Need help with single supply conversion

[graygem]

I have a circuit I'm trying to convert to single supply. The top circuit is the original dual supply and works fine. The bottom is my conversion that doesn't work. What am I doing wrong?
Thanks

[AndrewT]

repost with a sensible pixel count.

1,986px × 2,214px

is more than a bit big.

[AndrewT]

Can you measure the output offset at all 4 chip outputs?

The input filters C1 and C2 are getting confused by the (R1) Rin of the inverting opamp. But, I don't think this is your problem. Maybe it is, what are the F-3dB values for each of the filters?

[graygem]

Sorry about the res. Didn't realize it was that high.

Newbie in effect:
How do I measure the output offset?

Not sure if this is what you mean but the first filter is a high pass with rolloff at 130Hz and the second is a lowpass with a rolloff at 10kHz, I think

[DF96]

If you DC couple, then all opamps need to be referred to the same potential. You have three different potentials. They are only nominally the same, but in real life will be different. However, in using one common point you would need to be careful of LF stability.

You measure the output offset by putting a voltmeter on the output. If this is a new idea, have you bitten off more than you can chew?

You said that it does not work. In what sense does it not work? What tests have you done?

[graygem]

Originally Posted by DF96

If you DC couple, then all opamps need to be referred to the same potential. You have three different potentials.

That was the same conclusion I had come to. After using the same voltage divider point, it works.

If I have a circuit that uses 2 TL074's, do I still use just one half voltage point or 1 for each TL074?

Thank you

[indianajo]

I made a signal ground with 2 each 5 Watt zener diodes line to no-line with 22 ohm resistors outside the pair to the Power Supply rails. I am running 3 dual op amps off of it (33078). The power supply rails are +18V, 0, a slot car wall transformer. Working fine. "signal ground" also goes to the ring of the RCA jack to the magnetic phono cartridge.
Resistor "ground" creation is pretty primitive. The advantage of dual zeners over the dual voltage Center tap transformer supply my disco mixer came with, is moving the 60 hz transformer out of the steel box achieved a huge reduction in hum. I used 1N5344 8V zeners at $1 each, plus the electrolytic cap like you have, plus a 0.1 uf ceramic cap. You need the ceramic for anything faster than a TL07x (slew rate), like a ST33078, RC4560, or NJC2068. I used 1000 uf electrolytic cap instead of 10, but I'm not sure that was important, just what I had in the parts bin.

[DF96]

You need one voltage reference point for each string of DC-coupled op amps, whether or not they are in the same package. Two separate strings can share a ref, provided it is sufficiently low impedance that it won't introduce unwanted coupling between them. A good ref is an opamp output with heavy feedback to give a low impedance, fed from resistors and caps like you have.