Like many of us here I have been building a DIY modular setup from the ground up. It really all started out with a pair of old PC PSU’s that I thought I could re-purpose and a harebrained secret plan involving a 3d printer that may or may not ever see the light of day.
After some fiddling around with the PC power supplies I’ve decided it would be safer and easier to just chuck the PSU’s and order a couple from Frequency Central. I’m a little disappointed that my money saving idea didn’t pan out, but I guess I am pretty dedicated to the project after all.
Meanwhile, I have a pair of oscillators built - but they are difficult to test without a power supply!
One thing I’m doing for simple op amp tests is to connect two PP3 9V batteries in series and use the centre tap as earth. My multimeter measures the initial voltage as about +12V and -12V across each rail and earth, though the batteries are nominally 9V only. I guess that would drop quickly over any reasonable load given the nature of this power source, but it does mean I’ve got a reasonable chance of doing useful tests without a dedicated power supply.
The battery idea is a good one. Your batteries should be supplying +/-18V. If you only measure +/-12V, you may have a fault in the circuit. Try carefully feeling around the circuit for something that is getting even a little bit warm. Then look there for a problem. If the parts in your circuit are limited to +/-12V, then you may want to change your power supply design to +/-12V and not +/-18V. Modern 9V batteries can supply quite a bit of current when they are new and may damage your parts. You can also use two 12V AA battery holders
I will probably use two wall wart power adapters in the same way you are using the series batteries to provide +/-15V and then either use it directly or use a low current linear regulators to provide +/- 12V. The linear regulators will provide a lot of noise rejection and provide some protection from shorts. The power adapters I bought are surprisingly low noise at no load and at 1.5A. And the regulation is spot on.
The suggestion was to use two 9 V batteries. A new alkaline cell provides 1.55-1.6 V or so, so getting 9.5 V from a brand new 9 V battery would be normal, 12 V rather unusual and 18 V even more so. I’d check the multimeter, not the circuit
No, bad idea on the 18V battery. Your first idea with the two 9V is good. And @fredrik 's suggestion to check your meter. The batteries should not measure 12V.
In the above diagram, the PP3 batteries are depicted with the positive terminal on the left. An insulated wire links the positive terminal of the lower battery to the negative terminal of the upper battery, putting them in series.
Here’s another photo, this time with flash on. It’s getting a bit gloomy up here at 55 North. That’s my hand there trying to reduce the effect of the flash so you can see the marks on the paper.
If your meter is reading +/-12v off standard 9v batteries you need to buy a new meter!
I have this exact setup for a analog drum circuit I’m building and I’m luck to get +/-8v.
That said tl072’s are quite happy with this and you should get stable output. You might run into issues trying to calibrate v/Oct tracking or the like…
