| Gabster |
Yep, another heatsink post. But as everyone knows, heatsinks are often the hardest parts to find so there's a lot to talk about.
I'm building the Aleph 2. Therefore I need to dissipate 300W of heat per monoblock (You can see my concept below)
I've spoted a heatsink but I need a double check from the pros.
Here it is
I'm planning to use 12 of them per monoblock as shown below (3" high each).
Here's what I think:
> 300W of heat overall: 25W of heat per transistor/heatsink
> For 3" high heatsinks, thermal resistance = 0.82ºC/W
> Therefore each heatsink has a temperature raise of 20.5ºC [25W*0.82ºC/W], which sounds very good to me.
Furthermore, Aavid sells this extrusion profile in bar of 8' which is very handy (could have my heatsinks up to 4" high).
What do you guys think?
regards,
Gabriel |
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| rtirion |
25W per 0.83C/W sink will not be enough. I think you are forgetting to add the thermal resistance from the insulation plate (mica, kapton, ceramic, silicon or whatever). You must isolate every FET from each sink. This will add anything from 0.5 to 1.5c/w of thermal resistance. This will depend on the type of insulation plate.
You can find a lot more info on this, if you check the older threads.
Regards |
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| Apogee |
Hi Gabriel,
Nice Drawing!
A couple of considerations:
a) The internal heatsinks will run hotter than the ones on the outside of the case. The older PS Audio 200C amps had a similar design and I know from talking with the designer that they regretted that design...
b) I agree that you also have to take into account thermal resistance from the insulator etc.... Figure on ~ 1.0 c/w from the insulator if using mica...
c) Thermalloy is very expensive as to purchase from. They seem to have no interest in supplying us small guys... You might consider M & M Metals, VEP or R-Theta...
http://www.mmmetals.com/index.html
http://www.vepinc.com/
http://www.r-theta.com/indexf.html
d) Finally, if you increase the heatsink length be sure to use the proper multiplier for the change in thermal resistance....the dissipation change is not linear... The models on the Thermalloy website work well for this...
Hope this helps!
Good luck,
Steve |
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| Keld |
Hi
This is more a question than an answer.
Please correct me if I'm wrong cause im new into this
I calculate the final temperature like this: x=(P*(a+b+c+d+e))+amb.
Where:
x= junction temperature
p=power in watt
a=junction to case(C/W)
b=case to insulator(C/W)
c=insulator(C/W)
d=insulator to sink(C/W)
e=sink to air(C/W)
amb=room temperature
example: TIP3055 with good insulator, 25W and the sink as in the above post I end up with this figures:
x=25(1.4+0.07+0.3+0.07+0.83)+20
Final temperature X=86.8 C
Am I on the right track or??
Keld |
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| Gabster |
Hi folks.
I'm starting to lose faith in that project since heatsinks don't stop to grow larger. My first idea was to build an Aleph 4 in the current box design, but I realized I had to go for the Aleph 2...splitting the heat in two boxes.
Now that we talked about numbers, I would like to talk about real life comparisons.
Here's an example:
Mark Finnis built an Aleph 4 (here) using 12"x14" heatsinks for each channel (168in² of heatsink surface per channel).
Using my design (4" high heatsinks) I get 240in² of heatsink surface per channel (per Aleph 2 monoblock). Furthermore, the heat would be more evenly distributed on many heatsinks (instead of all transistors at the center of a huge heatsink).
Even if my heatsinks inside the casing will get hotter, the larger heatsink's surface should counterbalance this.
Since this is not a commercial amp, I don't mind having it hotter than usual class A amps. My goal is really to have slim design.
If you tell me that the Aleph 4 generates less heat, maybe I could simply split the Alpeh 4 in two casings...
What do you guys think? Maybe Mark Finnis himself could comment.
regards,
Gabriel |
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| gnomus |
| If you isolate the heat sinks from each other and the chassis using 6-32 nylon screws and thin nylon washers you will not need any mica insolaters. This greatly increases heat exchange between the mofet and heat sink. Use a metal screw to mate the mosfet to the heat sink. I did this for my SOZ. |
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| WayneS |
Gabster....
Have a look at my Aleph 2's posted on the Pass Labs website. Gives you a starting point on what you can achieve in terms of chassis design. |
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| Gabster |
WayneS, your aleph's look great. Simply.
Where did you get those bolts you used to hold the faceplate...I've been seaching some like these for months.
Looking at your amp's proportions (what are the exact dimensions btw?), I strongly believe that my design is doable (mine will be thinner but larger; depth will be comparable).
ciao,
Gabriel |
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| jbateman |
I have seen extrusions like that being auctioned off at ebay...you might check there.
