Hi all:
i have an american tube amp, 110V, and here in chile we use 220/230V.
I currently power the amp through a 220/110 transformer, wich is heavy and noisy..i hate it..
I thought about rewinding the power transformer, but that can be expensive..
so i thought of this:
Putting a big diode in series with the AC line, so the AC voltage swings only half amplitude, getting aproximately 110V AC (swinging from 0.7V to 150V or so).. then put a big dc coupling cap , so the swing is +-75V (thats about 110V RMS)..
am i crazy and want to destroy my amp? or i ´ve got something here?
I don't have an answer for you, but your idea sounds like it probably won't work. Tube amps want lots of current, and that would have to be a huge capacitor to be able to supply that much current. Maybe about as big as your amp.
And I have the general impression that converting 220 to 110 is tricky business that requires either brute force (like your transformer) or lots of thought and trickery (like universal-input switching power supplies).
Seriously I think your best bet would be shopping for a new power transformer that fits your amp.
The AC still swings to 220 +/- on both ends of the transformer so a diode won't work but a bunch of high power zener doides end to end straight off the AC might work like you do on the centre tap of a trans secondary but they'd be big mothers. If you've got a 30W amp that'd be 270mA at 110V, given the amps 350VAC so a 25V zener dropping 270mA is about 7 watts so 10W zeners is what you'd want. If you needed two chains of zeners to earth off the neutral and active I'd think it might be a viable option to get a tranny wound even if it was a straight forward 220/110 at the voltage wattage rating you require.
You're not crazy - just unschooled in that part of transformer technology, and smart enough to ask first.
And it would likely destroy your amp unless you used a DC blocking cap that's as big, heavy, and much more costly than the transformer. All of the power for the amp has to go through the cap. Most caps are not rated for letting a lot of power through. You'd probably need motor-run rated caps which are rated for letting through lots of AC power, and they're heavy and expensive. If the cap fails, your amp's power transformer dies in fractions of a second.
I should have added more detail. A half wave rectified 240Vac is half-sines of 346V peak separated by flat spaces of equal width. The DC voltage level is the average of that, or 0.318 times the peak. The series cap blocks out that peak, but now the two unequal "halves" of the waveform go into your amp's transformer. The rectifiers on the secondary can only conduct on the half-sine peak because it's bigger, and now the unequal DC current pulses "walk" the voltage on the cap until equal current-time integrals flow on each half cycle, and this messes up the volt-time equality the primary needs. The transformer saturates a little bit to one side. That may or may not be fatal to the transformer over a longer period of time.
The 220-110 transformer you're using - is it an isolating transformer or an autotransformer? An autotransformer for a few hundred watts isnt' all that heavy. I suspect you're using an isolating 220-110. And if the transformer is really rated for 220 and you feed it 240, you may be getting the extra hum from saturating the primary of the autotransformer.
ohh thanks for your responses..
i have seen the diode trick used with soldering irons for half power, but with xformers is another story..
I simulatd the idea in LTC, and saw all of what R.G. said..the AC output of the diode is a 150Volts peak with valleys at 0 volts, but the wave is fairly assimetrical. of course, the RMS voltage is about 110V in amplidude, but with a DC component that would saturate the xformer´s core permanently (as RG said, it may kill the xfrmr)..
i tested a coupling capacitor, and with the equivalent load of a transformer, the cap would have to be humongus (like 50.000uF)..
so i´d better stick with my isolation transformer and brake my back everytime i move it (it´s a peavey triumph pag120, a really heavy amp)
Here is another possibility.
Here in the states, 110 vac is your standard household voltage. But there are appliances that need 220 vac to work properly. What they do is run two separate 110 lines to the electric panel (breaker box) and where needed run a 220 vac circuit by combining the two 110 lines (kind of). There is no ground on a household 220 circuit, although neutral and ground often share the same bussbar, you have 110, 110, and a neutral. But it is supplied as two separate 110 lines. More modern houses do have a ground with 220 circuits.
