I am currently planning the stages of building a two way active studio monitor as part of a school project. As of now the crossover unit is going to be placed before the two power amps. I'm not sure if this information is relevant but I am looking at being able to produce 90dB at 1 metre away from the speaker.
I was just wondering what things need to be considered when choosing a chip amp?
Also if anybody had any recommendations of chip amps that I could use that would be great.
I understand that this may be very vague so please ask any questions that may need answering to help you help me.
Thanks!
I was just wondering what things need to be considered when choosing a chip amp?
Also if anybody had any recommendations of chip amps that I could use that would be great.
I understand that this may be very vague so please ask any questions that may need answering to help you help me.
Thanks!
The 90dB SPL figure you're targetting is going to depend on the power from the amp but also the efficiency of the drivers you use. Say you have 87dB efficiency (that's dB per Watt of input power) drive units, then your amp must contribute 3dBW i.e. 2W. Since the vast majority of drivers you're likely to choose are going to be better than 84dB you're not needing more than a 4W amp to achieve this.
The next consideration is the impedance of the drive unit, which will normally be between 4 and 8 ohms.
A chipamp which will meet your requirements is the TDA8566. You only need the one chip per speaker, its a two channel design.
The next consideration is the impedance of the drive unit, which will normally be between 4 and 8 ohms.
A chipamp which will meet your requirements is the TDA8566. You only need the one chip per speaker, its a two channel design.
I am currently looking on a Vifa D27TG-35-06 tweeter which has an 87.4dB efficiency at 1W/1m, am I correct in saying this will mean I will need to have about a 2 Watt amp for this stage to get a 3dB increase?
I am unsure as of yet on what woofer I am going to use.
The Vifa D27TG-35-06 has an impedance of 6 ohms, is this the same as the impedance of the drive unit that you mention?
Thanks very much for the help!
I am unsure as of yet on what woofer I am going to use.
The Vifa D27TG-35-06 has an impedance of 6 ohms, is this the same as the impedance of the drive unit that you mention?
Thanks very much for the help!
Your tweeter calculation is correct, yes. Amps are not normally specified for 6ohms, so to be on the safe side we'd need to ensure the amp is capable of 2W into 8ohms.
I didn't mention any specific drive unit, rather I was waving my hands around to indicate the normal impedances available to you. Its common that the woofer isn't quite so efficient as the tweeter so probably its best not to choose an amp until you've settled on that. However the TDA8566 I suggested has a lot of power in hand.
I didn't mention any specific drive unit, rather I was waving my hands around to indicate the normal impedances available to you. Its common that the woofer isn't quite so efficient as the tweeter so probably its best not to choose an amp until you've settled on that. However the TDA8566 I suggested has a lot of power in hand.
Most chipamps 20W or more should be able to do this - but the important things, if lower powers are a necessity in your project, is the general dB/W of the bass speaker and for good bass, the size of the bass cone..... in both cases normally the larger the better... perhaps you could furnish us with an idea of what sort of drivers you want to use?
I now have visions of a 20W TDA2050 driving an 18" woofer to ear-shattering levels-LOL
Perfect so if I were to use the Vifa P17WJ-00-08 which has an impedance of 8 ohms, and the Vifa D27TG-35-06 which has an impedance of 6 ohms, I would still be able to use the TDA8566?
It was also mentioned that the TDA8566 is a two channel design.
Does this mean that the two signals after the crossover are considered the channels?
It was also mentioned that the TDA8566 is a two channel design.
Does this mean that the two signals after the crossover are considered the channels?
it is a dual design, 2 x 2 amplifiers in bridged mode.
Note: Bridge mode uses 1 amplifier at each end of the speaker, means you use two amplifiers per speaker. Bridging effectively doubles the output swing capability, and in theory should quadruple the output power for a given supply rail. It is used in car radios (as indeed this chip is intended) to get more power from relatively low supply rail.
You have 4 amplifiers in one TDA8566 package so you have 2 sets of 'bridged' amplifiers... This means you could run them
a. In stereo 1 set feeding each left and right channel speakers.
b. mono; 1 set feeding treble, the other set feeding bass speaker. Then you'll need another doing the same for the other speaker.
Note: Bridge mode uses 1 amplifier at each end of the speaker, means you use two amplifiers per speaker. Bridging effectively doubles the output swing capability, and in theory should quadruple the output power for a given supply rail. It is used in car radios (as indeed this chip is intended) to get more power from relatively low supply rail.
