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Raka 5th June 2003 01:02 PM

2 or 4 bridges?

just a small question:

I connected my gainclone to a 250VA 18V trafo, with two bridges, and sounded ok (not enormous, but ok). I thought that if there were four bridges (that is one per rail, two per channel) I will have two nice power supplies sharing the trafo, supposed to be good thing.
Well, I fired it up and...

The diodes started to get bored and decided to BOOOMMMM to have a laugh at me.
I don't know if I made a connection mistake, but my question is if there are advantages using 4 bridges?

Don't tell me to try, because I run up of diodes: 16! ;)

mhennessy 5th June 2003 01:46 PM

Are you only one transformer?


Mark ;)

Raka 5th June 2003 02:02 PM

Yes, I'm using only one transformer. Is possible to use only one transformer and 4 bridges?

JOE DIRT® 5th June 2003 02:12 PM

give us an idea on how you hooked it up>????

Raka 5th June 2003 02:32 PM

Well, I duplicated the bridges, two for channel, and then connect the trafo to the input of the bridges. so simple, isn' it?
For each output wire of the trafo I derived two wires to each input of the bridges. Would be there any problem with this? Do I short anything this way?

JOE DIRT® 5th June 2003 02:39 PM

thats fine on what you did with the lets say you have 2 + and 2- each are they hooked up to each channel?

Raka 5th June 2003 02:53 PM

2 Attachment(s)
Something like that

sam9 5th June 2003 03:25 PM

I'm not sue I understand the issue. The transformer gives you 250VA to work with. Adding bridges isn't going to change that. As long as it can handle the current, a single bridge is normally sufficient. One rated 25A-35A with a metal case and bolted to the bottom of the enclosre ought to be adequate. There are arguments for one bridge per rail, but those seem to be to compensate for a problem somewhere else.

mikelm 5th June 2003 03:57 PM

two bridges are supposed to sound better, I'm just in the process of building a 16 diode PSU.

but apparently it's best to run 4 wires to each amp & connect the two grounds at the earth star in the amps.



mhennessy 5th June 2003 03:58 PM

Looking at the diagram, it ought to work fine. I suspect that you made a mistake during hook-up, or one of the bridges is faulty. Try separating the earth connections of the two channels, and measuring the potential difference between them...

As far as I know, this is the theory behind seperate rectifiers for each channel: a loud sound in of the channels causes the supply rails to fall slightly because of the increased current demand - with common rectifiers, the other channel will see its supply rails fall, and the stereo image might suffer as a result.

I'm not sure how much of a problem this is in practice, and I'd be worried by the extra complexity and scope for errors bought about with the extra rectifiers. I'd also be worried about the "cleanness" of the earth connection, because although they come from the junction of seperate rectifiers, they get tied together by your star-earth (or preamp or source if you maintain seperate L/R star earths)

When I was using a single transformer, I stuck to common bridge rectifiers for both channels. For what it's worth, I think it's far better to go for completely seperate power supplies - mains transformers aren't too expensive really...


Mark ;)

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