[Peter_S]

Hello All.  I am looking for input from those who understand such things....

I have a pair of Audeze LCD3's that have both single-ended and balanced cables. I understand that the single-ended cables take the positive signals (+) from each channel and return the signals to a common ground.  I understand that the balanced cables take the positive (+) from each channel and return each channel to the amps negatives (-) for each channel.  At one point I was thinking of using a pair of 300b monoblocks to power my LCD3's, and Audeze told me that I could simply do this by hooking their 4-pin balanced connector to the R+, R-, L+ and L- terminals of my amplifiers (with proper pin matching).

At this point in time, I having a Korneff 45 SET amplifier built for my LCD3's.  The planar magnetic headphones can handle the 2-3 watts put out by the 45 SET amplifier. The amp builder is planning on providing both speaker terminals and a single-ended headphone jack.  I'm wondering if I should ask for both single-ended and balanced jacks, or perhaps just a balanced jack.  Or, if he only provides a single-ended jack for headphones, if I can attach the LCD3's to the speaker terminals as discussed above.

I understand that the amp design does not make a true balance signal, using either: a) two amplifier circuits for each channel to process the normal and inverted signal, or b) a balancing transformer to invert the signal and create a normal and inverted output per channel.  Asking for either of those options would go beyond the basic amplifier design.  So, if neither of those options are used, my questions are:

1) is there any value to including a 4-pin jack for the LCD3 balanced cable as described above?

2) Is it possible to have a 4-pin XLR jack and a 1/4" single-ended jack on the same amp?  Are there issues with the fact that the single ended jack has a common ground?

Thanks in advance for your advice.  Peter

PS - wiring diagram for LCD3 balance cable below:

[Peter_S]

PS - I forgot to mention that the 45 tube amplifier is stereo, not two monoblocks.

[mgalusha]

Since the amp will have output transformers it should not be a problem to wire a 4 pin output with separate grounds as shown in the drawing. The key being that the output of the transformers is floating and doesn't have one side grounded.

[Quiet Earth]

Also, when you wire an unbalanced connector in parallel with a balanced connector, both connectors become unbalanced. I think you would need a switch of some sort to separate the two.

I would be more concerned with the transformer's output impedance at the headphone jack rather than whether it's balanced or single ended.  If the primary goal of the amp is headphone use then a standard 8 ohm speaker tap might not be optimal for a 50 ohm headphone load. It would be cool if the amplifier was made with an eight ohm transformer tap hardwired to the speaker binding posts, and a 16 or 32 ohm tap hardwired to the headphone jack. I don't know if that was a consideration or not, but that seems like the best way to use a tube amp for both situations.

Let us know how it turns out.

[Peter_S]

Good suggestion QuietEarth.  Here are the specs for the headphones:

•Impedance:  45 Ohms, purely resistive
•Efficiency:  91 dB/1 mW