Natsemi LM3875 amplifier projects

[Gregory Toomey]

I'm interested in the NatSemi LM3875 "Audio Power Amplifier" which is single
IC amplifier @ 56W. There have been some very good reviews of commercial
amplifiers made with this chip.

There are readily available for about $14 but has anyone seen any kits in
the electronics mags - 240V toroidal transformer, nice box, etc

gtoomey

 

[Unbeliever]

"Gregory Toomey" <nospam@bigpond.com> wrote in message
news:1830476.k2y3tLrxR6@GMT-hosting-and-pickle-farming...

I'm interested in the NatSemi LM3875 "Audio Power Amplifier" which is
single
IC amplifier @ 56W. There have been some very good reviews of commercial
amplifiers made with this chip.

There are readily available for about $14 but has anyone seen any kits in
the electronics mags - 240V toroidal transformer, nice box, etc

gtoomey

Sorry Greg,
No box or 240V Xformer, but google found:

http://www.tech-diy.com/chipamps.htm

Cheers,

Alf
alfkatz@remove.the.obvious.ieee.org


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[Phil Allison]

"Gregory Toomey" <nospam@bigpond.com>

I'm interested in the NatSemi LM3875 "Audio Power Amplifier" which is
single
IC amplifier @ 56W. There have been some very good reviews of commercial
amplifiers made with this chip.

** The LM3875 suffers from severe limitations in output current ability -
see the Safe Area curves on the data sheet.

The "Spike" protection circuitry prevents damage to the puny internal
power transistors but ruins the ICs ability to drive many nominal 8 ohm
speakers let alone 4 ohm ones. A designer using this IC would have to be
able to specify the loudspeaker load to be used make sure it did not fall
below 8 ohms impedance or possess a significant phase angle in the lower
half of the audio band. This restricts the usage to mini all in one audio
systems and the like. Any so called review that failed to mention of this
point was written by a know nothing dickhead.

BTW A much better IC for hi-fi amp use is the TDA7294 which uses power
mosfets in the output stage.

There are readily available for about $14 but has anyone seen any kits in
the electronics mags - 240V toroidal transformer, nice box, etc

** DSE already sell a nice looking 80 wpc stereo amp with large flat
package output transistors ( not ICs) and toroidal tranny that is cheaper
than any kit with similar performance:


http://www.dse.com.au/cgi-bin/dse.storefront/4081dc8f0cebc18e2740c0a87f9c07a
a/Product/View/A2760




........... Phil

 

[Gregory Toomey]

Phil Allison wrote:

"Gregory Toomey" <nospam@bigpond.com

I'm interested in the NatSemi LM3875 "Audio Power Amplifier" which is
single
IC amplifier @ 56W. There have been some very good reviews of commercial
amplifiers made with this chip.


** The LM3875 suffers from severe limitations in output current ability -
see the Safe Area curves on the data sheet.

The "Spike" protection circuitry prevents damage to the puny internal
power transistors but ruins the ICs ability to drive many nominal 8 ohm
speakers let alone 4 ohm ones. A designer using this IC would have to be
able to specify the loudspeaker load to be used make sure it did not fall
below 8 ohms impedance or possess a significant phase angle in the lower
half of the audio band. This restricts the usage to mini all in one audio
systems and the like. Any so called review that failed to mention of
this point was written by a know nothing dickhead.

BTW A much better IC for hi-fi amp use is the TDA7294 which uses power
mosfets in the output stage.




There are readily available for about $14 but has anyone seen any kits in
the electronics mags - 240V toroidal transformer, nice box, etc



** DSE already sell a nice looking 80 wpc stereo amp with large flat
package output transistors ( not ICs) and toroidal tranny that is cheaper
than any kit with similar performance:


http://www.dse.com.au/cgi-bin
dse.storefront/4081dc8f0cebc18e2740c0a87f9c07a
a/Product/View/A2760




.......... Phil

Thanks for that, I'll have a look at that chip.


Over on www.diyaudio.com this has turned into a cult!

"May I also say, and I think there is a general consensus formed, that the
best results are from one chip from only one manufacturer, and in a line of
related chips from this manufacturer, one stands out as the honey (and
curiously enough, 47 Labs isn't using it) and that is the LM-3875T.

Whatever conspired to create the LM-3875T, if you believed in horoscopes or
otherwise believer in fate (not exactly me), then certain things came
together, happenstance or otherwise, to produce something to marvel at. Let
us not reason why, but merely be thankful."

gtoomey