My new mini-A. I really like it!

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First: Thanks Nelson, Grey, and Brian!

Hello,

I am proud of the true completion of my solid state project. It is a Mini Aleph based on Brian's recent boards.(very nice boards)

I am using 2 irf150(to-3) devices per channel. My psu is dual mono with 2 220VA +-14.6v toroids. They were +-20v but I unwound them a bit. I am using <-2*15,000uf-.5R-1*15,000uf-> crc per rail. There is negligable to no hum or buzz.

The to-3s are mounted on a 10mm copper plate each which is bolted to the heatsink with a .5" alu spacer and 16*8-32 machine bolts. All surfaces were lapped flat on a glass plate and of course grease was used. The sinks are~7"x6"x1.5" and a total of 4 sinks in the Aleph 3 style.

All I/O is on a nylon plate routed into the rear sink...with the exception for AC in, which comes in the bottom. The legs are lacquered red oak..

I have lifted r13(r19) for full bias and that works out to be about 1.3A with my 16.8v rails. Heat sink temp tops out at 48c under any conditions and actual temp at the device has not exceeded 52c! The whole thing works super!

The sound tops anything I have heard (biased opinion of course) here provided the volume kept reasonable. Actually, I can't believe how this ~10watt amp can belt it out. It truly sounds tremendous. This will run my eminence psd2002 compression drivers in a Beta 12 scenario. I'm building an Aleph slightly smaller than the 30 to run the woofers. Active XO.
 

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Re: Is that an earth-con on the bolt for the toroid?

TroelsM said:
Ok, I'm a bit drunk (don't ask..) but it seems to me that you could run into trouble and make a short on the transformer with that white wire running from the bolt...

TroelsM
Denmark (01.03, saturday..)

you are correct. The short would have to occur after the coated wire, insulation covering the wire, insulation covering the transformer, and coating over the transformer secondaries is permeated. Then, you are correct, there would be a problem:)
 
He he...

I don't think that you see my point. (Maybe there isn't one at all..)

If the bolt in the center of the transformer is connected to GND (the case?) and you make the bolt the "star-ground" of the whole amp, then you would have a big problem if the GND-speaker-terminal (or the input-GND) for some reason is connected to the case. That would make a shorted winding on the transformer and a fuse will (hopefully..) blow.

Please correct me if I'm wrong.

TroelsM
 
I don't think that you see my point. (Maybe there isn't one at all..)

I'm sorry..I don't see your point. Seeing that my name is NOT Nelson Pass, I am no expert either. But, my opinion is that:

The center bolt on any toriod in pretty much any amp is attached to the chassis, ..why is mine different? Whether it has been deemed star ground <or> not, it is still a point that IS ground. If everything around it is insulated, where is the danger?

Don't get me wrong here. It is possible that I am being stubborn and pigheaded, and am blind to the issue. If so, help me someone..I don't see it!

Thanks,
Marc
 
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mpmarino said:
why is mine different? Whether it has been deemed star ground <or> not, it is still a point that IS ground. If everything around it is insulated, where is the danger?

If the bolt throu the middle is connected to the chassis at both ends (ie bolted to the chassis at the bottom & the top is used as a star ground at the top with wires over the top of the toroid, you have created a shorted turn. Not a good thing -- will cause premature death of the amp..

And from this pic it indeed looks like you have done that.

An externally hosted image should be here but it was not working when we last tested it.


dave
 
TroelsM,

If this is what you meant by 'shorted turn', then I now see what you are talking about... I had no idea. Thanks for pointing that out.

Dave,

Thanks for helping to drill that into my thick skull.

I am still not clear on where the 'short' would occur, but I can get a grasp of what 'could' happen. I've got to think about this for a while. It's nice to learn something new....

edit...
It seems the easiest way to open the shorted turn would be to isolate the bottom of the bolt from chassis and run a ground over the top to star. This would remedy it..right?
 
back with only a small hangover...

Hey.

I'm glad that someone understood my drunken arguments.. I think its a big mistake to use the bolt for any other purpose than mounting the torroid.

To see why the center-bolt could be a bad place for the star-GND think about this scenario: You connect the amp to a pre-amp with a normal shielded phono-cable. The shield now connects your star-GND to the GND of the pre-amp (in most cases..). If the two chassis touch each other and make contact you would "melt" something because of the very high currents running in the "short". Actually the Poweramp would probably survive and the current would destroy the phono-cable or something in the pre-amp.

Hope you se my point. (Still hoping that there is a point..:D )

Cure: Make a new ground-point somewhere else on the chassis and use that instead of the transformer-bolt.

TroelsM
 
I'm glad that someone understood my drunken arguments.. I think its a big mistake to use the bolt for any other purpose than mounting the torroid.

I do understand and I apologise if I was a bit 'flip' in my response. I was ignorant of the issue. I have fixed the problem and the bolt that mounts the toroids has been 'interrupted' by a 3/8' threaded phenolic ground isolator. The loop is broken. A wire has been taken from star to earth at power entry. This was the only way I could fix it without a re-design. Thanks for your sharp eye! I feel better now.

Marc
 
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