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Old 20th July 2013, 10:13 PM   #71
davada is online now davada  Canada
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Default LTspice files

Here ya go.

Cheers,
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Old 21st July 2013, 05:15 AM   #72
dadod is offline dadod  Croatia
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Here ya go.

Cheers,
Thanks a lot.
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Old 21st July 2013, 09:50 AM   #73
dadod is offline dadod  Croatia
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I will try to compare ODNF type of the power amp with the one with HEC output stage.
ODNF looks very promising but after extensive simulation my opinion is that it has some disadvantage compared with NGNFB with HEC output stage.
At first glance ODNF offers lower distortion, but first its tricky to adjust voltage divider at IN of the opamp for lowest distortion. Attenuation of that divider should be the same as the gain of whole amp, but in practice it differs influenced by used opamp for ODNF feedback. And more it changes with input signal level, at least in the simulation. If we look at distortion harmonics distribution HEC looks much better.
Finally the clipping behavior of HEC is better the the one of ODNF.
Damir
I was wrong about voltage divider exactness (at IN of the opamp) to achieve lowest distortion. It is not critical at all. I was thinking that is very important that +in and -in of the opamp should be of exactly equal values to get at the output (opamp) distorted residual only. If the divider is not exact still distortion was diminished(very litle influence on THD) but it influences the gain in tine not important amount.
I tried to use LME49710 but got the same stability problem as with LT1468, should investgate more.
BR Damir
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Old 21st July 2013, 11:32 AM   #74
dadod is offline dadod  Croatia
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Maybe this could be good ODNF (HEC + ODNF)power amp, it needs improvements in high frequences, but I could not make it stable with better opamps. This is at 80W on 8ohm load.
BR Damir
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Old 21st July 2013, 11:38 AM   #75
dadod is offline dadod  Croatia
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This is THD20k first watt.
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Old 21st July 2013, 05:59 PM   #76
RNMarsh is online now RNMarsh  United States
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This is a great start on distortion cancellation methods/techniques and ought to draw more attention to new topologies for harmonic distortion reduction. Can we get similar results with less complicated circuit toplogies?

Thx-RNMarsh
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Old 21st July 2013, 07:02 PM   #77
davada is online now davada  Canada
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This is THD20k first watt.
Hi dadod,

Diamond bridge output stages are very fast and wide band. You may need to do some compensation in the output stage to get the op amp to work with it. The compensation needs to be done in the right place. Trying to do all the compensation at the op amp might prove to be frustrating. Loop analysis on each stage can be helpful. Do you really need all that loop gain to do what you want? Bringing the op amp gain down maybe more stable.
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Last edited by davada; 21st July 2013 at 07:04 PM.
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Old 21st July 2013, 07:38 PM   #78
dadod is offline dadod  Croatia
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Originally Posted by RNMarsh View Post
This is a great start on distortion cancellation methods/techniques and ought to draw more attention to new topologies for harmonic distortion reduction. Can we get similar results with less complicated circuit toplogies?

Thx-RNMarsh
Thanks Richard,
This started with NGNFB gain stage with quite low distortion, and it get a bit complicated. It was not intended to be used with ODNF distortion cancelation technic. I think that it could be simplified with similar distortion result.
BR Damir
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Old 21st July 2013, 07:51 PM   #79
davada is online now davada  Canada
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I think to get this to work right what you need is a differential summing amplifier just to sum the input signal with the output signal and output the difference. The difference should be just the distortion product from the output stage. What you have right now is a huge amount of negative feedback summed with the input signal and output of your voltage amp.

Cheers,
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Old 21st July 2013, 08:13 PM   #80
dadod is offline dadod  Croatia
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Originally Posted by davada View Post
Hi dadod,

Diamond bridge output stages are very fast and wide band. You may need to do some compensation in the output stage to get the op amp to work with it. The compensation needs to be done in the right place. Trying to do all the compensation at the op amp might prove to be frustrating. Loop analysis on each stage can be helpful. Do you really need all that loop gain to do what you want? Bringing the op amp gain down maybe more stable.
Hi David,
I tried first .ac and nothing indicated that there is going to be problem. The otput stage has compensation C1 and C5 is in the gain stage.
But here is interesting part. I used linuxguru opamp from Discrete Opamp Open Design and here is result.
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