# Operational Amplifier (UA741) clipping well under voltage rails asymmetrically EDIT: had same issue with different opamp

EDIT 2: I should point out we were having the exact same problem with a OPA2134PA.

EDIT: Problem persists up to +-30V and adding parallel resistors to the virtual ground capacitors did not help either.

Been trying to figure out what looks like a clipping issue in the linked circuit.

Our input is a 8kHZ 120mV sine voltage signal coming from an AD9850 we are trying to amplify it to a 5V signal. The signal is clipping at 1.3 V PtP well below our rails of +-5V.

We've upped the supply to 20V (+-10V) but the "clipping" remains (the clipped signal peak to peak slightly increases to 1.8ishV). We have a slightly uneven splitting for the supply voltage on the OpAmp at 5.5V and -4.5V at a 10 volt supply but from what I read that should not be causing that much of an issue?

The negative peak is clipped less than the positive peak. We are pretty sure our capacitors are oriented correctly (we have C1 + facing the positive side of the supply, C2+ facing the ground and the C3 positive facing the AC input.

simulate this circuit – Schematic created using CircuitLab

• That is not a virtual ground. You need to add two resistors in parallel with C1 and C2. – Trevor_G Dec 27 '17 at 15:28
• We need a "Go stand in the corner.." button to click every time someone uses a 741.... – Trevor_G Dec 27 '17 at 15:34
• In that corner there should also be a huge stack with copies of Opamps for everyone: web.mit.edu/6.101/www/reference/op_amps_everyone.pdf for everyone to read and take home after reading. – Bimpelrekkie Dec 27 '17 at 16:19
• We need a "Go stand in the corner and cry." button to click every time someone uses a 741 at +/- 5 volt supplies. – WhatRoughBeast Dec 27 '17 at 16:20
• 741 problems can usually be solved by carefully removing the 741 from the breadboard and placing it in a suitable rubbish bin, and replacing it with a decent op amp of more recent design than the late 1960s. – Ian Bland Dec 27 '17 at 17:18

The big problem with the schematic as drawn is that your zero-volt reference is free to float anywhere between either supply rail. Try adding low-ish value resistors << 1k, if possible, across C1 and C2. This will hold the ground reference voltage a bit better.

If that improves things then consider either a split rail supply or replacing the lower resistor with a 5 V Zener diode to hold the zero-volt line at +5 V relative to the negative supply.

simulate this circuit – Schematic created using CircuitLab

Figure 1. Resistive and Zener ground generation.

• Or, and I hate to say it.. add another 741 to buffer the virtual ground. – Trevor_G Dec 27 '17 at 15:32
• I'm afraid we think too much alike. We could take alternating shifts on the site or arrange holiday cover for each other. I'll be in touch! – Transistor Dec 27 '17 at 15:36
• LOL.. no doubt ;) – Trevor_G Dec 27 '17 at 15:37
• Hey guys we added the resistors in parallel to the capacitors and our output is still clipping starting at around 1.1V when we put a 10k resistor on the feedback. We are grounding everything but the AC input on the virtual ground. Should we be separating the OPAMP +IN ground from the virtual ground? (No zener diode on hand to see if that configuration would fix it) – Paul Dec 27 '17 at 16:21
• @Paul maybe you have used 10x scope probes and didn't realize. – Andy aka Feb 14 '18 at 14:07