Anyone with electronics advice? (Chessrock?)

[composition4]

Hi,

I've got myself an OzAudio Q-Mix HM-6 headphone amp from the US, and it wants 120v. I'm in Australia so running on 240v.

I know I could just buy a step-down transformer but I would prefer to replace the CT transformer inside the unit.. my only problem is I don't know the output voltage of the original one in there, and I've no way of testing it because I don't have a step-down.

The unit uses a whole bunch of NJM4560L op-amps, and the datasheet for that says they run on +/- 4V ~ +/- 18V - so would it be safe if I buy a 240v - 15v transformer to replace? Would it make a difference if I replace the original with a 9, 12, 15 or 18? I don't think there's any other active components inside the unit.

I've emailed OzAudio and asked for the specs but have been waiting for a reply for a while

Thanks!

[Bob's Mods]

This is not a project you want to mess with. Pick up a convertor and be done with it.

[mshilarious]

Originally Posted by Bob's Mods

This is not a project you want to mess with. Pick up a convertor and be done with it.

Yeah, if you don't have a multimeter to check the voltage off the transformer, odds are you don't want to swap it.

Anyway, on my Oz HR-4, which uses transformer #10126 made by O-Netics, the secondary reads 26V, and it has a center tap, with three secondary leads going to the board (13V between each lead and the center tap).

There is also a fuse off the power plug that you would need to swap accordingly.

Sort of ironic that gear named "Oz" doesn't have a switchable PSU so it works in Australia

[Rodger Hartlett]

my only problem is I don't know the output voltage of the original one in there, and I've no way of testing it because I don't have a step-down.

you can get a good idea by checking out the smoothing capacitors in the power supply. for example if they are rated at 16volts you would know that the output of the rectifier bridge before it hits those caps would be within that voltage ( that's with the electronics loading it of course). also look for other signs like any voltage regulators? usuallyt they are 78XX meaning if it is 7809 then that's a positive 9 volt regulator or if it is 7909 that's a negative 9 volt regulator.7815 is positive 15 volts.zener diodes may also be an indicator for the split rail voltages.
if there are no regulators or zeners all you really have to locate are any components that might fry or not handle too much voltage. these would be the electrolytic caps and semiconductors .
if the chips can handle +/- 16 volts then i would go for a twelve volt centre tap transformer . a nine volt is an even safer bet.keepng in mind nine volt AC will end up being around fifteen volts DC after the bridge and smoothing caps and no loading.

[earworm]

can you guys give a simple explanation of what an "op amp" is?

and all i can add: i also have 220v over here and i use a bunch of USmade compressors, i suggest you get yourself at least one stepdown convertor, maybe a good idea to get one with two outlets, cause you might buy more US equipment in the future

[Big Kenny]

http://hyperphysics.phy-astr.gsu.edu.../opampvar.html

[dgatwood]

Originally Posted by Rodger Hartlett

you can get a good idea by checking out the smoothing capacitors in the power supply. for example if they are rated at 16volts you would know that the output of the rectifier bridge before it hits those caps would be within that voltage ( that's with the electronics loading it of course).

Of course, all you really know is that the voltage is less than the cap rating. If the cap is in a device that's small, heat becomes a factor, and even 35v caps can fail within two or three years in the presence of... oh... 12 volts. (This phenomenon is more commonly known as the "Graphite Airport Base Station Problem" or the "PC motherboard Capacitor Problem". Search for either of these sets of words in Google for fun.)

Originally Posted by Rodger Hartlett

also look for other signs like any voltage regulators? usuallyt they are 78XX meaning if it is 7809 then that's a positive 9 volt regulator or if it is 7909 that's a negative 9 volt regulator.7815 is positive 15 volts.zener diodes may also be an indicator for the split rail voltages.

Bear in mind, though, that it isn't uncommon to see a voltage divider prior to such a regulator. While those regulators typically can only handle from slightly under the rated voltage up to maybe half again more, it's not hard to build a voltage divider on the input to such a regulator that really screws up that assumption. If that happens, you'll have to read the color bands and do the voltage divider math.

Originally Posted by Rodger Hartlett

if there are no regulators or zeners all you really have to locate are any components that might fry or not handle too much voltage. these would be the electrolytic caps and semiconductors .
if the chips can handle +/- 16 volts then i would go for a twelve volt centre tap transformer . a nine volt is an even safer bet.keepng in mind nine volt AC will end up being around fifteen volts DC after the bridge and smoothing caps and no loading.

Odds are, the voltage of the secondary will be printed either on a label on the side of the transformer or on the paper coating around the windings. This is usually a much more reliable way of figuring out what the heck you're looking at.