At the temperatures we run them at, I think most MOSFET failures are due to temperature cycling, rather than thermally-accelerated diffusion. So if you leave it on 24/7, I expect you could get away with considerably hotter die temps.
https://www.google.com/url?sa=t&rct..._MOSFETS.pdf&usg=AOvVaw2liAXFUT7wfsRgULe2SLiZ
Cheers,
Jeff.
Weirdness with my Aleph: when I first finished the amplifier there was a ever so slight hum on the right channel. Nothing intrusive but even with placing the signal input wires at a different angles/distances I could never get rid of it.
Fast forward in time to last winter - a major storm took out the power for many neighborhoods. When power came back after three days of being off it took me a few months to realize that the hum had switched to the left channel with the right being completely quiet. What the heck? Reversed phase?
Note: My house was built in 1961 and all of the original outlets were two prong but grounded at the metal AC box not the outlets. I replaced these all with three prong AC outlets, grounded properly.
Fast forward in time to last winter - a major storm took out the power for many neighborhoods. When power came back after three days of being off it took me a few months to realize that the hum had switched to the left channel with the right being completely quiet. What the heck? Reversed phase?
Note: My house was built in 1961 and all of the original outlets were two prong but grounded at the metal AC box not the outlets. I replaced these all with three prong AC outlets, grounded properly.
Hello all, I've finally made the jump and ordered boards and 4u chassis to build an Aleph J as my first DIY amp build so may be needing some assistance along the way!
The first of many questions I will likely have is that I have ordered this transformer:
RKD 400/2x18
But am now a little concerned as the spec sheet says maximum ambient temperature of 40c which I'm hoping will be ok but not too sure what the ambient temperature inside an Aleph J would be? Any advice greatly appreciated as I do still have the choice to return it if it's not going to be suitable..
The first of many questions I will likely have is that I have ordered this transformer:
RKD 400/2x18
But am now a little concerned as the spec sheet says maximum ambient temperature of 40c which I'm hoping will be ok but not too sure what the ambient temperature inside an Aleph J would be? Any advice greatly appreciated as I do still have the choice to return it if it's not going to be suitable..
Looking at Antek, where I order most of my transformers from, I dont even see a "Max enviornmental" voltage listed. I would think 104 F inside a case would not be hard to get to.....likely the transformer is conservatively rated, but this is a good question.
A baby sitter (or different transformer, if it actually is problematic) would cure problem. My guess is that it is conservatively rated, or maybe specs vary with higher heat, and isnt a problem.
That said, I cant tell you the number of times I have been dead wrong....and what I don't know would fill a battleship.
The physical weight of this transformer and similar Antek is almost identical, 9 lbs, for what that is worth.
Russellc
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Thanks Russellc. I'm hoping as the transformer is slightly over rated at 400VA that they are referring to maximum operating temperature at maximum load. However, as you say, I have looked at several other transformers and none of them state a maximum ambient temperature at all so it's hard to compare!
@mpa check out Airlink transformers in the UK. I have used them with good results. Add on an interwinding screen and a Goss band. Delivery is pretty quick to.
Airlink Transformers
Airlink Transformers
Ditto Marra, the one I usually buy is the CM0500218, 500VA 1x 230V 2x 18V with electroststic screen & GOSS band.
Playing with Quasimodo I found the snubbing component values to be:
Cx 10nF
Cs 150nF
Rs 24Ω
Thanks for all the replies guys! Glad to hear there is an RKD transformer out there working in an Aleph J. Thanks for the link Marra, they look like a great option. Might return the original one and get one of those instead!
Can I just ask what benefits using a transformer above 300VA and larger than the original 15000uF PSU caps would give me? I am going to be using the amp in a system with active crossover so it will be working above 100Hz only.
Can I just ask what benefits using a transformer above 300VA and larger than the original 15000uF PSU caps would give me? I am going to be using the amp in a system with active crossover so it will be working above 100Hz only.
Further to this point, take a look at the spec sheet here:
https://web.archive.org/web/20180412085044/https://www.tortech.com.au/Toroidal.pdf
Not the same make (my Aleph J is running a Tortech) but it is also spec'd with a 40 °C maximum ambient. However, note that there is also a spec for temperature rise. I combined the 2 to work up the top end temperature that I could work with.
My bet is that the Block transformer works to a similar basis but the manufacturer simply hasn't advertised this detail... what do you think?
EDIT:
Also, that's probably why there's sense in going for a VA rating slightly above the minimum so that the unit will not be running at its limit and therefore at its warmest.
If that's not it then I'm interested to read the explanation.
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Wow, I wish all manufacturers provided complete specs like that.
As for oversizing the transformer, as I understand it working somewhat below its maximum reduces both temperature and the chance of hum.
Cheers,
Jeff.
[Edit: I wouldn't return the Block. I think it will be just fine.]
For the noobs that are more noob then me here is one of Papa Nelson’s articles scroll down to the part about transformers. PassDiy
There is one more article Mr Pass wrote specifically explanation of transformer oversizing but I couldn’t fine it. It time to re-mention for the noobs. To read al the article on PassDiy
Don’t forget FIRST WATT
Read until the Wee hours and your eyes glaze over and you forget you have a wife or other. As I did trying to find that last piece of Secret information to achieve audio Nirvana.
There is one more article Mr Pass wrote specifically explanation of transformer oversizing but I couldn’t fine it. It time to re-mention for the noobs. To read al the article on PassDiy
Don’t forget FIRST WATT
Read until the Wee hours and your eyes glaze over and you forget you have a wife or other. As I did trying to find that last piece of Secret information to achieve audio Nirvana.
Further to this point, take a look at the spec sheet here:
https://web.archive.org/web/20180412085044/https://www.tortech.com.au/Toroidal.pdf
Not the same make (my Aleph J is running a Tortech) but it is also spec'd with a 40 °C maximum ambient. However, note that there is also a spec for temperature rise. I combined the 2 to work up the top end temperature that I could work with.
My bet is that the Block transformer works to a similar basis but the manufacturer simply hasn't advertised this detail... what do you think?
EDIT:
Also, that's probably why there's sense in going for a VA rating slightly above the minimum so that the unit will not be running at its limit and therefore at its warmest.
If that's not it then I'm interested to read the explanation.
I think that the toroids can work above 40degC with no issues. I personally never had a problem with them overheating in class A amplifiers. Once again, the only problem with open-style toroids (non-potted) is if the plastic wrapping may become loose and allow windings to vibrate. Potted transformers seem like a great idea, especially if they are supposed to be supplying constant currents of around 2-3-4 amps. I'd call this a great long-term investment.
Re rating, I remember Nelson mentioned that there is no point in wasting VA rating; however, he had his transformers made as per VA requirement, BUT the iron was speced a level-up; If Aleph J requires 300VA transformer, he would go for 300VA windings, wound on iron speced for 400VA.