I see what you mean.
I understand that R27 can be used (e.g. by adding 47K pot; mentioned in #585) to adjust the bias. If I go for 29-30V rails (as mentioned above by Zen Mod in order not to fry the JFets) I hope to be able to bias it so the heatsinks do not get too hot. Kerafol should ensure that the Mosfets can transfer their heat to the heatsinks fast enough, so I not to have to worry about them (but I will check casing temp. anyway, just to make sure).
Would that be OK?
Might be wise to check if that is actually true.
See Scanspeakman's build, here or at the zelfbouwaudio forum.
He used the largest Modushop case for his ExtremA build, the 5U-500 has 60% more heatsink area than the 4U-400.
Ended up with 65-70C heatsink temperature. (which correlates with the heatsink type/size)
Are you sure about the 5U 500mm? According to what he wrote on zelfbouwaudio.nl, he used the 5U 400mm.
forum.zelfbouwaudio.nl • Toon onderwerp - Nog een ExtremA
Thoseheatsinks are only 25% larger and because they are higher (but not wider) they are not that much better at dissipating.
I do not know how much he needed to dissipate, but if he runs 2 channels @ 100W class A (I assume RMS) I am not surprised he ran into trouble!
I will check my sinks as soon as I get my new meter.
Oops, my bad.
From his posts here, somehow i gathered he got the latest supersize model. (me should read again myself, before posting a reference)
5U heatsinks still do 1/8th better C/W than 4U height, but you may be right on the dissipation capability.
Only explanation i can think of is that the stamped mounting profiles are very effective in guiding some of the heat to the panels.
Would be nice if you can confirm the dissipation/temperature numbers of your Aleph2.
(In my experience, bumping up the dynamic bias level is not equivalent to raising static quiescent current. The preferred mix may depend on the kind of loudspeakers used)
From his posts here, somehow i gathered he got the latest supersize model. (me should read again myself, before posting a reference)
5U heatsinks still do 1/8th better C/W than 4U height, but you may be right on the dissipation capability.
Only explanation i can think of is that the stamped mounting profiles are very effective in guiding some of the heat to the panels.
Would be nice if you can confirm the dissipation/temperature numbers of your Aleph2.
(In my experience, bumping up the dynamic bias level is not equivalent to raising static quiescent current. The preferred mix may depend on the kind of loudspeakers used)
I am collecting parts to build an Aleph J with 2 channels in 1 enclosure with the channels sharing a common PSU.
I have a question about transformers.
I was able to buy 2 Amplimo 225VA 2 x 10.5V 10.7A toroids for a good price and thought I would use these transformers with the secondaries in series to give 21V/10.7A (for each transformer). I plan to use one transformer for each rail.
Is this a good option?
Placement
I plan on placing them in the front of the enclosure. I can either place them side by side or on top of each other (mounted horizontally in both cases). I have seen both in photo's of other builds.
Is there a preference?
What is the minimum distance (to each other, and to the front panel and heatsinks) in both placement options?
Thanks,
Albert
I have a question about transformers.
I was able to buy 2 Amplimo 225VA 2 x 10.5V 10.7A toroids for a good price and thought I would use these transformers with the secondaries in series to give 21V/10.7A (for each transformer). I plan to use one transformer for each rail.
Is this a good option?
Placement
I plan on placing them in the front of the enclosure. I can either place them side by side or on top of each other (mounted horizontally in both cases). I have seen both in photo's of other builds.
Is there a preference?
What is the minimum distance (to each other, and to the front panel and heatsinks) in both placement options?
Thanks,
Albert
If you keep the bias level the same, the transformers will be loaded by more than half of their nominal rating.
Better not to stack them if you have the room, but most important factor is adequate ventilation, transformer temperature rise at 50% load is about 15C over ambient.
(Sphinx PJ16, 2 stacked 500VA toroidals per channel, relay parallel/series switched for 100W Class A in 8-4-2 ohm load)
Better not to stack them if you have the room, but most important factor is adequate ventilation, transformer temperature rise at 50% load is about 15C over ambient.
(Sphinx PJ16, 2 stacked 500VA toroidals per channel, relay parallel/series switched for 100W Class A in 8-4-2 ohm load)
yes. and you sayd it draws over 50% of that.
so over 225W. i thougt it was around 150W for 2ch.
Thanks Jacco and AudioSan.
