Why did my amp start on fire?

[soundNERD]

so like this?? ( quick sketch - dont know how id live without good ol Paint )

[carlosfm]

Independent secondaries.
4 wires coming out of the trafo.

[soundNERD]

Oh ok, so what I have in my picture won't work?

I don't want to mess with the coils of the transformer. I don't think I'm skilled enough to mess with that kind of stuff yet.

[falcott]

Originally posted by soundNERD
Oh ok, so what I have in my picture won't work?

Hi soundNERD. This is basic stuff: To create a suitable power supply with +v / 0v / -v output, you need two separate secondary windings in your transformer. What you have right now is just one, with a central tap. That one winding needs to be separated into two at the point of the central tap, so you have two windings that have no electrical connection with each other. This will result in two pairs of wires coming from the transformer (if you ignore the two primary input wires), each pair of which goes to its own bridge rectifier.

You could make a regulated supply with a central tapped transformer, but for that you would need both a positive AND a negative regulator (e.g. LM317 and LM337, which handle only 1.5A each). I don't think that there are any negative regulators available to suit our purposes here (i.e. 5A or so).

[Netlist]

Guys, If soundNERD feels he is not skilled enough to tackle this he shouldn’t be pushed.
This can be basic stuff for a lot of us but let’s not forget that messing with trafos can be dangerous.
I’d suggest we try to find a more suitable and less dangerous solution.


/Hugo

[falcott]

Just lending a helping hand ...

... not encouraging anyone to cut open their transformer.

So, soundNERD, to concur with Mr Hugo, if you feel that you're not up to modifying a transformer and you still want a regulated supply, you will have to buy a transformer with dual secondary windings... Sorry

[lazyfly]

This may be a silly idea but I'd suggest making something cheaper and simpler first off. Like a CMoy headphone amp that'll run off 9-18VDC (batteries).

http://tangentsoft.net/audio/cmoy-tutorial/

Once it's running as expected you may have picked up enough info and a little more confidence that you can hook it up to a small transformer. Then, once that is running as expected you can give the higher voltage gear a go - hopefully with a new found confidence and approach. You'll have a great little headphone amp to boot!

Just a thought.

*edit - forgot the link.

[soundNERD]

Thanks to all,


But I guess what I really want to know is just why it won't work even if I use seperate bridges and filter caps.

[soundNERD]

I think i'm going to go with a bridge/parallel OPA541 since my trafo wont work with a 549 (still waiting to find out why...). As long as it's an 8 ohm load, the amp won't start on fire, right? Or should I invest in a new trafo and build a 549 amp?

[soundNERD]

I now have a 175VA 18-0-18V transformer.

If I were to rebuild my bridged 541 amp, and run it off of this transformer, would it even be possible to burn up the chips?

I'm redesigning it with a bridged 549, though, and without the DRV134, since I don't think it will make that mcuh of a difference with a sub amp.

I just want to know if it's worth putting back together.

thanks!