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Old 12th May 2012, 09:01 PM   #41
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Quote:
Originally Posted by Kaplaars View Post
Hi David,

Thanks for your input! Hmm, that gives food for thought. My motivation behind mounting the tunnel coolers together and place them like post 32 was to get better air circularion since the air can flow directly in and out the cabinet through the tunnel.

Basicly there are two fans, one which sucks air from outside and blows air through the tunnel. At the end of the tunnel I mount another fan which sucks the air out of the tunnel and blows it out of the cabinet (not in the picture). That would fit just right from side to side. Therefore I have to drill two holes in the cabinet at each side, so air can flow freely. When I mounted the tunnel coolers as in post 24 there would be less circulation of air was the idea. On the other side, in the new 'mounted' configuration differences in temperature are indeed almost inevitable :-(

In the original Krell configuration the tunnel coolers were placed upright, but I find that the least best option. It would give two ugly holes on top and two at the bottom for optimal airflow.

I think that it is a good idea to experiment a bit with the best configuration before I drill large holes in the cabinet.
"if" I had to use fans, I would use just one at the end of tunnel (one fan= less noise) it will pull the hot air trapped inside tunnel out.
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Old 12th May 2012, 09:36 PM   #42
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Hmm that would also be an option. Although, the tunnel cooler would in that case not fit precisely from one side to the other in the cabinet.

To be fair there is not very much noise from the fans. Noise is reduced a lot when I run the fans with less 'juice'. For example, when I run them at half speed they are almost inaudible, but still a lot of airflow. I am thinking about some kind of fancontrol which moderates fan speed with temperature. But first find some time to realise this :-)

Last edited by Kaplaars; 12th May 2012 at 09:38 PM.
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Old 12th May 2012, 09:41 PM   #43
AVWERK is offline AVWERK  United States
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You don,t need alot of fan speed so the idea of pulling air around the toroids and caps is a moot point. It does make a difference however if you are using more than say 1200 rpm. What becomes an issue with high fan speeds is noise due to close proximity of the incoming air.
Your last picture is great for low noise since their is no objects to impede incoming air but bad for even heat distribution
So looking at how Krell did theirs was the best overall configuration for both fan noise and even heat in the available enclosure.
Their orientation was the best overall compromise for both considerations
I like to keep fan speeds under 1000 rpm if I can,t meet the space requirements. And that is very close to the turn on voltage for DC fans.
It becomes really, a first and paramount design requiement when doing a layout for the chasiss

Regards
David
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Old 13th May 2012, 01:56 PM   #44
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Andrew, Andrew, Andrew... what is your problem. You keep nagging that it is a bad idea to place NTC's parallel. OK maybe, but why? Is it that hard to underpin your theorem? I don't know.... but you keep refusing to give a constructive answer. It is like I state driving on 3 wheels is a bad idea, but I don't say why it is a bad idea. A critic dutchman asks why, but all I say, read the English. What English, were is the explanation? Luckaly CBS240 explained it, so it is no longer necessairy.

Other thing, you state that bypassing the rectifier diodes with capacitors is a bad idea. Again, OK, can be, but why? Still got no answer from you. Again CBS240 was the helping friend. Is it that strange to ask why?

But Andrew, lets not spoil this threat with our little discussion. To be fair my initial question had nothing to do with the NTC's. My initial question was about the series capacitor. The NTC's are NOT really my problem, and to be fair this config works perfect, it switches the two 1 KVA toroids perfectly on, and no fuse is spoiled. :-)
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Old 14th May 2012, 09:46 PM   #45
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Hi Friends,

Little update about the series capacitor were I did not know the meaning of. Learned from a Dutch forum that it does no harm to the amplifier :-) When the capacitor makes short circuit the amplifier just turns on, so no problem there (I should have know that! :-)).

The amplifier is always in a sort of standby due to this capacitor. But with very little current. In ideal circumstances the current in stand by is: L = 2.Pi.U.f.c, so in my case that is 2*pi*230*50*0,000000022 = 1,6mA. That explains why the current drops almost to zero when I put a little load after the soft start.

The function of the capacitor is to damp little sparks which occur when the relays disconnect (Lentz law).
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Old 14th May 2012, 10:11 PM   #46
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the reason for 2 and 2 NTC's in parallel and the 2 pairs in series, is so they can handle more current then 1 NTC without changing the cold resistance.
can't see any problem with that
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Old 14th May 2012, 10:39 PM   #47
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Hi AudioSan,

Thanks four your input! That is what I thought too :-). I think I just leave it the way it is.
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Old 14th May 2012, 10:54 PM   #48
kvholio is offline kvholio  Netherlands
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Quote:
Originally Posted by AVWERK View Post
Kap
I would place the fans to blow each channel out the back instead of thru a long tunnel.
You will get about a 15 to 20 C difference between the in and out temps on these sinks the way you have them positioned.
I know this to be true since I done this on my Synder monoblocks. Even though it never did any harm, you really want consistant temps across the sink if at all possible and that would be a short heat sink with fan

I see you actually had the correct orientation in post 24

Regards
David
AVWERK is correct, Kaplaars.
the last configuration you've shown will mean you have one channel running hot, the one furthest from the fan pushing air through the tunnel.
The air entering this channel will already be hot from running through the first half of your tunnel.

Groet,

Klaas
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Old 17th May 2012, 03:12 PM   #49
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Hi Klaas,

Hmm, I hope the temperature does not get to hot. Aesthetically I think that this is the best looking configuration. I got inspired by A D&B amplifier. David & Ben used this concept comercially. They made beasts of Class A amplifiers, which I think are even more beautifull than Krell. This is an example:
Click the image to open in full size.

Fortunately the tunnel coolers are easy to separate, so if temperature gets out of control it is not very hard to choose a different configuration.

By the way, I added extra capacitors parallel to the big electrolytic caps. The capacitors are a bit overkill, but I have a lot of these in stock. The advantages with this caps overweight potential disadvantages, but if it turns out that they do more bad than good I can easily remove them.

Click the image to open in full size.
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Old 17th May 2012, 04:27 PM   #50
DRC is offline DRC  United Kingdom
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Connecting 2 NTC resistors in parellel will almost certainly result in 1 being hot and having a low resistance while the other is cold and having a high resistance. Clearly one of them will end up carrying almost all the current and, quite possibly, be outside it's safe operating area (which is likely why you didn't just use one in the first place).

dc
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