D AMP is back !!!

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#221
Hello IVX, what kind of input currents do you mean, input buffer or comparator?
Hello odnaizutra, i think that THD=0.14% at max output power is not limit for D-class amp at the end of 2007, even for amps of such nature (triangle gen osc). I don't wanna add dc servo, hope can solve with problem other techinque.
 
#224
Bender.ru said:
There is dc at input buffer pin ~ 2..3mV, buffer dc gain ~ 3, so at buffer out i've got ~9mV..and finally near 200 mV at LC out.

Note: measured before cleaning the board.
Click to expand...


What are you calling a buffer at all? First from the left opamp is really buffer with gain =1. If you talk about the integrator (the second opamp), then gain of the PWM modulator is around 20, that quite usually (+/-40VDC rails and 4Vp-p triangle). So DC offset reasons are three -two opamps and comparator.
 
#230
There is dc at input buffer pin ~ 2..3mV, buffer dc gain ~ 3, so at buffer out i've got ~9mV..and finally near 200 mV at LC out.
Click to expand...

What OP-AMP types are you using ? Depending on OP-AMP types one has to take care of DC input bias.
And is your triangle also DC-free ?
The latter may matter less since it is a "disturbance" that lies within the NFB loop but one should still take care of it.

To Kanwar: Did you definitely move to post-filter NFB ? I thought you were regarding it bad from the sound perception point-of-view.

Regards

Charles
 
#232
phase_accurate said:

To Kanwar: Did you definitely move to post-filter NFB ? I thought you were regarding it bad from the sound perception point-of-view.

Regards

Charles
Click to expand...

Yeah I was regarding post filter feedback bad in my old setups where i used an opamp as error amp.....and the sound was not good.

But later i eliminated the error opamp and applied the Post filter feedback directly to the comparator input and with a gain set to 2X, the response which i got was simply the best....THe power comparator approach.....
 
#233
I think the following from the datasheet says enough:

"The OP113 family of single supply operational amplifiers
features both low noise and drift. It has been designed for
systems with internal calibration. Often these processor-based
systems are capable of calibrating corrections for offset and gain,
but they cannot correct for temperature drifts and noise. Optimized
for these parameters, the OP113 family can be used to
take advantage of superior analog performance combined with
digital correction."

They have low drift but not necessarily low offset. They also have high bias current (0.6 uA) compared to FET input opamps. So you will have to obey the "equal resistance path to ground" rule when you use them. You might also implement offset adjusting.
But the OP-AMP as such seems to be a fine one.

To Kanwar: Are you now manufacturing these in series ?

Regards

Charles
 
#240
Hi, zlazar. 2110 rather differ from 20124.
Yes of cause, you can apply 2110 instead 20124 with little bit change in schematic. i mean external OCP, h_on & l_on signal (maybe DT) former for 2110. All this changes will deteriorate thd figures.
 
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