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Old 26th September 2009, 04:16 AM   #121
Bigun is offline Bigun  Canada
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Aspen Headphone Amp
I will download shortly...Any problems with the capacitor producing phase shift to the feedback ?
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Old 26th September 2009, 04:35 AM   #122
keantoken is offline keantoken  United States
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Quote:
Originally Posted by Bigun View Post
I will download shortly...Any problems with the capacitor producing phase shift to the feedback ?
I just extended the AC simulation... It turns out this produces a ringing at 3Hz! This won't be stimulated by normal music, but it would ring for a few mS say, when you plug in the headphones. Hmmm...

EDIT: just found the solution: put a 1.5k resistor in series with C15. I guess this acts as a dampener... But it also seems to acttt as a sharp cutoff filter for frequencies below 5Hz. Maybe we should move this cutoff to 20Hz, just for conformity. (then again, do we want to be able to hit that "brown note"?)

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Old 26th September 2009, 04:51 AM   #123
keantoken is offline keantoken  United States
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Here is the plot...

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Old 26th September 2009, 06:15 AM   #124
MJL21193 is offline MJL21193  Canada
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A cap multiplier sim showing ripple reduction:

117.PNG

Orange trace is picked from the bridge rect at the first smoothing cap.
Scale is 50mV

Black trace is output from the cap multiplier.
Scale is 5mV

Blue is output from the amp into load with input shorted.
Scale is 5uV

Performance is quite good for this simple solution and I'm leaning toward this now myself.
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Old 26th September 2009, 06:24 AM   #125
keantoken is offline keantoken  United States
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A Darlington should be safer than a CFP in this application.

I've been experimenting with the strange NFB arrangement... I think it would work with dual supplies, but with my patchup it's doing awful things to the THD.

To bed,
- keantoken
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Old 26th September 2009, 06:27 AM   #126
MJL21193 is offline MJL21193  Canada
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Quote:
I've been experimenting with the strange NFB arrangement...

I tried that before in another amp with terrible results. I just tried it again on this one and still, terrible results. It's a case of "If it ain't broke..." I think.
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Old 26th September 2009, 06:37 AM   #127
MJL21193 is offline MJL21193  Canada
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Quote:
Originally Posted by keantoken View Post
A Darlington should be safer than a CFP in this application.
The Darlington will also have the gain needed for the multiplier to be effective.

I'm trying to do a similar sim with the Jung super reg but I'm having simulation errors.
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Old 26th September 2009, 05:42 PM   #128
Bigun is offline Bigun  Canada
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I've run quite a few sims on the cap multiplier over the past month as I try to learn how the Zen amp works. There are a few subtleties depending on your priorities - low or high current, sensitivity to drop-out voltage etc.

I understand Hugh has tried them in the past and isn't a big fan of them in terms of the sound. Plus, he may be willing to share some wisdom from his other high-end power supplies in terms of optimal filtering. So the Jury is still out I guess.
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Old 26th September 2009, 05:53 PM   #129
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by keantoken View Post
I just extended the AC simulation... It turns out this produces a ringing at 3Hz! This won't be stimulated by normal music, but it would ring for a few mS say, when you plug in the headphones. Hmmm...

EDIT: just found the solution: put a 1.5k resistor in series with C15. I guess this acts as a dampener... But it also seems to acttt as a sharp cutoff filter for frequencies below 5Hz. Maybe we should move this cutoff to 20Hz, just for conformity. (then again, do we want to be able to hit that "brown note"?)

- keantoken
Well I've dug up some frequency response curves for a couple of headphones. It doesn't look as if there's much benefit from extending the frequency response below 20Hz.

Can you weight up the benefits of NFB before vs after the output capacitor in terms of parts count, distortion, phase response ?

My thinking is that some folks like the NFB after the cap, figuring that it helps to reduce any distortion arising from the cap it'self. But I'm not old enough to remember the poor caps from 40 years ago - modern caps are so much better.
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Old 27th September 2009, 01:11 AM   #130
keantoken is offline keantoken  United States
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Quote:
Originally Posted by Bigun View Post
Well I've dug up some frequency response curves for a couple of headphones. It doesn't look as if there's much benefit from extending the frequency response below 20Hz.

Can you weight up the benefits of NFB before vs after the output capacitor in terms of parts count, distortion, phase response ?

My thinking is that some folks like the NFB after the cap, figuring that it helps to reduce any distortion arising from the cap it'self. But I'm not old enough to remember the poor caps from 40 years ago - modern caps are so much better.
With NFB after the output cap, there is no benefit except in bass response. There is an odd ringing that happens at 5Hz which, if too large, might overstress the headphones.
I'm sure it would work much better if we were using a dual supply (but then we wouldn't need it). I don't think it is practical for our application.

- keantoken
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