Yes you need bigger heatsink, class AB eficiency is 60-70% about 20-30W will be disipate on heatsink at full power.
Thank you sir for your prompt reply!
There will be total 6 Amps like this in my case for my stereo 3 way system.
Wow! I guess I will have to spend my next month's salary on Aluminium.
Did you check how big heatsinks ppl put on their 3886 chip?
As I know these chips have 1C/W thermal rezistance meaning it is useless to put a bigger heatsink, because the chip can not dissipate more heat. If you put 500 times bigger thing on it, it will still be the same hot. But if you like to waste money.
The one you have on the pic is already less than 1C/W as I know.
As I know these chips have 1C/W thermal rezistance meaning it is useless to put a bigger heatsink, because the chip can not dissipate more heat. If you put 500 times bigger thing on it, it will still be the same hot. But if you like to waste money.
The one you have on the pic is already less than 1C/W as I know.
From a certain point it is useless to use a bigger heatsink. Maybe if he puts in a 3 times bigger he will get 10% less heat.
Same reason ppl use heatpipe in CPU cooling because a chunk of metal is a crap heatsink. Heat spreads slowly. But also the chip is unable to give all the heat away instantly. But please explain then.
add a 1C/W sink (Rth s-a) to a 1C/W device (Rth j-c). Make allowance for the interface, say 0.5C/W for Rth c-s.
The total Rth j-a is 2.5C/W
Now do the same using a 30C/W sink. The total resistance is 31.5C/W
Pass 1watt from junction to air for the two arrangements.
What are the predicted junction temperatures (Tj)?
Now tell me it makes no difference !!!!
The total Rth j-a is 2.5C/W
Now do the same using a 30C/W sink. The total resistance is 31.5C/W
Pass 1watt from junction to air for the two arrangements.
What are the predicted junction temperatures (Tj)?
Now tell me it makes no difference !!!!
I was talking about his present heatsink. Not using your hand for cooling.
As I sad he already has a about 1C/W heatsink and doesn't need a bigger one. Didn't say he should use a 30C/W sink...
Sorry if I was not clear. I though he is using the heatsink on pic #178.
What heat sink are you using csom?
It also matters how it is set. If face down like on the pic, then you get lot worse cooling. Need ground clearance also.
As I sad he already has a about 1C/W heatsink and doesn't need a bigger one. Didn't say he should use a 30C/W sink...
Sorry if I was not clear. I though he is using the heatsink on pic #178.
What heat sink are you using csom?
It also matters how it is set. If face down like on the pic, then you get lot worse cooling. Need ground clearance also.
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Som
The pic on post 178 looks like your sink is fine for a chip amp like a LM3886. I am betting you could get away with 2 chips per heatsink and I dont think you could fit more anyway. I have put very small sinks on LM3886 and overheating wont destroy them, they just stop working well til they cool down. So its pretty easy to figure out when your sink is to small.
Like Wagner said you need the fins to be at a 90 degree angle to the floor, vertical. As you noticed even a very very slight breeze will make the sink much more efficient. Many people use tiny fans at very slow speeds to increase the efficiency of the heatsinks.
Uriah
The pic on post 178 looks like your sink is fine for a chip amp like a LM3886. I am betting you could get away with 2 chips per heatsink and I dont think you could fit more anyway. I have put very small sinks on LM3886 and overheating wont destroy them, they just stop working well til they cool down. So its pretty easy to figure out when your sink is to small.
Like Wagner said you need the fins to be at a 90 degree angle to the floor, vertical. As you noticed even a very very slight breeze will make the sink much more efficient. Many people use tiny fans at very slow speeds to increase the efficiency of the heatsinks.
Uriah
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First, thank you so much Mr Wagner and Mr. Miles, Andrew T and all, our respected experienced members who always extend their hands to help out noobs like myself.
For me, electronics theory, math, physics etc. are my really long-forgotten things of the past ( some 20+ years ago, I guess ) and my Real life profession is just polar apart from these. Everything has gone with the wind except my soldering and PCB making skill. Sad but true.
From this stand point, I might not understand all or give apt feedback to the technical questions. So kindly bear with me.
I just want to build a "great and yet simple to build" system that is tested/endorsed by all of you, the audio gurus, to satiate my age old craze of owning a great amplifier. That is why I am so dependant on all of your wisdom. And to be honest I'm re-learning from all your wise words and "following" your advice.
Here I attached some photos of the heatsink that's being used with one LM3886. Other photos are just for size comparison.
In India, where I live, it's next to impossible to get a heatsink with tech-specs. I really have no other way but to guess with trial and error what is working in my case.
I just purchased this big piece from a shop with a rough guess. So, to all...... kindly carry on giving your much needed and valuable advices.
Thank you once again.
