XLR to RCA Adapters

Mitch2, Rwwear, and the rest of the community: Supposing the amp in question is a nice... a VERY nice (!), little vintage EL-84 job, single-ended, of course... and you want the cream de la cream minimalist input/driver circuit for it (DIY) -- you'll need phase-splitting somewhere (at the input, or maybe even as a parafeed phase-splitting "driver" transformer, given the low voltage swing those EL-84's are looking for) -- how would the step-down versions of the Jensen transformers sound vs. the normal 1:1's? I note that 1) These are rated to handle some pretty high voltages, if need be, 2) They would present a MUCH more source [output stage] friendly load used at the input, and 3) the specs on paper far exceed those for the 1:1's. Has anyone auditioned the difference in some context?

Off hand, I don't know the input sensitivity of Podolaw's BAT, but with the tube preamp, he should have some voltage swing "to burn" with a typical Red Book spec output on the source. Then, too, advancing that volume control usually improves both channel balance tracking and the quality of sound. Does this make some sense to anyone else?

Yes, the pro to consumer Isomax gives you the step-down ratio (so as not to have higher output pro gear overloading a commercial consumer unit with no volume control at the input). I'm assuming they'll make this up for you with any combination of connectors you want -- maybe with your own choice of ratio as well... It wouldn't hurt to inquire. If this route sounds good to you, do compare the data pages. Folks with rolled off (up to about -3dB at 20K) NOS chip DACs, or RIAA EQ's down about one dB at 20K might well prefer not to stack another transformer in the signal path whose FR starts to roll off before 20K. I saw step-down options on site rated to 60k, and even 180K, depending on the circuits that bookend the transformer.

One more thought: If you can get custom as easily as the advertised stock items, you might give some thought to eliminating two XLR connectors by having a flying balanced lead hardwired into the Isomax unit at its output. Perhaps Jensen could accommodate you with your lead of choice if you provide 'em with the desired bits; or tackle that end of it DIY.

Another thought, though I am not the transformer answer guy, I do note that these Jensens (and most?) input transformers of this type want to be loaded by 10K up to 25K for these applications. Your preamp may not like to see this kind of load reflected at a 1:1 ratio -- and don't just go by what someone says "will work": distortions, conventionally measurable or not, tend to increase into lower impedance loads, even with [tube] preamps presenting an output impedance of only several hundred+ ohms. So check this out carefully.

Then, too, I'd guess the BAT's input impedance would need to be modified one way or another -- and IT may not like this change. An advantage of the 4:1 impedance step-down ratio shown for the pro to consumer Isomax is that it takes a 10K impedance across its secondary, and reflects 40K back to the preamp output. All that costs you is some overall available gain in your amplification chain; you probably have a surplus of that on tap as things currently stand.
No, the transformer approach is less than elementary when tube impedances are involved.

Oh, and one more thing... You COULD get a cathodyne (split load) type phase inverter pair made up as an adjunct to the inputs on the BAT. This would get you past the issues I outlined above, at the expense of more circuitry (never a free lunch...). You'd need a power supply for that circuit (not too complicated, in this case), and it would also have the downside of needing a very small value cap at its input so that the circuit can be biased. This sort of thing is also known in a somewhat different context as a bridging adapter. Something in the 6DJ8/6922/7308 range would do. Some feel even lower impedance tubes are better for this (5687, ECC99, D3a triode connected, et.al., down to the circa 800-1200 ohm Rp jobs -- there are various choices for the latter, but their characteristics tend to be all over the place, necessitating tube selection.

Astronaut Norm Thagard designed solid state versions of this in order to bridge FOUR (or was it EIGHT?!) H-K Citation II's for his monster tube system. He published a detailed write-up in 'AudioXpress' (then 'Audio Electronics', I believe), the DIY magazine. It all worked out great, reported Norm.

So, it can be done... Are you sure you want that BAT?

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.

Fine job again, Al. Bill Whitlock and team have documented transformerless input receiver schemes that improve significantly on the all too common poor designs out there in the pro world (with respect to the issues Al has raised); but these would not normally be considered too pretty from the audiophile standpoint. I vote as well for a close reading of the Jensen literature, even if you are not a prospective transformer user (unless you're already a world class expert on grounding issues in sensitive systems -- this stuff is beyond elementary). Check the K & K Audio website for links to Dave Davenport's detailed discussion of similar issues: a second, somewhat different perspective on the same problems can throw some very helpful extra illumination on the important concepts. And again, Mr. Yaniger's piece is on point here.

For Atmasphere: Your knowledge, helpfulness, and long experience is much appreciated here. If you follow the set-up in your second paragraph above to the letter, Mr. K.,(and I highlight your spec of short cables in this case), are you better off using one of the Jensen input transformers, for some of the reasons cited earlier in the thread... or should you employ the line output type? I allow that the answer may be different, depending on the preamp in question. Thanks.