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Cheap LM1875 thread - who wants one? **All gone!**

Started by joecool85, June 22, 2006, 09:21:52 AM

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Bob N

ok.... I went back through everything.... 12.6 out of both sides of the transformer.... 8.1 volts out of the diodes... That's where I'm losing the voltage.... This is without the amp circuit connected and just the power supply and transformer... I've been through everything 10 times at least checking for errors.... I haven't found any bone-headed mistakes anywhere... polarity on the caps is right as well.... Any other suggestions to look at?

joecool85

Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Bob N

They're installed exactly the way it shows in the instructions.... I'm gonna put it away for a bit to clear my head.... If you guys think of anything, go ahead and post it.... I'll come back to it after the storms come through.....

RDV

All the diodes are facing the same direction with the metal sides towards the big caps?

RDV

Bob N


joecool85

I would double check all the solder connections are solid.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Bob N

I already double checked it and touched all solder connections with the iron again.... Still the same result..... I'm wondering if a diode or two are shot.... I've seen stranger things happen.... I'm gonna get this damn thing if it kills me.... I hate these flaky things that go wrong... LOL All In Alll though, it was a very easy build outside of this .....

joecool85

I'm guessing that must be it.  Did you check out the pictures I did in the documentation?
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

trevize

ok i was able to find the transformer (it a 200va from ebay but it was cheaper than the 70va in the electronic store near house). And this weekend I'm going to build the amp.

Just one question: what kind of fuse should i use (value, slow blow or not...)?

joecool85

Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

syndromet

I found a ransformer with  18V, but it only has 2 wires on the secondary side. Vould that work, or do I need one with 4 wires?

joecool85

I don't think you can use that...on that same note, I don't think I've ever seen a transformer with only two secondary wires.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

syndromet

#57
what would happen i I bridged the + sides and - sides? like this:


This is the Transformer:
Transformer 1
Transformer 2

steve_m

Joe,

I believe a transformer can only have two wires on the secondary, i.e. no center tap. You have to use a full wave diode bridge instead of the instead of the more common full wave diode rectifier setup.

Hammond has a good .pdf file you can download which shows the various setups:

http://www.hammondmfg.com/pdf/5c007.pdf

steve

Quote from: joecool85 on July 22, 2006, 07:08:28 AM
I don't think you can use that...on that same note, I don't think I've ever seen a transformer with only two secondary wires.

RDV

For the PS you're working with:

You'll need either 2 transformers like the one you have, or a center tapped, or a dual secondary transformer. A single un-tapped secondary transformer will not give you two seperate AC voltages no matter how you wire it. You need to do a bit more research on power supplies before you proceed. I'd recommend ESP(Rod Elliott's website). http://sound.westhost.com/index.html

RDV