Also, HSK-260 at www.surplussales.com might be cost effective if you can make your amp 6 inches tall. |
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| jbateman |
| The temp rise you've calculated will be an increase from AMBIENT. With all those sinks in one box the ambient temp will be much higher than the typical 40 degrees used in most calculations, where the sink is exposed to room temperature air. |
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| Nelson Pass |
Gabster,
I think the sinks you propose will be OK. Worst case
is that they run a little hot. |
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| Gabster |
Hey folks,
As Apogee stated, the people at Aavid Thermalloy don't seem to care about small orders. Therefore, I have to look somewhere else.
R-Theta has an interesting model that would suit my design. Does anyone ever place an order there? Can I expect an reply from them?
regards,
Gabriel |
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| alaskanaudio |
Gabster,
R-Theta heat sinks are excellent. I have placed small orders with them for custom heat sinks and they have no problem with these.
R-Theta also has a nice online software package to help with heat sink design and device placement so that all devices will operate at near identical temperatures. The software will also calculate junction and heat sink temperature profiles. In the past they had a few bugs in this software but those have likely been fixed.
The type of fins you specify will depend on wether you are using conventional air flow or forced air. I use conventional along with very slow rotating fans. Forced air fins have closer spacing. Base thickness can also be specified. I would rate R-Theta at the very top of the list of heat sink suppliers.
Some individuals find it hard to find heat sinks. I find that heat sinks are really not that hard to find they are just expensive to buy. For the a power amp dissipating 300 to 500 watts per channel expect to pay about between $1.50 and $2.00 per watt for a two channel amplifier. Thus spending $600 on good quality heat sinks for a two channel amplifier dissipating 300 watts per channel is not unreasonable.
In many commercial products the case and heat sinks can easily add up to half or more of the total parts costs.
John Fassotte
Alaskan Audio |
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| WayneS |
Hi guys,
Here's where I have a bit of experience.
I echo the pricing info of some posters but disagree with others. There are commercial suppliers that have very high prices for small quanitities. I got my sinks from M&M Metals in Irving Texas. Use the R-Theta calculator though it is great for sim'ing your sinks.
My sinks were under $20 each and I used 2 per side of the amp. So that's $160 total for sinks for a pair of amps that cost north of $1200. You can easily pay $1000 for similar sinks though, and the highest price I got was about $2000 for similar sinks. So you can see that there is basically an order of magnitude range on heatsink pricing.
Gabster.....
On the bolts to hold the front panel. Interesting thing, that. My buddy actually found them. They are chromed cap head bolts from a custom biker shop !!! If you can find a place with more tattoos and leather per person than you've ever seen before in your life, then you're in the right place. I bet any Harley shop will have similar for 10x the price...... THey cost me about $1.00 each. I drilled a hole that would clear the threads, then drilled another hole, larger, that would clear the head, but barely. Its tricky as you want the holes to be perfectly concentric. You have to do it on a drill press. Control the depth of the larger hole so that you have the same depth for all the holes - also allow enough material under the shoulder of the bolt so that the panel doesn't pull off because the material is too thin !!!!! I like the chromed look also, though I can't take the credit for the idea.... It adds a lot to the front of the amp IMO, but its a taste thing. I'm really glad my pal found them.
More on bolts.... the pic on the website was taken when I didnt have the tops bolted down. The bolts I used there are the black grade 8 button head bolts. They give a "softer" appearance than using cap head bolts in that position. I may try some cap head bolts there one day to see how it looks.
Amps outside dimensions are 9" high, 12" wide, 14.625" deep.
I doubt you can make the case thinner as my toroid barell clears the sides as is.... be careful here. Use a CAD program to model your amp before you start getting case parts bought. That way you will be less likely to scupper a bunch of expensive parts.
Thanks for the kind words on the finished amps. |
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| alaskanaudio |
I forgot to mention that the cost of heat sinks is affected by whether or not you can utilize a stock extrusion or not. If you have to have a custom type or perhaps a custom length then cost will go up substantially. So attempt to find a stock extrusion that will work to save cutting and other engineering charges. Also anodizing requirements may also add to the costs. How you intend to mount devices also effects on the type of heat sink that can be used
The cost I mentioned in my prior reply are for custom heat sinks and are thus quite a bit higher than using stock items purchased in small quantities. They are however realistic. I have also purchased heat sink extrusions by the pound. This really reduces the cost if you order say 1000 Lbs at a time. Get a lot of individuals to combine a order and lots of $ can be saved.
John Fassotte
Alaskan Audio |
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| Gabster |
I'll request a quote at MMmetals as well. I'll see what comes out.
ciao,
Gabriel |
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| WayneS |
Gabster....
