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Aspen Headphone Amp

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#961
Adding the CCS...
 

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#962
Consider the distortion levels, Kean, they are VERY low and the non-linearities in the CCS will have little effect on the audio signal for two reasons; output is controlled by the buffer EMITTER, which is in turn set by the VAS, and the negative feedback is very powerful as we have such high OLG. A mosfet is cool, sure, but it takes about four volts off the output, limiting us to 16Vpp with clip first appearing on the positive rail. With a bipolar, we can get around 20Vpp. This added headroom is good use of available resources. A 90dB/mW headphone of 2K impedance needs 18Vpp to achieve around 99dBA, which is loud, but we all know some like it HOT.

Hugh
 
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#964
Hello Hugh and guy's

I've just seen my email and reply to it.

As I reply in my email it's a very good circuit Hugh, low distortion, stable, and it should sound like an SE amp with better resolution than the previous SE circuit.

All-right, I vote yes for this one.

Ok for a CCS.

Thank

Bye

Gaetan
 
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#969
keantoken said:
It gets better with practice. 😉

I should know considering I've been doing all the specialized simulation here...

- keantoken
Click to expand...

You've certainly made more contributions that I have managed. Still, it seems we have a 'team' that comprises of lots of very useful skills for the project.

Have you considered if it's worth the trouble extending the simulation to include a small passive model of the headphone rather than a simple 'pure resistor' ?
 
#970
I'm like the backup-guy who simulates when things get sticky. 🙂

I'm certainly not alone here in simulations, though I make an effort to show the differences that usually aren't simulated for whatever reason. I make it a point, if it comes down to guessing and speculating, to simulate instead of guesstimate. I've made some contributions, but I'm limited in that anything I say can't be definitive; I haven't built more than 10 real circuits in my life.

In short, I talk a lot, but don't have anything to show for it.

As for a reactive load simulation, I don't know how necessary it is and I heard it said that headphones are much less reactive than loudspeakers. I think the largest issue where this is concerned is with an AB amp, where it might cross over into B during low load impedances; but this isn't a problem with the current class A design.

- keantoken
 
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#972
Can somebody pls explain the value of R3 in the latest SE schematic for me? Is it a pot to adjust the offset, or what does the value "1020.3" mean?
(Well, I might have missed a few posts already...)

I appreciate very much this discussions&develepments @this thread - thank you.
 
#974
Hi Lohk,

Nice to see you here!!

This is the precise value of resistor needed to achieve zero offset. In practice, it would simply be a 4K7 resistor supplying a blue LED, around 2.5V, with a 1K pot across it. The wiper would supply the bias voltage, suitably decoupled with a cap.

There is, of course, no readily available resistor of that size! However, even there were, the bias would still vary with applied voltage, so it's adviseable to have a voltage source in that position. An LED is useful, of course, as it gives a visual indication of operation.

Hugh
 
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