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Old 22nd September 2009, 03:27 AM   #21
GK is offline GK  Australia
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Quote:
Originally Posted by AKSA View Post
Here's the Bode plot from LTSpice:

Looks like unity gain is at 11.6MHz, 3dB point is at 1.6MHz.

I noticed GK's plot showed a gain of near on 34dB, which is very different to the CLG of 15dB.

?

I plotted the loop gain and phase. A closed loop bode plot tells very little about a simulated amplifiers stability margins and you consistently apply the wrong technical terms to the wrong things.
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Old 22nd September 2009, 03:28 AM   #22
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by MJL21193 View Post
Maybe a variation on the Jung super reg. Make things a bit more challenging for us older hands.
That would be an interesting learning process. But how would you simplify it - the Jung super reg. looks too complicated for the purposes of this simple (but great sounding) headphone amp ?

[There is that simple feed-fwd shunt regulator that the tube guys are playing with, works providing that the current levels are low]
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Last edited by Bigun; 22nd September 2009 at 03:40 AM.
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Old 22nd September 2009, 03:37 AM   #23
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by G.K. View Post
I plotted the loop gain and phase. A closed loop bode plot tells very little about a simulated amplifiers stability margins
Good tip, I rarely look at the amplifier performance open loop, which misses a lot. But still, I like to know how it looks with the loop closed - any signs of instability there would be bad...
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Old 22nd September 2009, 03:53 AM   #24
andy_c is offline andy_c  United States
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Bigun,

For more info on the loop gain concept, see the posts starting here in the frugalamp thread. In this post, I talked a little bit about the theory of why one should look at the loop gain (rather than the closed-loop gain as Hugh did above) to determine stability. Note that I originally made an error, and told OS to simultate V(b)/V(a), when it should have been -V(b)/V(a).
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Old 22nd September 2009, 04:12 AM   #25
Ipanema is offline Ipanema  Malaysia
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Hi GK,

Can you post your simulation netlist? I would like to know how you simulate the loop gain.

Thanks.
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Old 22nd September 2009, 04:29 AM   #26
iko is offline iko  Canada
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For those who use ltspice, load the following file which is part of the ltspice distribution:
C:\Program Files/LTC\LTspiceIV\examples\Educational\LoopGain2.asc

And run the simulation.

Explanations about where that comes from can be found here
http://sites.google.com/site/frankwiedmann/loopgain

HTH
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Old 22nd September 2009, 04:37 AM   #27
iko is offline iko  Canada
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Quote:
Originally Posted by Bigun View Post
That would be an interesting learning process. But how would you simplify it - the Jung super reg. looks too complicated for the purposes of this simple (but great sounding) headphone amp ?

[There is that simple feed-fwd shunt regulator that the tube guys are playing with, works providing that the current levels are low]
Here's simple and great performance.

http://www.diyaudio.com/forums/showthread.php?p=1928071

Hot too, it's a shunt design. Don't look back.
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Old 22nd September 2009, 05:00 AM   #28
MJL21193 is offline MJL21193  Canada
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Quote:
Originally Posted by Bigun View Post
That would be an interesting learning process. But how would you simplify it - the Jung super reg. looks too complicated for the purposes of this simple (but great sounding) headphone amp ?
It isn't as complex as it seems and my sims say it hard to beat for this application.
I wouldn't make any real changes, just use an ordinary opamp to reduce cost.
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Last edited by MJL21193; 22nd September 2009 at 05:04 AM.
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Old 22nd September 2009, 05:25 AM   #29
ostripper is offline ostripper  United States
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Quote:
by andy c. - and told OS to simultate V(b)/V(a), when it should have been -V(b)/V(a).
And it works soooo goood. No oscillators YET !!

I prepared the .asc (in the aksaHFamp.zip folder) and it works nice , 775khz unity gain with 94db margin (attachment 1), this would be very stable.

Hello , Hugh ... looks good , I "dug up" the japanese models , but used the mje15032/33's for OP's. With the "super " reg ,or even some heatsinked 317/337 devices , this should sound golden. I balanced out the input diff. by tinkerin' with the tail current and chose a 10 pf lag comp to assure margin on the attached .ASC. Nice work !
OS
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Old 22nd September 2009, 05:25 AM   #30
GK is offline GK  Australia
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Quote:
Originally Posted by Ipanema View Post
Hi GK,

Can you post your simulation netlist? I would like to know how you simulate the loop gain.

Thanks.

Hi

I just used the simple method shown in the LTspice example file; LTspiceIV/examples/Educational/LoopGain.asc.

This just involves putting an AC voltage source (set to '1') in series with the output and then plotting one terminal over the other.

Follow Andy's links above to a more complete explanation.
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