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-   -   I have an odd transformer issue (want to build the gainclone) (http://www.diyaudio.com/forums/chip-amps/21692-i-have-odd-transformer-issue-want-build-gainclone.html)

Jerry Parker 18th October 2003 11:47 PM

I have an odd transformer issue (want to build the gainclone)
 
After looking at several websites, I looks like it would cost close to 100 US dollars for a torridal transformer of approxmiatly 35volts that would have enough current capability for a 4 channel gainclone. However, I have an E core transformer right here that has a 230v primary, and 28,14,48,24 volt secondaries. I will be running 120vac power, so all of the secondary ratings are half of that. Is there any way I can use all of the secondaries perhaps by wiring in a series or parallel fashion to get close to 35 volts? The transformer is very large, however it doesnt tell me how many amperes each secondary leg is rated at.

Keep in mind, I need the amplifier to do 50w constant for each 4 channels, as I plan to biamplfy and actively equlize and crossover my main speakers using the new Behringer 2496. So I will probably need 10amperes+ at 35volts.

Thanks!

Peter Daniel 19th October 2003 02:20 AM

You should be aware that the wattage of transformer also drops as you decrease the primary voltage. Maybe not by half, but substantially at least.

Jerry Parker 19th October 2003 02:59 AM

Peter:

Thanks for the tip, but I already figured that :)

However, the transformer is quite large, and I would imagine it would be large enough to do around 300-400va total.

Any ideas on how to wire the secondaries? I don't believe they are rated at the same amperage :(

Jerry Parker 19th October 2003 03:04 AM

"Primary 230V Secondary 48VCT 7A & 28VCT 3A
or Primary 115V Secondary 24VCT & 14VCT

115/220V Input Dual 41VRM 6.1A"

Actually I found the above specifications on the website, its a Signal BL-1752.

If I wire the secondaries in series that should work great right? But what about the issue that the 14v rail is only rated at 3A while the 24V rail is rated at 7A?

Oddly though on top of the Transformer it has a 28v tap as well

:confused:

Peter Daniel 19th October 2003 04:45 PM

So lets say you have 24V CT and 14V CT. To get 50W out of your amps you need double 24V AC secondaries, or 48V AC CT.

How do you plan to connect the existing secondaries (on your transformer) to get that?

JOE DIRT® 19th October 2003 05:59 PM

Jerry muti tap transformers are built for a specific reason and most of the windings are for control purposes especially in audio for low level circuits....usually the highest voltage is for any type of power circuit...I would advise against trying to tie with the other secondaries

DIRT®

Jerry Parker 19th October 2003 10:07 PM

Well if you guys advise against tying the secondaries together, I suppose it won't work then.

I saw some 5A 40V secondary transformers on www.partsexpress.com I bet those would work great (They are only 10 dollars each) and 2 would work great, unfortunatly they are out of stock :(

Do you guys know of any place that could sell me a ~40v secondary E-core or torridial transformer that does at least 10amps for less than 50 dollars?

Jerry Parker 21st October 2003 09:55 PM

Does anyone else know where I can get a transformer for less than 50 dollars us (preferably less than 30) that has a 40 or 45 volt secondary that does at least 10 amps?

Peter Daniel 21st October 2003 11:31 PM

Try Apex Jr. But he carries mostly toroids. Just recently I bought at least 10 from him.

If you are really into EI transformers, I have few of them. Ea. one is 250VA and have double 18V AC secondaries. It would be on the lower end of voltage ratio, but the amp would work great with 4 ohm loads. I can sell them $20 ea.

JoeBob 22nd October 2003 12:37 AM

When you put in 120V into the primary you'll get 24V AC out of the 48V tap and that will be close to 35V DC when rectified, if this is what you want. Be regardless of the VA of the transformer, you'll have to check what amperage it's rated at (for the 48V tap) and that's the max it can suply, even when 120V is on the primaries. If it's not enough, you're going to have to buy a new one.

But with all those extra wasted taps, it would be much simpler to buy a transformer rated at the voltage you want.


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