My (full aluminium) enclosure has internal measurements: width 360mm, height 165mm and depth 400mm.
The transformers are relatively small, 110mm (diameter) x 45 (height), so I should have plenty of circulation within the box. Side by side (with a few cm's spacing) will not be a problem.
The top and bottom of the case are perforated, so I expect to be able to draw air through the enclosure.
As to the VA rating, I agree that the power used will probably be a bit higher than 50% rated capacity, but given the conservative estimates of Amplimo I hope to get away with it. I understand NP used a 300VA Piltron transformer for the originals. At 150% of that capacity, I have a little room to play with the bias and higher voltage. No chance of a real "turbo" though!
Now for something completely different.
The idea is to get as much heat from the Fets out of the box through the heatsinks. We do not want the heatsinks radiating into the box.
Would it be a good idea to insulate the heatsinks. I could imagine applying some kind of material to the surface of the heatsink that is inside the box to stop it radiating into the box (see attached foto; this is not an Aleph J but a photo I pulled of the web and photoshopped to illustrate the point I want to make).
Anyone ever seen this done (DIY or commercial)? Does it work?
Thanks,
Albert
Attachments
this is a modushop 4U 400mm? it will handle the power. do not insulate the heatsinks. its better that the heat comes out in the chassis, then beeing trapped in the baseplate of the sinks. those chassis are well vented. a buddy of mine are running JLH 40W classA froom the same chassis. and it only get a little warm. far from hot.
this chassis can handle 240W if the ambient is normal.
this chassis can handle 240W if the ambient is normal.
Yes, that's the one. I have Aleph 2 monoblocks using the same chassis (aprox. 300W dissipation each; still waiting for my thermometer to check the temperatures but we used a 75 degree Celsius switch that has never been activated).
wow. thats good. BTW. aleph2 has about 270W dissipation on the sinks. the rest is rectifiers and such.
nelson say 25C above ambient. but that is worldwide. some has 30C ambient
so if your ambient is 20C (witch i think is about right) you can go up to 35c above ambient and even higher without problems.
that also depends on the sice of the room. the bigger it is, the more forgiving it is to temp rises
i had to drop my aleph2's here. the rised the ambient with about 8C but the room is only 12m2
nelson say 25C above ambient. but that is worldwide. some has 30C ambient
so if your ambient is 20C (witch i think is about right) you can go up to 35c above ambient and even higher without problems.
that also depends on the sice of the room. the bigger it is, the more forgiving it is to temp rises
i had to drop my aleph2's here. the rised the ambient with about 8C
but the room is only 12m2
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No, would only have some meaning if the rest of the case was not made of metal.
If keeping the heatsink heat out of the amp is of importance, more logical would be to design the power amp with exterior heatsinks, e.g. '80s Krell KSA/KMA with the star-shape heatsinks.
What you do see are amp boards of close to same size, mounted to the heatsink with stand-offs.
Thus creating a vented tunnel, with openings in the bottom and top of the case.
The boards serve both as an insulation shield for the rest of the amp interior, and help to channel the air flow.
(there's an occasional Class A power amp model with an extra wall mounted on the inside to separate the output stage from the supporting hardware)
i've seen some atempts on that. the smartest was a bottom plate bended up and went all the way up. then you have the airflow from the bottom and out the top.
but i don't know if the gain is nothing to whrite home about. moder nature takes care of the vents with the air pressure
hot air climbs. negative pressure accurs. and cold air will be sucked inn to get the pressure at atmosferic
read this : http://www.diyaudio.com/forums/pass-labs/215729-help-f5-gamut-style-mosfets.html
ignore that diode ........... but capacitances are enormous
ignore that diode ........... but capacitances are enormous
Hello ZM, it passed such a long time and I didn`t manage to finish the amp.Will try to do it the next months, this time for sure
I want to use rifa peh200 4x47kuf/channel and an enclosure made from FR4
Interesting topic...just gave an eye to first posts.will do a better check tomorrow cause now it`s late for me and got work to do tomorrow.
Thx again and sleep tight cause I guess you`ll do the same as me...go to sleep
I want to use rifa peh200 4x47kuf/channel and an enclosure made from FR4
Interesting topic...just gave an eye to first posts.will do a better check tomorrow cause now it`s late for me and got work to do tomorrow.
Thx again and sleep tight cause I guess you`ll do the same as me...go to sleep