Just noticed something. Your toroid in the drawing is far too small unless you have 2 of them stacked on top of each other. You need about 1500VA for an Aleph 4 or 2... |
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| djk |
| The thermal resistance of 0.82*C per watt is for a 100*C rise.With a power input of 25W the resistance will be 1.134*C per watt, or 28.3*C above ambient.This is a common mistake.This profile is best for forced convection.Under moderate convection the thermal resistance drops from 1.134*C/W to 0.310*C/W, the poor performance under natural convection (and good performance with forced convection) is due to the close fin spacing.A length of 7" of this profile would have a thermal resistance of 0.825*C/W with a 25W input under natural convection. |
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| FEThead |
Keld,
You are correct. |
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| Gabster |
Wayne,
I hope you're talking 1500VA for two channels otherwise this project is on its way to the closet.:mad:
The transformer I wanna use is 625VA 6" dia. and I figured out it was enough for an amplifier outputing 300W of heat and 100W of sound.
:confused: ,
Gabriel |
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| Apogee |
Gabriel,
Please don't give up...
Perhaps consider building one of the smaller Alephs in the same chassis... Your design looks very nice...
I've recently had the experience of listening to an Aleph 0s (stereo) through a pair of Apogee Stages. We hooked it up not expecting much because it was only rated at 40 watts.... We were blown away to say the least!!!
My point is simply that you may be very surprised at what this design is capable of driving... Do you really need 100 watts per channel?
Rather than send it "to the closet" why not choose a particular model that is more closely suited to your chassis design???
On the other hand, take a chance and build exactly what you propose. The experiment will allow you to learn exactly what works properly and what doesn't. Through this you will learn what to do differently the next time... It may end up costing $$$ though for the lesson...
The comments from all of us are simply in the interest of wanting you to succeed and for you be very happy with the outcome...
Again, don't be discouraged!!!
Best Regards,
Steve |
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| WayneS |
Gabster....
My Aleph 2s have 1000VA each and they're as small as you should go. As a reference - Nelson says: "1500VA" for an Aleph 2 is what you really want. My amps appear to be fine... but. It's not ideal.
But. For an Aleph 4, you would be fine with either 2x 625VA or a single 1500VA, for the 2 channels as you said. I think you're good to go.
W. |
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| JBL |
You don'T really need to buy already made heatsink. You can build it yourself using aluminum sheet or you can go at your local electronic repair shop. Some of them stock piece of electronic they where not able to repair or didn't repair. In those they are a lot of old audio amp whit massive heatsink.
And if your unluky with the repair shop building an heatsink is not that hard.(If you can build amp you can surly build heatsink.) One thing is that you make it larger than wath should be needed in order to get a good safety margin. |
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| Gabster |
JBL, as you say I don't think I'll go for new heatsinks since they'll need some reshaping (outside heatsink won't be square). I'll just wait until I find something used and interesting.
Wayne, I guess the most simple solution will be to build an Aleph4 in two boxes.
BTW, what is the difference between these two amps? They are delivering the same output power and schematics are pretty much the same...
Apogee, good advice, but I'll try everything I can to get those 100W amps. However, building an Aleph0 is also part of my projects as it would be more flexible.
Thanks folks, you're really bringing great support to my project.
ciao,
Gabriel |
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| BrianGT |
The Aleph 2 is biased higher and Nelson says that it sounds better.
It is also in the form of monoblocks as compared to a stereo amplifier.
--
Brian |
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| Gabster |
Well, I don't seem to be able to get that Aleph 2 out of my head.
I have rethought every millimeter of that amp to have that 1500VA transformer fiited.
I have added a section of heatsink above X6 boards. This way I get 240in² of heatsink surface which is very close to WaneyS' 260in². I just hope that my good heat distribution and a massive covers (top and bottom) venting will make heat acceptable (I'm very confident :D). As Mr. Pass say, the worst that could happen is that it will run hotter, one think that I don't really mind.
ciao folks,
Gabriel |
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| Jason Hubbard |
It looks like you are using aluminium bar to mount the MOSFETs to and using that to spread heat across the row of heatsinks.
This would result in reduced heat transfer as you are introducing another thermal interface into the equation - better to mount each MOSFET directly to the heatsink as this will reduce the junction temperatures of the devices - Each thermal interface is most likely going to cost you about 1 degree Celcius/w.
Copper would be better than aluminium at spreading the heat, but it's still far from ideal and will also cost you loss of efficiency.
Hope this helps |
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| Gabster |
The aluminium bar is used in case I have one heatsink per MOSFET because the chassis wouldn't be rigid enough otherwise. However, adding the bar would decrease the heat transfer but could add heat absorption...is this relevant?
