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LM3875 kit from Audio Sector in server case

Thought I would post up my project. I joined this forum about a month ago when I found out about the Gainclone. After reading up on it I n decided to go out on a limb and build one. This was my first kit and in the end I am quite happy with it.

The reason the case is so huge is....
Needed it to fit in a rack
Had the case empty in my rack
Was planing to build two kits into the one case

In the end now that I have built it I am quite sure that for my needs it will be loud enough. I have read other people say it but I will have to say it again. This thing is very small but packs much more punch than I thought it was going to. I switched from a Alesis RA150, 75W per channel. The LM3875 chip with 24V rails into approx 6-8 Ohm speakers is easily as loud. And sounds MUCH MUCH better.

Ok so on with the pictures already

The raw server case
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The built boards

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Layout and mounted boards
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Putting it all in the box.
Here you see the transformer. I had this one custom wound by SumR . They are based out of Toronto ON. I have nothing but the best things to say about them. I was dealing with Richard himself and he was very helpfull and got this one to me in about two weeks. It is a fully insulated 300VA with dual 24V rails.
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This is the the AC input and switch. It is taken from a computer power supply for ease. Here also is the every so sexy speaker and RCA connections :)
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Here it is all put together. I think this thing is going to be called the Dirty Spider
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Here it is all closed up and ready to get to work.
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When I did first turn it on I had the rare but know RF interference problem. I had to put a small capacitor across pins 7-8. It was somewhat tricky but not a big deal.
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An externally hosted image should be here but it was not working when we last tested it.
 
Mike-

Everything looks good except that Romex!! Get rid of that and cut up the server power cord instead.

Funny how yours is the opposite of Peter's Patek chip amps.

That is prolly the best use of a PC case I have seen because when they are filled with PC parts and operational that means WORK.

:D
 
The power company have caps across the line and neutral right out side your house.

Equipment manufacturers have put caps across the mains in electronics for decades.

And the aftermarket sells caps to put across the AC in your home <Quiet lines> and across the speaker terminals to help eliminate RF and grunge in cables.

http://www.soundstage.com/revequip/db04.htm

http://www.psaudio.com/ps/products/detail/noise-harvester?cat=power

Finally, had to look for this one...

http://www.walkeraudio.com/high_definition_links.htm
 
The angle of the picture may be causing some confusion.

That is a standard 3 pin IEC socket.

The center pin is the ground.

He has wires on all three pins.

He has 2 caps jumping from the hot and the neutral pin to the center ground to shut HF noise.

I'm going to break out visio and try to draw it quickly.


The caps are in parallel across the wires, not series.
 

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troystg said:
Mike-

Everything looks good except that Romex!! Get rid of that and cut up the server power cord instead.

Funny how yours is the opposite of Peter's Patek chip amps.

That is prolly the best use of a PC case I have seen because when they are filled with PC parts and operational that means WORK.

:D
Thanks for the feedback.
The transformer is from SumR. They are based out of Toronto. If you look in the original post there is a link to them. He works with many audiophiles. The service was fantastic. It is a small operation with quick turnaround, I got mind in about two weeks and it took four days just for the epoxy process. I paid about $100CND. I will be going to him for any further transformers I need.
As for Romex I assume that your talking about the "in-wall" power cable. It was the best thing that they had in the store I was at. I figure it gets power to flow smoothly for hundreds of feet it will be just fine for a foot :)
As for being the opposite of the Patek. That is for sure! You could fit about twenty of his amps in this massive case. I did try and keep the audio lines short enough and of equil lengths. I am happy to have the option to easily put another amp into it, and I HATE working in cramped spaces. If I ever feel the need I can build another kit and use my external crossovers to bi-amp.
Also Thanks for the kind words on the use of the case!

AndrewT said:
Let's find out what has been fitted from Line to Earth,
Then we can make informed comment.

The AC ground is attached to the case. From there power runs through the transformer into the rectifier. Each side of the rectifier and the left and right amps are all grounded to the case. I am very new to this and my understanding of electronics is next to nothing. I can tell you though that this amp (after installing the 300pf caps on the 7-8 pins the) is silent. As you can see I have no attenuation at all (I use an external passive attenuator for this). At full gain I have to put my ear an inch from the tweeter to hear anything at all. From even one foot there is no way to tell that the amp is on. There is absolutely no pop, click or thud when turning it on and off. I am in no way worried about the caps on the AC ground as this is the quietest amp I have ever heard.
 
"As for Romex I assume that your talking about the "in-wall" power cable."

Yep, Romex is a "brand name" for a brand of house hold construction wire.

It is better to use stranded wire there than solid but the world won't stop turning if not.

In houses it is ok because there is no "real" movement in the wiring. All contact is made at the receptacles so the solid stiff wire is not disturbed.


In portable / movable electronics the MAINS AC is generally stranded wire and if any, only the DC supply or output signal conductors are rigid.

Again, not the end of the world, but it is easier to work with, dress and secure the stranded wire.

Finally, yes you could do a surround system or an individually dedicated room house amp in that chassis.

:D
 
Looking at the picture and the wiring again..

I bet he didn't even put them on the IEC input socket!!!

I bet he made his connection at the switch! Those RF shut caps were probably put on by the server manufacturer...


Thinking about it further...

I bet the Server manufacturer didn't even put those caps on to block garbage coming in but instead to block the SMPS from splitting it OUT onto the line. That is the cheap fix to pass some of the CE codes for RF and EMI suppression in products.
 
troystg said:
Looking at the picture and the wiring again..

I bet he didn't even put them on the IEC input socket!!!

I bet he made his connection at the switch! Those RF shut caps were probably put on by the server manufacturer...


Thinking about it further...

I bet the Server manufacturer didn't even put those caps on to block garbage coming in but instead to block the SMPS from splitting it OUT onto the line. That is the cheap fix to pass some of the CE codes for RF and EMI suppression in products.

You are right I did not put them there. They are on the input socket. The socket and switch did come from the power supply that came with this case. But this case was never used as a server. It was a DVP system computer. They where very high end audio/video workstations for professional installations.

I took a macro shot of the input socket just to put any further debate to rest. Please note that they are both the same part number.

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