| JhonDoe |
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?
:xeye: |
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| peranders |
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. |
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| joan2 |
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 |
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| JhonDoe |
| In my case i got 10 ampere dual secondary (2x25-0-25) trafo, is this enough for a sigle channel? |
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| joan2 |
| quote: | Originally posted by JhonDoe
In my case i got 10 ampere dual secondary (2x25-0-25) trafo, is this enough for a sigle channel? |
yes, it should work... |
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| Matttcattt |
| quote: | Originally posted by peranders
In your case I'll believe 150-300 VA is normal if you are going to use the amp at home. |
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! |
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| joan2 |
| quote: | Originally posted by Matttcattt
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! |
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... |
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| JojoD818 |
JohnDoe,
from angeles city? i see your interested in building gainclones now JohnDoe. Good luck. |
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| Easyamp |
| quote: | | 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! |
500ma into even an 8 ohm load is only 2 watts peak how can you run a sub with only 2 watts? I*R=V which is 4v V*I=P which 2 watts. Also 25v dual secondary gives a static (no load) voltage of 35v per rail. rms math, 25v*1.41 =35v
but if that's all you GC need's then 60va is plenty. |
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| Jocko Homo |
But larger transformers sound better..........as they operate further from saturation.
Jocko |
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| JhonDoe |
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?
| quote: | | from angeles city? i see your interested in building gainclones now JohnDoe. Good luck. |
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? |
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| joan2 |
| quote: | Originally posted by Jocko Homo
But larger transformers sound better..........as they operate further from saturation.
Jocko |
runs cooler too!!
tony |
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| joan2 |
| quote: | Originally posted by JhonDoe
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? |
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 |
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| Matttcattt |
| quote: | Originally posted by Easyamp
500ma into even an 8 ohm load is only 2 watts peak how can you run a sub with only 2 watts? I*R=V which is 4v V*I=P which 2 watts. Also 25v dual secondary gives a static (no load) voltage of 35v per rail. rms math, 25v*1.41 =35v
but if that's all you GC need's then 60va is plenty. |
Well, thats how much it draws. It could be limited by my bench power supply I suppose... |
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| JojoD818 |
| quote: | Originally posted by JhonDoe
What 'bout you JojoD818? were u from? |
I'm from Valenzuela City. Malinta exit from NLEX. |
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| joan2 |
| quote: | Originally posted by Matttcattt
Well, thats how much it draws. It could be limited by my bench power supply I suppose... |
this just goes to show that our listening levels average in the 2watt or so levels.... |
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| Matttcattt |
| quote: | Originally posted by joan2
this just goes to show that our listening levels average in the 2watt or so levels.... |
Well, this was at full volume and my sub (Eminence Beta 15 (350W)) bottomed out with a 40Hz sine wave. :cool:
Not that that means much, but I was told the design would output 100W+ into eight ohms.
I dunno, its loud enough for my liking. :D |
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| joan2 |
| quote: | | Well, this was at full volume and my sub (Eminence Beta 15 (350W)) bottomed out with a 40Hz sine wave. |
if you mean you tested your woofer with a sine wave, then this is no surprise, energy content of sine waves is much more than music signals...
even if your woofer was rated at 350w it could still be damaged with a 2watt sine wave input... |
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| Easyamp |
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 |
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| JhonDoe |
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. |
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| Easyamp |
You want's some opa541?? I've got em, I have 2 for whoever wants them. They were samples from awhile ago.
first 2 reply get's them. |
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| JhonDoe |
| quote: | Originally posted by Easyamp
You want's some opa541?? I've got em, I have 2 for whoever wants them. They were samples from awhile ago.
first 2 reply get's them. |
If u can send it here in the philippines,, why not...
Ti's doen't have a stock for opa541 and 549...I'm still waiting for my order(sample) since last month.... |
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| Easyamp |
I'll send them But I ask that you pay for the shipping. If interested email me your address to support@easyamp.com and I'll give you a shipping cost.
Cheers, |
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| Steven |
| quote: | Originally posted by Jocko Homo
But larger transformers sound better..........as they operate further from saturation.
Jocko |
Do they? I mean, maybe they sound better but do they operate further from saturation? As far as I know saturation and maximum flux is determined by the primary voltage (higher voltage, more flux) and frequency (lower frequency, more flux) and not by secondary current. Even a small transformer can supply a lot of power, but only for a short moment because of overheating, not because of supposed saturation.
Steven |
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| Christer |
| quote: | Originally posted by Steven
Do they? I mean, maybe they sound better but do they operate further from saturation? As far as I know saturation and maximum flux is determined by the primary voltage (higher voltage, more flux) and frequency (lower frequency, more flux) and not by secondary current. Even a small transformer can supply a lot of power, but only for a short moment because of overheating, not because of supposed saturation.
