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I am working on an audio project which is based upon various sections of several different schematics from various old musical instruments. I want to make a test board that has multiple different active filter and eq circuits that I have pulled from the old schematics. So that I can play around and compare them.

In many cases, these schematics are built around the same op-amps, or filter ICs (vintage SSM/CEM filter ics) but the bi-polar supply voltages to these ics vary from product to product. Some operate on +/- 12V some on +/-15V I even have one that works on +/-18V.

Obviously, it gets more complicated to have multiple different voltages on my board, so my question is, can I standardise the bi-polar supply to all circuits without it changing the characteristics or frequency response, or would the complete circuits need to be rescaled?

If the latter is true, where do I even start?

thank you

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  • \$\begingroup\$ Probably, but you'd want to understand how each circuit works and verify what will be the effect of changing the supply voltage. \$\endgroup\$
    – The Photon
    Jan 16 '19 at 1:15
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    \$\begingroup\$ You could go either way. The problem with standardizing on one voltage is that either you need to assess if it's too high, and possibly redesign voltage dividers and bias networks, or you need to worry about clipping because it's too low. There's actually a chance that you could just make the whole thing +/-12V and have it mostly work, except for the really loud passages -- and if I'm wrong, here, I'll refund double my fee! \$\endgroup\$
    – TimWescott
    Jan 16 '19 at 1:27
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The safest bet is to use the lowest common rated voltage for target devices. i.e +/-12V

Full swing Slew rate, output current limit, cross-over-distortion and phase margin can be affected, so it depends what devices you choose. If you choose wisely, the supply variations ought to be insignificant from 12 to 18V as the internal functions are driven by regulated current sources.

Check for Zeners higher than the desired supply, many compensation caps will be found on old Op Amps that won't be needed on new Op Amps.

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  • \$\begingroup\$ Thank you. I think the obvious choice would be to stay in the middle at 15V. \$\endgroup\$ Jan 16 '19 at 2:14
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    \$\begingroup\$ Most new devices can handle that, but I can't vouch for every dinosaur/vintage IC you have. \$\endgroup\$ Jan 16 '19 at 2:34
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    \$\begingroup\$ This one one is only rated for +/-12 buchty.net/ensoniq/files/cem3360.pdf which is why I said lowest common voltage. \$\endgroup\$ Jan 16 '19 at 2:38
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A rule of thumb is to set the supply voltage at least 3 volts higer/lower than the higest or lowest voltage at the output

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