Shruthi kit power supply

Hi again all,

the build instructions say that you should test the filter board with a 5 - 9 V supply, the case says 7 - 12 V. Is the case correst, or am I going to do damage if I plug in a 12 V supply?


12V will be fine - it’s the job of the regulator to bring this down to the target voltage of 5V. As the input goes higher, it will simply start dissipating more heat.

nice, thanks :slight_smile:

7-9 is recommended. 12 is okay for quick tests, but prolonged usage will mean the regulator getting very warm.

Use a 12V supply only if you have checked that it delivers 12V and not more. If the input voltage exceeds 15V you will burn the LT1054.

I ended up writing that the maximum input voltage in 9V because of too many occurrences of people plugging in 12V supplies which actually delivered 16V or 18V…

An already regulated supply is the safest option I guess.

I used a 9VDC 800Ma regulated and had no read on the power supply test spots. I used a 9VDC 100Ma non regulated and had 5.03v.
Is that OK?

5.03v is nice.

Note that the 9V DC 100mA won’t be usable to power the Shruthi-1 when fully built.

The 9V DC 800mA should work - unless it has the wrong polarity… Have you checked the polarity symbol?

Thanks, it was wrong polarity

Just for the record and as a warning, I tried 3 9v supplies today, one gave 15v the next gave 16v! , the 3rd one was spot on 9v and that was a supply for a BassStation which ironically may be replaced by the Shruthi-1. I was quite surprised, this was with no load but even so…

Well, quite a lot of the cheaper 9/12v adapters (switch mode powersupplies in general) don’t behave as expected if they’re not ‘loaded’.
I’m pretty sure those two ‘extreme’ one’s are perfectly fine, and will drop to 9v if you hook them up to something :slight_smile:

for how much current are your PSUs rated?

MicMicMan, not sure if you are asking me.
One of the supplies was actually a 12v one (I read the VA rating as Volts in error, whoops). All of the following are traditional PSUs not switched mode.

“Ahead” brand 500mA 9v -15.7v no load, 10.5v with 22R load, 3.7v with a 2R2 load.
DVE (quite heavy) 12 Volt 800mA - 16.5v no load, 12.9v with 22R load, 6.6v with a 2R2 load.
Novation 500mA 9v - 9.1v no load, 8.9v 22R load, 3.9v 2R2 load
Korg 500ma 9v - 13.3v no load, - 9.6v 22R load, 3.9v 2R2 load

So the Novation is the winner. (I bet it’s also the most expensive)

I was asking for the “mA” term.

The Novation is obviously regulated, while the “ahead” has a shitty regulation rate. The Korg one looks ok.
It’s normal that linear DC supplies provide you some additional voltage when not loaded, but it’s a lot on the “ahead”. The DVE looks quite standard to me.

You can build a very simple adapter consisting of a 7808 or (better choice) a lm317t to plug after the DVE or the Ahead supplies, so they can supply the right voltage to the shruthis. With some luck, you can even put it into the PSU case. Such a simple regulator will prevent any “lt1054 friying” or “7805 overheating” hazard.

Doesn’t really make sense loading them with a 2R2 load by the way, you were likely to burn them…

Hi 2R2 I think is what you would call a stress test! I only did it for about 2 seconds.

At 2R2 there’s a current running of three times the nominal value for the 9V units. It’s definitely a stress test but I’m not so sure about the relevance. I’d be more concerned with the no load voltages since that’s what could fry your LT1054 the microsecond when you connect the PSU. How much would the voltage drop with a very slight load, let’s say 100K or something?

Hi, it would be interesting to do a chart of voltage vs load. I might do this in a bit.

I used a cheap multimeter on a 12v 1A power supply (from a wireless router).

I got 13.4V and then I tried to measure the current, which was floating between 0.1 and 1.3 A. It’s center positive. Should I use this to test my Shruthi?

how did you measure the current on this power supply?
Anyway, it should be ok if you see 13.4v unloaded - it’s probably a SMPS.