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Old 4th April 2010, 06:15 PM   #1381
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@ Sharpi31

nice discrete buffer,
can you post some details of buffer. How about Power supply
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Old 4th April 2010, 09:32 PM   #1382
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Thanks guys :-) copied ideas of others (mostly...).

The power supply is made of two 40VA 12Vac potted lighting transformers. The primaries of both and an additional earth wire are connected to the mains plug, and the secondaries and earth wire connect to the amp via a 3 pin XLR (earth plus one end of each secondary on pin 1, other ends of two secondaries on pins 2 & 3). The transformers were heading for the bin at work, and I thought I'd make use of them rather than see them wasted (I actually got three, and used the two with closest Vac on the seconadries).

The ebay fet buffer is discussed here: STEREO FET BUFFER on ebay

The big elna caps supply +/-17.5V to the LM3875 chips, which each have 2x 35V 470uF sikorel caps on the pins. The buffer gets about +/-17.2V from the four 220uF silmic II caps, that are supplied from the big elnas via a 22ohm resistor (each rail of each buffer channel is fed from it's own R & C).

The speaker terminals are from Maplin. I usually use speakons, but this amp is for test/play at work so screw terminals are handy.
Attached Images
File Type: jpg 100_0567.jpg (707.5 KB, 2021 views)
File Type: jpg 100_0569.JPG (970.4 KB, 1852 views)
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Old 5th April 2010, 12:01 AM   #1383
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It appears that you have input transformers AND DC input blocking caps..
(edit) That would be trafo and dc caps on the signal input path...

Is there a reason for both?
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Last edited by troystg; 5th April 2010 at 12:04 AM.
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Old 5th April 2010, 06:14 AM   #1384
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The input transformers are there to isolate the amp from sources with noisy ground (laptops etc.). The output of the FET buffer has a small amount of dc offset, so the coupling caps prevent this reaching the LM3875 chips.

Not the last word in audiophile minimalism, but surprisingly good. I've built several chipamps and this one sounds most full and solid (the unbuffered ones sound thinner in comparison). The additional coupling cap is a small price to pay for having the buffer.
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Old 5th April 2010, 02:20 PM   #1385
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Quote:
Originally Posted by sharpi31 View Post
The input transformers are there to isolate the amp from sources with noisy ground (laptops etc.). The output of the FET buffer has a small amount of dc offset, so the coupling caps prevent this reaching the LM3875 chips.

Not the last word in audiophile minimalism, but surprisingly good. I've built several chipamps and this one sounds most full and solid (the unbuffered ones sound thinner in comparison). The additional coupling cap is a small price to pay for having the buffer.
Gotcha.

I would have expected a DC servo or offset adjust on the buffer to compensate but yes a cap is just as effective.

And I like the compactness.
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Old 8th April 2010, 01:27 AM   #1386
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Smile Mini Gain Clone LM4765

I got 2 LM4765 from NS 3 years ago. I destroyed one when I tried to
hardwire and stop it for a long time. I has been built this amp again
but used PCB instead of hardwire and succesfully to build 25Wx2 amp
from this IC.

I prefer its sound than LM4780 (60Wx2). Even if its power lower than
LM4780 but its sound is more smooth and clearly.
Attached Images
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File Type: jpg GC4765_02.jpg (33.6 KB, 1527 views)
File Type: jpg GC4765_05.jpg (36.2 KB, 1477 views)
File Type: jpg GC4765_06.jpg (30.4 KB, 642 views)
File Type: jpg GC4765_04.jpg (35.5 KB, 761 views)
File Type: jpg GC4765_07.jpg (32.1 KB, 729 views)
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Old 12th April 2010, 07:56 AM   #1387
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Quote:
Originally Posted by okapi View Post
Hi, here are some photos of my audiosector LM4780 amps. I built monoblocks (1 lm470 in parallel) with separate power supplies so i could experiment with different configurations (biamp, bridge, use power supplies for other chip amps, power L, R, and surrounds, etc.)


EDIT - THESE IMAGES HAVE BEEN DE-LINKED DUE TO THE WEBSITE BEING REPORTED AS HOSTING MALWARE.

VIEW THESE IMAGES AND THIS WEBSITE AT YOUR OWN RISK. REMOVE THE XXXXX TO FIND THE CORRECT URL


http://www.tim.cheapo.ccXXXXX/images/SNB11160.JPG
http://tim.cheapo.ccXXXXX/images/SNB11022.JPG
http://tim.cheapo.ccXXXXX/images/SNB11127.JPG
http://tim.cheapo.ccXXXXX/images/SNB11121.JPG
http://tim.cheapo.ccXXXXX/images/SNB11127.JPG
http://tim.cheapo.ccXXXXX/images/SNB11132.JPG
http://tim.cheapo.ccXXXXX/images/SNB11133.JPG
http://tim.cheapo.ccXXXXX/images/SNB11136.JPG
http://tim.cheapo.ccXXXXX/images/SNB11143.JPG
http://tim.cheapo.ccXXXXX/images/SNB11155.JPG
http://tim.cheapo.ccXXXXX/images/SNB11151.JPG

i am presently designing a matching preamp that will look something like this:

http://www.tim.cheapo.ccXXXXX/images/preamp case.jpg

i would especially like to thank peter daniel for all his help, and Jim hahn for his guidance in the machine shop.
very nice work

Last edited by Jason; 14th April 2010 at 07:40 AM. Reason: Removed evil links
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Old 12th April 2010, 07:23 PM   #1388
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I'll go better than "nice".
Beautiful. But then I'm not married.
Would any ladies care to comment?
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Old 12th April 2010, 07:30 PM   #1389
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Stunning! Gorgeous!! Holy crap! Magnificent!

Cosmetically my favorite.
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Old 13th April 2010, 09:51 AM   #1390
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That one was my favourite design also.

I liked it so much i based mine on it. Still not close too as cool as that one though.

http://sphotos.ak.fbcdn.net/photos-a...78216_6842.jpg

http://sphotos.ak.fbcdn.net/photos-a...78226_3200.jpg

http://sphotos.ak.fbcdn.net/photos-a...78228_3955.jpg
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