You have 4 amplifiers in one TDA8566 package so you have 2 sets of 'bridged' amplifiers... This means you could run them
a. In stereo 1 set feeding each left and right channel speakers.
b. mono; 1 set feeding treble, the other set feeding bass speaker. Then you'll need another doing the same for the other speaker.
Its certainly one I love, wouldn't class it as my fave because the power output (more to the point, the output voltage swing) is a little bit low for my needs. But for the OP this certainly is not an issue.
I recommend this chip to newbies in the chipamp game because its such a simple one to get going. For example its designed to run on a single supply, a laptop brick can serve as a PSU (so long as its voltage isn't too high). It requires the fewest components to get a working stereo amp but is capable of high-end sound with attention to details. Its also very cheap (at least here, I buy recycled ones).
I see Arty has mentioned other positive points like ruggedness (it tolerates over-voltage very well).
@kevnaff - last time I checked, Mouser stocked the TDA8566.
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The 55W is for a 2ohm speaker/drive unit impedance, also I suspect measured at a high level of distortion (perhaps 10%). Translating that into a 6ohm impedance it would be about 20W.
The wattage you actually get depends on the signal you send it, in addition to the drive unit's impedance - if you want no more than 2W then keep the volume down. In fact, since our ears/brain works logarithmically, 20W only sounds about twice as loud as 2W.
The wattage you actually get depends on the signal you send it, in addition to the drive unit's impedance - if you want no more than 2W then keep the volume down. In fact, since our ears/brain works logarithmically, 20W only sounds about twice as loud as 2W.
that's fair do's.... I was reminded of the TDA1518 when I looked at the TDA8566 schematic, of which I believe it is a derivative. Have about 6 of those knocking around somewhere.
I suppose you might be able to push a few more watts out of them, too - you could double the power taking them to 18V (but no higher!).
I suppose you might be able to push a few more watts out of them, too - you could double the power taking them to 18V (but no higher!).
Assume an average listening level of 80dB with a headroom of 20dB for peaks, you need to build in some more reserve. I do not believe 20W is enough for a nearfield system except in the most undemanding situations.
You will also lose about 2dB in baffle step compensation (I use 1.5dB and I'm about 18" from the drivers). If you want to have an adjustable tweeter pad like a pro monitor, you will lose even more sensitivity.
Since one might want to listen close, you will need to have a pretty low crossover point to ensure proper integration at the listening postion and if you tailor the tweeter's own low-end response into your crossover, you will find that sensitivity plummets.
Overall, just because it's nearfield, it's not as if you need that much lower power than a regular home system. I would say about 20W on the tweeter and 40W on the woofer is adequate.
I run a system with two LM3886 chipamps on the woofer, a single on the tweeter and adjustable BSC pads and tweeter level pads. This means my actual system sensitivity drops by about 4dB for the woofer printed spec (itself usually a few dB is lost in actual driver). I find that just about adequate to not exceed the point where the distortion level starts to rise (for the 3886, this is about 30w).
The 8566 is a car radio chip. With all due respect, it is simple to use but is not developed for any critical audio application. The stated distortion level is 0.1% at 1W (assuming at 1KHz), which is by a few orders of magnitude worse than many other chips. Even the humble and cheap TDA2050 is 5 times better on paper, and the 3886 is a bit better than that and has enough power to do what you need. See the 20K/8 ohm graph from the datasheet. There is a nice layout of the 3886 available on this forum (don't use the Chinese PCBs, those are terrible). Layout is important in all these kind of amps.
Good Luck. You can see my monitor build here sans tech details, as this is a PC forum: https://www.techenclave.com/community/threads/diy-active-monitors.153054/ I used the Chinese boards but had to hack them quite a bit to get satisfactory operation. The 3886 is also used by Alesis and a bunch of other manufacturers for their entry-level monitors. So it has the street cred to do the job as well.
You will also lose about 2dB in baffle step compensation (I use 1.5dB and I'm about 18" from the drivers). If you want to have an adjustable tweeter pad like a pro monitor, you will lose even more sensitivity.
Since one might want to listen close, you will need to have a pretty low crossover point to ensure proper integration at the listening postion and if you tailor the tweeter's own low-end response into your crossover, you will find that sensitivity plummets.
