Hello..
Sorry for this stupid question.. I'm just a newbie in electronics my questions are:
In my country when i buy a transformer i can only get an EI laminated tranformer and the only rating i know about the trafo is their current rating.
Can someone explain to me the equivalent rating between Current and the VA value of a transformer?
I have plans to build a gainclone, a Bridge parallel of OPA541/549(2 chips per sides) for 1 channel. What sould be the VA/Current rating of the trafo?
Sorry for this stupid question.. I'm just a newbie in electronics my questions are:
In my country when i buy a transformer i can only get an EI laminated tranformer and the only rating i know about the trafo is their current rating.
Can someone explain to me the equivalent rating between Current and the VA value of a transformer?
I have plans to build a gainclone, a Bridge parallel of OPA541/549(2 chips per sides) for 1 channel. What sould be the VA/Current rating of the trafo?
VA rating is (V*V)/R at the secondary side.
The current is V/R this is valid for RESISTIVE load.
If you rectify and add smoothing caps the VA rating will drop. If you have a huge cap battery the VA will drop to half but as an average value the VA or DC watt out will be 0.9-0.7 of the VA of the transformer.
100VA => 90-70 watts DC continuously
100 VA + 100 000 uF => 50 watts or so out
The VA rating is also dependent how you plan to use the amp. It's only about the temperature inside the transformer. When you have reached 105 deg C inside a toroid transformer you have reached the max VA out take.
In your case I'll believe 150-300 VA is normal if you are going to use the amp at home.
The current is V/R this is valid for RESISTIVE load.
If you rectify and add smoothing caps the VA rating will drop. If you have a huge cap battery the VA will drop to half but as an average value the VA or DC watt out will be 0.9-0.7 of the VA of the transformer.
100VA => 90-70 watts DC continuously
100 VA + 100 000 uF => 50 watts or so out
The VA rating is also dependent how you plan to use the amp. It's only about the temperature inside the transformer. When you have reached 105 deg C inside a toroid transformer you have reached the max VA out take.
In your case I'll believe 150-300 VA is normal if you are going to use the amp at home.
hi,
i know what you mean, the current rating as stated on the traffo has no meaning to me....
for gainclones, you can use 12-0-12 or 24-0-24 traffos, like those off deeco in raon...you can choose one that used a 1 1/4 in center leg....
for a bridged type gainclone, you can use two traffos, 12-0-12 and bridge rectify them to have separate plus and minus 35vdc rails....
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30760&perpage=15&pagenumber=5
tony
i know what you mean, the current rating as stated on the traffo has no meaning to me....
for gainclones, you can use 12-0-12 or 24-0-24 traffos, like those off deeco in raon...you can choose one that used a 1 1/4 in center leg....
for a bridged type gainclone, you can use two traffos, 12-0-12 and bridge rectify them to have separate plus and minus 35vdc rails....
http://www.diyaudio.com/forums/showthread.php?s=&threadid=30760&perpage=15&pagenumber=5
tony
peranders said:
Why does everyone state such huge ratings for the transformers for use with gainclones? My subwoofer amplifier (gainclone) takes about 500mA at full volume, including the cooling fans, so I am using a 60VA transformer (25v dual secondary) which should give me +/-30v @ 1A, which is ample. For the circuit I am using (bridge + parrallel I) was advised to use a 300-500VA transformer!
Matttcattt said:
please note that in my country, traffos are overrated, i do not know what standards are being followed if at all....
therefore, even if they state 10 amps secondary, it could very well be just the same as your 60va traffo...
of course you can always get away with lower rated traffos, that's your call...
Thanks for info Joan2!!
since raon(Manila) is 3 to 4 hours away from Angeles city I cant find time to go there. Is there any toroind trafo here in our country? by the way, were you in manila?
Yes, i'd already finish 4 mono of them(2-OPA541 one inverted and one non-inverted)and(2-OPA549 one inverted and one non-inverted) last 2 months, only 2 of them are connected in my bench PS the 2 inverted(1-541 and 549 for the other)
What 'bout you JojoD818? were u from?
since raon(Manila) is 3 to 4 hours away from Angeles city I cant find time to go there. Is there any toroind trafo here in our country? by the way, were you in manila?
Yes, i'd already finish 4 mono of them(2-OPA541 one inverted and one non-inverted)and(2-OPA549 one inverted and one non-inverted) last 2 months, only 2 of them are connected in my bench PS the 2 inverted(1-541 and 549 for the other)
What 'bout you JojoD818? were u from?
