S.C.
That transformer is way too big for your application if you know your speaker's impedence curve dips not too much lower than 7 ohms and the phase angle is negligable. Dorkus has pointed you in the right direction. Go with two small 80VA-120VA transformers with 40-0-40 taps. You'll save money and have a better sounding amp.
That transformer is way too big for your application if you know your speaker's impedence curve dips not too much lower than 7 ohms and the phase angle is negligable. Dorkus has pointed you in the right direction. Go with two small 80VA-120VA transformers with 40-0-40 taps. You'll save money and have a better sounding amp.
dorkus said:
Actually when using primaries in series with 115V you also reduce the power rating of transformer (I don't know by what factor, but you may expect even 50% less power). The reason for that is that because voltage drops by half, the gauge of secondaries wire stays the same and with that lower voltage the wire can't supply twice the current since the gauge is too small. I know it from Plitron tech dept.
yldouright said:
why such small transformers? i am under the impression that larger transformers perform better (lower impedance, more linear). also, i am not sure two 120VA transformers will necessarily be better than one 240VA transformer. i used to think so, but after reading some of the transformer and gainclone threads and thinking about it some more i'm having my doubts...
i think if you go with a 330VA 25-25 that someone else suggested, you can not go wrong.
Peter Daniel, Dorkus
Let's clarify. Two 80VA 20V transformers, one per channel or two 160VA 40-0-40 in series for the impedence load described. A larger transformer can create HF noise in the supply cap from the high inrush current. My earlier comments about the nature of the LM chips should have explained the reason why 80VA is not small for a high impedence load but if you have information to the contrary, put it forward.
Let's clarify. Two 80VA 20V transformers, one per channel or two 160VA 40-0-40 in series for the impedence load described. A larger transformer can create HF noise in the supply cap from the high inrush current. My earlier comments about the nature of the LM chips should have explained the reason why 80VA is not small for a high impedence load but if you have information to the contrary, put it forward.
I believe there might be advantages in using bigger than required transformer for PS. Itmay also be the case that too big transformer is worse than a smaller one, but who's gonna find the right one? I just read review of Naim top preamp and it appears that they use 800VA transformer there. Also this thread may provide some interesting info: http://www.diyaudio.com/forums/showthread.php?s=&threadid=16486&highlight=transformer
2-12Vdc 650 amp/hr batteries , optima gel cells, as stated they never run out of power and i charge once a week overnight with dual chargers, the sound is very clean with very defined bass and clear highs , the only caps are on the P/S pins are 6.8uf and a 1uf between the pins which i found out gives a cleaner HF response at increased volume.
ron
ron
Peter Daniel
I did qualify my statements earlier by stating the guidelines I presented for transformers were for the LM chip type inverted gainclones. There may be other chips that structure their internal design to accomodate a beefier power supply. Do you know any of the specifics of that Naim preamp? Is it discrete or chip output? Class A, A/B? Does it use a coil to quiet that big transformer? There are lots of reasons to do stuff and they aren't always based on what sounds best. Naim could be using those transformers because they were cheaper than one manufactured per order.
I did qualify my statements earlier by stating the guidelines I presented for transformers were for the LM chip type inverted gainclones. There may be other chips that structure their internal design to accomodate a beefier power supply. Do you know any of the specifics of that Naim preamp? Is it discrete or chip output? Class A, A/B? Does it use a coil to quiet that big transformer? There are lots of reasons to do stuff and they aren't always based on what sounds best. Naim could be using those transformers because they were cheaper than one manufactured per order.
the term "regulation" as applied to transformers, is not the same meaning strictly as that for an lm7815 regulator, so there is realy no comparison...
regulation in transformers is simply the percentage of the difference between no-load to full-load over no load voltage, pretty much textbook stuff...lower values of course being always preffered....
I just like to select a transformer of as large as possible VA rating for two purposes:
- to have big enough to cover the draw of the circuit current.
- to pursuit probable transformer of low resistive and reactive components and so low voltage regulation of the transformer.[/list=1]Of course, if the sound is improved as an side effect, I welcome it.
Is my thinking wrong?
Noob confused
If 240VAC to 115VAC transformer will burn, then how come a 80VAC transformer? or just a 160VAC transformer/2 ? I don't get it, how 800VAC transformer work, if we don't even have more than 240VAC out off the wall? Even if the transformer divided by half it only be able to supply a little more than half of the rating. I am so. Damn, I need to study my physic again.
P.S can anyone answer my Current question, How can I determine how much current I need? Don't you guys pick a transformer by Watt too?
If 240VAC to 115VAC transformer will burn, then how come a 80VAC transformer? or just a 160VAC transformer/2 ? I don't get it, how 800VAC transformer work, if we don't even have more than 240VAC out off the wall? Even if the transformer divided by half it only be able to supply a little more than half of the rating. I am so
. Damn, I need to study my physic again.P.S can anyone answer my Current question, How can I determine how much current I need? Don't you guys pick a transformer by Watt too?
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=129-030&ctab=2
What do you guys think about this? Will this perfectly suit my situtation?
What do you guys think about this? Will this perfectly suit my situtation?
S.C. you are getting confused here!
A transformer may have a 240 VAC rating which menas that it operates from a mains supply of 240 volts AC.
The VA rating of a transformer is calculated from the secondary voltage it supplies multiplied by the current it can supply.
So as regards the current rating that you require, you need to know the VA rating, not the VAC. If you read the threads on this subject, you will see that a 'safe' choice is between 160VA and 250VA per channel.
So, as you are in the US, you need a transformer running off 120VAC and with a rating of 160VA-250VA if it is used for one channel, or 300VA-500VA if it is used to supply both channels.
If you want to know the current that a transformer supplies, simply divide the VA figure by the secondary voltage. If there are twin secondary windings, this figure must be divided by two.
S.C.
Nuuk has pinpointed the problem of your confusion adequately but for all your confusion, the transformer you linked would be ideal for the inverted gainclone and you only need one. The 5A it will provide is ten times what you'll need for the impedence load you wish to drive even under the worst conditions
jh6you
Nuuk has pinpointed the problem of your confusion adequately but for all your confusion, the transformer you linked would be ideal for the inverted gainclone and you only need one. The 5A it will provide is ten times what you'll need for the impedence load you wish to drive even under the worst conditions
jh6you
The short answer to this question is yes. Read up earlier in this thread to see why.
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