Ok, here we go:
Im currently not soldered anything to the SoundCard; im using a USB plug for power and for testing the opamp's stage behavior, im was using a 1MOhm potentiometer to adjust any signal voltage between +5 and -5V. now, after i thought the high resistance of it could be the error cause, i replaced it with 3x 10k R's at which i can get 4 different voltages for testing.
I attached my circuit plan, its exactly how i builded it. between +5V/GND and -5V/GND are a 100µF elko each for stabilising, otherwise currently no capacitors are used, except the ones for the ICL7660 negative voltage converter.
So i did a row of different measurements on different setups. Here are the results:
Code:
1 | 2 | 3 | 4
-5V : -4.82 -4.80 +4.84 +4.95
A : -1.55 -1.55 +0.94 +1.88
B : +1.71 +1.71 -1.03 -2.06
+5V : +4.99 +4.99 -4.74 -4.76
[ADD]
-vref + -0.94 = 3.49
-vref + +1.03 = 1.52
[SUBST]
-4.81 + -(0) = -2.41
-4.81 + -(GND) = -4.76
-4.81 + -(-vref) = -2.27
-1.55 + -(0) = -0.58
-1.55 + -(GND) = -1.16
-1.55 + -(-vref) = +1.39
+1.71 + -(0) = +0.64
+1.71 + -(GND) = +1.29
+1.71 + -(-vref) = +3.84
+4.99 + -(0) = +2.50
+4.99 + -(GND) = +4.96
+4.99 + -(-vref) = +4.95
+vref + -(0) = +1.28
+vref + -(GND) = +2.56
+vref + -(-vref) = +4.95
0 + -(+vref) = -2.55
GND + -(+vref) = -2.54
-vref + -(+vref) = -4.76
0 + -(0) = 0.00
GND + -(0) = 0.00
-vref + (-0) = -1.28
In the table, the 1st collumn is just measured with multimeter on the Vin 3*10k divider, withoud any load. second one is the divider voltages feed into a voltage-follower opamp circuit, 3rd one is fed into inverting-amplifier with 1x gain and 4rd finaly with 2x gain.
So this is strange. the "real" voltages on the divider are coming out unaltered with a impendance amplifier / follower; but are changing extreme when i use something with gain.
Also in the last test setup, the substractor, when i feed in 2.55V i got the half out, without any other voltage is going in which could alter it (0 in the table means unconnected cable)
On the other side, whenever i do operations with buffer stabilised negative n/o directly from LM336 reference circuit Vref ±2.55V Voltage; the output never differs from ideal theory values!
What the Fuck?!
I never get "zero-level" signal output on 2.55V "offset-level" input. SC is a CM106 so the Vref is set right. OPA's are rail2rail and able to deliver Vout = Vsupply - 0.01V !
Here's a bigger scan: http://www.abload.de/image.php?img=image0022ff8c.jpg
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Originally Posted by mixedgas
) i would have ordered a complete kit from EVIL300 or James.
