MOS-FET Amplifier Project v. RG-402 - AudioJunkies
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Old 08-05-2008, 09:14 PM   #1
 
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Default MOS-FET Amplifier Project v. RG-402

I have for years been fascinated with electronics, speakers, amplifiers, and other various things of the like. In the recent years I have designed and built a few speakers which I have been pretty happy with, but I still wanted to do something bigger, fancier, better. So I decided I would build my own MOS-FET amplifier. I did not and still donít have to knowledge to design everything in an amplifier all on my lonesome, especially from the ground up. SO, I cracked my old Electrical Engineering books and learned enough that I could look at designs and make educated choices for things used and which design had benefits over other designs.

After looking around, reading, and exploring the internet extensively I found a few designs that I really liked. One design I liked was just rebuilding a Hafler DH-220. My big drawback from this design is that it didnít meet my wattage requirements, which were about 200 Watts at 8 Ohms. I explored Ďhot roddingí the amplifier design by using higher power rail voltages and changing the 2SK134 with 2SK135 (or equivalent) and adding a more MOS-FETs. Some of the benefits of this design choice however were that parts are pretty much available and the main circuit board (PC-19 IIRC) is not too hard to find. Plus, thousands of people have build, worked on, modded, or used the Hafler designs, so if I was to hit any snags there would be a rather extensive support staff out there on the internet. But, I wanted to do something different so the quest continued.

The other idea or option that I had was to rebuild my H||H Electronics V800 amplifier. It fit all of my initial requirements, MOS-FET, 200 Watts @ 8 Ohms, used large power supply and was simple in design. However, there is pretty much only a hand full of people with any experience with this amplifier. And, the amplifier has already been built it would exactly be my own. So, I changed the power supply capacitors, cleaned it up a bit and continued my quest.

A third design I looked at was one I found on another forum. However this was a redesign of an old design and was much more difficult since I would have had to had a rather complex circuit board manufactured. Which is a haste I didnít really want to deal with.

So, I finally found what I was looking for in Rod Elliotís P101 Project on the Elliot Sound Productions webpage. After doing some thinking, and looking at his schematics they met most of my design goals, simplicity. So I purchased two of the P101 circuit boards and the quest was on. (Actually, side story the reason I ordered them was I was drunk and all floored about building an amplifier. So I blame this birth on alcohol. :laugh: )

Looking at several different models of MOS-FETs I decided to go with the Exicon ECX10N20 & ECX10P20. The alternative is the more common 2SK1058 & 2SJ162. I opted to go with the Exicon for a couple of reasons. First, Exicon Transistors are sold through one company Profusion PLC in England. K1058 & J162 are sold by anyone but the manufacture which has resulted in a disturbing number of people being scammed or receiving counterfeit transistors. Also, many people have found the Exicon transistors to be cleaner and faster than the standard Hitachi. I would defiantly do business with Profusion again in the future, great to order from and I didnít think the shipping was too far out of line. The power supply is a standard power supply using an 800 VA toroidal transformer and 60,000 uF of capacitance.

Just about everything else came from Mouser Electronics, Parts Express, or Dickman Supply (a local electrical and industrial supply house). It took more time than I expected to find and pick every component but getting a circuit board instead of a kit gives you great freedom on which pieces and parts you want to pick and use. Naturally I had to get the best of everything, which accounts for some of my parts costs. But, I will talk about that later. I also ordered 1.5 to 2 times the amount of parts I needed. Even if you buy 1% tolerance parts they can still vary. So, it is good to have spares and to match the parts so everything operates the same.

