Power Supply

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Hi, i have just bought a GainClone Kit from audiosector.com and i was wondering what kind of transformer i needed. i have read on a couple of website that toroidal were better for audio. but what do i need exactly i don'T really know much about transformers

or can i use batteries?? which option will be better???

Honestly, sounds like you need to use the search and do more reading before you dive in head first...

But regulated basically means that you have regulator chips or some precise way of controlling the output voltage.

In our case we can use something like an LM317T, LM337, LM350, etc etc etc as a linear voltage regulator.


Input 37V

Desired output 32V

Set regulator to output 32V.....Regulator must dissipate the 5V as heat.

There ya go, regulated voltage supply. If you want to see how they work exactly, go lookup LM317T on google, or go to www.national.com and lookup the LM317 and read the datasheet.

Also, there is a thread started by CarlosFM where he made an excellent regulated snubberized PSU. Don't use the design early in the thread, he has a later revision like 15 pages deep. Read through the entire thing.
120VAC comes into the transformer primaries

Transformer turns it into say... 32VAC

It goes through a rectifier which turns it into a pulsed DC

Capacitors smooth down the pulsed DC into a nicer DC

A regulator will keep the DC at a constant voltage.

In all honesty, pick up a basic electronics book. I actually have a spare book that is for non engineers here if you would like to buy it for $25+shipping that goes through all the basics very nicely. I highly recommend you take me up on the offer. You shouldn't be playing with line level voltage if you don't understand these basics. I'm not trying to be an ***, just telling the truth.
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


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


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

All depends on what DC voltage you plan on making your amp with.
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 ½” should be plenty for most applications if allowed to circulate in free air."
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.
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
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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