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Old 6th February 2009, 09:15 AM   #1
pra3718 is offline pra3718  India
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Default Amp in sub encloser with fan

I have mounted four TDA1554Q on 2x6" heat-sink. It becomes very hot within 5min. I have to install this all circuit in sub-incloser. If I mount a FAN on heat-sink is that right way ?
OR
How big the heat-sink is required for those four IC ? ( I am using 12V - 5 Amp. supply )
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Old 6th February 2009, 01:22 PM   #2
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Pd = U / (2 * PI * Rl)

Treat Rl as if it were 2 Ohm to compensate for the internal circuitry that gets 11 W out of 14,4 V.
I. e. 12 V and 2 Ohm -> 3,65 W / channel -> 14,6 W / IC. Assume an ambient temperature of 50 C in the enclosure. 150 C is the maximum permissible temperature. (150 - 50) / 14,6 = 6,85. That is the thermal resistance you need to achieve. The IC has 1 K/W, add 0,2 K/W for thermal grease. Your heatsink must remain below 6,85 - 1,2 = 5,65 K/W per IC. For four ICs it must be a quarter of that ~1,4 K/W. Something like keyword SK85 from this site.

This is assuming that you increase the power supply to double the size. With the 60 VA you have now, you can expect about half the possible output power, half the power dissipation, and a short service life, because it will be overloaded most of the time.
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Old 6th February 2009, 03:15 PM   #3
pra3718 is offline pra3718  India
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Thanks,

Being poor knowledge in electronics, I could not understand properly. You are requested to help in general way please.

In details.

1 IC (Stereo) 22w for Front Left woffer (20watt 4 ohm Speaker)
22w for Front Left tweeter (20watt 4 ohm)
2 IC (Stereo) 22w for Front Right woffer (20watt 4 ohm)
22w for Front Right tweeter (20watt 4 ohm)
3 IC (Stereo) 22w for rear left full range (20watt 4 ohm)
22w for rear right full range (20watt 4 ohm)
4 IC (Stereo) 22w for bass unit 1st driver 30watt 4 omh
22w for bass unit 2nd driver 30watt 4 omh

12-0-12 / 5 Amp Transformer supply.

Its sounding good for me. But I don't know how it is reliable? and I could not run this circuit more than 15 min continuesly.

I don't think it is overheating, but I wish to keep it as possible as cool the heat-sink.

If I add fan on the heat sink inside the bass incloser, it may disturb the bass wave ? Pl. help again.
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Old 6th February 2009, 03:58 PM   #4
sangram is offline sangram  India
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10"x4" is what you need, and a fan is also desirable to keep heat in check

PB has the best suggestion - if you can't understand it maybe you need to read a little more - try Decibel Dungeon. And Rod Eliot's ESP website. Both excellent references.

2"x5" is too small for anything, try the one PB has linked to as a guideline for something you can get locally. You can also use a fan, sometimes the effects are quite dramatic. You need to have a secondary supply for the fan, preferably with a separate transformer, to keep electrical noise out of the audio system.
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Old 7th February 2009, 08:37 AM   #5
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Quote:
Originally posted by pra3718
help in general way please.
If you want help, you should be more precise. A "12 V - 5 Amp. supply" is different from a "12-0-12 / 5 Amp Transformer supply". The first tells us you have 12 V rails and 60 VA. The second tells us you have ~15,5 V rails and 120 VA.

You have two choices, calculate for the worst case or Trial-&-Error, i. e. wait and see, if it works.

If you want to calculate, with those increased numbers your Pd will be ~6 W per channel -> 24 W per IC. You need ~4,2 K/W max per IC -> ~3 K/W heatsink per IC -> 0,75 K/W heatsink for all ICs together. The heatsink from the above link at least 100 mm long will get you on the safe side. A fan will bring the necessary heatsink size significantly down.

If you want to try and see, just wait for the thermal protection to switch the ICs off. It will probably happen on a hot day, when you listen to very loud music. Then decide, if you can live without music on all days that are hotter than that or increase the heatsink size.

Quote:
Originally posted by pra3718
If I add fan on the heat sink inside the bass incloser, it may disturb the bass wave ?
No, it won't. The noise from the fan could however be annoying. People tend to use a temperature control for the fan. That is either a thermostat that starts the fan, when a certain temperature is reached or a speed control that regulates the fan according to the temperature measured by a sensor. You should also have an indication, if the fan is really working (if you cannot hear it). Fans for computers often come with a connection for that.
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Old 7th February 2009, 01:19 PM   #6
pra3718 is offline pra3718  India
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Many many thanks to both of you.

I purchased single transformer which has thee out i.e. 12-0-12

to make DC I used

2 Nos - 6amp Diod & 2 Nos - 4700 mfd 25V Capacitor

Pl. find the attached picture.
Attached Images
File Type: gif diypsu.gif (4.6 KB, 541 views)
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Old 7th February 2009, 05:03 PM   #7
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That would result in a very inefficient power supply, wasting about half of the potential. A better solution is this.

Click the image to open in full size.

You need 2 rectifier bridges 6 A or bigger (or 8 diodes). Buy them big, they are cheap. And a big capacitor. You can use two, like in the drawing, but one bigger capacitor will do the same. Your 2 times 4700 F are a good value to start with or 1 time 10.000 F, choose the cheaper solution. If you can afford bigger values, go for it. It usually brings improvements in the bass.
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Old 9th February 2009, 09:20 AM   #8
pra3718 is offline pra3718  India
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Thanks to pacificblue

As you had posted about heat sink 8"x4", I purchased, installed & found heating problem solved at all. Thanks again.

I read your earlier post for power supply & I am going to build my new PSU as per your design.

I going to continue this thread to ask NEW question bcoz you know my new PSU & power amp (TDA1554q).

I need buffer amp/preamp to improve my poor input signal to amplify with TDA1554q. I found some website for buffer amp / active filter but supply was 15V & you know I have 12V. If any matching buffer circuit in your mind Please Post.

Thanks & Regards.
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Old 9th February 2009, 10:06 AM   #9
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The gain of the TDA1554 is 10. Line level should be 775 mV, which would result in 7,75 V at the output or 15 W with 4 Ohm speakers. Any normal source should be able to send the TDA into clipping.

What source do you use, that cannot deliver the 775 mV standard line level?

You don't have 12 V. The transformer has 12 V. After rectification and smoothing you get ~(1,41*12)-1,4 which is 15,5 V nominal.

You can use nearly any buffer/preamplifier with a single supply as well. You will need a virtual ground / rail splitter for single supply operation. In this article there is a section that explains how to use a single power supply on an opamp.
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Old 9th February 2009, 10:48 AM   #10
pra3718 is offline pra3718  India
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Thanks, you are educating me.

I understood, now I have 15,5 V Power Supply. (WOW)

As you stated TDA's output is 15Watt, & in datasheet stated 22Watt. i.e. I am doing something wrong. What should I do to get full 22Watt on 4 Ohm Speaker ?.

<WHAT SOURCE DO YOU USE > = I am using Chip DVD Player 5.1 (Six channel) <LINE LEVEL SHOULD BE 775 mV> Sorry, you know my knowedge level, i.e. 775 mV I can not tell you.

My DVD Players output has 6 Channel & accept SUB all channel sounds good. Sub sounds, but very poor. I thought, mono buffer amp may solved subs poor singal. Is that right ?

Yes, I am going to study your posted LINK.

Regards.
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