I have no idea, but maybe it is done in the same manner where you live. Check the incoming wires at your breaker panel and see. If so, its as simple as rinning a dedicated line where you want to plug in your amp.
Or you could even find out by checking your wall receptacles. Are they three prong? If so, with your dmm, put a test lead in the bottom receptacle hole and the other in either of the top holes, then the other top hole. If each reads 110 then just run off one of the 110 lines and neutral, and you do really need a ground for safety reasons.
Note that if you're not sure about what you're doing, sticking metal things in wall sockets is a quick and painful way to die.
Its worth checking the PSU inside the amp first as lots of amp designs these days have transformers that are capable of both 110/240. Its usually that the primary windings of the transformer are split. eg there is usually 2 primary windings that are wired in parallel for 110 volt operation, for 220/240 they are wired in series. So some equipment actually have wire links on the PCB to select which voltage you require. This saves manufacturing costs as the same PCB / components are used in both versions.
BUT be careful to check that this is possible as dealing with high voltages is dangerous. Also other components in the PSU circuit eg. caps might not be rated at the higher voltages.
If anyone else is able to explain this in more detail please do.
> An autotransformer for a few hundred watts isnt' all that heavy. I suspect you're using an isolating 220-110.
+1
first thing i did was check the transformer for a separate primary winding, but no, it´s only for 110V..
and jered..here we have 220V from the wall, with 3 wires, live, neutral and ground..
Alrighty then, scratch that idea. Good luck. Have you tried posting on an amp forum?
Daniel,
why is it noisy? ground loop? does it even has EARTH/GROUND conection for the AMP cable?
is not noisy..it just doesn´t have true ground
Quote from: earthtonesaudio on November 14, 2008, 02:50:20 PM
Note that if you're not sure about what you're doing, sticking metal things in wall sockets is a quick and painful way to die.
After months of tube amp building/work, I electrocuted myself for the first time three days ago.
The ironic thing is that I electrocuted myself plugging in my phone charger, I must have touched something by mistake. So after all the care I take with tube amps to not get electroed, I get shocked doing a mundane everyday activity. Great ;D
Lemme tell ya...If you've never gotten electrocuted before, don't do it. Its horrible :icon_eek:
Zach
i know, i´ve been shocked a couple of times and it sucks..thanks god never from power amp filtering caps..
Daniel, you've gotten shocked by 220 before? Pretty scary uh? I've only experienced 220 once and it was strong. Been shocked by 110 more times than I'd like to admit, but its not that bad. Instinct tells you to pull away and its done. Instinct does the same with 220,...but it doesn't want to let go! Thank god for circuit breakers. Took me a couple minutes to get my head clear, and a lesson learned I'll never forget.
Don't even want to think about filter caps, I ALWAYS discharge them.
you made a circuit breaker jump? wow.
once i touched the metal can of a cap of a running tube amp, and just felt a big púnch on the chest..it was a negative voltage filter, so the metal can was carrying the voltage..i was jumpy for like 5 minutes!!..it gets your adrenaline a boost..
from that day i allways put tape over the caps
Quote from: Jered on November 16, 2008, 08:38:39 AM
Been shocked by 110 more times than I'd like to admit, but its not that bad. Instinct tells you to pull away and its done.
Let me add a bit more caution to this. The reason it was "not that bad" was that you only made a high resistance connection to it. The amount of current needed to stop your heart is shockingly (sorry - I had to! :icon_biggrin:) small. Twenty milliamperes through the chest and you're history. Dry skin brushing against a smooth, dry metal surface can let through only enough to be bad.
If the skin isn't dry, metal has a sharp or rough surface to get past the dead skin layer, or you happen to be where your muscles contracting pulls you INTO the metal, not making you jump away, the current gets much bigger. The "instinct" you mention is your muscles firing from the electricity going through them, not from your nerves firing them. You have zero control of that, as it's not your nerves making the signals and your nerves can't cancel that out. If you happen to have grasped your hand around the charged metal and your other hand's or foot's response to the current is to press into the return path, there is nothing you can do. The current's going to hold you there and cook you. In this case, unless someone else can stop the current, you're dead.