JhonDoe said:
i'm from pasig city....unfortunately i don't know any torroids in manila except those from discarded japanese amps, i am working on one...last time i made a torroid was in early 90's which i used for a leach amp....
believe me, you will miss nothing from not having a torroid except perhaps its small outline as compared to an ei of same va rating...
i have built lot's of amps using ei's that are stone quiet rvrn eith volume controls turned all the way up....
tony
I'm not sure what to say, either I'm missing something or you guys are pulling my leg.
Even giving that most dmm's measure rms and not peak of the sine you would still only gain 1.41 times 2 watts which is the peak of the sine wave.
If you pump a 2 watt 40hz sine wave into a speaker that is rated at 350w (rms or peak not real important here considering the safety margin) and the speaker bottomed then either the speaker is rated for less then 2 watts or something’s a miss in the measuring.
The before stated .5A peak current load was the rail current not the output current and if this is a standard class AB GC then this .5a figure doesn't translate to output directly. The output depends on the efficiency of the amp, which is not 100% so the output will be less then supply. I've seen figures for some class A amps efficiency of less then 10%(output level dependent), I'm not real sure about AB GC's.
I’m curious how you are measuring the current load of your amp this could be the misleading point.
You said before you are running a mixed bridge parallel configuration, are you measuring in front of one of the chips or right after the bridge and filter caps, or the ac going into the bridge/caps? If you are using a dmm check that it will measure other then 60hz ac current if measuring after trnsfo I've had this problem before.
I stick a low value power resistor in line with one of the rails (.22 ohm or something) and measure the voltage drop and use ohms law to find current if I'm curious about the current load.
Also I'm curious of the voltage drop across a .22 ohm in line with the speaker at full volume, should be around a few volts if bottoming a 350w speaker.
You can make a lot of power from mixed bridge parallel GC's setup and I wouldn't be surprised if you bottomed out a driver but not with 500ma.
Cheers
Even giving that most dmm's measure rms and not peak of the sine you would still only gain 1.41 times 2 watts which is the peak of the sine wave.
If you pump a 2 watt 40hz sine wave into a speaker that is rated at 350w (rms or peak not real important here considering the safety margin) and the speaker bottomed then either the speaker is rated for less then 2 watts or something’s a miss in the measuring.
The before stated .5A peak current load was the rail current not the output current and if this is a standard class AB GC then this .5a figure doesn't translate to output directly. The output depends on the efficiency of the amp, which is not 100% so the output will be less then supply. I've seen figures for some class A amps efficiency of less then 10%(output level dependent), I'm not real sure about AB GC's.
I’m curious how you are measuring the current load of your amp this could be the misleading point.
You said before you are running a mixed bridge parallel configuration, are you measuring in front of one of the chips or right after the bridge and filter caps, or the ac going into the bridge/caps? If you are using a dmm check that it will measure other then 60hz ac current if measuring after trnsfo I've had this problem before.
I stick a low value power resistor in line with one of the rails (.22 ohm or something) and measure the voltage drop and use ohms law to find current if I'm curious about the current load.
Also I'm curious of the voltage drop across a .22 ohm in line with the speaker at full volume, should be around a few volts if bottoming a 350w speaker.
You can make a lot of power from mixed bridge parallel GC's setup and I wouldn't be surprised if you bottomed out a driver but not with 500ma.
Cheers
Hey Jojod818!!
Bro. I saw u're Parallel/bridge set-up in your website, got some questions!, did u use .1% or 1% res or special component for that set-up? how did u manage to match the output?
I'm planing to use opa541 in inverted setup(parallel/bridge) do u think this will work? what will be the maximum output power for this set-up?
Money and time for me is to tigh, gathering an info and safty measures before building it is my fist concern.
one more thing, can i use 5% resistor? i cannot find .1% not even 1% resistor anywhere in angeles city.
Bro. I saw u're Parallel/bridge set-up in your website, got some questions!, did u use .1% or 1% res or special component for that set-up? how did u manage to match the output?
I'm planing to use opa541 in inverted setup(parallel/bridge) do u think this will work? what will be the maximum output power for this set-up?
Money and time for me is to tigh, gathering an info and safty measures before building it is my fist concern.
one more thing, can i use 5% resistor? i cannot find .1% not even 1% resistor anywhere in angeles city.
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