The best would be to find full length heatsink with enough base thickness to bolt bottom and cover...
ciao,
Gabriel |
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| mefinnis |
Popular little thread, this ;)
A couple of general comments first. I am concerned with the desire of many would-be-Aleph builders to try to build the higher power versions.| quote: | | We hooked it up not expecting much because it was only rated at 40 watts.... We were blown away to say the least!!! |
Please remember dB is a log scale and going from a 60W Aleph5 to 100W will gain you slightly less than 3dB ...... but this move will cost a lot in terms of heat and required hardware.
The vast majority of our listening is <10W, unless you are one of these poor/silly folk who have grossly inefficient speakers. OK, 100W sounds much "sexier" and more "impressive" but in real terms most of us do not need the extra power. In fact, I was quite happy with my old A40!
I chose to build the A-4 because of chance toroid acquisition ..... not because I thought I needed it! Several have commented that my PS is a little small for the A-4 and they are correct. The toroids are way too hot for a commercial amp and their longevity is under constant suspicion.
Likewise, I have the compromise of 3-FETs per bank, so the junction temps will be higher than if I had used the recommended 6-FETs. Then my heatsink is less than optimal, given the idle temperature is about 68C. Again ..... longevity lives under a cloud !!!
Please remember, most of this hardware was bought surplus ... so there was no logical selection in the design :(
I am currently building a replacement for this amp. It will be an Aleph5 (actually, it may well have the Volks front-end) as a stereo monoblock. Case format not dissimilar from Wayne's "masterpieces" ......
My honest advice, if you are near the limit in heat and hardware, just build an A-5. Unless you are in a position where you will not cry if "smoke signals" appear.
cheers, mark
PS: my amp still sounds great ..... many hundreds of hours of service ..... hot, damn hot !!! |
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| Gabster |
Hi, I think a good analogy would be a comparison with cars. All makers offer various engines for each of their models. Often the difference between the less and the most powerful version can reach 100 HP. Since no one (should) use his car for racing, a 260 HP car should be useless. However, one day or another we all fell like hitting the gas and fell the incredible acceleration.
In audio, I like to have the same oppotunity: getting the most possible; Listening to music louder than I should be or having the possibily to do so.
Now, why does people don't get a 260 HP car?
1) Because they are reasonable.
2) They can't afford it.
So why do I want a 100W class A amplifier?
1) I'm not reasonable.
2) I can afford it.
:D
Furthermore, a 100W amp is a good asset and the power it can deliver will be highly appreciated when it will be required. Even if it is true that the majority of my listening is made at a lower level, I believe it is important to build the amplifier than will give me the best flexibily. After all, I'm still young and parties still keep an important place in my life!
:D
Please don't flame me for this, I said what I think and I'm sure I'm not the only one.
regards,
Gabriel |
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| Apogee |
Ok, it sounds like you're going for the 100w no matter what!
Go for it!!!! I can relate...
A couple of thoughts on your revised design...
a) Rather than mounting the fets to the aluminum bar that you show, why not instead run a piece of 20mm square stock as "rails" along the top and bottom edges of the heatsinks with heatsink compound between. Your drawing would look the same but the bar wouldn't be one big piece...but instead two smaller ones... This would allow the rigidity that you're looking for as well as solid mounting for the heatsinks themselves. It would also allow for mounting the fets directly to the heatsinks themselves - this would be much more thermally efficient...
b) Suggest using 6 - 10mm plate for the bottom (and perhaps top) of the amps. This would make the amps much more ridged as well as increase the thermal sinking...use heatsink compound between the above mentioned "rails" and the tops and bottoms of the cases... Attach the "rails" to the chassis in several places along their lengths to create good thermal transition...
c) Be sure to design your venting in the tops and bottoms for lots of airflow... I figure you've already taken this into account but I figured that I'd mention it anyway...
d) Based on your drawing, it looks to me like you still have a bit of available space between the heatsinks. What about locating or fabricating heatsinks with deeper fins? This should improve the dissipation factor a bit...
Just a few ideas...
Best Regards,
Steve |
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| Gabster |
Steve, you idea about the rails is brillant! I really like it.
thanks a lot,
Gabriel |
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| mefinnis |
| quote: | | I think a good analogy would be a comparison with cars. All makers offer various engines for each of their models. Often the difference between the less and the most powerful version can reach 100 HP. Since no one (should) use his car for racing, a 260 HP car should be useless. |
Well .... I really don't mind what you do, but this is actually a terrible analogy and reinforces my concern about many not undertanding the nature of the dB scale and how it relates to an amplifiers W-RMS rating.
