Amp in sub encloser with fan
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 6th February 2009, 08:15 AM #1 pra3718   diyAudio Member   Join Date: Jan 2009 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 )
 6th February 2009, 12:22 PM #2 pacificblue   diyAudio Member   Join Date: May 2008 Pd = U² / (2 * PI² * 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. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)
 6th February 2009, 02:15 PM #3 pra3718   diyAudio Member   Join Date: Jan 2009 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.
 6th February 2009, 02:58 PM #4 sangram   diyAudio Member   Join Date: Sep 2002 Location: India 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.
pacificblue
diyAudio Member

Join Date: May 2008
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.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)

pra3718
diyAudio Member

Join Date: Jan 2009
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
 diypsu.gif (4.6 KB, 547 views)

 7th February 2009, 04:03 PM #7 pacificblue   diyAudio Member   Join Date: May 2008 That would result in a very inefficient power supply, wasting about half of the potential. A better solution is this. 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 µF are a good value to start with or 1 time 10.000 µF, choose the cheaper solution. If you can afford bigger values, go for it. It usually brings improvements in the bass. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)
 9th February 2009, 08:20 AM #8 pra3718   diyAudio Member   Join Date: Jan 2009 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.
 9th February 2009, 09:06 AM #9 pacificblue   diyAudio Member   Join Date: May 2008 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. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)
 9th February 2009, 09:48 AM #10 pra3718   diyAudio Member   Join Date: Jan 2009 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 ?. = I am using Chip DVD Player 5.1 (Six channel) 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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