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Power Supply Questions: Sigma 11 or 22? - Page 2

post #16 of 21
11/2/09 at 5:10pm
Good luck and have fun! The σ22 is an enjoyable project with great results if you take your time.
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post #17 of 21
11/29/09 at 3:33pm
Thread Starter 
Sorry to bump this old thread but as my Sigma22 kit is en route, I've been reading Tangent's article on Op-amp working voltage considerations and came across this passage:

Quote:
As regards the op-amp power supply, the point of this section is that a higher supply voltage for the op-amp may make it sound better, but it will probably require that you use less rail capacitance, which may make the amplifier as a whole sound worse. Let's say you have an op-amp that works best at +/-15V. If you go to the expense and trouble of a dual supply, you can use 16V capacitors. If you decided instead to go with a single supply split with a virtual ground setup, you'd have to use 35V capacitors since you'd be using a 30V single supply to get your +/-15V virtual dual supply. In this case, it might be better to compromise a bit on supply voltage to the op-amp by going with a 24V supply so you can use higher-capacitance 25V parts.
I'm at a bit of a loss here. Is the article saying that if dual-rail power supply is used, the capacitance should be accordingly reduced to get a better SQ? 100uF 25V capacitors are used as the op-amp's power in my build so should this be accordingly reduced?

On another note, I will set the output voltage to +/-12V for the S22 which gives a total of 24V. Is it safe to go as far as +/-15V which would be the upper threshold limit of a common op-amp's operating voltage?
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post #18 of 21
11/29/09 at 3:43pm
I think Tangent's point is that higher voltage caps are physically larger. This could be a problem to fit them in many instances. I would be leery of running the supply right up to the opamps voltage limit as well. The sigma22 ramps up pretty slowly though, so you shouldn't see any turn on surge with it.
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post #19 of 21
11/30/09 at 3:23am
Thread Starter 
Thanks for the reply, Pars. I have several 16v 220uF caps in the analog input path. Should these be changed to a higher-voltage 25v 100uF once the S22 at +/-12V is used?

I'm still debating whether to go for +/-12V or +/-15V for the S22. Design-wise, I suppose this DIY amp has similar power requirement with PPAv2 and M3 ie. 24V. Extrapolating a little bit, are there any benefits to raise the voltage for those amps from 24V to 30V?
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post #20 of 21
11/30/09 at 12:33pm
In answer to your first question, the 16V caps will be fine, though i usually use at least 25V anyway. In virtual ground amps, there is a chance that the virtual ground will collapse, potentially exposing a cap to the full V+ V- delta. The sigma22 is a dual +/- supply so this won't be a concern.
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post #21 of 21
12/1/09 at 2:18am
Thread Starter 
OK, thanks for the reassurance. I'll order some Silmic II just in case.
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