Steven |
I don't know the magnetics well enough to judge, but Kuei
has suggested an alternative solution which is in line with
your reasoning. Use two transformers instead of one and
connect their primaries in series, thus underrating them.
You also need to connect the secondaries in series two and
two, or choose transformer with a different rated secondary
voltage. |
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| Matttcattt |
| quote: | Originally posted by joan2
if you mean you tested your woofer with a sine wave, then this is no surprise, energy content of sine waves is much more than music signals...
even if your woofer was rated at 350w it could still be damaged with a 2watt sine wave input... |
I understand this, and thats why I said that it didnt mean much.
| quote: | Originally posted by Easyamp
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. |
I am currently powering the amp with my bench power supply (2x 0-30v 1A) and it has ameters on each output. they both read about 500mA.
I havent tried the resistor/ohms law method yet. |
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| joan2 |
| these are traffos handmade by me, smallest at 15va, biggest is 3000va... |
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| JhonDoe |
| quote: | Originally posted by joan2
these are traffos handmade by me, smallest at 15va, biggest is 3000va... |
Hey Bro.. nice trafo! can u send me the big one? hehehe...
How much the maximum current rating for that trafo(the big one)?
Are you going to sell that? if yes, for how much? |
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| joan2 |
hi,
the BIG one is intended for a leach amp that can do 1000watt per channel at 2ohms...it weighs in at around 25kilos...
specs are:
1. primary 220volts
2. secondaries: main= > 120volts center tapped, auxilliary windings, 140volts center tapped at 1amp, 12 volts at 2 amps
the one beside it with a copper banding is suitable for a bridged gain clone and can power up to 6 chips....i can sell that to you if you need it.....
or i can make one custum wound to your specs...
all my traffos have secondary windings that are bifilliar wound, i know of no other winder in manila doing biffiliar secondary windings besides me.... |
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| JojoD818 |
Tony,
Good luck with those trafos, you'll need a gorilla to move your gear around the house with that size. :bigeyes:
Johndoe,
You can use wahtever resistors you have, just match them with a good DMM and your off. This is audio electronics, not rocket science. ;)
JojoD |
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| JhonDoe |
| quote: | the one beside it with a copper banding is suitable for a bridged gain clone and can power up to 6 chips....i can sell that to you if you need it.....
or i can make one custum wound to your specs...
all my traffos have secondary windings that are bifilliar wound, i know of no other winder in manila doing biffiliar secondary windings besides me....
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How much did it cost for a-- let say, 20 ampere dual secondary(25-0-25)? and what are bifilliar wound?
| quote: |
You can use wahtever resistors you have, just match them with a good DMM and your off. This is audio electronics, not rocket science.
JojoD |
The problem, I dont have a DMM.. is there another way to match resistors w/ just an analog testers?
Ok guys! JojoD and Joan2, just another question..
What are u using for desining your PCB? I mean for Foil pattern of a PCB. I got a hard time eching a PCB, actually i used to print that pattern in a blank(white)sticker in a laser printer and stick it on the PCB and slice it using blade cutter. pls help me guys... tnx.. |
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| joan2 |
hi,
tell me hopw many chips you want to use for your amp, as a rule of thumb each lm3886 will use a 70va traffo....so depending on how many chips you'll use for your amp, i can design a taffo for that.....
masking tapes can also be used for cutting out the traces on your pcb prior to etching, i use that method for single runs, silkscreen for multiple runs....
another option would be poin-to-point wiring which does not use pcb's, you can find lots of examples here, specially those done by peter deniels.... |
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| Nisbeth |
| quote: | Originally posted by Easyamp
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 |
The standard for power measurements are to use bandwidth-limited pink noise as a test signal, but a music signal has a much lower energy content than that, typically only 1/8th. Unless you drive your amplifiers into heavy clipping, rating the supply for 1/8th of the max. current draw (Output power/efficiency) is OK. Professional amps will have beefier PSUs, typically up to 1/3rd of max. current draw to cope with clipped signals and continuous loads.
That said, you can get considerable sonic benefits from upgrading the PSU, but from a purely technical point of view it's not necessary to deliver full power into the speaker.
/U.
EDIT: See www.ub.utwente.nl/webdocs/el/1/t000000d.pdf (chapter 2) for more information. |
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| JhonDoe |
| quote: | | tell me hopw many chips you want to use for your amp, as a rule of thumb each lm3886 will use a 70va traffo....so depending on how many chips you'll use for your amp, i can design a taffo for that..... |
I'm planing to build Bridge/parallel configuration, maybe 3 or 4 chips per side and i will use that trafo for stereo setup(12-16 chips all).