A difference between cars of 100HP will be dramatic. You will accelerate at "break-neck" speeds in the more powerful car. The top speed may be 50-100mph greater. The more powerful car will invariably have better suspension and breaks, etc., etc. That is, to drive them at any speed, will be a vastly different experience.
Now lets come back to our beloved Alephs ..... the only difference will be about 2.5dB ..... ie. you might get 108 versus 106 dB. The "character" of the amplifier will be essentially the same. Their "acceleration" will be the same, their "cornering" will be the same ..... and so on.
In a "blinded" listening test, I suspect you would never be able to tell me relaibly which was which.
cheers, mark
PS: Good luck with the project and enjoy .... I really do mean this :)
PPS: Grey et al., yes I do appreciate their are small differences between the Alephs in terms of relative biasing etc. ..... but as some-one who spent his youth in turbo-charged Porsches I couldn't let this analogy slip through ;) |
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| djk |
| The difference between 60W and 100W is 2.218dB, Windows has a calculator under accessories. More to the point; in program material with a lot of bass below 100hz 3~4dB is double perceived loudness in the 80~90dB range. |
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| Gabster |
Mark, my analogy was not pointing to the fact that the difference is not noticeable, but that it is not mandatory (Please don't make me sound like I cannot make the difference between a car or another...I would never trade my Audi for any of those same priced american cars. However a '98 Porsche Turbo would be considered ;)).
Maybe I've been misunderstood but what I really wanted to say is that when you care about it, each HP or watt counts...and if you can afford it, then it is obvious that you should go for it. I understand what you're saying: that a 100W aleph will not sound better (even if someone was pointing that Mr. Pass say that the Aleph 2 sounds better), that it will not give an unbelievable output power increase. I know what a dB SPL is, please believe me.
thanks for carrying about my project,
Gabriel |
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| GRollins |
I've just glanced through this thread, and perhaps I missed something...but if the intent is to build a pair of Aleph 2s, then a 1500VA transformer is not necessary. You can easily use a 600VA (Plitron has, I believe, 625VA) or 750VA, if you want a little more elbow room. I use 1kVA transformers on my Aleph 2s without the least bit of trouble, and regard that as excessive; purely for sonic (as opposed to thermal or electrical) reasons.
As regards wattage, Mark is quite correct. I tend to go for more power for two reasons: One--my drivers are only so-so in efficiency, being somewhere in the mid 80s dB-wise. Two, I really, really hate the sound of clipping, and am always astonished when I go to hear someone's system, hear obvious clipping and they're grinning like a madman, saying,"Doesn't it sound great?" Well, frankly, no. For starters, turn the damned thing down so that the amplifiers can breathe a bit. One of the first comments by people who listen to larger amps is that they sound more 'dynamic' and reproduce the peaks 'without strain.' Well, <i>duh!</i>
Just had this experience yesterday afternoon, in fact. The guy reportedly has $40,000 in his listening room alone. (12" thick walls, various sound treatments, etc. etc. etc.) He's sitting there telling me how great his system is. And, in all fairness, it's pretty good. But he's playing it too loud, and it's clipping, and he doesn't seem to notice. The same old story. I could say more, but I think I'll reserve some of the juicy parts for the 'listening' thread I keep threatening to write.
More power costs more money and creates more heat. But it makes a difference. Horn folks are in better shape here, since even small amps are shown to better advantage, but for those of us who chose (for any number of reasons) not to use horns, power is a good thing to have, even if you don't play particularly loud.
Grey |
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| mefinnis |
Actually I meant to comment on this bit before. Someone correct me, but my "rule-of-thumb" for transformer VA rating is at least 2x the constant current draw for the amplifier.
The Aleph 2 dissipates a little over 300W/channel, so 600VA would be acceptable and as Grey suggests 750VA would be fine.
I don't disagree with Grey's comments on power/clipping either .... simply, if you do have relatively inefficient speakers and like it LOUD, then you are better off in the X600 territory than going from 60 to 100W.
If you want an Aleph, go for 1.2 monoblocks ..... "some like it hot"
Even the great man sacrificed pure Class A to go into the higher power 'X' realms ...... didn't matter because for 99% of the amps use they are in class A mode anyways.
cheers, mark |
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| Gabster |
| What is the actual transformer in the original Aleph 2 monoblock? |
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| GRollins |
600VA, I believe.
Grey |
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| BrianGT |
I guess I overdid it...
I just picked up 2 custom made 1000VA transformers for my pair of Aleph 2. They are pretty heavy.. 15lb each.
I was pretty sure that I recall Nelson stating 1000VA is the minimum.
