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Old 26th November 2012, 12:06 PM   #31
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But (there's always a but), you can still build a very good and simple power amp with darlingtons. Find Motorola app note AN-483B, 15-60 Watt Amplifiers using Complimentary Darlington Transistors and try the final circuit. (I have it somewhere if you can't find it on-line) They give a design table for different power levels and the parts aren't all that critical. I've run one of these for decades as part of my tri-amped system. Long ago I did have an Integral Systems 100W/ch amp that used a simple pair of darlingtons on each channel. It had no protection circuitry and wasn't known for reliability, but I had no trouble with it. For the lower power considered here, the darlington approach has some merit, though still nowhere near as good spec-wise as the discrete circuit I posted. Question- do you think the RCA and other simple circuits have any advantage over a decent chip amp, say 3886? I ask that in all seriousness and don't have any answer or preconceived notions.
I may be barking up the wrong tree, but at least I'm barking!
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Old 26th November 2012, 01:20 PM   #32
maouna is offline maouna  Greece
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I found the application note but it is in spanish language. I have built two channels with LM3886 based on an Elektor circuit. Comparing it to a descrete amp i built 2 years ago based on RCA and other simple circuits i must admitt that the sound colors have more ''life'' than LM3886. NMOS200 and P3A sound better than LM3886 as well. LM3886 has a ''plastic and flat'' sound.

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Last edited by maouna; 26th November 2012 at 01:23 PM.
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Old 26th November 2012, 03:53 PM   #33
Bigun is offline Bigun  Canada
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Originally Posted by Conrad Hoffman View Post
You can do way better than that old RCA circuit. I built one back in the '70s as my first amp project. It worked well, but we've moved on!
For sure, modern designs measure better and sound cleaner and more dynamic.

I haven't built many SS amps, but of those that I did, the one that still graces my desktop is the one based on the RCA schematic. It just sounds so nice. Sure it's not a higher performance amp. But I never tire of the sound, I find much to enjoy and little to criticize. It's fund to build, not difficult to debug and tune. It's just about my favourite.
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 26th November 2012, 05:06 PM   #34
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Maouna, that schematic shows the simple diff front end everybody has used forever. Just adding the current mirror and extra resistors as I showed, even if you change nothing else, will improve the amp greatly. I can't tell from the picture but I think they wound the output inductor around a resistor. It's best not to do that!

As for the RCA circuit, yes I can't really fault it in terms of sounding nice and being a good place to start, but I just can't leave well enough alone!
I may be barking up the wrong tree, but at least I'm barking!

Last edited by Conrad Hoffman; 26th November 2012 at 05:09 PM.
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Old 26th November 2012, 10:54 PM   #35
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Perhaps those aren't TIP3055/2955 you are using there? It might well benefit from some good,
modern power transistors like say, 2SC5198/A1941 or FJA4313/4213.
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