A truly deadly situation happens on stage when a guitarist holds the grounded strings of a guitar with one hand and grabs a "grounded" microphone with the other. He (or she) is usually hot and sweaty, so the skin is wet and its resistance is low. The hands are folded around the metal objects. And if either the amp or the PA has a ground lift and a bit of AC leakage, it's all over. Or if a guitarist has a leaky amp and is standing on a wet grounded surface. Exactly these situations have happened. Dying at a workbench is also common, it just doesn't make the news.
There isn't any shock that is "not that bad". Except for static electricity zaps where the energy is low, they are mostly all potentially (sorry again) deadly.
The rhythm guitarist in my old band used a secondhand PA head for his amp, and the ground wire was cut on it. He had a habit of walking up to a person (like me) who was using a properly grounded amp, and grabbing their arm or guitar strings. Needless to say the band didn't go very far. :P
Some things you can do to help protect yourself from shock and/or electrocution are:
-Get and use an outlet tester and check all the outlets you will be using.
-If that's not possible, use a wireless system.
-Or, use a ground fault circuit interrupter on your gear.
-If that doesn't fit your style, use the "back of the hand" trick and slap every surface you might touch while playing. If you get shocked, your muscles will tense and pull your hand away, which is a lot better than grabbing on and not being able to let go. Plus the resistance of the back of your hand tends to be higher than your palms so the shock isn't as bad.
Why not try a variac?
Quote from: michael_krell on November 16, 2008, 12:32:03 PM
Why not try a variac?
A variac is a bigger, heavier, more flexible version of a 220-to-110 autotransformer.
kinda offtopic, but in one guitar, i took the wire that connects the bridge(and consequently the strings) from the circuit because of that potencial problem, though it ended up a bit noisier(the guitar)
is this a good way to prevent that or there is a better way?
Quote from: R.G. on November 16, 2008, 11:15:51 AM
Quote from: Jered on November 16, 2008, 08:38:39 AM
Been shocked by 110 more times than I'd like to admit, but its not that bad. Instinct tells you to pull away and its done.
Let me add a bit more caution to this. The reason it was "not that bad" was that you only made a high resistance connection to it. The amount of current needed to stop your heart is shockingly (sorry - I had to! :icon_biggrin:) small. Twenty milliamperes through the chest and you're history. Dry skin brushing against a smooth, dry metal surface can let through only enough to be bad.
If the skin isn't dry, metal has a sharp or rough surface to get past the dead skin layer, or you happen to be where your muscles contracting pulls you INTO the metal, not making you jump away, the current gets much bigger. The "instinct" you mention is your muscles firing from the electricity going through them, not from your nerves firing them. You have zero control of that, as it's not your nerves making the signals and your nerves can't cancel that out. If you happen to have grasped your hand around the charged metal and your other hand's or foot's response to the current is to press into the return path, there is nothing you can do. The current's going to hold you there and cook you. In this case, unless someone else can stop the current, you're dead.
A truly deadly situation happens on stage when a guitarist holds the grounded strings of a guitar with one hand and grabs a "grounded" microphone with the other. He (or she) is usually hot and sweaty, so the skin is wet and its resistance is low. The hands are folded around the metal objects. And if either the amp or the PA has a ground lift and a bit of AC leakage, it's all over. Or if a guitarist has a leaky amp and is standing on a wet grounded surface. Exactly these situations have happened. Dying at a workbench is also common, it just doesn't make the news.
There isn't any shock that is "not that bad". Except for static electricity zaps where the energy is low, they are mostly all potentially (sorry again) deadly.
I've never been connected with both hands, usually just a brush against a wire in a junction box with the 110. The 220 I was wrapping the wire with electrical tape and my finger found a nick in the wire insulation. It something I'll never forget.
Our heart monitors on the ambulance have a feature that allows you to electrically pace a slow heart. You take two sticky pads and place one on the front of the chest and one on the back. You then set the monitor to pulse electricity through the pads at a set rate, which passes the current through the heart. It's kind of neat, you start with the current at 10ma and slowly increase it until it "captures", that is the heart starts to beat from the current being passed through it. I'm not sure what voltage it operates at, but most hearts capture at around 70-80ma. We try to sedate people first, but it is definitely something that people complain about when not sedated! You can watch the pectoral muscles twitch every time it fires.