--
Brian
gte619j@prism.gatech.edu |
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| HarryHaller |
It won't hurt a thing except your back picking them up.
H.H. |
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| Gabster |
| Mr. Pass, if you read this, could you please confirm? |
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| mefinnis |
If you read Nelson's article on power supplies ( http://www.passlabs.com/pdf/powersupply.pdf ), he goes for 3x the power draw:| quote: | | If the stereo amplifier is rated 200 watts per channel pure Class A, it will draw about 1000 watts all the time, meaning that about 3000 watts of power transformer is called for, no less. |
However, prior to this he uses the term "several times" and other sources I have read suggest 2x as an acceptable minimum, which is what I stated.
I am quite confident you would be fine with 750VA. If I had 1000VA toroids I'd be completely happy - more doesn't hurt here :)
My reason for raising this issue is more for budget minded constructors looking at purchasing toroids, or ordering them custom made. The additional cost of 1000VA cf 750VA in $$$/weight/size isn't to be ignored.
cheers, mark |
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| roddyama |
Part of the trick here is that transformers with a higher VA rating will be designed with bigger gauge wire to source more current, so as a result, the series resistance will be lower. This, in turn, will give your supply better voltage regulation. You want to minimize the transformers series resistance to minimize your IxIxR losses which are equal to the voltage drop across the tranformers secondaries.
The lower your final rail voltage, the more important this becomes, because you have less voltage to spare. A 2V drop with 50V rails is <5% which is acceptable. The same 2V drop on the Aleph 3 25V rails is nearly 10% which can start to be a problem.
Rodd Yamashita |
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| Gabster |
I got the quote from R-Theta for the 24 heatsinks required to realize my cassing. 8.54$CND each (US$5.70...if buying 25) plus 25$CND (US$16.67) setup charges. This will be expensive but acceptable since they suit my specifications.
I found out that R-Theta have a sale office 15 km from where I live...I would have saved a lot on shipping if it would have the factory.
regards,
Gabriel |
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| Mark A. Gulbrandsen |
I am building a pair of Aleph 2's and have gotten back a very reasonable quote form M&M Metals. Thought I would post it here and see what you guys thought. The MM5060 is almost cheaper new than to go with Surplus sinks. I am going to use the MM5060 Heatsink and there will be 6 per Amplifier(3 down each side). 2 Devices per sink. It will give the amp a sort of industrial look to it.
"Price for 12 parts of MM5060 is 17.39 each."
"Price for 4 parts of MM5047 is 118.92 each."
"Delivery in 2 to 3 weeks."
http://www.mmmetals.com/pages/extru...truded_page.htm
Although I have not done any calculations yet I feel that 6 of these per amp should out work nicely. Any feedback here would be appreciated and thanks in advance.
Mark |
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| wuffwaff |
Hi Mark,
an Aleph 2 needs about 0,1°K/W per mono to dissipate the 300 watts (+30°K). Didn´t find any specs but if your heatsinks are about 6 x 0,1 = 0,6°K/W it will be enough.
william |
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| janneman |
Bill,
Don't you mean: 6 heatsinks of .1°K/W gives .015°K/W which is better then the .1°K/W requirement?
Jan Didden |
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| UrSv |
Jan:
The heatsink requirement is 0.1 °K/W per channel. Mark is planning on using 6 pieces which means that each piece needs to have maximum 6 times the requirement in order to meet the requirement as a set. That is 0.6 °K/W which divided by 6 for total for the 6 pieces is 0.1 °K/W. I think you misunderstood (I know you know this stuf WAY better than I).
Mark:
Without getting into detail about insulation and other things and what it does to hotspots and junction temperature:
A heatsink is rated for a temperature increase in degrees (Kelvin or Centigrade) per watt it is asked to dissipate. If a heatsink is rated at 1 °K/W (or 1 °C/W for that matter) that means that the heatsink will have it's temperature increased by 1 degree for each watt led into it. Consequently it will increase it's temperature by 10 degress for 10 W (it is not quite linear but for this discussion we pretend it is). Now, if we use two of those heatsinks rated at 1 °K/W then they will dissipate half of the power each, effectively meaning that they get 5 W each giving a 5 degree increase acting is they were one heatsink at double the capacity (HALF the rating) of the individual. (Mathematically this is kind of like resistor in parallell sharing the current between them, two 1 ohm resistors in parallell makes 0.5 ohm i.e. two 1 °K/W heatsinks make one 0.5 °K/W heatsink).
Taking 6 heatsinks the same type means that the total temperature resistance (which it is called) is one sixth of that for the individual piece. So, if you need 0.1 °K/W and you have a bunch of 0.6 °K/W heatsinks you would need 6 of those to get what you need.