But before that, i wanna know how much it will cost? If u can give me a resonable price (presyong kaibigan) and if i got enogh budget i will take it...
I just saw u're profile, are u really a computer technician? do u own your own shop? |
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| joan2 |
| quote: | Originally posted by JhonDoe
I'm planing to build Bridge/parallel configuration, maybe 3 or 4 chips per side and i will use that trafo for stereo setup(12-16 chips all).
But before that, i wanna know how much it will cost? If u can give me a resonable price (presyong kaibigan) and if i got enogh budget i will take it...
I just saw u're profile, are u really a computer technician? do u own your own shop? |
i have one such traffo with me now, it is rated for about 700va, please email mo so i can give the cost and other details to contact me....i am ashamed to discuss money matters here....
actually, i am an OFW electrical engineer doing construction work for oil and gas refineries, last time i was working for Chiyoda Corporation, a japanese construction firm...last station was in singapore's jurong island projects, smp, teijin, and exxon....
i am a computer technician as hobby also, including audio....
tony |
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| JhonDoe |
| quote: | Originally posted by joan2
i have one such traffo with me now, it is rated for about 700va, please email mo so i can give the cost and other details to contact me....i am ashamed to discuss money matters here....
|
here... armagedon_auf@yahoo.com
QUOTE]Originally posted by joan2
i am a computer technician as hobby also, including audio....
tony [/QUOTE]
well.. we are in the same field, i'm working as a computer Technician in one of University here in Angeles city.... |
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| joan2 |
hi,
we used to get traffo irons from angeles and dau, ex-clark air bases, with the americans out of there, are there still irons that can be bought from your end, i am interested on grain oriented steel, the ones with stipes on the core?
jojo als gets his jan type 9pin tube sockets there, you know where we can buy this stuff from your end?
you can call me at home anytime, i have my shop in the house so i am home most of the day and specially at nights...
tony |
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| joan2 |
hi'
you got mail!!!! |
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| JojoD818 |
| Maybe we should have those military bases back here! I miss my friends V-8 Camaro, whose parts are only available in Dau. :D Straight from Clark Air Force Base. |
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| JhonDoe |
| quote: | | i have one such traffo with me now, it is rated for about 700va, please email mo so i can give the cost and other details to contact me....i am ashamed to discuss money matters here.... |
hi,
Tony can u send me a pic of that trafo? and also give me the actual mesurements.
The price u gave me is higher than i expected, but performance is my main concern you know what i mean..
what about the delivery cost? i mean is it included in u're price?
I'm asking this because i have a pal here in angeles making and costomizing trafo. the price is cheap but the problem is i'm not satisfy w/ his work.. |
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| joan2 |
hi,
core is 1 1/2 in stacked to 3inches depth....weighs approx 8kg...
no load voltages are:
1. 54 volts center tapped @ 12amps
2. 2x 12 volts @ 2amps
with cover shells and painted flat black..
secondaries are bifilliar wound, voltage readings from either ends from the center tap are exactly the same.....
i can deliver the traffo to your city, angeles...gusto ko ring makarating dyan!!!
tony |
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| JojoD818 |
Deliver and then clubbing... hhmmm. :D
Angeles City is soooo cool! :hot: especially at night. |
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| joan2 |
besides i have long wanted to go to AMERTRON inside clark airbase, my kumare is working there, time i paid her a visit...
johndoe,
i can even make you one that is bigger than that.... |
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| JojoD818 |
| quote: | Originally posted by joan2
besides i have long wanted to go to AMERTRON inside clark airbase, my kumare is working there, time i paid her a visit...
johndoe,
i can even make you one that is bigger than that.... |
:dead:
Hahahaha. |
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| JhonDoe |
| quote: | Originally posted by joan2
hi,
core is 1 1/2 in stacked to 3inches depth....weighs approx 8kg...
no load voltages are:
1. 54 volts center tapped @ 12amps
2. 2x 12 volts @ 2amps
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Is it capable for driving stereo amp?
| quote: | Originally posted by joan2
i can deliver the traffo to your city, angeles...gusto ko ring makarating dyan!!!
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Not now tony, masyadong maraming trabaho ngayon dito sa university, preparing for opening classes next week. we need to prepare all the computers in the laboratory(300+ computers).
can u wait till next month?
| quote: | Originally posted by JojoD818
Deliver and then clubbing... hhmmm. :D
Angeles City is soooo cool! :hot: especially at night. |
ye! tha't a good idea!! hehehhe
| quote: | Originally posted by joan2
johndoe,
i can even make you one that is bigger than that.... |
Bigger??? same price??hehehe |
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| joan2 |
hi,
i have another option for you, i can go to your place, and i can teach your rewinder how to make traffos like i do....
this should lower your costs substantialy, you only have to pay for may passage....
tony |
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