XLR to RCA Adapters

"When one considers the noise cancellation properties of balanced, then you can easily see the reason for superior audio. Less noise equals better sound. "

I auditioned Joule-Electra LA-150Mk2, then I owned LA-300ME for an year and now I am blessed with LA-450ME. All these preamps have balanced amplification in the gain stage but (except 450) their inputs and outputs are single ended i.e. Joule-Electra split single ended on inout and add on output.

As much as I tried to hear any (AMY!) noise when I place my ear to the speakers I hear nothing, nada, ziltch, zero etc.

I cannot remove noise I do not hear !!!!! I am sure theere are other SE preamps without producing noise and one shoyld be careful what kind of IC he has

Most "audiophiles" love word "balanced" without realizing the immense difference between balanced input/output and balanced signal processing (amplification here) which cancel not so much noise as DISTORTIONS !!!!!!!! and this make immense difference in distortion-free music presentation.

Of course there are many instances where hum is not a problem. I just like balanced because you never know when adding a component or a new light fixture or dimmer will create a problem.

08-22-11: Bob_reynolds
Mitch2,
Just curious... Why did you select an input transformer when your amps have balanced inputs instead of an output transformer, like Model DM2-2RX?
Wouldn't it be theoretically better to have shorter RCA cables at the preamp and longer XLR cables to the amps?

Bob, that's an excellent question.

I'm not entirely sure of the answer, but I believe it relates to differences in inter-winding stray capacitance (i.e., between primary and secondary) of output transformers vs. input transformers. I've noticed that the schematic representations of the Jensen input transformers that I've looked at all show Faraday shields, which would greatly reduce that stray capacitance, while none of their output transformers that I've seen include those shields. I have no particular knowledge of why that may be; presumably it has some relation to the fact that output transformers have to be able to drive much longer cable lengths.

Lack of a Faraday shield in the output transformers results in very substantial inter-winding capacitance. For instance, the this output transformer is spec'd as having 22,000 pf of capacitance between windings, as measured at 1kHz.

A result of that capacitance will be that the input stage of the amp would see, "looking back" at the output of a preamp + output transformer combination, an impedance which is very unbalanced between the two legs at high frequencies (since one side of the transformer primary is connected to preamp ground, while the other side is not). That imbalance will significantly degrade the cmrr of the amp's balanced input stage, at the high frequencies for which that capacitance becomes significant.

Hopefully someone more knowledgeable about transformers than I am will comment further, but I suspect that the explanation is along those lines.

Best regards,
-- Al

Yes, Al, I think you have it right. Bob, the up to 60K bandwidth I mentioned above was for the Jensen output transformer, and the out to 180K was for the step-down input version -- with Faraday shield. For more on the benefits of input transformers, see Stuart Yaniger's DIY buffer preamp article at DIYaudio.com. Stuart [sp?] graphically shows how the Jensen input tranny not only lowers input noise, but also how it lowers his simple circuit's distortion. Interesting... almost like magic. This treatment is relatively in depth, from an audiophile's perspective; but not overlong.

No one's mentioned the other advantage of deriving your balanced (or quasi-balanced, if you prefer) signal at the BAT's input -- the simple practical advantage of using the far more common unbalanced
interconnect from the preamp... more common for Audiogon shoppers and experimenters, anyway.

Hi guys, I just had a chance to check in and see Bob's question about the input transformers. I believe these minimized any impedance differences, as long as you keep the balanced IC's from the transformers to the amps very short. Jensen says 1M or less, but shorter is better. Of course the ideal approach would be to mount the transformers internally with RCA inputs to the amps.

Between talking with Jensen and going over their literature, I remember that the input transformers were clearly the better approach for the rca/XLR interface. Virtually no sonic penalty with regards to measurements (I believe some very small input loss - like 1.5 dB) which I cannot detect even when comparing to balanced preamps. They work with loads as low as 10K ohm and I believe the impedence issues are somewhat related to the load, and to the transformer to amp cable length. My highish 100K ohm input amps result in an optimal impedance situation. The transformers also provide noise rejection benefits. Here is a link to read,[url]http://www.jensen-transformers.com/datashts/pi2xx.pdf[/url]

The guys at Jensen and the associated documentation do a better job of explaining than I can. Compared to giving up equipment you like the price of trying the transformers make them a stupid easy decision. I remember initially trying the output transformers based on someone's suggestion but they were noisy and didn't sound good, I called Jensen and they told me "you want the input transformers." They swapped me for the input transformers and I later purchased their mono version to keep cables very short - mine are like 2 feet long from the transformers to the amps. Call Jensen, they are very friendly and knowledgeable.