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-   -   Is this transformer too much? (http://www.diyaudio.com/forums/chip-amps/21248-transformer-too-much.html)

Illusus 8th October 2003 03:18 AM

Is this transformer too much?
 
I just bought a torroid on a chance buy. Dual secondaries -
0 - 40, 0 - 40, secondary current 2.81 amps.. I'm guessing 230va. Is it too much voltage for a 3875 based gainclone? I read that, sonically, better results are achieved with lower voltages. If it's not recommended that I use this transformer, what should I do with it?(and don't say "give it to me" ;) ) Trades?

millwood 8th October 2003 03:21 AM

one way to use it, if the transformer has dual primaries and you live in a country with 110v ac, is to put the dual primaries in serial, and your transformer will output 20v ac on the secondary.

Nuuk 8th October 2003 08:02 AM

Yes, it's far too high for the LM3875. You may be able to use it for a regulated supply and lower the voltage. See Pedja's site for more details.

peranders 8th October 2003 08:46 AM

30 volts AC are max but 20-25 V is better. + - 42 VDC is max for this IC. +-47 VDC max without signal, what does this mean really? Maybe it have something to do with the protection circuitry?

Why don't you build a discrete amp instead?

millwood 8th October 2003 04:05 PM

Quote:

Originally posted by millwood
to put the dual primaries in serial, and your transformer will output 20v ac on the secondary.

essentially you wire the primaries as if you will be using 220v AC but using it instead on 110v AC mains. That way, you get half the rated voltage on the secondary, which sits nicely with the chip.

Illusus 8th October 2003 10:05 PM

Thanks for your replies guys. The transformer has single primaries so millwood's suggestion is out. I may use it in a regulated ps for another project, I looked at pedja's regulated supply for gainclone. The voltage regulator he used, lm338, is rated at 40v max input, I am unsure of running anything at it's max tolerance, this would be a good time for ordering samples to try but these only come unpackaged as samples. For now, I am just going to keep this as a nice paperweight untill I find a project for it, I paid less than $20 . I am sticking to my original parts list for the gainclone, I'll experiment with something else.

millwood 8th October 2003 11:09 PM

illusus, if you have two of those transformers, you can parallel the primaries and do what I had suggested.

millwood 8th October 2003 11:46 PM

Quote:

Originally posted by millwood
illusus, if you have two of those transformers, you can parallel the primaries and do what I had suggested.

I meant to say put the primaries in serial. sorry.

Illusus 9th October 2003 12:22 AM

Yeah I wish I had two, but no such luck. oh well. I've been planning on going through the Zen tutorial, maybe all five stages, or skip to the penultimate. I'm sure the transformer will come in handy there, as well as the ten 10 000mfd 125V caps I bought for five canadian bux ;).


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