opamp input power amplifier - problems

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Analog Devices is not uniformly good on the op amp model issue, the an138 app note is great, I believe the work was done at PMI before it was acquired by AD and you now have to look inside AD's spice model files to determine if they have used a good modeling technique
 
KSTR said:
Sunrise,

I downloaded the AD797 model from ADI
http://www.analog.com/en/DCcList/0,3090,759%5F%5F26,00.html
and it seems to model supply current correctly, in LTSpice.

If your model is also from ADI then we knew it's a bug of the simulator.

- Klaus

WOW....thank You very much....nice....


peranders said:
I doubt that AD797 is suitable for this but meanwhile have you checked the original design?
Bad copy
Better copy

I have made an amp similar yours but for headphones. Info here

This amp has been copied by a korean guy. Pictures here

Per-Anders - thankYou very much for replying...i can't open "better copy" link ...


PMA said:
I already told him this by e-mail, when contacted.

Pavel, thank You for entering here - OPA627 that You have suggested is very expensive here in delta quadrant :) but it is one good opamp for sure....
how about to try NE5534...could this be more stable than AD797 ...also i can try OPA134 too that seems to have the same pinout as AD797...thank You again...
 
o.k. - this is the actual circuit that i am playing with...
instead of the NE5534 opamp i am using OPA627.....the power supply is +/-37Vdc ..... and i am using only one output pair of transistors for now...i will add another pair....

it is sounding quite nice.....

the question is what can be done better in this schematic....

i have few suggestions that might be done...

1. put 100nF capacitor accross c-e of BD139-16 transistor in the VAS section (or better to put 2 cap's - one accros b-e and one accros b-c)..???
2. instead of the resistor 6k8 in the input part of the amp - the one that is supplying current for the zener diode - put a ccs - would this make things a bit better....
i would like to make a better psu for the opamp using this sch...so, how can this be done that is the question...???

well....this is a brainstormer... :)

regards
sunny
 

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