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Old 18th March 2012, 06:42 PM   #181
JensH is offline JensH  Denmark
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Is the LME49720 the optimum choice for the servo? I would have thought that a FET op-amp with a low offset would be better here. And then perhaps increase the value of R14 and R17 to attenuate noise from the op-amp?

With the LME49720 there could be 11mV offset from the offset current + the 1M resistors. With e.g. LF411 this could be reduced to 0.5mV from the offset voltage. The error from the offset current would be only 25uV (typical at 25 deg C) and 100uV max.

Of Course National would like to sell a lot of LME49720's, but it may not be the best choice for the servo.
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Old 18th March 2012, 07:49 PM   #182
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My thought would be to use lme49990 for the gain stage
and opa132 for the servo...
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Old 19th March 2012, 06:24 PM   #183
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Nice layout, Neb! Do wonder about that transformer, it seems a bit small. Judging from va rating it should be ok but at max current it is perhaps a bit skimpy (not that you'll still have eardrums at max current :-) ).
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Old 28th March 2012, 05:03 PM   #184
qusp is offline qusp  Australia
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might I suggest you add an soic8 pattern inside and connected to the dip8 so people can choose to use soic8 directly instead of having to use an adapter? just about all modern high performance opamps are nolonger made in dip8, only SMD and high bandwidth/speed chips and their decoupling will perform better if connected to the PCB and opamp pins directly
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Old 30th March 2012, 11:42 PM   #185
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Quote:
Originally Posted by RocketScientist View Post
http://www.national.com/pf/LM/LME49600.html#Overview
Just an engineering question, what are the advantages of placing a buffer in the feedback of the non-inverting configuration as shown in the schematic? I'm sure the answer lays in a lump of nodal calculations but asking an engineer saves me a little work
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Old 31st March 2012, 11:30 AM   #186
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You add a buffer if the load is too heavy. A buffer will increase distortion performance and the possibility to have a heavier load.
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Old 31st March 2012, 12:19 PM   #187
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Quote:
Originally Posted by andrelim View Post
I am still learning about electronics, so please pardon any stupid questions i ask.
Is is possible to use the LME49600 in a headphone amp by itself?
My source has no problem driving my headphones to high volume, and it should be ok to have no gain.
Yes, I believe so. Most sources have plenty of voltage to drive the headphones to maximum, but not enough current. The LME49600 can provide the current.
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Old 31st March 2012, 12:22 PM   #188
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Quote:
Originally Posted by JustFJ View Post
Did anyone try to build this eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices ? their design used lme49710 + lme49600, or any comment?
Yes, I built that amp and wrote about it here:
My Head Phone Amp Project

Jim's Audio boards are good quality in my opinion, with complete gold plating and plated through holes. The schematic as provided has way too much gain, but that's an easy fix.

A servo is not required.
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Old 31st March 2012, 12:51 PM   #189
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It would be fun to make discrete version of the this chip. It looks to me like a variation on the diamond buffer from Walt Jung.
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File Type: gif LME49600 schematic.gif (21.2 KB, 393 views)
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Old 31st March 2012, 01:39 PM   #190
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I have made a version called SSB01
Parts on both sides and it's a 4-layer board.
http://www.diyaudio.com/forums/blogs...e-pcbs-me.html
Click the image to open in full size.
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Last edited by peranders; 31st March 2012 at 01:43 PM.
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