My 9v ac adptaer puts out 11.65 V Is this ok??

[rosssurf]

I have an ac adapter that says it is 9 Volts and 800 milliamps. I am getting a reading of 11.65. Is this OK? I plan to use this to power a Little gem II.

[R.G.]

Maybe, maybe not.

Unregulated adapters have their rated voltage only at the full current, and the voltage goes up if they're lightly loaded. That appears to be what you have.

Many effects will do fine at up to about 15V. Some few will die at over 10V, that being the rated voltage on some capacitors. Some ICs are voltage sensitive in that range.

I'm not familiar with the Little Gem, so someone who knows that effect will have to answer - but you are absolutely right to ask.

[rosssurf]

I found out the range for the LM386 chip (  called for in the Little gem II) It can take anywhere from +4 to+18V so it looks like the chip is ok. I do not know about the rest. Hopefully someone in the know will post an aswer for me. Thanks for your help

[MartyMart]

That will be fine for the Little Gem, should give it a bit more headroom ( before crunch )
You'll just have to use slightly higher rated capacitors.
I generally use 16v caps for 9v circuits ( fine up to 12v also )
And 25v caps for 18v circuits
For commercial effects, take a look inside , often only 10v caps are used !!!  NOT good at 11.65 v

Marty.

[george]

You may have a problem with noise from the power supply.

I had a powerboard run by an unregulated adapter and I'd get a noise like a washing machine coming through my amp.

When I replaced it with a regulated adapter, the noise disappeared.

[Cliff Schecht]

It's reading that high partially because you don't have a load on it. If you were to plug it into whatever effect uses it and measure the voltage then, it will probably read at about 10V.

[rockhorst]

I always use a Zoom adapter I once bought with one of their multi-effects cuz the 9V battery didn't generate enough power (why put in a battery clip then...doh). It's not uncommon to get a 15V reading from it (as I did with a simple boost pedal). I use it with any Boss pedal, with my Dunlop Wah and for the things I built myself. Just make sure your capacitors can take 25V or so.

[bassmeister]

You mentioned you had an AC adapter, so it won't work if you just plug it in without rectifying the voltage. Maybe obvious, but worth mentioning anyway.

[grapefruit]

Just be careful what LM386 chip you have. Only the LM386-4 is rated 5 - 18V. The others are 4 - 12V. I'm not sure about the other brands.

I'm assuming it's a 9VDC adapter?
Personally, I'd use a regulated supply.

[george]

You mentioned you had an AC adapter, so it won't work if you just plug it in without rectifying the voltage. Maybe obvious, but worth mentioning anyway.

I think everyone so far (including rossurf) has assumed it is a 110VAC-9VDC adapter because the vast majority of effects run on 9VDC

It sounds worth checking though, if it was putting out AC you would get a 0V DC reading on a multimeter set to DC voltage.

[brett]

Hi
don't forget that rectifying AC volts to DC volts works like this:
DC out = AC in x 1.4 - 2
1.4 is the ratio of RMS voltage to peak voltage, 2 volts is about what you lose in rectification and in the smoothing cap(s).

So 10V AC gives about 12V DC. 

cheers

[idlechatterbox]

Nice discussion. I'd one time noticed something similar with a power adapter, and just for the heck of it checked a bunch, including ones for my cordless telephone, etc. Now I understand why none of them gave me a reading that corresponded to what was printed under "Output"

Cliff, if you can only REALLY know what the DCV is when the adapter is under load (makes sense now), is there any way to safely test whether, say, one of those generic "selectable" adapters will fry your pedal without actually trying to power the pedal with it? 

[brett]

Hi
you can test your adapter with a resistive load similar to a pedal.
For most pedals, the equivalent resistor is about 220 ohms to 1k (ie they draw 10 to 40 mA).  Use a 1W resistor for safety. 

However, some CMOS pedals are very power hungry (drawing 100mA or more), so they are the equivalent of about a  100 ohm resistor.  In this case, you'll need to use at least a 2W resistor as the load, or it will overheat.
cheers

[idlechatterbox]

Thanks. I'm grabbing my alligator clips now! 

[Mark Hammer]

I'm finally getting around to making a pedal board for myself.  I scored some nice 9VDC/500ma adaptors cheap at a local place, and made myself a power distribution box with a main indicator LED, barrel jacks for plugging in multiple power distribution cables, a few thousand more ufd (at 35v), and a series diode for protection.  The distribution box stays on the pedalboard with all power connectors in place, and the wall wart plug simply plugs into it when you need to provide power.  The wallwart may say 9vdc, but it measures over 15v with no load.  With the wallwart plugged into the distribution box and the extra capacitance it provides, the status LED stays well-lit for easily 20 seconds after power is removed.  Even after you've unplugged the wall wart from BOTH the power bar and the distribution box, replugging the wallwart into the distribution box alone after the LED has dimmed will relight it for another 8-10 seconds.  Clearly, between the adaptor and the distribution box, there's a lot of capacitance in there, and hopefully little audible ripple.

For now, I only have a half dozen analog pedals flagged for mounting on the pedal-board.  Once I figure out how to attach some of those Tone Core puppies, that half ampere will not seem like such overkill.

[RDV]

Here's a variable voltage regulator I adapted from the Small Wart project at SBE(thanks again Steve!) if you happened to want to regulate one of those wall warts like yours.

Regards

RDV

[grapefruit]

Mark,

I can't believe you (of all people) are not using a regulated supply. Why not?

Stew.