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haven't tried, but methinks 200VA per channel is plenty.
i reviewed a commercial gainclone using LM1875 and 75VA per channel, and it was clearly in need of more juice, but the sound was servicable. with more than twice the VA and a LM3875 it should sound quite good. whether dual mono 200VA transformers sound better or worse than a single 400VA transformer i'm not sure of, but since Peter settled on the latter it can't be all that bad.
i reviewed a commercial gainclone using LM1875 and 75VA per channel, and it was clearly in need of more juice, but the sound was servicable. with more than twice the VA and a LM3875 it should sound quite good. whether dual mono 200VA transformers sound better or worse than a single 400VA transformer i'm not sure of, but since Peter settled on the latter it can't be all that bad.
If you use a single transformer with dual secondaries (like all the toroids I've come across) then using two seperate transformers will be alot more money for a gain in performance that I can't detect (I've tried and I noticed no difference, maybe if you use a single winding to power two channels it would be noticable). Also if using a winding per channel I'm guessing you'd get better matching between the suply voltages, using two different transformers might have slightly different voltages.
I am looking at the 25v+25v 330 VA toroidal at Parts Express. Will that drive me for two channels? If so, that would be great, as it helps to get me down to two sources (Parts Express and Digikey) for the guts. Still shopping Ebay for a funky enclosure, tho.
Thanks,
GnD
link: http://www.partsexpress.com/pe/show...St3=-60351621&DS_ID=3&Product_ID=123268&DID=7
Thanks,
GnD
link: http://www.partsexpress.com/pe/show...St3=-60351621&DS_ID=3&Product_ID=123268&DID=7
Hi,
No way you can do calculations like that...a 500VA xformer can draw/deliver 500W...but it won't with the gainclone.
The thing is, with a well designed xformer the spare power allows the xformer to regulate the supply to some extend.
The power rating of the amp will utimately depend on the powerdevices in use and their bias.
Cheers,
No way you can do calculations like that...a 500VA xformer can draw/deliver 500W...but it won't with the gainclone.
The thing is, with a well designed xformer the spare power allows the xformer to regulate the supply to some extend.
The power rating of the amp will utimately depend on the powerdevices in use and their bias.
Cheers,
GrahamnDodder said:
You could read http://www.passdiy.com/projects/zenv5-8.htm about the power transformer rating: ¡°The power transformer will need to have the voltage and current rating appropriate to the draw of the circuit. In general, you should use a transformer whose VA rating is more than twice that of the circuit draw.¡±
Bricolo said:
In addition to your question, If I read an advertisement:
“This new model-S amp is 50W+50W (A/B class). Its power is lower than the model-F of 100W+100W (A/B class). But, this new model-S has the same size of transformer used for the model-F and so it reinforces the earthquake base sound.”
Is this convincing argument about the big transformer?
Regulation... Narrrh..!
Hi folks,
Couldn't keep my nose out of this thread
One said that the bigger xformers give better regulation.
Nope, the xformer doesn't regulate (that would require active controlling circuit (like a 7815 voltage regulator does it)).
What matters is its output impedance.
It's as simple as that. A lower output impedance (bigger xformer, other factors like type, materials etc. kept the same) will have less voltage drop as the power amp draws current.
Instantaniously the current comes from the capacitor(s), but they can't do it alone, and the energy needed to re-charge them after a current surge can only come from one place. The Xformer!
Therefore the overall voltage drop will be limited as the xformer VA rating increases.
Easy, isn't it?
see ya'
Jennice
Hi folks,
Couldn't keep my nose out of this thread
One said that the bigger xformers give better regulation.
Nope, the xformer doesn't regulate (that would require active controlling circuit (like a 7815 voltage regulator does it)).
What matters is its output impedance.
It's as simple as that. A lower output impedance (bigger xformer, other factors like type, materials etc. kept the same) will have less voltage drop as the power amp draws current.
Instantaniously the current comes from the capacitor(s), but they can't do it alone, and the energy needed to re-charge them after a current surge can only come from one place. The Xformer!
Therefore the overall voltage drop will be limited as the xformer VA rating increases.
Easy, isn't it?
see ya'
Jennice
Would you please...
Take the time and read my reference to the ACTIVE regulation like the 7815 NOT being present.
Hence, I has trying to get to the core point of the subject, namely the output impedance and lack of active regulation electronics.
Hence, my statement/oppinion isn't wrong, but I apologise if my english isn't perfect. I was trying to compare the differnce between active regulation vs. simple output impedance.
Jennice
Take the time and read my reference to the ACTIVE regulation like the 7815 NOT being present.
Hence, I has trying to get to the core point of the subject, namely the output impedance and lack of active regulation electronics.
Hence, my statement/oppinion isn't wrong, but I apologise if my english isn't perfect. I was trying to compare the differnce between active regulation vs. simple output impedance.
Jennice
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