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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.
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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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Quote:
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.
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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!
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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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