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Originally Posted by Butcher
There is an impedance "matching" issue to always consider when connecting professional audio gear.
In order to have an efficient (and therefore good sounding) transfer of signal, the input must be rated for at least 10 times to 100 times the impedance rating of the source.
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I can't think of any case where 10:1 ratio of load to source impedance would be insufficient for connecting to line level devices or a microphone to a mixer input. Even a 5:1 ratio presents negligible load to the source.
RCF doesn't quote the input impedance for that speaker, but I wouldn't be surprised if it is in the neighborhood of 10K ohms in the line input mode. The Boss GT-10 has a 2K output impedance. Assuming a 10K input impedance a 5:1 ratio of in to out is perfectly acceptable. There is no need to use a transformer.
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The little inline lowZ to highZ transformer you have is designed to plug professional mics into guitar amps. Not sure exactly what it is doing for you in terms of impedance using it backwards.
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It is called bi-directional reflection of the impedances. Inserting the 1/4" (high impedance) side of the transformer into the Boss, and sending the XLR side (low) reduces the source impedance seen by the speaker and raises the destination impedance seen by the Boss processor.
There is voltage change, a corollary of the impedance change.
If you want to know the theory behind it, download the Bill Whitlock's chapter on transformers, published in the Audio Cyclopedia.
http://www.jensen-transformers.com/a...%20Chapter.pdf
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The best approach is to pick up an inexpensive DI box (ART, Whirlwind etc.) for about $50. Run the 1/4" out of your pedal into the DI box input, then the DI box XLR output into your powered speaker or a mixer etc. That also converts the unbalanced signal into a balanced signal which will be much more interference resistant (use as short a 1/4" cable as possible).
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That's one way to do it, and a legitimate approach, though I see no real disadvantage to connecting the GT-10 directly to the RCG speaker.