Dear all,
I'm interested how can such a PA-class 8x100W (RMS)@8R amplifier be specified to 2400VA power at the device's back panel at the AC inlet (this isn't the issue) when it's transformer is rather small. Compared to my own, several types of toroidal transformers, this transformer should not be rated for more than somewhere between 200-500VA or so .. ?
But if I look at the specs, something's wrong.
What do I miss here ?
Assumptions:
1. Is this amp about a "classic" - typical overrated kind of animal, where specs are nowhere near reality ? (But in the PA world I wouldn't expect that, there specs need to be delivered, period).
2. Or is it overloading the small toroidal transformer and at the same time let it run hot (because of active cooling) ? Even in such a case, 100˚C would already be too much for such and I still doubt this trafo is enough for feeding all these 8 channels with this size, keeping up with the specs.
3. Or is it a switching PSU which by design can be built for huge powers with relatively small transformers compared to linear PSU-s ? (But then, the current must be huge, running through the transformer).
So what's the big magic here ?
Specs here and 2 photos for understanding my question and worries.
The situation is: one such fully functional transformer is for sale in a DIY group, built out from such an amplifier (no typos) and we simply all wonder how the hell can a transformer of this size (estimated to 250-300VA) feed the device it was built in. The full specs are missing but anyway, this is it. It's either a big-current, enormously strong transformer in an unbelievably small size, or it's part of a switching PSU where they're inherently smaller than their same spec'd linear PSU brothers.
Dimensions: Diameter ⌀13cm, height 11cm, not a big one.
What might be the trick and last but not least, what might be the specs of this transformer ?
1 primary - 230V
2 secondaries - one (80V with center tap?) and one 22V.
Thank you & see attachments.
I'm interested how can such a PA-class 8x100W (RMS)@8R amplifier be specified to 2400VA power at the device's back panel at the AC inlet (this isn't the issue) when it's transformer is rather small. Compared to my own, several types of toroidal transformers, this transformer should not be rated for more than somewhere between 200-500VA or so .. ?
But if I look at the specs, something's wrong.
What do I miss here ?
Assumptions:
1. Is this amp about a "classic" - typical overrated kind of animal, where specs are nowhere near reality ? (But in the PA world I wouldn't expect that, there specs need to be delivered, period).
2. Or is it overloading the small toroidal transformer and at the same time let it run hot (because of active cooling) ? Even in such a case, 100˚C would already be too much for such and I still doubt this trafo is enough for feeding all these 8 channels with this size, keeping up with the specs.
3. Or is it a switching PSU which by design can be built for huge powers with relatively small transformers compared to linear PSU-s ? (But then, the current must be huge, running through the transformer).
So what's the big magic here ?
Specs here and 2 photos for understanding my question and worries.
The situation is: one such fully functional transformer is for sale in a DIY group, built out from such an amplifier (no typos) and we simply all wonder how the hell can a transformer of this size (estimated to 250-300VA) feed the device it was built in. The full specs are missing but anyway, this is it. It's either a big-current, enormously strong transformer in an unbelievably small size, or it's part of a switching PSU where they're inherently smaller than their same spec'd linear PSU brothers.
Dimensions: Diameter ⌀13cm, height 11cm, not a big one.
What might be the trick and last but not least, what might be the specs of this transformer ?
1 primary - 230V
2 secondaries - one (80V with center tap?) and one 22V.
Thank you & see attachments.
Attachments
Sorry but I dont think that is a 2,4KVA traf. I own both 1,4KVA and 5KVA. My 1,4 looks considerable more beefy than that even if the height is a bit uncommon on these.
13cm diameter - thats 5,1 inch.... puny 🙂 then double hight.... I'd say... 750VA max...
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13cm diameter - thats 5,1 inch.... puny 🙂 then double hight.... I'd say... 750VA max...
//
Firstly the amp is probably not able to give out 2400W while staying cool and undistorted - the "real" power out is probably lower.
Secondly, you're missing that the energy content of a typical musical signal is lower than a sinewave, so if the amp is playing music it draws less energy from the PSU than the measured output would lead you to expect. I'm no expert on this, but the energy content is said to be between 1/8th and 1/3, with 1/8th being roughly equivalent to "domestic" scenarios, and 1/3 being a worst-case for PA use over longer durations. This means the PSU must "only" be able to supply between 1/8 and 1/3 of the power needed (= full power output of the amp * its efficiency at full Pout).
Naturally there is a some additional complexity here (especially with an SMPS) where you need to look at regulated vs. unregulated PSU design, voltage drop at full power, current-limiter thresholds, thermal performance etc. but as a simple calculation then you can probably get pretty close with 1/3*Pmax*N to gauge requirements.
The last factor is of course as you describe, that if you exceed the rated power of a PSU then it just might get a little hotter but continue to work, and in some scenarios than may be perfectly OK.
I have seen smaller x-formers in a Crest 8 x 100 watt amplifier, when it works fine don't f u c k with it.
Willem.
Willem.