XLR to RCA Adapters

All of the line output transformers I have ever seen need some kind of load, but its not so much for transient response as for flat frequency response.

Proper transient response and flat frequency response of course go hand in hand, especially in the HF/ultrasonic region, where a poor quality transformer tends to resonate.

But for a bit of perspective, I pulled out a John Hardy M-2 mic preamp and ran a couple of sweeps. This uses a Jensen JT-11-BMCF output transformer, and its response deviation between 150, 600, and 100K loads were all within +/- 0.1 dB of each other from 20Hz to 50KHz. Measuring the AP System One itself (Bruce Hofer's patented transformer output circuit) delivers virtually indistinguishable performance into all three loads (less than +/- 0.01 dB of each other) from 20Hz to 200KHz.

Pretty good for a bit of iron, eh?

Forgive me, but I skimmed through this thread and could not (or did not) find the answer about what is best to use between balanced amp and single ended preamp. In my case a balanced only Burmester 911 MK3 and RCA only Concert Fidelity CF80-LSX. Right now I am using Burmester adapters.

Talk2me, several references to your amp that I've seen indicate that it has rca as well as xlr inputs. Is that not the case with your particular amp?

In any event, the reason you didn't find an explicit answer as to the best way of interfacing rca outputs to xlr inputs is that there is no answer that is universally applicable and universally agreed upon. Relevant variables include cable length, component impedances, susceptibility to ground loop effects, rfi/emi environment, deep bass extension of the speakers, etc.

In your case, I found a post somewhere indicating that the balanced input impedance of your amp is an unusually low 2,000 ohms. If so, that probably rules out the Jensen input transformer approach, and limits you to a choice between a Jensen output transformer, such as their model DM2-2RX (the "RX" version is the same as the "XX" version referred to in the data sheet, except that it has rca input connectors), or the adapters you are presently using, or adapter cables. As Mitch2 suggested, you should speak with a Jensen rep before finalizing a choice of one of their transformers.

See section 2 of this paper for further information. Note that for all three of the methods that are illustrated the cable has symmetrical signal and return conductors (i.e., it is not a coaxial unbalanced cable).

Regards,
-- Al

Pretty good for a bit of iron, eh?

It is indeed! Did you get a chance to check the bandwidth at 10Hz and 5 Hz also?

It is indeed! Did you get a chance to check the bandwidth at 10Hz and 5 Hz also?

I just ran an existing scripted procedure on the M-2, and it started at 20Hz. The Gen-Mon results I did manually, but I neglected to change the LF end of the sweep. And the System One only goes down to 10Hz . . . for subsonic results I have to use a function generator, then measure with a 'scope . . . big pain. THD results are even tougher; I need to use a DSO sync'd to the generator to acquire the waveform, average 64x to reduce noise, perform an FFT with a rectangular window sized to the exact generator frequency, then calculate the THD from the sum of the harmonics. Ugh.

Jensen's datasheets are probably more accurate at subsonic frequencies than my measurements . . . Deane Jensen was actually a pioneer in many of the techniques used to acheive accurate results in this region.