AudioRoundTable.com: Silicon Valley

Home » Audio » Silicon Valley » LM3875

Show: Today's Messages :: Navigator :: Polls
E-mail to friend

LM3875 [message #10197]

Sat, 18 September 2004 15:38

Gnational
Messages: 5
Registered: May 2009

Esquire

I have a small bone to pick-
Why do so many people talk about "gainclones" when what they really mean is a LM3875 chip amp? No disrespect for 47 Labs but I mean really! The heart of the circuit is the National Semiconductor LM3875. That's really all there is to the "gainclone" so why do so many people refer to practically every chip amp someone builds as a gainclone? I might offer a suggestion that we refer to them with the actual part numbers in respect for the company that makes them instead of whatever cute name is thought of by the seller.
Bone picked. End of Rant.

National Semiconductor LM3875

Report message to a moderator

Re: LM3875 [message #10198 is a reply to message #10197]

Sat, 18 September 2004 21:14

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Well the thing is if you look at the applications data it suggests a much more complicated circuit than the 47 labs guy utilized. So if he devised the gaincard and you build a copy; ergo, what to call it?
I don't know; sounds better than calling an electronic device a"Foreplay".

Report message to a moderator

Re: LM3875 [message #10199 is a reply to message #10198]

Sat, 18 September 2004 21:50

Gnational
Messages: 5
Registered: May 2009

Esquire

The applications data shows using the chip with only an input resistor, two feedback resistors and a feedback capacitor.
Add a +/- power supply and you have instant amp.

LM3875 Applications Data

Report message to a moderator

Re: LM3875 [message #10200 is a reply to message #10199]

Sun, 19 September 2004 07:41

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

So Gnational, what other goodies have you got to share. This little LM3875 amp sounds pretty good. I find it gets a little squirrely as you apply power but at low levels it has a pleasent tonal quality and nice bass. For some reason it reminds me of my old NAD 3020. That version I built with the basic parts will shortly be superceded by the "high end version" as soon as I get around to assembling it.
You sound knowing, any tricks up your sleeve with this amp? Thanks J.R.

Report message to a moderator

Re: LM3886 [message #10201 is a reply to message #10200]

Sun, 19 September 2004 16:37

Gnational
Messages: 5
Registered: May 2009

Esquire

For a little more juice, try the LM3886.

LM3886 Applications Data

Report message to a moderator

Re: LM1875 [message #10202 is a reply to message #10201]

Sun, 19 September 2004 16:39

Gnational
Messages: 5
Registered: May 2009

Esquire

For a little less, try the LM1875.

LM1875 Applications Data

Report message to a moderator

Re: LM1875 [message #10203 is a reply to message #10202]

Mon, 20 September 2004 11:04

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Thanks Much for the info. I don't know if power is what I need, I think maybe there are some applications adjustments that can take this amp to another level, I just don't know what they are. Any ideas?

Report message to a moderator

National Semiconductor Amp Modules [message #10204 is a reply to message #10203]

Mon, 20 September 2004 16:53

Gnational
Messages: 5
Registered: May 2009

Esquire

The entire amp circuit is on the module's IC substrate. The only external circuitry required is a power supply.
Beyond that, use the amp modules as suggested in the applications notes. In particular, refer to the external
components description section. There you will find specific guidelines for component values.

Report message to a moderator

Re: National Semiconductor Amp Modules [message #10205 is a reply to message #10204]

Mon, 20 September 2004 17:13

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Thanks again; so those are the optimal values and there really are no ways to improve on the published components?

Report message to a moderator

Re: National Semiconductor Amp Modules [message #10206 is a reply to message #10205]

Tue, 21 September 2004 16:51

Skip Pack
Messages: 51
Registered: May 2009
Location: Hollister, California

Baron

I've built an inverted 1875 based amp using Scott Nixon's boards,
and a couple of BrianGT's standard kits. Others are awaiting my
attention. I have driven One Pi Studios with the 3875 and 2 Pi
Towers with the 1875. With that efficiency, I get plenty of volume.

In the chip amp forums, there is a train of thought that you need
regulation to take the 3875 much above 20 watts for a less sensitive
speaker as the power supply ripple starts to be heard whereas the
chip's amazing ripple rejection does the job below the voltage where
the power is becoming more intermittent due to the lack of power
supply smoothing capacitance.

Everybody seems to agree that simply adding capacitance to the
unregulated amp dulls the music. I'm not knowledgable enough to
assess this position, but I sure like them on the Pi's.

Skip

Report message to a moderator