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Old 28th August 2008, 08:04 PM   #1
bm0rg is offline bm0rg  United Kingdom
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Talking First chip amp finished - LM4780

First amp and first thread. It all happens at once!

Well after a year of researching, designing and building I have final finished my first amplifier or should I say amplifiers (built two the same.) Having learned so much from this site I thought I should show you the results.

The amp uses 2 bridged LM4780 which is claimed to deliver 120 watt. Each chip has its own 300x100x40mm heatsink with a thermal resistance of 0.4 K/W

The power supply consists of 1 300VA 25+25V toroidal transformer and over 73800uF of capacitance. PCB SS 95x220mm

4 inputs 3 selectable 1 pre in.

Phono stage using VSPS circuit. (Redesigned PCB to 55cx43mm for the power supply and phono stage to 70x68mm. Separate 50VA 12V toroidal.

I have learned lots of new skills doing this project. Electronics was something hadn't done until a year ago and all the skill techniques that go with it such a pcb making. I wouldn't have had the time if I hadn't decided to do it as my A-Level design and technology project, which was a bit of a risk as he school got rid of it s electronics department and teacher 2 years ago which was not handy!

Well it works and am very impressed with the sound after comparing it to my dads AudioLab 8000S and 8000P they have edge but they were bi-amping the B&W DM603 were as my amp was driving them in he non bi-amp configuration. Didn't use both as one is still at school.

This is the first of many.

So here are some photos follow link.

[url]http://www.benmorgan.lazyaudio.co.uk/Media/slideshow.html?backgroundColor=%23000000&reflectio nHeight=100&reflectionOffset=2&captionHeight=100&f ullScreen=0&transitionIndex=2[url/]

Comments welcome!
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Old 28th August 2008, 08:15 PM   #2
zei is offline zei  Sweden
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Very very nice.!

great work. inside pics?

/JZ
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Old 28th August 2008, 09:17 PM   #3
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Beautiful enclosure. I agree, we need pics of the inside, as well as the back.

With the component values I'm building mine with (techdiy bridged kit), a 25+25V transformer puts out almost 230W! I'm assuming your gain is lower. I'm going to be getting about 115W with a 18+18V transformer. All of this is according to the overture design guide spreadsheet.

Do you have any heat issues? How is the bass?
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Old 28th August 2008, 09:34 PM   #4
bm0rg is offline bm0rg  United Kingdom
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Maim power supply
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Old 28th August 2008, 09:35 PM   #5
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back plate
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Old 28th August 2008, 09:40 PM   #6
bm0rg is offline bm0rg  United Kingdom
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This is an image of it a couple of months ago. The complete one at school is slightly different. Should be able to get it back in about 10 days
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Old 28th August 2008, 10:05 PM   #7
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Quote:
Originally posted by Redshift187
Beautiful enclosure. I agree, we need pics of the inside, as well as the back.

With the component values I'm building mine with (techdiy bridged kit), a 25+25V transformer puts out almost 230W! I'm assuming your gain is lower. I'm going to be getting about 115W with a 18+18V transformer. All of this is according to the overture design guide spreadsheet.

Do you have any heat issues? How is the bass?
Hi redshift187, thanks for the comment.

First of all heat issues. Well its not such a problem finding heatsinks with a low enough thermal resistance its finding a isolator pad with a low thermal resistance. First time i assembled it and tested it the Spike protect of the chip kicks in. Having assembled it a second time due to the panels needing to be sandblasted i put a good quality thermal past in between the heatsink and the isolator and the isolator and the chip this seems to work currently i have measured a outside chip temp of 74 degrees C

Secondly these chips are on the bridged techdiy board the board is fine easy to assemble.

Third Bass. I would say that this amp compared to the marantz 4400sr I used to use is much deeper and more controlled. I did find that at max output with out the good quality thermal past it seemed to have trouble powering the B&W DM603 mid/bass compared with the audiolab amps powering them. Not sure if this was to do with the thermal conductivity was not great or because this is a bridged LM4780 rather than a paralleled LM4780 which would be better for speakers that don't have very nice impedance curves. I read some where that the dm603s are not easy to drive.
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Old 28th August 2008, 11:03 PM   #8
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Default Re: First chip amp finished - LM4780

Congratulations on a nice-looking working prototype.

Quote:
Originally posted by bm0rg
over 73800uF of capacitance.
This is a lot of capacitance. Have you considered what the current at switch-on is likely to be?

w
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Old 28th August 2008, 11:15 PM   #9
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Default Re: Re: First chip amp finished - LM4780

Quote:
This is a lot of capacitance. Have you considered what the current at switch-on is likely to be?

w [/B]
Having taught my self from scratch my electronics knowledge is not great. Sure I can understand that there would be a large current being drawn at start up. If I have high current rectifiers then everything should be OK is this so. Please correct me if i'm wrong would like to know!
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Old 28th August 2008, 11:51 PM   #10
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Default Re: Re: Re: First chip amp finished - LM4780

One of the factors usually given consideration when designing a PSU is inrush current

Quote:
Originally posted by Rod Elliott
to ensure that nothing is stressed so much as to cause failure after a few years of operation
If you read as far down this page as the above quote, you will have a clearer understanding of why this might be an issue...

Oh, you should have some fuses in there. Post a picture or explicit diagram of the mains wiring, or make sure you read the appropriate bit of the site I pointed you to.

w
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