Aleph J illustrated build guide

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#2,103
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
 
#2,104
Only turn off thump, and my commercial version of Aleph 5 makes the same thump as well. It's not loud, and I don't think it would be harmful to the speakers, but it is loud enough to make me worry when 115dB horn driver is directly connected to the amp. 🙂
 
#2,105
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!
 
#2,106
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.
 
#2,110
#2,113
Steve Duffy said:
HI I'm planning to build and Aleph J next. How many MOSFETs should I get to allow for matching?
Click to expand...

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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#2,116
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.
 
#2,119
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.
 
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