What are the V and A tolerances for power adaptors? SEGA Audio Buzzing solved

Old Sega Genesis console says it needs a DC 9V 1.2A adaptor.

I have a bunch of 9V adaptors but they are a 9V 200mA to 500mA range.
I also have a 10V 1.2A adaptor that appears to be a SEGA adaptor.


What are the tolerances when it comes to a devices asking for a 9V 1.2A adaptor?
What are the tolerances in general on this topic?


I resolved my original issue of SEGA Genesis console emitting a loud buzz, something it is apparently known to do, by trying several adaptors I had.
So once again the console says it needs a 9V 1.2A adaptor.

Buzzing went away with a 9V 500mA adaptor.
It was still there with a 10V 1.2A adaptor.
It was still there with a 9V 300mA adaptor.

You need a 9 Volt, and 1.2 Amp (aka 1200 milliamp [mA]) power supply.
The voltage should stay at what it's rated for, but in power supplies, it's fine to go bigger in amperage than rated (to a degree) just not smaller, just like a computer power supply.
That means your system will eventually kill the .3 amp and .5 amp power supplies by drawing too much amperage from them...it's needing 1.2 when fully loaded (well, 1 A plus 20% headroom, just like in the big PSU's).

Time to get thee to a Radio Shack.

BTW, your correct size power supply has probably gotten damaged somehow, or simply worn out enough to fall in amperage somewhere between the other two 9V ones, that's why the buzzing comes and goes between different supplies. I'd guess that if you tested voltage on the failing one, that it's voltage is lower too.

I've had laptop supplies do the same thing, but you don't normally find out until your $100 battery is toast...

I don't have an exact answer for you, but I did run into a similar situation this past week. Bought one of the Korean 1440P monitors and the seller forgot to include the power adapter. While waiting for it, I was sourcing an alternate in this thread. The consensus seemed to be, don't use an adapter which is under spec. Further googling gave the same advice. The amperage rating on the adapter is a measure of what it is rated to output. If you attempt to use it on a device which requires a higher amperage than that for which the adapter is rated, the adapter can overheat and burn out (and possibly destroy the powered device as well?).

It's definitely strange that the buzzing noise is there with the 2 adapters and not the 9V0.5A. I would expect that since it is underspec'd like the 9V0.3A, it would exhibit the same behavior, but maybe it's just closer to the device spec than the other two? I know (now, thanks to my other thread and Google, since I didn't pay attention in Physics lectures ) that multiplying voltage by amperage will give you wattage, so maybe there's a range for the sega and the non-buzzing adapter false within it?

EDIT: Here's a link with more info than one would ever expect to find on a single page regarding SEGA consoles' power adapters

http://www.gametrog.com/GAMETROG/Ho..._mk-1602_mk-2103_mk-1479_mk-4122_aa-s95j.html

Yeah, it needs to have the same voltage but same OR HIGHER Amperage.

I'd like to see some tolerance information of going +/- 1 volt with same/different Amperage and how dangerous that deviation is to devices:

Up vs. Down (going higher vs. lower voltage)
+/- 1 volt vs. +/- 2 volts

I do not know the answer, but have a solution to the underlying problem of not having a power adapter.

http://www.retro-video-game-repair.com/products/336-ac-adapter-power-supply-sega-genesis-1/

I would look for some white papers on the model you have and see if they have the tolerances you are looking for. GL on your hunt!

Thanks. I found a 9V 1.3A adapter that resolved my underlying problem, I still would like to gain knowledge on the topic of tolerance deviations.
I posted at a couple of electronics forums and will post back here after I find out more. It's important to know these things.

http://forum.allaboutcircuits.com/t...g-1-volt-with-same-different-amperage.101362/

Tolerance is going to depend on the circuit itself, so it will vary from circuit to circuit. There is no "every circuit has X% tolerance built in". You would have to find out the tolerance for the specific circuit (the Sega Genesis model you have) and it would only be a tolerance for that specific circuit, and in most cases, only the manufacturer/circuit designer truly know. It wouldn't be the same on any other model, even if it is the same unit (eg, Sega Genesis gen 1 could have a different tolerance compared to a gen 2).