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Old 11th August 2008, 09:26 AM   #11
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Here's the THD20 FFT plot at ~0.5 mW into 32 ohms. It's reasonable, given the simplicity of the circuit.
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Old 11th August 2008, 09:38 AM   #12
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Here's a pic of the perfboard prototype (single channel only), just to verify the output stage concept. It seems to work much like the simulation, thus validating the concept of a saturating active load using a BC337-25. The phones are generic Chinese-made stethoscope-type in-ear buds stated to be 32 ohms.

I used Nichicon Muse SW and MV sub-miniature caps (bypassed by a film cap at the input), and a Rubycon YXG for the output DC blocking cap. When connected to an Ipod (3G), the bass is improved and there is more audible detail. However, there is some sibilance and other odd-harmonic artifacts, so it's a mixed bag overall, sonically. I believe the concept can be refined further, but the design space is heavily constrained by the 1.5V rail. Lots of things can be done with 3V, but at 3V one can just as well use a Maxim 9724/9725 and cut out the drudgery.
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Old 11th August 2008, 11:32 AM   #13
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Nice work, linuxguru

I hope some more people here will try your circuit(s).

They are Perfect Diy Audio projects (if we do not want to go Blowtorch )

Good diyaudio, as being:
--- low cost
--- few parts
--- easy & clean (no mains hum) supply = battery
--- good hi-fi performance


Lineup
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Old 11th August 2008, 11:56 AM   #14
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Thanks, Lineup - I hope to try one of your more serious dual-rail high-end headphone amps eventually.
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Old 11th August 2008, 12:05 PM   #15
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I have a couple of headphones amplifiers at this board.

What is good enough for driving Headphones (32 ohm - 600 ohm)
is ALWAYS good for Line PreAmplifier application, too.

So, a good headphone amplifier, can have several uses. Very often.
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Old 11th August 2008, 12:25 PM   #16
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Hi Lineup

I have just finished wavebournes little headphone amp and going to listen to it today and tomorow then i will let you know about the sound. Some minor tweaks to be tried too, then ill look at one more amp. Where can i view that circuit of yours which you plotted the harmonic spectrum for???

Linuxguru, nice looking circuit as usual, have you built this amp, what does it sound like??


Alex
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Old 11th August 2008, 12:43 PM   #17
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homemodder

I think maybe you mean my BC368 BC369 output amplifier???
It is a complementary with 2SK170 / 2SJ74 input.
Uses low impedance current feedback!!!
The output is very powerful Class A (3+3 paralleled BC368/369) 100-120 mA idle PUSH-PULL (gives >200 mA current class a output)

It is one of the most interesting amplifiers I ever simulated/figured out.
Have not built it, yet.

Eventually you can try to replace the output
with one pair BD139 / BD140.
I do not think it would change very much of the performance.
Quote:
Complementary Class A Preamp using BC368-369
9th July 2008 .. by Lineup
Complementary Class A Preamp using BC368-369

Regards
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Old 11th August 2008, 01:17 PM   #18
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Lineup, nice looking circuit too, very similar to cavali which I have built, from what I can remember it was a more simple design, having included a mosfet, jfet and bjt. On first listening I rate Wavebournes circuit better than the cavali but then again it has been some time since I listened to the cavali. Wavebournes was right, his circuit is powerfull enough to blow my eardrums with my HD600s. It completely blogs my girlfriends whineing away, very very good circuit wavebourne come up with.



I have a problem getting hold of 2sj74s, the shop I purchase parts from had 12000 pieces, sold all to someone about 3 weeks back, me thinking maybe a Mr Curl or Hansen. There is a race on for these jfets. Now they sitting with 17000 2sk170s and no complimentaries.

Alex
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Old 12th August 2008, 01:54 PM   #19
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OK, back to our regularly scheduled programming - the 5-BJT topology on a 3V rail.

The latest version gets rid of the VAS capacitive bootstrap, and takes advantage of the fact that Vbe of Q4 stays fairly constant to get the collector load bootstrap for Q2 directly from the emitter of Q4. The closed-loop gain has been increased to ~10, and some biasing changes allow output swings of 300 mV. Quiescent current increases slightly to ~14 mA at 2.4V, and ~16 mA at 3V (still manageable). As before, it will work with a supply rail as low as 2.4V, but with increased distortion compared to 3V.

THD20 and sonics remain in the same ballpark. Here's the schematic (the layout has been changed to make the signal flow clearer and simpler):
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Old 12th August 2008, 02:01 PM   #20
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Here's the THD20 FFT plot for ~310 mV output swing (1.5 mW into 32 ohms) with a 3V supply. H2 is at ~ -86 dB, H3 is ~ -115 dB, and everything else is below that:
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