Attachments
Thank you so much Uriah! Very well thought out words as usual.
So nicely explained!
I had a plan to use 2 chips per piece.
And may be I'll have to use Mr. Mile's fan control ?
That heatsink is for sure fine for two chips. If you only have one sink I would attempt three chips. You might get away with it.
I don't know which fan control you mean but usually to run a fan real slow you need to start it up at a goid speed then slow it down as they don't like to start turning slow but once started they will continue at a slow speed. A potentiometer controlling fan current or regulator voltage will do the job. Do you know what I mean? Do you need better explanation on the fan?
I don't know which fan control you mean but usually to run a fan real slow you need to start it up at a goid speed then slow it down as they don't like to start turning slow but once started they will continue at a slow speed. A potentiometer controlling fan current or regulator voltage will do the job. Do you know what I mean? Do you need better explanation on the fan?
Thank you again Uriah,
I've got it from your words now.
Kindly have a look at this link at post# 385. Can I use it in the amp ?
http://www.diyaudio.com/forums/analog-line-level/167363-mic-line-eq-preamps-39.html#post3435753
Sorry it took me some time to find the post.
Mr. Mile should make an index of his gems scattered all over the fora.
There are fans that you can use on 5V and they start on 5V or lower. (like the one I use Coolink swif 1201 starts on 3.1V)
Don't know what kind you have access to. If you use PC fans, there are test and videos showing from what voltage they start. You can also use resistors that lower with heat (termistor).
Test site I checked for fan: CoolingTechnique - YouTube
Don't know what kind you have access to. If you use PC fans, there are test and videos showing from what voltage they start. You can also use resistors that lower with heat (termistor).
Test site I checked for fan: CoolingTechnique - YouTube
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Thank you sir.
As you've rightly guessed, 12 volt PC fans are easier to get here.
But I will look for the 5v ones as per your suggestion.
Can I use a 7805 regulator with rectification and filtration from the separate 12 volt tapping of the main transformer to power up the fan/ 2 fans?
Thank you sir.
I will check both with thermistor and then 7805 and post my findings here.
That youtube link you've posted is a great resource.
Som
yes the schematic you linked will be cheap and easy to build and should work fine but I am not sure if it is designed to slow the fan down to a crawl or keep it going medium to fast speed. Its controlled by a 10k ohm negative temperature coefficient thermistor (10k NTC) so that means temp increase gives a resistive decrease to the thermistor, making the fan spin faster.
You could try a LM317 powering the fan. Use a 100R trimmer resistor(at cold start you would trim til the fan actually turns on) in the LM317 circuit along with a PTC thermistor that gets lower in value with cooler temp. So you might try an Epcos B59008C60A40 that will start at around 4V and will increase to around 13v at 60 degrees C if you put a 1300 ohm resistor in parallel with it. Just an idea to automate it.
yes the schematic you linked will be cheap and easy to build and should work fine but I am not sure if it is designed to slow the fan down to a crawl or keep it going medium to fast speed. Its controlled by a 10k ohm negative temperature coefficient thermistor (10k NTC) so that means temp increase gives a resistive decrease to the thermistor, making the fan spin faster.
You could try a LM317 powering the fan. Use a 100R trimmer resistor(at cold start you would trim til the fan actually turns on) in the LM317 circuit along with a PTC thermistor that gets lower in value with cooler temp. So you might try an Epcos B59008C60A40 that will start at around 4V and will increase to around 13v at 60 degrees C if you put a 1300 ohm resistor in parallel with it. Just an idea to automate it.
Thank you so much. I love the way you explain so nicely. It's really a great help.
I have some LM317 ICs with me
I will try to obtain other parts to give it a try and post photos soon
@csom This is a bit OT
Sir, i am really angry with you x-( you got me into Diy world, and i jumped into overtly ambitious 6 channel TDA2050 and 2x tda7293 for subwoofers project with two really huge transformers and 9 chips in my hand :\ then i suddenly realize you have graduated to GAINCLONE just like the cult following it has. so the TDA 2050 recieves no more love from you? what will i do with these chips now :\
Sir, i am really angry with you x-( you got me into Diy world, and i jumped into overtly ambitious 6 channel TDA2050 and 2x tda7293 for subwoofers project with two really huge transformers and 9 chips in my hand :\ then i suddenly realize you have graduated to GAINCLONE just like the cult following it has. so the TDA 2050 recieves no more love from you? what will i do with these chips now :\
LOL.
Who says TDA2050 is bad?
It's excellent too. And Low cost. They are like Mini-GainClones as referred to by some audio gurus. As I said many times, my earlier active 3 way TDA2050 system can easily outperform many commercial systems. And I love their quality. Trust me, they are super cool too when used wisely. And we, the DIYers, are always in search of the next dream amp.
All the best.