The above replies from Jan and William could be somewhat confusing as William started from the requirement and gave you what was need for each piece if you were to use 6 of them. The anwer is 0.6 °K/W as William said (remember 0.6 per piece giving 0.6/6 °K/W = 0.1 °K/W). Jan assumed that you were talking 0.1 °K/W sinks (which would be PRETTY big) which in his calculations gives 0.1/6 °K/W = 0.17 °K/W. Both are correct calculations but William gave you what is needed per piece and Jan described a dream for all of us (?).
I DO apologise for the lengthy answer
/UrSv
Read more: http://www.aavidthermalloy.com/technical/index.shtml |
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| Mark A. Gulbrandsen |
While they may reduce wiring lengths by a bit they would be so expensive as to not be practical. These guys won't talk small quantities. Good luck.......and so on. I've already tried Thermalloy and Wakefield. Bah!
Fortunately I have access to a verticle mill so I could do a similar thing with the M&M heat sink and mill the back so its just flat, and for only 12 bucks! Also mounting the transistors on the M&M won't be difficult at all and the wire lengths can still be kept to a minimum by mounting the 2 TO-247P's to the center flat of the heatsink and the PCB to the side wall. That way there shouldn't be much more wiring than if I had hand wired on two large flat back heat sinks.
As far as the look goes who would say the Krell KSA-80 was a bad looking amp. I thought its looks made a great statement about the capabilities of the amp as a whole. Ditto for the Threshold series that had massive side sinks. Just don't trip and fall into em. Ouch......
Mark |
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| jag |
Mark,
Can you pl provide a schematic of how you plan to attach MM5060 to the amp sides. The shape is really wierd :confused: |
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| Mark A. Gulbrandsen |
| There are two ways it could be done. If the back is milled flat then it would attach by allen screws through the top and bottom of the center mounting area. Two at the top and two at the bottom. |
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| Mark A. Gulbrandsen |
| Both devices are mounted horizontally in the channel with the connecting PCB on the side channel... as looking down from the top. Yes, new PCB's will have to be made but thats no real big deal. |
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| fcel |
Mark,
By the above quote, do you mean:
1. Cut off the few fins on the bottom (as seen by the picture from your post) and then install screws via the top and bottom chassis plate?
2. Or you mean install screws from the top and bottom chassis plate and thus the bottom few fins will be hiding under the top chassis cover plate?
3. Either way, is it rigid enough to withstand rough handling? Say, somebody pick up the amp using the heatsink as a handle? I know this sounds like a worst case but you never know. Or you have some other forms of bracing?
I have always wondered how one would install this shape of heatsink since they looks good and they are not necessary very expensive. |
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| fcel |
Jag,
I don't mean to offend anybody but the approach that you just posted seems to be the "previous style" of doing things. From everything that I've read so far on this forum, it appears that people are building amps or pre-amp with the guts inside the chassis and only exposing the heatsinks. Peter Daniel influence?! My guess is that Mark is also approaching it from the "present style" of building things and I'm also interested in how he go about doing it. |
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| Peter Daniel |
Jag,
This is very interesting design. It looks like someone was trying to built SS amp from a tube amp perspective. I like it. |
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| Peter Daniel |
As to Marks heat sinks I wouldn't mill the ends, too much work and you loose dissipation.
They have mounting holes on ends and you use them for bolting sinks to chassis wall. If the wall is at least 1/4" thick you can easily lift the amp by the sinks and nothing will brake (maybe your back only;) ). It would be the best to mount fets on the sink and use short pieces of wire as an extension. I built Zen amp using similar heatsinks before and it worked great. |
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| Peter Daniel |
| Here's how I did it: |
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| roddyama |
Mark, Fcel,
You could mount the milled heatsinks to a flat aluminium plate (See attached) and mount the devices to the plate. This would solve the left-right, 2 devices per heatsink issue. Although, the al plates will add to the cost.
Just a thought,
Rodd Yamas***a |
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| Peter Daniel |
| Front and rear panel were directly bolted to the sinks, sinks were bolted together. They were just enough to dissipate ZENs heat. |
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| Peter Daniel |
| quote: | Originally posted by roddyama
Mark, Fcel,
You could mount the milled heatsinks to a flat aluminium plate (See attached) and mount the devices to the plate. This would solve the left-right, 2 devices per heatsink issue. Although, the al plates will add to the cost.
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And then 3 sinks per side wouldn't be enough. You'd rather have to use 4. |
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| Mark A. Gulbrandsen |
Here is a pair of single ended amps that I built last fall. These are the largest version of that particuluar style heatsink, and about 9" tall.
