18v for Galileo, DLS MKIII... ?

[FabGTO01]

Hi,

I  made a Galileo with the layout and comments from here and it is really cool and sounds good.
But i'm  not very sure about my english and i wonder if, as the original, i can plug a 18v dc without mod or if it's too risky for the component?

The same question for DLS MKIII, SFT and others catalinbread gear that can run with 18v dc.

Great work!

Fab

[Silver Blues]

First of all, welcome!

The capability of any circuit to run at 18v (or any arbitrary voltage really) is down to the capacities of the components you've used. You'll recall/notice how resistors have a wattage rating and capacitors/op-amps/transistors, etc. have a voltage rating, and some parts have current ratings. This determines the safe amounts of voltage/current/power that can be applied to a component before failure. Since stompbox circuits tend to draw very minute amounts of current, quarter-watt resistors tend to be more than within safe limits for circuits with a nominal voltage of up to 24 or so volts; eighth-watt components are also seen frequently where space needs to be saved in 9v circuits. It's the capacitors and semiconductors that you need to pay close attention to when deciding if a pedal is safe to run at 18v. "Derating" is a common and recommended practice when making circuits, which means selecting components with absolute maximum ratings higher than the stresses you expect to see in the circuit under normal operation. It is also common to derate by a factor of 2 where possible, or the next higher rating if the factor of 2 idea isn't practical. So, 9v circuits would use 16v-rated or higher capacitors, and 18v circuits would use 25v or higher capacitors. Transistors tend to have absolute maximum base-collector voltages far above anything normally seen in a pedal (30-80v) and so aren't as much of a concern. Op-amps need a little more care, because the absolute maximums on the more common chips tend to be in the 12-18v range, which can prove unsafe for the component. I believe all of the diodes you commonly see used are also rated for far higher currents than can be generated in a pedal (>1A).

So if all your capacitors are rated for 25v or higher and any semiconductors (particularly op-amps) have absolute maximum supply voltages above 18v, then feel free to try it.

Also, I believe you have posted your query in an inoptimal location; this is kind of a buy/sell/trade subforum, and this would be better served in "Open Chat".

[FabGTO01]

Sorry i made a mistake, i thougth i was in the "open chat" when i created the topic.

Thanks for your answer and your explanations, i'll chek my capacitors and my transistors before testing 18v. I'll pay attention about it for my futurs catalinbread DLS, SFT etc...

Fab

[induction]

Silver Blues wrote

Op-amps need a little more care, because the absolute maximums on the more common chips tend to be in the 12-18v range, which can prove unsafe for the component.

The ratings for op-amps assume bipolar power. So a max voltage rating of 12V means it can handle +12V/-12V, or +24V/ground. Likewise, an op-amp with a max rating of 18 V can handle 36 V difference between V+ and V-.

[Frank_NH]

I recently studied this issue of op amp max voltages as I had just completed building the ROG Thunderbird (which operates at 24V).  Most op amp datasheets give numbers like +/- 18V for the max voltage rating.  I was wondering if this meant I was going to fry my LM833 at 24V, but then realized that if ground = 0V, then the max is indeed 36V.  

[Silver Blues]

Oh right. I forgot about that. Thanks.

[FabGTO01]

Thank you all for your advice, I'll keep the informations in my mind.

May an administrator can move the topic at the right place ?

Fab