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hifimaker 19th November 2008 11:16 PM

F Series First Watt Transformers
I'm perfboarding an F1 and maybe an F2. Is a 250va 18-0-18 toroidal transformer undersized for a mono bloc for these amp types?

What would be the ideal VA rating?

Thank you!


gl 19th November 2008 11:36 PM

Hi David,

You're fine for a monoblock. Some might even consider 2 chans from that transformer.


Nelson Pass 20th November 2008 12:11 AM

VA ratings are a bit dicey. One manufacturer's 250 VA is another's
100 VA.


hifimaker 20th November 2008 12:20 AM

Thanks guys for the help.

I'm looking at an Avel-Lindbergh Y23 series. They have a 160VA and 250va in 18-0-18 at Parts Express with a free shipping special offer.

They seem like a good vendor and could probably assume the VA ratings are accurate?


GRollins 21st November 2008 01:02 AM

Avel Lindberg is all right in my book.
The thing about VA vs. Watts is that sometimes it's apples to apples and sometimes it's apples to elephant boogers. Setting aside the relative quality that you might expect from one manufacturer or another, the VA only equals W if the load is purely resistive. Once the load becomes reactive (not to be confused with radioactive), then you get into power factor correction. Depending on how far off the current and voltage peaks are from one another, you can get wildly differing numbers.


preiter 21st November 2008 01:33 AM

Have any recommendations for choosing a transformer then?

I was also looking at the Parts Express transformers. Is the 225VA enough for an F4? The next step up is 330VA. They don't have 18-0-18 in that size, but I could get 35-0-35 and wire the primaries in series.

Babowana 21st November 2008 01:54 AM

I'm using 18-0-18 300VA covering both channels for F4.
I don't see any problem at all.


SCD 21st November 2008 04:13 PM

I built mine with Plitron.
Very nice transformers. It runs cool and is dead quiet.

Tea-Bag 21st November 2008 06:38 PM

I use these puppies from ANTEK 18v+18v @ 400VA.

No problems with them. I think Nelson tested a members at one point and found them acceptable. They are fairly inexpesive.

hifimaker 21st November 2008 06:39 PM

This is the best audio forum. Thank you so much for the guidance. I wish I could buy you all a beer. :drink:


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