Is Higher VA always better? and Avel close or Antek exact? - Page 2 - diyAudio
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Old 9th October 2012, 04:25 PM   #11
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Quote:
Originally Posted by imaginarytime View Post
Charlie,

You wrote AN- models from Antek. Seems that the AS designation is specifically designed for audio, and cost about $5.00 more than the AN versions.

Not sure if this was an intentional distinction.
Honestly, I just opened whatever was in about the right VA and secondary voltage range so that I could get to the datasheet. The AN models do have the screen, which helps for audio but I think would be more important for a preamp than a power amp.

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Old 27th November 2014, 03:15 AM   #12
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Originally Posted by sreten View Post
Chip amps and big transformers is a design oxymoron.
It's funny you mention that because I was planning on powering a 4-channel LM3886 amp with one giant 10 lb 650 VA IE transformer and I did start feeling a bit oxymoronical after thinking about it some.
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Old 27th November 2014, 03:32 AM   #13
jcx is offline jcx  United States
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bridged paralleled 6-8 chip amps/channel can push some power into even not too polite multiway passive XO loudspeaker loads that have impedance dips

even with active XO/biamping you may want bridged/parallel chip amps for the low frequency driver

Last edited by jcx; 27th November 2014 at 03:39 AM.
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Old 27th November 2014, 04:06 AM   #14
JMFahey is offline JMFahey  Argentina
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Oxymoron?

IF you need , say, 120VA and "to play it safe" you spend a ton of $$$$$ to buy a 650VA one, to boot pay a small fortune in freight and afterwards it does not fit inside the cabinet, ok, it wasn't exactly a wise decision.

But if you already have it or got a junkyard/surplus one for pennies ... go for it.
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Old 27th November 2014, 12:58 PM   #15
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Jimmy154 View Post
It's funny you mention that because I was planning on powering a 4-channel LM3886 amp with one giant 10 lb 650 VA IE transformer and I did start feeling a bit oxymoronical after thinking about it some.
using the standard guidance that works for all ClassAB amplifiers (VA = 1times to 2times the total maximum output power) the 650VA will successfully power two channels of 150W to 300W to each channel, i.e. a total of 300W to 600W.

For a 4 channel amplifier the 650 VA could power 75+75+75+75W to 150+150+150+150W.

These max power numbers are within two chip and three chip implementation capabilities.
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Old 27th November 2014, 01:03 PM   #16
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A bigger transformer means more stray flux to get into the small signal circuitry and cause hum. It also means less free space inside the cabinet to get said circuitry away from the transformer.
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Old 27th November 2014, 02:11 PM   #17
AndrewT is offline AndrewT  Scotland
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Quote:
bigger transformer means more stray flux
Does it?
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Old 27th November 2014, 02:23 PM   #18
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Well, why don't you list some reasons why a bigger transformer might have less stray flux than a smaller one?
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Old 27th November 2014, 02:32 PM   #19
AndrewT is offline AndrewT  Scotland
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Bigger size allows more even winding of the turns.
Lower flux in the core means less flux to leak out.
Less current than peak capability means less field around the wiring.

Maybe someone who is expect in transformers could come in with experimental results.
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Old 27th November 2014, 02:54 PM   #20
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To a first order, the flux in a transformer core depends only on the primary voltage and frequency. To a second order, it actually decreases with increasing loading of the secondaries.

The designer will place the flux density near to the saturation point of the core, to save money. A bigger transformer will have the same flux density as a small one, hence more flux in total and more leakage flux.

If you want less flux leakage, you have to specify a lower flux density. The designer will use more primary turns than he normally would, and the transformer will hum less and leak less flux, as the core never gets near to saturation and its permeability remains high. This is often done for power transformers in audio equipment.

The point is that the flux density is independent of the size. A bigger transformer does not have less core flux than a smaller one, and a lightly loaded transformer does not have less core flux than a heavily loaded one.

I can't comment on the other two points.
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Last edited by scopeboy; 27th November 2014 at 03:00 PM.
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