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Old 2nd July 2005, 08:24 AM   #11
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For choosing the secondary voltage figure it like this....

-when you rectify the AC into DC, you will get your input * 1.414
-Figure at least 3 volts DC drop across a regulator if you are making a regulated PS

so.....

V(out,DC)=1.414*V(in,AC) - 3

or....

V(in,AC) = ( V(out,DC)+3 ) / 1.414

All depends on what DC voltage you plan on making your amp with.
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Old 2nd July 2005, 09:41 AM   #12
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There's a lot of advice for beginners here:

http://www.decdun.fsnet.co.uk/gainclone.html#gcpsu

The author of this page seems to favour 20-volt secondaries.

Tim.
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Old 2nd July 2005, 11:01 AM   #13
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I see the company you bought the kit from provides a guide on its web site.

The guide include advice on construction, and selecting a transformer; it says

"This shows that transformers with 18-22V secondaries are well within reason for many common commercial and DIY speakers. A transformer with 25V transformer secondaries can also be successfully with less of a safety factor."

By the way, it also has advice on heatsinks (heatsinks are not supplied with the kit, but you will need them.)

"The last consideration for chassis construction is heatsinking. This amplifier does not require huge heatsinks. Successful implementations have used computer heatsinks without fans, solid pieces of bar stock or aluminum angle and others rely on standard large heatsinks. An aluminum plate around 3 x 3 x should be plenty for most applications if allowed to circulate in free air."
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Old 2nd July 2005, 03:38 PM   #14
Aghead is offline Aghead  Canada
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In canada probably the best source for toroidal transformers is electrosonic in toronto, usually their shipping is not brutal.

for this chip you likely want 22 VAC secondaries, and the VA is up to you. expect to pay about CAD$70. larger transfos are not that much more costly.

too high DC voltage will quickly fry the amp with a low impedence load even at low volume.

i really don't understand the vastly huge factor of safety recommended in these threads for power transformers. commercial designs almost never use huge transformers compared to the amp outputs.

is there anywhere a thread discussing how small versus large transformers SOUND? or is it just an opinionated theoretical discussion .

in most normal listening, the power output is less than a watt per channel, and power dissipated by the amp at this level is going to be maybe 20 watts total.

a large transfo (>200VA) will use more power than that simply idling with no load.

> 200 VA for a 2 channel chip amp doesn't make any sense to me.
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Old 2nd July 2005, 08:55 PM   #15
VoLCoM is offline VoLCoM  Canada
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so you say that 200VA will be enough for a two channel Amplifier? and i should go with like 20-25 volts secondary voltage??? i shouldn'T have any problems? i just need to find an online store that sells some and that accepts Paypal! or someone who has one of them or one that could work who's going to sell it to me
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Old 4th July 2005, 02:43 AM   #16
Aghead is offline Aghead  Canada
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exactly, try this:

http://www.e-sonic.com/acc/products....command=detail

but you should be able to find someone with an old amp in the basement for parts with a perfectly good transfo.

lots of people have "upgraded" (har har) to 5 channel surround...
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Old 4th July 2005, 09:49 AM   #17
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parts express in the US is a great place for some good quality torroids.
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Old 4th July 2005, 03:38 PM   #18
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would they have a 48 volt center tapped tordial? ( 24v +/- and ground)
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Old 4th July 2005, 04:26 PM   #19
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Quote:
Originally posted by ThSpeakerDude88
would they have a 48 volt center tapped tordial? ( 24v +/- and ground)
Not sure, go look.
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Old 10th July 2005, 06:08 AM   #20
DonoMan is offline DonoMan  United States
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I want to do (2) LM3886, (1) LM3875, and (1) LM4700 from one transformer... Now the 4700 is the killer, I want 22V for it, not 24V... Technically, 24V should be ok, but I don't want to cut it that close.

Any suitable transformers (300-400VA) in the $50 range? Plitron is $62.95 for 300VA and $72.31 for 400VA, which is more than I want to spend. The 330VA Avel from PE would be great, but it's not available in voltages I want..

Should I just go for 24V and use a couple of extra diodes for just the 4700? I'd prefer not to do that, but if it's my only option without paying $20 extra each for a minimum of 2...
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