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Old 1st November 2011, 05:55 PM   #31
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The LM1875 is, interestingly, quite different from its newer "Overture series" brethren (which in turn all use the same basic topology). At the very least, the equivalent circuit looks a lot less intimidating, but there also are lots of other differences. Spec wise, the '1875 has a peculiar kink in its THD vs. output power graphs; as a result, distortion in the critical 1 W area is a lot higher.

Taking a look at pricing, the '1875 is a good bit cheaper (at least 1/3) compared to any of its successors, but as mentioned, for good reason. (Or maybe its internals have long since been replaced? It's not looking bad at all when measured here, even though the '3886 still does better at 4 times the gain.)

In which order did these chips appear anyway? There's a bewildering array, with at least the single amps 1876, 3875, 3876, 3886 and 4700 and the duals 1876, 4765, 4766 and 4780. All of them prefer the lighter 8 ohm loads, but for some reason 4766 and 4780 seem particularly bothered by 4 ohms if you look at 20 kHz distortion.

Speaking of the LM1876, this one actually finds use as output driver in at least one line of (well-reputed) commercial headphone amps, tweaked for lower gain.

As for the OPA549 mentioned earlier in this thread: en = 70 nV/sqrt(Hz), yikes. That's one noisy bugger, noisier even than ye olde LM386. Maybe that's why people like it, noise tends to "soften" the sound. Oh, and GBW = 0.9 MHz. Color me unimpressed.

Last edited by sgrossklass; 1st November 2011 at 06:22 PM.
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Old 1st November 2011, 06:30 PM   #32
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/grmbl @ edit time limit...

The measured LM1875 setup also had reduced GBW (via "small cap on input") to keep it stable, of course, so that probably compensates for the lower gain.
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Old 1st November 2011, 08:49 PM   #33
tmblack is offline tmblack  United Kingdom
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The lm1875 sounds great, but the LM3886 has an edge crispyness that is, well yikes!
Same for LM3776.
On the OPA549, sound is very good as a unity gain buffer. Use a good preamp for voltage gain.
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Old 1st November 2011, 08:53 PM   #34
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Default 1875 vs. 3886

I currently have a pair of active speakers set up using the 3886 for the midrange, and the 1875 for the tweeters. I have been running this setup for about 2 years. Technical arguments aside, the 3886 is a much more functional amp for my purposes. The 1875 has a terrible thump at power cycling, and has necessitated a relay to protect my drivers. I would not recommend using the 1875 without some additional protection for any sensitive drivers.

Louis
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Old 25th May 2013, 05:29 PM   #35
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Here is the LM1875 powered by a old pc-psu, I think it sounds pretty good. A perfect first time project.
LM1875 20W audio amplifier veroboard sound test - YouTube
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Old 25th May 2013, 06:19 PM   #36
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I don't know about the 3886 VS 1875 (I like both) but ...

I'm liking the 1875 right now: I get much lower offset (1875 : 5mV, 3886: 20mV), they're dead quite (no hiss, hum, or turn on/off noises ...) and cool as a cucumber!

1875, top, non-inv (full schematic--input AC coupling off-board), inv (minimal)

1875 top non-inv, inv.jpg

1875, bottom,, non-inv (full schematic--input AC coupling off-board), inv (minimal)

1875 bottom non-inv, inv.jpg


and I'm running them right up to their limits:
Spec: Vsupply max +- 30V
Me: +- 29V

Shhhhhh, don't tell Andrew ...

(+10% on the power lines and I'm done for!)

Last edited by AudioLapDance; 25th May 2013 at 06:23 PM.
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Old 26th May 2013, 07:33 AM   #37
AndrewT is offline AndrewT  Scotland
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You have made and informed decsion. Noting wrong with that.
You have assessed the consequences and decided to accept the risk.
Again nothing wrong with making an informed decision.
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Old 26th May 2013, 07:40 PM   #38
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I'm just yanking Andrew's chain , but given what's happening in the DC blocker thread I thought I better clarify.



Variations of DC Main Filter against buzzing Toroid Transformers - what is the right?


DON"T run your LM1875 at +/- 29 Vdc!

Your house voltage can actually vary quite a bit and +/- 10% is not unusual so for me my 111 Vrms could spike to 111V + 11.1V = 122.1 Vrms.

If you're using a chipamp with an unregulated powersupply (most are) this means that your chip ps voltages will also spike + 10%.

For an idiot like me that means 29V + 2.9V = 31.9 Vdc on my poor LM1875 (Max +30Vdc)!

This could cause the chip to fail.

Now we're into failure modes of the 1875: if you're super lucky nothing will happen, if you're slightly lucky the chip will just die and output 0 V, if you're lucky the chip will put out a small +2V glitch before it dies and hopefully your speakers survive ...

Now we get into the unlucky : if your unlucky the chip will put out +15 V for a while before it dies (do you like the smell of woofer in the morning?), if you're really unlucky it will oscilate / clip then put out +32 Vdc then die (hope you didn't like those tweeters too much?) and if your really unlucky something unpredictable and even worse will happen!

DON"T run your LM1875 at +/- 29 Vdc!


Now what I didn't tell you is that they're just hooked up to my lab speakers (no big deal), I've tortured them and they've survived and I've monitored my house voltage and it doesn't seem to spike (but it could!). So I'm not as insane as I first appear.

Hopefully that makes sure no one blows a chipamp.

Cheers,
Jeff

(Sorry Andrew, my previous post was a little on the irresponsible side. Remember, they're usually misinformed not deliberately trying to misinform.
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Old 27th May 2013, 05:07 AM   #39
bimo is offline bimo  Indonesia
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My LM1875 amplifier:

It is best chip amp that I ever heard, but I have not try LM3886 yet.
Sadly, it was surpassed by my transistor amplifier easily.
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Last edited by bimo; 27th May 2013 at 05:10 AM. Reason: typo
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Old 27th May 2013, 05:21 AM   #40
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Not a low-enough impedance PSU for the chip to give its best methinks.... More caps!
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