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Old 12th January 2015, 01:13 PM   #1
kevnaff is offline kevnaff  United Kingdom
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Default Chip amp for my power amp

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!
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Old 12th January 2015, 01:30 PM   #2
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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.
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Old 12th January 2015, 01:40 PM   #3
kevnaff is offline kevnaff  United Kingdom
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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!
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Old 12th January 2015, 01:49 PM   #4
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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.
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Old 12th January 2015, 02:14 PM   #5
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by kevnaff View Post
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!
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
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Old 12th January 2015, 02:44 PM   #6
blu_glo is offline blu_glo  England
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blimey - there's some time delay going on here, when I posted my message no-one had answered either on the main list nor this page....
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Old 12th January 2015, 02:50 PM   #7
blu_glo is offline blu_glo  England
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looks like Vifa P17WJ-00-08 is almost perfect match (in sensitivity) to your suggested tweeter and would work with either of the chips you have had suggested above.....
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Old 12th January 2015, 04:26 PM   #8
kevnaff is offline kevnaff  United Kingdom
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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?
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Old 12th January 2015, 04:47 PM   #9
blu_glo is offline blu_glo  England
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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.
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Old 12th January 2015, 04:48 PM   #10
blu_glo is offline blu_glo  England
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Abraxalito - I'm interested why you recommend this chip, - is is a personal favourite?
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