The enclosure was another story. I had leads go cold, emails not returned; metal shops would not call me back. So I was in a bit of a hard place. However, I lucked out. I had a junk amplifier that we took out of an install which was totally toasted. So I stripped the case, cleaned everything up and mock fitted everything. It worked out rather nice, much nicer than if I was to build it from scratch out of aluminum sheet metal. The amplifier was a Ross Systems "MegeAmp 800". Since it wasn't working so I had no bad feelings about destroying that amplifier. I stripped all of the paint and refinished it with a 'rough' texture paint. The pictures don't do it justice but it turned out pretty nice. The only thing that angers me a little is that as I started my final coat of paint I ran out. SO after a quick drive to the store I am back and ready to paint only to find the nozzle on the can is screwed up. So, I might restrip the front and redo it with a can that works...

The amplifier boards are done, the soft start circuit is done, the DC Protection circuit is done, all that is left is the power supply & mounting.

That's pretty much it for now. Will keep you updated!
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Old 08-05-2008, 09:15 PM   #2
 
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Here are some pictures of the first circuit board:



Parts:



Soldering Station:



WLW :woot:



First Complete Board:





Test Fit:



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Old 08-13-2008, 01:34 AM   #3
 
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Sweet!

If you want a simple amplifier, have a look at the National Semiconductor LME49810. It's almost an amp on a chip - just add precisely matched output transistors. I'd be interested in how you compared the sound.

http://www.national.com/pf/LM/LME49810.html
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Old 08-14-2008, 02:06 PM   #4
 
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I like using discrete components. I've always have mediocre luck with 'one' chip components. A lot of people like them, which I don't blame them they are easy and simple to use. But, still.

Thanks, for the recommendation. If I ever build another amplifier I'll check it out.
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Old 09-15-2008, 06:07 PM   #5
 
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So it is up and running. Both channels. It sounds pretty damn nice. No noise or anything that isn't supposed to be there. Right now I have hooked it up only to cheaper speakers (just in case something bad were to happen). But, I am getting up the nerve to use it on my 703. That will be the real test of how good it sounds.

I will post some pictures later.
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Old 10-03-2008, 03:31 PM   #6
 
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I'm a slacker... I still haven't posted pictures.

But they are coming I promise...
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Old 10-30-2008, 05:05 PM   #7
 
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Picture time? First of all don't mind the awefule wiring. I've been reconfiguring and changing things around. And for the sake of time I am cutting the wire quickly and not organizing it.

I've got a few more things I want to try to make it sound even better. But, right now I've changed the bias current to 30 mA instead of the specified 15-20 mA and it has cleaned up a lot of the weird distortion I was hearing. It also had made the amp sound a bit warmer. Also, I changed out the input capacitors with a different type and a slightly higher value. Which has helped with a bit or noise I was getting on the left channel. Also, rewired the XLR connectors and changed the wiring on the filter capacitors.

I am planning on adding a few bypass caps to absorb some of the switching noise from the rectifier and I want to do a split powered system using two rectifiers. Still also need to finish the soft start circuit so my power center stops hating on me when I turn this amplifier on.



Anyway, pictures:





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Old 10-30-2008, 05:10 PM   #8
 
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BTW, since my modifications to my power supply circuit the amplifier drove a 8 ohm load to 45.939 Volts with out clipping at 1kHz which is about 263.8 Watts...


I would have kept going by my pre-amp source ran out of steam and was maxed out. The cooling fins got a bit warm needless to say.
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Old 10-30-2008, 05:13 PM   #9
 
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I also need a bigger case, and if I could would go with a larger heatsink.


Anyone know where I can get a case? Or big ass heatsinks? (Besides conrad in Australia)

With a bigger case and heatsink I would separate the drive boards from the outputs, add 2 more MOS-FETs per channel (N & P not L & R so a total of 8 more MOS-FETs) and move some things around to give everything more space to breath...
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Old 11-12-2008, 11:09 PM   #10
 
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I've recently increased the bias current slightly higher to 35 mA just out of curiosity. I think it gets too warm now. Also, it doesn't come out of Class A until 1.78 Watts. Which is pretty high, I'm looking for about 1 watt before any of the transistors shut off.


Next modification, dual rectifiers and bypass caps.


I also need to draw up a schematic, when I do that I'll post it.
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