The other measure of electricity we use is joules- people are defibrillated at 360 joules, but abnormally fast beats are shocked with as little as 50 joules. You get a zap of either monophasic or biphasic energy across the heart to (hopefully) reset the heart's internal pacemaker to a regular beat. Unfortunately for us electronics hobbyists it also works in reverse- a good zap can send the heart into a potentially fatal rhythm- too fast or too slow in one section or another of the heart.
The closest thing you can convert joules to is foot pounds, and 360 joules = 265 foot pounds, which is why the first step in a witnessed cardiac arrest was to literally pound someone with a closed fist in the center of the chest (precordial thump). It was supposed to perform a similar function to the electricity. Thankfully we don't do that anymore, it does seem a bit barbaric but was standard practice up until a few years ago. This was only if there was not a defibrillator handy. I bet that there's some footage of this on youtube, someone needs to do a search.
I really enjoyed learning about all that stuff in paramedic school... imagine my excitement when i realized that a heart monitor was basically an oscilloscope!
Sorry Daniel, didn't mean to hi-jack your thread. My bad.
Quote from: Jered on November 18, 2008, 07:13:44 PM
Sorry Daniel, didn't mean to hi-jack your thread. My bad.
by no means be sorry..this thread has become incredibly useful and interesting!!!!!!!
that defribrilator post was just what i like to read on the forum..knowledge is knowledge...
I can't believe I'm reading this stuff.
It's like we are living in third world countries.
Like the man said:
Quoteuse a ground fault circuit interrupter on your gear
One day the power went out while I was playing. Thinking that I'd blown the output valves (again) I went to make a cup of coffee. There in the kitchen were my kids (aged about 8 and 13) with a metal knife, trying to extract some toast from the toaster.
Are you or your kids worth $20?
Ground fault/earth leakage devices are the best, cheapest investment you'll ever make (equal to smoke detectors).
For those that already know this, apologies for the lecture. For the rest, your choice is to learn the easy way or learn the hard way.
Quote from: brett on November 18, 2008, 10:50:17 PM
Ground fault/earth leakage devices are the best, cheapest investment you'll ever make (equal to smoke detectors).
Please use carbon monoxide alarms too, trust me, they are worth it.
Zach
Quote from: brett on November 18, 2008, 10:50:17 PM
I can't believe I'm reading this stuff.
It's like we are living in third world countries.
Like the man said:
Quoteuse a ground fault circuit interrupter on your gear
One day the power went out while I was playing. Thinking that I'd blown the output valves (again) I went to make a cup of coffee. There in the kitchen were my kids (aged about 8 and 13) with a metal knife, trying to extract some toast from the toaster.
Are you or your kids worth $20?
Ground fault/earth leakage devices are the best, cheapest investment you'll ever make (equal to smoke detectors).
For those that already know this, apologies for the lecture. For the rest, your choice is to learn the easy way or learn the hard way.
Here in CA its the law that any receptacle within 8 ft of a water source has to be GFCI protected. Most people don't bother with it until they try to sell the house. Older houses can be a bitch because there is no ground except cold water pipes. Houses built in the 70's sometimes have aluminum wiring. Another nightmare if you want to sell your house.
What´s a GFCI? never heard of them....
Ground Fault Current Interruptor.
An outlet or breaker which looks for either the presence of current on the safety ground wire or a difference in current between the line and neutral wires. In either case, there is current in the circuit which goes in through the line wire and out by either the ground wire or simply leaks out of the circuit. Both are conditions in which the leak could be through a human chest, and so the monitor circuit opens the circuit within milliseconds to protect the hypothetical human.
All hair dryers are equipped with these nowadays, for example.
The problem with a variac is that it is 1. expensive, and 2. gives you (or someone else) the opportunity to set it to any voltage - including a lot of wrong ones!