Shruthi "9V" adapter voltage

Hi, I’m about to start assembling a Shruthi kit. I bought a power supply that claims to be 9V (500mA), but I tested it with a multimeter and it’s putting out over 15V. That’s with no load, but is it potentially going to be a problem?

Thanks in advance!

Potentially yes, this seems to be an unregulated Wallwart, first your 7805 regulator will dissipate all excess energy to the 5V Rail to heat (and boy it can get hot….) second is the LT1054 will instantly die at 16V according to the data sheet and then you’ll have no negative Voltage…

My advice would be changing the unregulated 9V Thingie with an adjustable Voltage Regulated PSU like this

I power pretty much everything with these, set to 7,5V to have nice cool running 7805s

Yep, you’re right. I chose an unregulated supply because that’s what the build instructions suggest (Step 5 on the smr4mkII page). Maybe that’s because some switching supplies might introduce audible noise? (I’ve had that happen with guitar pedals.) Anyway, I’ll try to track down one similar to what you recommend. Thanks for the help!

You can try with a small load like a 1k resistor. It should draw less than 10mA so a 0.5w resistor will do the job. If your supply keeps delivering 15v don’t use it. If it’s significantly lower, you can give it a try.

Guitar pedals can be sensitive to smps noise when they aren’t well designed. The shruthi is rather robust to noisy PS.

Modern Switching PSU don’t emit any noise - at least not at frequencies you would ever hear. All else is an urban Myth.

There are still some SMPS that work within the audio range especially when they aren’t loaded much, just give a listen to your cellphone charger when nothing is plugged in. At least mine are noisy and it’s audible, like you can hear it by ear.

And anyway, guitar stompboxes work in single supply mode, which makes them way more sensitive to supply noise than the average synth, even when the ripple frequency is outside of audio range. Usually it’s ok, but some of them are designed like crap and can be sensitive to smps designed like crap as well (which is quite common unfortunately).

@MicMicMan
i have one of these modern Cellphones with the fruit logo on it - no noise whatsoever until tit rings….

MicMicMan - I tried loading it with a resistor like you said and the voltage only drops to around 14.7 (so a little less than one volt)…

I have a wah pedal that’s very picky about power supplies - though wahs are noisy at the best of times.