I'm running my EL84 Baby Huey with balanced/differential inputs like that, with no feedback, driven by the balanced differential outputs from my DAC. It sounds very good.
I'm putting Jensen JT-11P-1 line input transformers into a couple of other amps I'm building and may retrofit them to the Baby Huey. That way I can try feedback as well.
I include RCA sockets in all the amps too but they're unwired.
I'm putting Jensen JT-11P-1 line input transformers into a couple of other amps I'm building and may retrofit them to the Baby Huey. That way I can try feedback as well.
I include RCA sockets in all the amps too but they're unwired.
True. But I've salvaged a bunch of transformers from some equipment I was given and I want to make it easy to switch to RCA inputs to increase the usefulness of the amps once I no longer need them.
Hi Chris,
I have for quite a while connected my balanced XLR output CD player to my SE ended input 01A tube preamp using a Jensen JT11P1 to convert the balanced signal to SE. Works great.
Lately, at the suggestion of a diyaudio member, I connected pin2 of the DAC XLR to RCA signal positive and pin 3 of the XLR to RCA signal negative/return at the preamp and to my surprise, it works perfectly. I ignored the XLR pin 1. My preamp has a wooden chassis, so no chassis connection which I suppose means fully floating. Help me to understand why this works. I also detect no volume change between this method and the Bal to SE conversion route using the transformer. Just a very slight difference in overall tonality.
Thanks. nash
A good way to look at the situation is to begin at the input transformer's primary. Ignoring some tiny stray capacitances, the primary floats completely independent of whatever voltages appear on either of its ends (which are of course also the input terminals). "Like a bird on a (high voltage) wire" - L. Cohen. The only signal passed through the transformer is the difference between the voltages at the primary's ends.
Let's look at the signal path first: you have the minimally required two conductors between your source (DAC) and the transformer's primary. A Jensen transformer has such a high CMRR that you can practically ignore any common-mode interference. You'll have a quiet system no matter what, probably even unshielded, it works so well. If your DAC has balanced, both polarities driven, outputs you will get 6dB higher differential voltage sourcing across both polarities of each channel's output than if sourcing from one polarity to (signal) ground. If the DAC has an "impedance balanced" output you'll get either the comparatively 6dB lower output or none at all, depending on choice of polarity.
Now to shielding: by forcing the connecting cable's shield to also carry signal return you allow the connecting cable to add (to signal) interference that cannot be removed by even a perfect differential input, like your transformer effectively has. This is why signal and shield need to be carried in separate conductors for best possible performance; interference must be kept to common-mode and not allowed to become differential-mode.
In home audio we violate best practice all the time, and usually nobody notices or cares. We run more than one two conductor signal path between components, often with Earth (safety) grounds in common. This gives three paths for each channel's signal return: 1, through it's designated "shield" 2, through the other channel's "shield" (exactly as good a conductor, so exactly as much signal current) and 3, (usually) though the common safety Earth conductors (big wires but longer, still matters). It's all pretty sad, but we march on like it's still 1939. Good enough for HiFi - usually.
But you have the best possible situation, having invested in Jensen input transformers. Keep your signal away from the shields (separate conductors) and experiment with grounding the shields at one or both ends. Without strong RF interference, grounding at one end is usually best, normally the low impedance end, at the source (your DAC). Use XLRs, pin2 to pin2, pin3 to pin3, and possibly lift pin1 at the transformer end, or possibly the DCA end. You probably won't be able to discern a difference without a lot of measuring equipment that nobody (even me, and I love test equipment) has. And pat yourself on the back for planning ahead.
All good fortune,
Chris
ps: that diyAudio member was wrong, to be blunt
Let's look at the signal path first: you have the minimally required two conductors between your source (DAC) and the transformer's primary. A Jensen transformer has such a high CMRR that you can practically ignore any common-mode interference. You'll have a quiet system no matter what, probably even unshielded, it works so well. If your DAC has balanced, both polarities driven, outputs you will get 6dB higher differential voltage sourcing across both polarities of each channel's output than if sourcing from one polarity to (signal) ground. If the DAC has an "impedance balanced" output you'll get either the comparatively 6dB lower output or none at all, depending on choice of polarity.
Now to shielding: by forcing the connecting cable's shield to also carry signal return you allow the connecting cable to add (to signal) interference that cannot be removed by even a perfect differential input, like your transformer effectively has. This is why signal and shield need to be carried in separate conductors for best possible performance; interference must be kept to common-mode and not allowed to become differential-mode.
In home audio we violate best practice all the time, and usually nobody notices or cares. We run more than one two conductor signal path between components, often with Earth (safety) grounds in common. This gives three paths for each channel's signal return: 1, through it's designated "shield" 2, through the other channel's "shield" (exactly as good a conductor, so exactly as much signal current) and 3, (usually) though the common safety Earth conductors (big wires but longer, still matters). It's all pretty sad, but we march on like it's still 1939. Good enough for HiFi - usually.
But you have the best possible situation, having invested in Jensen input transformers. Keep your signal away from the shields (separate conductors) and experiment with grounding the shields at one or both ends. Without strong RF interference, grounding at one end is usually best, normally the low impedance end, at the source (your DAC). Use XLRs, pin2 to pin2, pin3 to pin3, and possibly lift pin1 at the transformer end, or possibly the DCA end. You probably won't be able to discern a difference without a lot of measuring equipment that nobody (even me, and I love test equipment) has. And pat yourself on the back for planning ahead.
All good fortune,
Chris
ps: that diyAudio member was wrong, to be blunt