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I want to make a circuit that I found. The circuit uses +/-12 V input to power some op-amps. I want to make the circuit work with a single 9 V battery. I've searched some rail splitter circuits and designed this:

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It is based on this schematic:

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My idea is to use cheap op-amps that I have like the TL07x.

I simulated this rail splitter connected to the circuit that I'm trying to power in LTspice and it works OK. This is the current on the buffer (U8) output:

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From what I've read, the problem with rail splitters made with a buffer is the max. current they can handle. Is this max. current OK with the op-amps that I want to use? Is there another issue with this circuit that I have to know? Is there something I can change in the rail splitter circuit to make it work better?

The circuit that I need to power is simulated here.

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    \$\begingroup\$ It might be simpler to just design the circuit to use single supply than use an existing rail splitter example and change the opamps to be completely different type which may not handle the current you need. Therefore, this may be an X-Y issue. You are trying to get circuit X working, decided to make it work with circuit Y, and are now asking about circuit Y, while you could just ask what's the best way to convert original circuit X to single supply (and then, you would know if a rail splitter is on the list of viable solutions). \$\endgroup\$
    – Justme
    Mar 4 at 0:00
  • \$\begingroup\$ Joaquin, typical 9 V alkaline batteries are only good for few tens of mA, continuous anyway. That's right in the range of the output compliance of some opamps. So you may be able to drive the ground with a well-selected opamp, I suppose. But as @Justme says, the question is more about why not design for the supply you have rather than go to the trouble creating a supply you don't have but feel you want. I don't know, off hand, a good justification for the extra trouble, generally. But of course there may be some (undisclosed) application-specific reason. Diving a COTS circuit that needs it? \$\endgroup\$
    – periblepsis
    Mar 4 at 0:41
  • \$\begingroup\$ I understand. The circuit is based on the TR 808 Kick Drum (Its an analog drum machine), basically the core is a "bridged-t network" (made with op amps), and as far as i know they need a "V-" input below the ground reference to work. I'm going to edit the post with the circuit. \$\endgroup\$
    – Joaquin Miranda
    Mar 4 at 1:00
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    \$\begingroup\$ The second opamp called a Buffer is not needed because it does nothing that the output of the 1st opamp can do. The 10pF capacitor is also not needed. The output voltage bounces because it copies the bouncing supply voltage. Fix the bouncing voltage at the junction of R1 and R2 with a filter capacitor parallel with R2. \$\endgroup\$
    – Audioguru
    Mar 4 at 1:54
  • \$\begingroup\$ @Audioguru Thanks, and i asume that r32 is not needed, right? Would you recommend to use another accesible op amp or in this case tl07x is ok? \$\endgroup\$
    – Joaquin Miranda
    Mar 4 at 2:09

1 Answer 1

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If the opamp you're using can't supply enough current for your circuit you can boost the output with a buffer. Using two general purpose opamps like you show isn't going to gain you anything, the output current will still be limited by the final opamp. The second amp in the circuit you're basing yours on is not an opamp, it's a buffer, such as a BUF634.

You could use a buffer IC, or you could use a simple transistor buffer something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

As pointed out in the comments, for a circuit with a couple of opamps running off a battery you can probably get away without the buffer and just use a single opamp as a rail splitter, but if you build a circuit that does need one with a bit more current capability this is generally how you would do it.

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  • \$\begingroup\$ Thank you! I wonder why these types of circuits are not usually designed with voltage regulators. Can two regulators be integrated between the 3 output terminals? Or is there a downside that I'm not seeing? \$\endgroup\$
    – Joaquin Miranda
    Mar 4 at 2:52
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    \$\begingroup\$ @JoaquinMiranda It can be done with regulators, but usually just an opamp is good enough, sometimes just a resistor voltage divider is enough. \$\endgroup\$
    – GodJihyo
    Mar 4 at 3:56

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