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PostPosted: 15 Feb 2009, 01:22 
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Joined: 11 Feb 2009, 00:18
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I am in quite a predicament as I am in search of a cheap 110-120v to 100v transformer. Those things are not cheap! I am somewhat new to this, have a couple of builds under my belt including a PC PSU conversion with an added voltage regulator, its adjustable from 1.5v to 22v @ 0.5a.

Now its time for more voltage, as I am very interested in building a nice 60w+ power amp with some of the many high voltage audio amps i've acquired.

My big question is, is there anyway I could skip the transformer and just have a current regulator on the mains input of a PSU, to go from 15a to 5a, then a 4 diode full-wave rectifier, and then a heavy duty adjustable voltage regulator?

I really appreciate any and all input upon this issue.


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PostPosted: 15 Feb 2009, 12:15 
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I wouldn't reccomend running an amp directly off the mains supply.
It's simply too dangerous, and anything connected to such an amp will also be at risk.

Cutting corners for the sake of cost will result in more trouble than it's worth.


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PostPosted: 15 Feb 2009, 13:18 
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Joined: 06 Jun 2008, 20:12
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Location: Houston, TX
I say dont do it man!
So what amp are you considering building?
Ri

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PostPosted: 15 Feb 2009, 13:57 
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Thanks for the input so far! Is there any specific reason why not to do such a thing? I'm not planning on doing it if its not safe, just like to know things.

As for what kind of amps, everything im planning on doing is solid state until I "think" im able to tackle a tube amp project. To copy a Marshall JCM800 is my dream 8-)

I currently have a few different chips, LM3886, LM1875, TDA2040, TDA2050, TIP31 and some others. The first bigger amp I do, i'd like to use the TIP31 I have. I also have two car audio amps i've been wanting to tear apart to get chips from, one amp is 4x25w and the other is 2x100w. The possibilities are endless, as long as I can supply proper voltage and current haha. I guess the proper know-how would make a big difference to :|

Any ideas on where, or what appliances i could score a transformer of such voltage output?


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PostPosted: 15 Feb 2009, 14:04 
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30v has a lot less chance of killing you than that from the wall. Most amps run on low voltage, solid state anyway. Dropping the voltage down with a voltage regulator will make a huge amount of heat as it basically shaves the voltage you dont want right off the top of the voltage you do want and then has to turn that extra voltage into heat. So lets say you are pumping out 60 watts at 30V and regulating down from 120. That 60W is coming in at 2 amps. 120V-30V = 90V. 90Vx2A = 180watts of heat to dissipate. Thats a huge heatsink that will rival the cost of your transformer.
A lot of regulators cant handle that difference in voltage.
Uriah

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PostPosted: 15 Feb 2009, 18:27 
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I do have access to blocks of solid aluminum, all shapes and sizes. None of those are finned though. I do also have 2 more PC psu's that are both capable of 5v3a, 10v1.75a, 12v0.90a, and 22v0.5a. Is it possible to link two of them together to make say 22+22=44v @~1a?


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PostPosted: 15 Feb 2009, 19:03 
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Yeah, probably you could do that and then use the LM1875. It wants about +-25V but hmm, actually where are you going to get the negative voltage from? Do those output DC or AC? If AC, which I doubt, then you are going to be fine but if DC then maybe not so much.
Ri

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PostPosted: 15 Feb 2009, 21:54 
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Oh No! All PC power supplies output in DC, as far as I know. Negative voltage, damn is that what Vce stands for in transistor datasheets? Are there ways to convert a 25v+ to a -25v and still have the positive 25v?


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PostPosted: 15 Feb 2009, 22:26 
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merlintso wrote:
is that what Vce stands for in transistor datasheets?

the ce in Vce refer to the collector and emitter of the transistor. The have nothing to do with the type current. The V stands for Voltage. Depending on where in the data sheet you are reading Vce can have different meanings.

Please be careful, if you are not sure then don't.

Regards,

Alan

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PostPosted: 15 Feb 2009, 23:20 
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Yes, I took a gander at a datasheet after posting that and saw that Vee was used as negative voltage input.


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