This Aleph J build is a "helping hand" to a friend who could not get it to work. I have built a second Aleph J for another friend, but that one i built from "scratch", having full control from the beginning. No problems with bumps when turning on and off on that one, so I do not think this a special problem with the Aleph J. To day I found another mistake that have been done. Signal in is RCA phono, but my friend had mounted signal in cables to the balanced input. This is now also fixed. But still there was a small bump turning down the amplifier. The solution was to use a speaker protection board that I have. Now Aleph is very quit.
Eivind S
Eivind S
Hello All,
The question of methods for fastening the mosfets to the heatsink was recently asked in the AmpCamp thread but I thought I'd ask it hear as well because it isn't specifically mentioned in the build guide. What is the suggested or best way to ensure a consistent clamping or pressure to the heatsink when tightening the bolt/screw for the mosfet? Forum member Variac mentioned he likes using spring washers. I don't see any in the Aleph J build guide so I'm curious what methods others in this thread have used? Is tightening the screw "snugly" sufficient? Do the Keratherm insulators provide enough "Spring" tension to prevent the screws from loosening? I don't want to burn up the mosfets when I finally get around to powering up and testing the amp.
Thanks!
The question of methods for fastening the mosfets to the heatsink was recently asked in the AmpCamp thread but I thought I'd ask it hear as well because it isn't specifically mentioned in the build guide. What is the suggested or best way to ensure a consistent clamping or pressure to the heatsink when tightening the bolt/screw for the mosfet? Forum member Variac mentioned he likes using spring washers. I don't see any in the Aleph J build guide so I'm curious what methods others in this thread have used? Is tightening the screw "snugly" sufficient? Do the Keratherm insulators provide enough "Spring" tension to prevent the screws from loosening? I don't want to burn up the mosfets when I finally get around to powering up and testing the amp.
Thanks!
There is a specific inch lb rating for torquing the screws but I am too lazy to look for it and unless you have a torque wrench it would be useless to know. You do not want to tighten them too much because you will raise the hole and the contact will not be even but it must be tightened enough for good contact. Snug is the word frequently used.
Papa commented on TO247 part mounting here:
http://www.diyaudio.com/forums/pass-labs/8319-proper-mounting-247-devices.html#post91527
http://www.diyaudio.com/forums/pass-labs/8319-proper-mounting-247-devices.html#post91527
For those who do not have access to a torque wrench or driver, I posted some information here:
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5-35.html#post4720878
http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5-35.html#post4720878
More Info on Mounting Torque
Although Papa's comments are still there, the links are dead because it's been 15 years. The link below has nice information on most size semiconductors.
https://www.fairchildsemi.com/application-notes/AN/AN-4166.pdf
Jac
Although Papa's comments are still there, the links are dead because it's been 15 years. The link below has nice information on most size semiconductors.
https://www.fairchildsemi.com/application-notes/AN/AN-4166.pdf
Jac
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This is always hard if you don't have a torque wrench. I would add to the above advice, if using a spring washer, tighten until the spring is fully compressed. Then add another 1/8 of a turn or so (about 45 degrees). My rule is always to turn the screwdriver "gently with finger tips" never gripped with your whole hand.
I can't accurately answer your question, but I'm sure other person will give you a good number.
My thought is why not let somebody else do the work for you, somone who is already set up for matching and who has already has large numbers of parts to match? Unless you enjoy this kind of thing, matching my own has always seemed more expensive that buying matched sets.
I'm in the US and have bought match triples from Bfpca in Canada with good results. There are a couple of other guys in Europe doing the same thing. There may be someone in N.Z./Oz/Asia as well. Anyway, here is Brian's thread in the Vendor Bazaar to give you an idea of costs and such.
http://www.diyaudio.com/forums/vendors-bazaar/269728-matched-fets-available.html
Good luck.
Jac
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I bought a tube of IRF240's for my BA-1. A tube from the factory is 25 and all were pretty close without matching, within .1V. I prefer to match my own, cheaper if you consider you will have some left for other projects. For a one time builder buying a matched set may be the best deal. When you buy a tube you have a better chance of getting more matches, same run and close together. The first of a run of transistor is probably not close the the last of a run. This was the case for tubes when tubes ruled and tubes have a closer tolerance than transistors.
As others have said, it is better to buy IRFP240 in large quantities if you intend to build more amps in the future. And, once you build one, you will probably build more later, even if you don't plan on it...
Another MOSFET option, which I used, is to replace parallel pairs or IRFP20 with a single IXYS IXFH74N20P. This is the same idea as Zen Mod's suggestion to use IRFP150.
Another MOSFET option, which I used, is to replace parallel pairs or IRFP20 with a single IXYS IXFH74N20P. This is the same idea as Zen Mod's suggestion to use IRFP150.