio forum I know of), HTGuide, the DIY section on AVSForum, etc. You can learn a lot about speaker development. There are also sites like sound.westhost.com and bcae1.com to learn some generics. All just depends on how much time and money you want to spend. If you're happy enough now then leave it be until you're no longer happy with it.BTW, check outwww.parts-express.com. I order a lot of my speaker components from Madisound, but Parts Express is also great and has a good selection of cheap drivers as well, should you want to add a tweeter or upgrade or whatever. I don't personally think it's worth adding a separate tweeter with that coaxial, though.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 24, 2014, 06:03:50 pm
content: Quote from: microbug on April 24, 2014, 03:51:32 pmAs I said earlier, I suggested a tweeter before I knew you had a loudspeaker with a tweeter built in. Actually, having had a closer look, I see that it's not a separate tweeter, but a "whizzer" cone. Even so, I would suggest you listen to it before deciding if a separate tweeter is required.I agree entirely with the sentiment from Anks - go with what you have as it will probably teach you something. Don't expect perfection on the first outing, just be prepared to experiment until you're happy. That's how it works - it's very unusual for projects to go according to the book, despite how they might appear when presented afterwards. Even in the commercial world a lot of the time. Learn to enjoy this uncertainty, because that's where the real joy and discoveries are found.

author: microbug
author_rank: Frequent Contributor
timestamp: April 24, 2014, 06:52:38 pm
content: I read over all the posts again. Whether or not I add a tweeter depends on how good the loudspeaker I have at the moment are at high frequencies. As I said, I have no experience in this domain but, by my ear, it certainly sounds a lot better when I enable the "treble booster" EQ on my iPod. Unfortunately I can't do that with every device because not all have an EQ setting (and as far as I can tell, it just limits the bass rather than making the treble any louder). Taking this into account I will try to find a tweeter that will fit the max 35mm diameter, but if that isn't possible / tweeters that small aren't worth having, I'll just go without (and not parallel the loudspeaker I already have). The only other change I'll make is adding a boost converter set to 13V so the amp isn't affected by the battery voltage drop.I don't expect perfection, I just want to do the best I can with my constraints!

author: Holograph
author_rank: Regular Contributor
timestamp: April 24, 2014, 07:23:24 pm
content: Quote from: microbug on April 24, 2014, 06:52:38 pmThe size of a driver (be it a tweeter, mid, or woofer - though not so much subwoofers) should be matched to the system. Smaller drivers weigh less and can typically use a relatively larger motor because the smaller cone has less flex. This means they can play higher in frequency. Also, with typical dynamic speakers (especially cones) there is a property known as "beaming" where essentially larger cones have less angular dispersion than smaller cones. If you had speakers in your living room with a relatively large 2" tweeter and you sat directly in front of your speakers, you would be okay. But if you had friends over and they sit way off to the side, they will hear a lot less treble than you. But if you were using a nice 3/4" dome or ring radiator tweeter (like the excellent Vifa XT19 19mm ring radiator my DIY front speakers use) your friend will get sound that is much closer to what you hear (though still not perfect).The upside to larger drivers is that they can typically handle more power, have more excursion capability (Xmax / Xmech), and can play lower in frequency range. Edit: Oh, and as previously explained, they are often more sensitive, though not always. Depends on the motor design.There is also a downside to larger angular dispersion: Your room is likely to cause more reflections which can cause phase issues and the "combing" effect. There are ways to mitigate this but not that easily, so for a budget system it's something you'll just have to deal with. It shouldn't be a super major issue, though.Since your woofer/midrange is fairly small, you should be able to get away with a small tweeter like 3/4". If you had a 6.5" or especially 8" woofer (without a midrange i.e. staying with a 2-way system instead of a 3-way) then you would be more likely to need a larger tweeter to match, because a larger woofer will roll off (and start beaming) sooner than yours, so ideally the tweeter would be able to cross over at a lower frequency.As a side-note, I prefer 3-ways for high-end home speakers, but there's always a tradeoff - the crossover. They become more complex and expensive and you really want to avoid having to using L-pads to match the volumes in a passive crossover. An active crossover isn't so much of an issue if you have enough amp channels (in your case you don't but this is more general speaker knowledge anyway).If you do use a separate tweeter with that woofer, I'd clip the tweeter lead for the coax. It's probably just using a 1st-order filter consisting of a capacitor. Don't try to remove the cone, though, or you will probably destroy the speaker (and if you didn't, you'd need to buy a dustcap for it to cover the hole).

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 25, 2014, 08:54:47 am
content: Quote from: Holograph on April 24, 2014, 07:23:24 pmAs I said a couple of posts back, it's not a coax unit. I thought that at first from looking at the OP's pictures, but having looked at the manufacturer's info, it's just a "whizzer".

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: April 25, 2014, 09:18:02 am
content: Quote from: microbug on April 24, 2014, 06:52:38 pmRather than relying on source devices to do this, I'd include tone controls. Dead simple - just a "Baxendall" job would probably do. And with a loudspeaker project like this, it would be customary to build in some equalisation into the amp itself, often separate from the tone controls. Have a look at that powered speaker project I linked to earlier for an example. There was a time when all half-decent transistor radios had EQ built in to give the little 'speaker some help in the cabinet, and that's partly why old radios sound so much nice than many of the modern ones you can buy today.As I mentioned earlier, tone controls are not considered socially acceptable in the hi-fi world, where complaints of poor tonal balance are addressed by equipment "upgrades", or magic wire or other voodoo. Strange that tone controls aren't allowed in an amplifier when most crossovers have tone controls built in to account for "baffle step" and drive unit anomalies, but these are invisible to audiophiles who think their equipment is designed with pixie dust.However, in the real world, there is no such thing as the perfect recording, the perfect loudspeaker, the perfect listening room, and tone controls are extremely useful. For something that is small and portable, it'll need all the help it can get.

author: GamerAndds
author_rank: Regular Contributor
timestamp: April 25, 2014, 12:04:25 pm
content: I know tha I'm "Preaching to the choir here" so to say but all these chips should be externally balanced, that way throwing on a simple pair of TO220's or something similar can be done easily. Personally love the STK4050 for this reason! But I also have a thing about paralleling amps... Each amp would have to be "100%" the same because of there not your going to be dragging one another down. And for that point it dosent really make any sence. Your not going to be amazed by the improved response IF you even hear it.

author: dannyf
author_rank: Super Contributor
timestamp: April 25, 2014, 12:41:47 pm
content: QuoteThere is nothing preventing you from connecting a gate driver + two mosfets on each output pin and hook it up to a high voltage supply for more power.Topology wise, this particular chip has no feedback (post or pre filter) so the performance may not be great.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 25, 2014, 12:49:36 pm
content: Quote from: microbug on April 24, 2014, 02:31:41 pm@microbugI can recommend, however, I'm lazy todayall your answers you want are here, fragmented.. its a rather long thread 100+ pages I'm sure you will have fun.http://www.diyaudio.com/forums/class-d/104402-boominator-another-stab-ultimate-party-machine.html

author: microbug
author_rank: Frequent Contributor
timestamp: April 25, 2014, 02:56:08 pm
content: See you in a few days then!EDIT: That thread is huge – I'm serious about a couple of days. If anyone is less lazy, feel free to help!EDIT 2: I have found a more recent (Jan 2006) version of the TA2024 datasheet. I don't think it will be much more help but I have attached it anyway.