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Old 26th September 2008, 06:38 AM   #71
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Originally posted by ostripper

I thought the DIY'er assumed responsibility for building a project. I would think that we CAN discuss it
as long as we post a disclaimer warning of the dangers
associated with actually building it.

Many projects here at DIYaudio deal with VERY deadly DC
voltages (one flash and your ash) but we still discuss
Conveniently, the name of this thread is "Beginner's Gainclone, HiFi LM1875, The Amplifier Board" and in-depth discussions of other circuit boards is off topic.

I have read that the chipamp forum of does contain a permanent thread offering power supply directives. That is only an observation.

I wouldn't touch that topic with an eleven and a half foot double-insulated pole--because you know where it would. . .
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Old 26th September 2008, 06:52 AM   #72
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Originally posted by ostripper
. . . BTW, I think national semiconductor is the copyright owner
for this amp /base design...I CAN sell them commercially
or in any manner I wish, according to natl.semi (they want
to sell more chips).
If you'll notice, its not the base design as listed in National Semiconductor's PDF. The base design's usage under its copyright is included within the purchase price of the amplifier chip.

A design based on a chip can still be a unique design. So, copyright was declared in order to protect the diy community. In this case, the copyright declaration prevents anyone from restricting (capturing, preventing) the usage of this particular amplifier design.

EDIT: National Semiconductor is the sole exception (of course).

If you'd like to mass produce mine, you need only change a few component values and also make a layout change because that would make a different design. Have fun! It a nice amp.
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Old 26th September 2008, 02:14 PM   #73
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Location: Smoky Mountains , Tennessee
thats what I thoght.. I did build LM1875 amps , they make dandy
rear channel amps for HT. Simple, compact , and as compared
to some of the monster amps in the forums ,quite safe. At +- 30v
you could reasonably avoid shock hazard unless you DIY'ed
in the bathtub...
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Old 26th September 2008, 04:28 PM   #74
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Do please be careful around voltage, amperage, and high capacitance. In that combination, the lower voltage is still quite powerful.

Lately, I've been working on 30w versions that run cold. Old-fashioned AB amplifiers with linear power supplies can be surprisingly efficient when they're tuned towards "only audio." The whole thing, transformer included, is barely bigger than a coffee cup.
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Old 27th September 2008, 05:36 PM   #75
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Here is a good way to start, has anyone tried this kit.

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Old 3rd October 2008, 10:18 AM   #76
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Originally posted by ostripper
At +- 30v you could reasonably avoid shock hazard unless you DIY'ed in the bathtub...
I've got permanent burn scars from a 36 volt battery from when I first got into diy in my teens (and I most certainly was not in the bathtub). Any power source deserves respect as given the right set of unfortunate circumstances, it doesn't take much to do considerable and long lasting harm.
- Dan
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Old 3rd October 2008, 02:40 PM   #77
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Default Okay guys,

Not for use in the bathtub, not for use in the shower, and not for use as an outdoor barbeque grille. (cautionary statements from 1978 Amana RadarRange manual)
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Old 8th January 2010, 03:00 PM   #78
tommy_o is offline tommy_o  United States
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Thank you for the wonderful thread -- I am well on my way to building my first GC using this LM1875 design. I do have a few questions, and I apologize for bringing back a year old thread.

The first and most daunting question I have is about the power supply board. I plan on using the Avel 250VA 18V+18V toroidal transformer in stereo mode with one PS board. This is the suggested transformer from While I have read the DD powersupply page and it has been wonderfully helpful, especially with safety and warnings, I am having trouble visualizing the end product. Dan, post #59 is extremely helpful. Would the Avel transformer and your powersupply work appropriately without modification? The transformer is the only part of great expense in the project, and I would like to get it right the first time around.

Is there a concise thread that covers the basic construction of the powersupply? The sticky thread is over 500 posts long, covering far too many details for me to keep straight.

Thank you!
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Old 8th January 2010, 04:32 PM   #79
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Yes, that transformer is workable and the 18+18 vac 160va version will work just as well. Here is a clue for the means to connect it.
This unit replaces the single rectifier seen elsewhere in this thread.

This is a photo of a dual rectifier, suitable for connecting a dual secondaries transformer. Each secondary winding "powers up" one bridge rectifier. See photo. It is a pair of 10a rated, clearly marked, bridge rectifiers. Imagine flashlight batteries that are within a two-cell flashlight when you look at this photo.
Attached Images
File Type: jpg Rectifier-dual 001.jpg (21.5 KB, 1185 views)
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Old 8th January 2010, 04:40 PM   #80
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Here is an optional transformer that can power two of LM1875 amplifiers for a Stereo build. The price is lower and the performance is excellent.

Click the image to open in full size.
Allied - 6K274VBR - Allied Electronics
This is a center tap transformer, so it uses only one bridge rectifier.
A big 20a one piece bridge rectifier unit is generally recommendable for chip amplifier stereo builds.

With an EI core transformer, the cabinet layout is slightly more critical. Use the heatsink as a wall/fence/barrier to shield small signal areas away from the transformer. This layout is common to most classic amplifiers. Or, simply use a larger enclosure and increase the space between (distance away from) small signal areas (potentiometer, chip, rca jacks).
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