I wish I know CAD well enough to wing up a drawing for you all as to how I would mount the heatsinks with the fins cut off. Basically there would be a top and bottom angle attached to the front panel and back panel. The heatsinks would be attached to these rails by at least two countersunk allen screws top and bottom. The complete heatsink can be attached to the chassis at the large L part of the fin. Krell did it that way and it was very strong indeed. |
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| Mark A. Gulbrandsen |
Here is how I attached the semis and PCB to the heatsink.
They work well, run VERY hot but not excessively. No problems so far. I also very much like Rod's idea of attaching the heatsinks to an alumnium plate. It would have to be at least tooling plate as it needs to be perfectly flat, and not to thick, say 1/4" at most. INstalling the heatsinks on the top plate is certanly possible and I do like the look but I think that withough making swiss cheese out of the chassis top for air circulation it is not the best way to go. The side mounting affords unrestricted air movement to move upwards through the sinks.
Mark |
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| fcel |
Mark,
So, you do mean having part of the heatsink fins being cut off. Isn't that too much work? |
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| roddyama |
Peter,
| quote: | | And then 3 sinks per side wouldn't be enough. You'd rather have to use 4. |
True, there is less surface area for heat dissipation, but only by about 10% because of the added surface area of the plate. Although, it's clear your implementation of this style heatsink looks great.:cool:
I do like that Mark Finnis retro look as well.:cool:
Rodd Yamas***a |
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| fcel |
| Mark .... I just saw your last pix post of the gold heatsink. I assume that's for your other amp. I saw holes on the gold heatsink and I assumed your new heatsink has holes on it too. Can't you just use those holes and mount it to the chassis L plate without doing any cutting of the fins? |
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| Peter Daniel |
Rodd,
To me it looks more like 30%. The support plate wouldn't be helpful much. From specs it looked like those sinks were about 0.7 K/W so they were underrated already. |
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| fcel |
Peter,
I have seen that pix of your Zen heatsink but never really notice how it's installed. Now, I see that you have bolted the 2 heatsink together and then bolt them to the front and back plate. That's a quick and easy way!
Is there anyway someone can move this later portion of this thread to "useful tools and technique"? |
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| Peter Daniel |
I found that simplest solutions always work the best. That's why I don't recommend milling and L brackets for mounting transistors. Although it might look good visually with PCB and all but it's no good for heat transfer and devices longevity.
Fcel, if you feel like doing it, you can copy the interesting parts to useful tools and techniques.;) |
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| fcel |
| Peter ... I just cut & paste this thread from P4 to "useful tools and technique". |
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| Mark A. Gulbrandsen |
FCEL,
Thats exactly how I intended to do it. I also have a bunch of heatsinks exactly the same as Peter used on his ZEN. But I only have 10 of them and they are a bit smaller too. I am going to save them for a smaller Aleph project.
Mark |
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| jag |
the approach that you just posted seems to be the "previous style" of doing things.
fcel:
I was not trying to say that you should put all components outside the chasis, but that the heatsinks can be mounted vertical to plane of mounting either on the top (as done in that picture) - similar to the single ended amps shown by Mark above -or on the sides . The only problem with that is that air circulation is not as effective. But, now having seen Peter Daniel approach above, I like it a lot better - no milling and good air circulation. |
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| fcel |
Mark,
Now that I know how to install these type of heatsink, by any chance do you have pricing for MM5061 (slightly bigger than MM5060 which you said is ~$17@)? If not, I can check out further/call them. |
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| ekp |
My ideal heatsink has circuitry on one side of it and forced air on the other. It seems that impinging air flow (blowing air down into the fins and letting it out the ends) is better than flowing air from end to end. So while there are some heatsinks that accept the fan at one end, I have yet to find one that accepts a fan to impinge (like the microprocessor setup).
BTW, a little air flow helps out quite a bit. I did a bit of calculation last night and the air flow required to equal convection cooling is quite low. Since I assume fan noise is an issue, one might try a low speed motor and large blades.
Eric |
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| D3 |
I have had a brief look at this thread...........I am building a compact Aleph-X.........at around 100w............
The device will be pushing out arround 300w of heat from sinks +
40-50watts from ps etc.........
I am using copper busbars and mounting the fets direcetly to this...running the bar 'live'..........this give excellent thermal transfer..........the bar is then isolated from main heatsink using silpad along the whole length of bus bar..............giving a very large thermal junction area. This my help the guy in the original posting..............I bought 250mm x 50mm x 12mm bars for £8 each....or $14.....not bad really....
My design will also use mild air cooling.... |
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