Jensen JT-11P-1, unbalanced inputs. - diyAudio
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Old 14th July 2013, 11:31 AM   #1
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Default Jensen JT-11P-1, unbalanced inputs.

I'm currently using a dac with a passive resistor iv straight into a power amp via its unbalanced inputs. My power amp also has balanced inputs with Jensen transformers doing the conversion. I made an adapter cable RCA-> XLR and tested the dac to power amp via Jensen and for some reason the sound appears more well defined. What could be the technical reason for this? Surely it is another obstacle in the path of the signal if the transformers are not doing what they were made for (ie. balanced to unbalanced conversion).....
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Old 31st July 2013, 04:00 AM   #2
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Anyone have some thoughts on this? Keen to understand what happens when one passes an unbalanced signal through a transformer which is intended for converting xlr to rca...
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Old 31st July 2013, 04:13 AM   #3
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The JT-11P1 wasn't made for balanced to unbalanced conversion, although it can perform that function seeing as its input is inherently balanced. Its primary function is as an input transformer providing both high common mode rejection as well as galvanic isolation.

How did you wire your adapter cable? RCA hot to pin 2 and ground to pin 3?

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Old 31st July 2013, 04:26 AM   #4
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Hi Steve - yep, spot on (pin 1 is just the shield on a normal xlr->xlr cable).
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Old 31st July 2013, 05:45 AM   #5
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In that case, ther shouldn't be any meaningful difference. Cool thing about transformers is that they will give you excellent common mode rejection even if you feed them from an unbalanced source. Check out the common mode rejection figures in the data sheet for test circuit 3 (unbalanced source) versus test circuit 2 (balanced source).

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Old 31st July 2013, 06:01 AM   #6
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Very interesting!
100dB for the unbalanced input.
107dB for the balanced input.

7dB difference in the 60Hz test circuits, huge in terms of CMRR.

I wonder whether this is actually an 'audible' element of an amplifier?

Another stat on the datasheet is of interest - the typical voltage gain is -2.3dB.
I wonder if this drop in voltage is somehow affecting the listening at a subconscious level. eg. using the amplifier directly through it's RCA (unbalanced inputs) gives a slightly louder, less 'organised' sound....
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Old 31st July 2013, 06:11 AM   #7
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Well, just listen without any music playing. If you don't hear any noise, then...

Yeah, the 2.3dB insertion loss is due to the source impedance and the winding resistance of the transformer which gives it an output impedance of 2.34k ohms and then the transformer's loaded with a 10k resistor.

All else being equal, if you compared an amp with the transformer to one without, the one without would be just slightly louder which could effect the perception of quality. But hey, just turn up the volume on the one with the transformer.

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Old 31st July 2013, 06:29 AM   #8
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Yes – I’d say you’re correct. The combination of a slightly quieter background, and a little less volume (noting that recordings these days are almost insanely loud) probably gives the overall effect of a slight improvement as compared with the unbalanced input.

Whatever the case, there certainly isn’t any sonic degradation – the sound of these transformers is stunning.
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Old 1st August 2013, 08:05 AM   #9
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I am new to this transformer idea... If I have a DAC with 2 WM8741 with dual differential outputs, should I just connect VoutRP1 + VoutRP2, VoutRN1 + VoutRN2(with summing resistor of around 1K to each DAC pin) to each end of the jensen transformer? The Jensen secondary would have a 10K resistor in parallel. I only need SE output to my preamp, do not need any additional gain from the transformer.
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