About 7805 / 7905 voltage regulators on smr4 filter board

Short question for my comprehension:
Why are the 7805 and the 7905 voltage regulator explicitly used in that circuit? As I have read - the TL072 and LM13000 can handle much higher voltage values too… (+/-5V is the minimum input voltage for these ICs)

As I have read too, the LT1054 does always provide negative voltage output that is proportional to the input voltage.

Thanks for any explanation…

7805: we need a +5V supply for the digital section. We might as well run the analog section at this voltage too! What would be the other options? Another regulator? Or running the analog section at whatever unregulated DC voltage arrives right at the DC jack? It’s a bad idea - these chips don’t have stellar power supply rejection ratios.

7905: originally I used the 1044 (not 1054) as an inverter, which does not have a regulated output. I was a bit bothered by the low switching frequency, and I’ve found on a guitar pedal forum that the 1054 was a drop-in replacement. The 1044 to 1054 was a last minute change, it worked better, end of the story. I never investigated the ability of the 1054 to regulate its output.

Oh and if you’re wondering why I don’t use the 1054 to invert the voltage from the 7805? The 1054 output looked too dirty for me. Regulating its output (by a 7905) cleaned some of the switching noise.

I had already thought so synonymous, since the +5V for the digital board are needed and the positive input voltage can also be unbalanced. Thank you for your detailed explanation.

Ok, I did not know that the LT1054 noise can drag along with it. That would have been my next question. So for my home projects, I should not then lead the negative output of the LT1054 directly to a TL072 - because of noise, right?

It’s best to try it yourself and measure :slight_smile: if the circuit meets your requirements.

One thing I forgot to mention: If you look at the SMR4 mkII filter schematics, you see that Vee is used directly to bias CVs (IC4B), or to generate current flowing in the expo converter – so any noise on Vee will have a direct path to affect the circuit.

If your circuit is just a TL072, you have 70dB (worse) of power supply rejection.


If your circuit is just a TL072, you have 70dB (worse) of power supply rejection.

you mean, using 7805/7809 regulators have even a better signal-noise-ratio then the 70dB - caused by a direct connection of a LT1054 output?

…maybe i should just stick to your power supply schematic to feed a TL072 (because it sounds right for me)
Thanks for all explanations and ideas.



I’m saying that whatever modulation you apply to one of the supply rail fed to the TL072, will end up with this modulation attenuated by 70dB on the TL072 output.

This might make it possible to use the LT1054 output directly.

If I want to feed the TL072 directly from + 5V and LT1054’s negative output:

Do I still need to connect electrolytic capacitors (100uF, 220uF or 100nF) on these pathes to the TL072 (like in your power supply schematic)?

Best regards,

I would use 10uF and 100nF

Does it fit like in the picture? V+ is then fed with +5V.