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francesco81rs 22nd June 2012 08:25 AM

Input trasformer for lm3886
1 Attachment(s)
I wanted to ask you a suggestion on the connection scheme more suitable to use this (Lundahl LL1545A) as a line input transformer.
I attach the pdf transformer.

Thanks to all

AndrewT 22nd June 2012 02:20 PM

Use it as a bal to unbal at the input to the 3886.
I'd suggest you use 1:1 for the 10k:10k impedances and load the output with the recommended components.

If your source is not balanced then keep your transformers on the shelf.

KSTR 22nd June 2012 08:52 PM

The L1545A can of course be used with unbalanced source, it will make ground loops a non-issue and will also provide blocking action for radio frequencies and it will be low noise as well. Source should have no DC, in doubt a series capacitor should be used (the amorphous core is well suited for AC coupling). Further, the 2:1 and 4:1 options can help use high input signal levels.

francesco81rs 22nd June 2012 10:52 PM

Thank you for your replies.
I wanted to be more accurate to say that I wanted to use it to connect 2 boards (3 x LM3886 in parallel) in bridge.
As is well set the output connections in this case?
I also wanted to take advantage of the transformer so that it can accept both balanced and unbalanced input.
it is good to go through a switch between balanced and unbalanced input?
Or not necessary?

Thanks to all

KSTR 23rd June 2012 01:21 AM

Feeding two amps for bridging is very easy as well, just use the L2B or L4B config.

A switch for bal/unbal input is not really necessary. I'd use a XLR + 1/4" TRS combo jack (Neutrik) and connect the xformer input for standard balanced. For unbalanced feed, use a RCA to 1/4" adapter, this autmatically shorts pins 1 (GND) and 3 (cold) of the XLR.

francesco81rs 25th June 2012 10:00 AM

Thanks for the suggestion.
But i would install in my amply both types of connectors.
So in this case, i'm note sure if it's necessary a switch or just simply connect together pin2 of the xlr with the cold pin of the rca, and of course connect together the GND of 2 connenctors.

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