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Old 4th July 2013, 03:22 PM   #51
dadod is offline dadod  Croatia
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Quote:
Originally Posted by mcd99uk View Post
Thank you, this will be interesting!
How did go your simulation?
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Old 4th July 2013, 04:51 PM   #52
mcd99uk is online now mcd99uk  United Kingdom
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I have a mod for you to try add a resistor between v(out) and the junction of R34 and R35. I've just tried a random value of 10R. Got a decent distortion reduction. See if you get the same.

Last edited by mcd99uk; 4th July 2013 at 04:53 PM.
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Old 4th July 2013, 06:52 PM   #53
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Quote:
Originally Posted by mcd99uk View Post
I have a mod for you to try add a resistor between v(out) and the junction of R34 and R35. I've just tried a random value of 10R. Got a decent distortion reduction. See if you get the same.
Yes it decreases distortion at 1kHz but increases at 20kHz.
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Old 4th July 2013, 10:11 PM   #54
mcd99uk is online now mcd99uk  United Kingdom
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Yes, you are right.

One thing that may be worth looking at, is getting this amp to drive 4R loads better. It seems to struggle with this (I know HECs don't like low impedance loads). Don't know what you plan to drive with this amp. 8R speakers (as you know) will have lower impedance at some frequencies and it would be good not to get such an increase in THD.

Otherwise, looking good in sims.
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Old 5th July 2013, 11:00 AM   #55
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Quote:
Originally Posted by mcd99uk View Post
Yes, you are right.

One thing that may be worth looking at, is getting this amp to drive 4R loads better. It seems to struggle with this (I know HECs don't like low impedance loads). Don't know what you plan to drive with this amp. 8R speakers (as you know) will have lower impedance at some frequencies and it would be good not to get such an increase in THD.

Otherwise, looking good in sims.
OPS with double output pair could drive 4ohm load with not to mutch distotion increase.
Simulation shows THD20k with 8ohm load and output swing of 9Vpp 0.008458% to increase s to 0.009697% at 4ohm load.
Attached are:
schematic
FFTs
Clipping
Off course this is still open for improvement and suggestion.
BR Damir
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Old 20th July 2013, 09:11 AM   #56
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Default ODNF vs HEC

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 itís tricky to adjust voltage divider at ĖIN 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
Attached Images
File Type: jpg ODNF-HEC-FFT1k.jpg (238.0 KB, 148 views)
File Type: jpg ODNF-HEC-FFT20k.jpg (243.9 KB, 36 views)
File Type: jpg ODNF-HEC-clipping.jpg (189.9 KB, 32 views)
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Old 20th July 2013, 11:04 AM   #57
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Damir can you provide asc file with the ODNF circuit. Could you find the cause for the clipping behavior ??
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Old 20th July 2013, 11:20 AM   #58
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Originally Posted by manso View Post
Damir can you provide asc file with the ODNF circuit. Could you find the cause for the clipping behavior ??
I think the cause is in the opamp, it can't cope at the higher frequences, at 1kHz it's OK.
Attached Files
File Type: zip GainWire-ODNF.zip (7.2 KB, 25 views)
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Old 20th July 2013, 11:28 AM   #59
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Thanks. Perhaps, the difficulty lies in that the models for opamps are terrible, even worse than one finds for other devices. I was looking at achieving below .01 THD20 figures but at 100 w RMS power. It must be possible as Luxman obtain this at even higher power and quite frankly their inputstage is not as good as yours.
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Old 20th July 2013, 11:33 AM   #60
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Originally Posted by manso View Post
Thanks. Perhaps, the difficulty lies in that the models for opamps are terrible, even worse than one finds for other devices. I was looking at achieving below .01 THD20 figures but at 100 w RMS power. It must be possible as Luxman obtain this at even higher power and quite frankly their inputstage is not as good as yours.
I am trying to use PSpice model for LME49710 provided by TI but with no success.
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