Cheap, good, GC toroidals:

[carlosfm]

Am I buying cheap?

I always order my toroids to a factory here in Portugal.
I ask what I want, because they are always cuustom made.
The last one I bought is:
Primary: 230 V
Secondary: 18-0, 18-0, 5 A

That's a dual secondary (not CT), 180VA.
Price?
27.5 Euros.😎
+ P&P (around 4.5 Euros here).

Am I buying cheap?
Deam, they look beautiful.
And they always send the metal disc, two rubber circles and a screw to mount it.

 

[antomas]

Hi Carlos,

Price seems very good. Would you please post details? I'd be interested in a few 2x20V transformers. If they build the transformers on demand, why not asking for perfection-on-4-ohms?


Massimo

 

[carlosfm]

Hi Carlos,

Price seems very good. Would you please post details? I'd be interested in a few 2x20V transformers. If they build the transformers on demand, why not asking for perfection-on-4-ohms?


Massimo

You can ask what you want.
But this one is 2x18V because this GC I built with LM1875 chips.
BTW, beautiful.
You can even ask 4 secondaries, two for each channel.
The limit is your imagination.
You ask the price to them, I don't know, they don't have a price list, it's always a custom built.
First I send a fax to ask for the price, and the details of what I want.
They repply, and I order it.

I'm going to be out for some time, work is killing me.

Anyway, here's what I have from them (I always order by fax, they seam to forget to check their e-mail ).

Company:
FTE

Address:

Estrada da Varziela - Zona Industrial I
3060-197 Cantanhede - Portugal

Tel.: (351) 231 429 747 Fax: (351) 231 429 747
E-mail: ftelec@mail.telepac.pt

 

[carlosfm]

BTW

If you order anything from them, tell them I recommend.
My name is Carlos Machado, they may already know me.
Maby next time I order they make me a good discount.😀

 

[antomas]

Carlos,
thanks very much for the information. If I'll contact them I'll surely mention your recommendation (I'm searching for some italian manufacturer before looking elsewhere).

I just noticed that the 20V issue should be either a mistake in my calculations or a mistake in the LM3875 datasheet. According to the datasheet, a +-27V supply->2x20V transformer should be ok on 4Ohm. Instead, the National-supplied spreadsheet says that a +-27V supply makes the chip reach its current limit. Maybe a 2x20V trasformer is safe only with the LM3886.

Thanks once again!
Massimo

 

[jackinnj]

GC Power Supplies -- keep your eyes out

if you see some of the older Sorensen SSD48-4 supplies -- they could make an excellent GC Switching Supply and show up from time to time at less than $10 -- they weigh about 5 pounds, will put out a surprisingly, well very surprisingly clean 48 Volts, 4 amps -- you will need 2, obviously -- I measured the switching noise at 20mV on top of 48 VDC, and there was no tell-tale radiation onto the a.m. band. Here's a graph of the noise pulse and the ripple on the 48V rail:

 

[jackinnj]

this is what they look like:

 

[Scribble]

So whats a good recommended custom transformer? im aiming for either stereo (two LM3875TF) or 4 channels i would use for bi-amping (four LM3875TF GC's).

22v with dual secondaries at 400va?

Maybe the 22v is a bit small and i should go for 25v?

Would the 400va be too small to run 4 channels?

Im aiming to use the Peter Daniel PS schematic and GainClone schematic as well.

BTW im in Australia so im on the 240v lines.

im looking at getting a custom job from www.torema.com.au


Thanks for your time,
Joel

 

[jackinnj]

don't forget that the LM3875TF is designed to handle less power than the LM3875T.

 

[Variac]

Hey Jack,

So you need 2 Sorensens to get V+ and V- ?
I've been interested in switching supplies since I was told that these high quality ones are a whole different animal than computer supplies. Good info

48 V is a bit high though , right? or can they be adjusted?
Maybe perfect for an Aleph

 

[Lurien]

I have been trying to find a decent transformer for my GC project. Browsing through the digikey catalog I saw this:

http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=164&M=166J44

Specs: 115VAC 44VCT 1A

Any idea if this would work, or is 1A too little?

 

[jackinnj]

i don't think that it's a good idea to try and use one with "floating" ground. The adjustment on these particular supplies is, I believe, 44 to 56 volts. They will put out 44 volts even with a line potential of 70VAC.

the telcom supplies for distributed voltage have 48VDC out.

 

[Squalish]

A) that isn't a toroidal tranny, meaning you shouldn't have it in the same enclosure as the amp

B) that is too low. The lm3886 has the capability to supply 68 watts per chip sustained, 120 peak, with maybe a 20 watt waste heat involved. Shoot for a minimum of 90va per channel. Most go with 150-250va per channel. Many prefer oversizing their toroids because they claim it produces better sound, so some go up to around 500va pc, but I doubt that that would improve things much.

 

[jackinnj]

A) that isn't a toroidal tranny, meaning you shouldn't have it in the same enclosure as the amp

Note that the power supply for the GAINCARD is separate from the amp units themselves.

 

[Squalish]

Yeah, I wasn't objecting, just noting.

C) VCT usually means single secondary with a connection in the middle, meaning that many of the PS schematics using dual bridge rectifiers won't work with it.

 

[AudioFreak]

Dual Bridges will work with CT transformers ... you just dont get the advantages of dual bridges with dual secondaries.

 

[Peter Daniel]

Yeah, I wasn't objecting, just noting.

C) VCT usually means single secondary with a connection in the middle, meaning that many of the PS schematics using dual bridge rectifiers won't work with it.

It is usually possible to convert center tapped secondaries into two separate secondaries. So far I didn't find a TX I couldn't modify.

 

[MantramAudio]

Re: Re: Toroids

Oh well. I also got a superb deal on a tape wound toroid at www.coilws.com. $38 for a 235VA. 6 week turn around 🙁 and still waiting. I recently went back to look around,and the same transformer is $50! Makes me wonder if someone didn;t have a SNAFU on the web site!

Just a followup on my transformer experience from coilws.com. It has been the worst experience so far in my GC building. I placed the order August 15th and still no transformer. They just order and import them from China, they have no US stock. They didn't state that when I ordered. I've had many rounds of "Let me check and call you back" with no call backs.

I called and requested the order be cancelled, and chargebacks are next.
😡

 

[uvodee]

chargebacks

yep and next thing you'll know is that they charge you a restocking fee of 15 pct with a minimum of $ 35.00 .....

and eventually they will blame it on China and You.

Jean-Pierre

 

[carlosfm]

Re: Re: Re: Toroids

Just a followup on my transformer experience from coilws.com. It has been the worst experience so far in my GC building. I placed the order August 15th and still no transformer. They just order and import them from China, they have no US stock. They didn't state that when I ordered. I've had many rounds of "Let me check and call you back" with no call backs.

I called and requested the order be cancelled, and chargebacks are next.
😡

At least they had a good price, huh?
Good price and no transformer?
Man, that's a sad story.
Guys, be careful when buying over the net and dealing with people/companies you don't know.