Overall, just because it's nearfield, it's not as if you need that much lower power than a regular home system. I would say about 20W on the tweeter and 40W on the woofer is adequate.
I run a system with two LM3886 chipamps on the woofer, a single on the tweeter and adjustable BSC pads and tweeter level pads. This means my actual system sensitivity drops by about 4dB for the woofer printed spec (itself usually a few dB is lost in actual driver). I find that just about adequate to not exceed the point where the distortion level starts to rise (for the 3886, this is about 30w).
The 8566 is a car radio chip. With all due respect, it is simple to use but is not developed for any critical audio application. The stated distortion level is 0.1% at 1W (assuming at 1KHz), which is by a few orders of magnitude worse than many other chips. Even the humble and cheap TDA2050 is 5 times better on paper, and the 3886 is a bit better than that and has enough power to do what you need. See the 20K/8 ohm graph from the datasheet. There is a nice layout of the 3886 available on this forum (don't use the Chinese PCBs, those are terrible). Layout is important in all these kind of amps.
Good Luck. You can see my monitor build here sans tech details, as this is a PC forum: https://www.techenclave.com/community/threads/diy-active-monitors.153054/ I used the Chinese boards but had to hack them quite a bit to get satisfactory operation. The 3886 is also used by Alesis and a bunch of other manufacturers for their entry-level monitors. So it has the street cred to do the job as well.
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Yes, very similar. TDA1518 is noisier by virtue of having more gain (40dB). Less capable output stage though, with lower peak current.
One of the great things about these chips is - higher than 18V just puts them into mute, doesn't damage them. That, and under-voltage protection too is a useful feature which requires external components on other chips.
@sangram - I take it you've not listened to the TDA series of chips. I've built many an LM3886 (nothing fancy like MyRef, mind) and the TDA8566 beats it for SQ despite poorer on-paper specs for distortion. TDAs deliver better PSRR in practice than typical LM3886 designs. I agree layout is critical for great sound and the designers of the TDA family took care in the chip design to make layout as easy as possible for great SQ. Take decoupling - they put the power pins together and they used more than one pair. So lower inductance decoupling is much easier than on LM3886. There's also a separate signal ground pin.
Actually I have 
though not the 8566. My most weird experience was with a $500 Japanese amp using the TDA1554 (Philips, pre-NXP). It sounded all right but not worth the money.
With a good layout it is possible to get LM chips to sound great - better than multi-thousand dollar commercial products. My personal preference is for P2P but that's not practical inside a monitor. The big problem with the LM chips is getting the layout right, but Tom and others have some really great info on those subjects on the forum, even for vanilla implementations (not composites like the MyRef).
In any case, I would still suggest a little more power for such a design because of the need for clean headroom of about 10dB at the very least above the listening level and the efficiency losses that are quite unavoidable in such designs. Personal preferences will vary, but IMO in a monitor accuracy is of prime importance.
though not the 8566. My most weird experience was with a $500 Japanese amp using the TDA1554 (Philips, pre-NXP). It sounded all right but not worth the money. With a good layout it is possible to get LM chips to sound great - better than multi-thousand dollar commercial products. My personal preference is for P2P but that's not practical inside a monitor. The big problem with the LM chips is getting the layout right, but Tom and others have some really great info on those subjects on the forum, even for vanilla implementations (not composites like the MyRef).
In any case, I would still suggest a little more power for such a design because of the need for clean headroom of about 10dB at the very least above the listening level and the efficiency losses that are quite unavoidable in such designs. Personal preferences will vary, but IMO in a monitor accuracy is of prime importance.
Hardly fair comparing DIY-sweated-over-details chipamp designs with a commercial offering (Speaking here as one who used to do commercial chipamp designs). P2P is easier to do with TDA8566 than LM3886 due to the lower component count. I also forgot to mention that power supplies (after getting the layout right) are next most important and having only a single rail aids that task considerably. Getting the right layout is far easier with the TDAs IME.
I agree Tom's threads are excellent resources but hardly suitable for a newbie.
(Speaking here as one who used to do commercial chipamp designs). P2P is easier to do with TDA8566 than LM3886 due to the lower component count. I also forgot to mention that power supplies (after getting the layout right) are next most important and having only a single rail aids that task considerably. Getting the right layout is far easier with the TDAs IME.I agree Tom's threads are excellent resources but hardly suitable for a newbie.
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