Musician vs. audiophile

P.S: It occurs to me that the 100K input impedance of the BAT amp probably means 50K for each of the two signals in the balanced signal pair, and the measured 14K balanced output impedance of the preamp at 20 Hz (assuming the Six-Pak is not installed) probably means 7K for each signal. So when the subs are connected the one signal in the balanced signal pair that is connected to both the sub and the power amp would be loaded by 50K in parallel with 50K, which is 25K. 25K/7K is a ratio of about 3.6, still not good! Also, there would be a significant imbalance between the impedances of the two signals in the balanced signal pair, given the high output impedance of the preamp, which is also not good.

All of this assumes, though, that the balanced and unbalanced outputs of the preamp are not driven by separate and independent output stages. That is the case with most preamps which provide both balanced and unbalanced outputs, but I don’t know for a fact whether or not it is the case here.

Regards,
-- Al

Charles1dad 12-30-2017
I believe most if not all BAT power amplifiers have input impedances of 100K ohms.

Right you are, Charles, as usual!

Repeter, as Charles indicated the input impedance of your amplifier is spec’d at 100K (much higher than the input impedances of the majority of solid state amps). And the input impedances of many and perhaps most JL subs are spec’d at 50K unbalanced/10K balanced. So provided that you are using balanced connections between the preamp and power amp and unbalanced connections to the subs impedance compatibility is probably not the **major** contributor to the issue. Although it nevertheless is probably contributing significantly to the bass issue you described, given the **extremely** high 14K balanced output impedance of the preamp at 20 Hz (assuming the Six-Pak option is not installed), and given that the 100K and 50K loads together constitute a load of 33K. 33K/14K is a ratio of about 2.4, far short of the generally accepted rule of thumb guideline of a minimum ratio of 10 at all audible frequencies. With the consequences of that shortfall being particularly compounded by the wide variation of the preamp’s output impedance over the frequency range.

Also, it is still quite possible that if the cables to the subs are particularly long and/or if they have high capacitance per unit length their capacitance could be affecting the upper treble content of the signals received by the BAT power amp.

Regarding ...

Repeter 12-30-2017
Cabling from pre to power amp would be Nordost. Could these long (2 meter) flat silver (Ag) play into flat/dull performance at low volume? FYI, I used them to drive my Sophia 3s and Geoff Poor (BAT) recommended the massively improved Audioquest CV-8s. So.. Could driving my power amp with these be a weakness?

... I’m not sure I follow this. I thought the CV-8 is a speaker cable. And what specific model are the Nordost interconnects?

Regards,
-- Al

To add to my previous post, many McIntosh solid state amplifiers have balanced and unbalanced input impedances in the vicinity of 20K. Driving impedances in that vicinity will almost certainly be a problem for your preamp, if it does not have the Six-Pak upgrade installed.

Regards,
-- Al

I suspect that an impedance compatibility issue is contributing to the problem. Your BAT VK-3iX (I assume that is what you meant) has output impedances for its XLR and RCA outputs that are very high and that also vary widely across the frequency range, at least if your unit does not have the optional Six-Pak upgrade. From Stereophile’s measurements:

The VK-3iX’s output impedance was also high, and this might well have an effect on sound quality, depending on the input impedance of the partnering preamplifier [I assume he meant "amplifier"]. The unbalanced source impedance varied from 7k ohms at 20Hz to 1460 ohms at 1kHz and 2650 ohms at 20kHz, while the balanced figures ranged from a very high 14k ohms at 20Hz to 1850 ohms in the midband and above.

You didn’t say what amplifier you are using, but those numbers definitely indicate that sonic issues **will** arise with many and perhaps even the majority of solid state amps.

Also, I suspect that like most JL subs your subs probably provide only line-level inputs, and you are either driving the power amp from the preamp’s XLR outputs and the sub from the preamp’s RCA outputs, or vice versa. Many and perhaps most preamps providing XLR and RCA outputs do not drive the two pairs of outputs from separate output stages, and the signal provided to the RCA connector for each channel is the same signal that is provided to one of the two signal pins on the corresponding XLR connector. If that is the case with the VK-3iX the input impedance of the subs and the capacitance of the cables to the subs (especially if those cables are relatively long) can both have audibly significant effects on the signals received by the main power amp, that are reproduced by the main speakers. So if you already haven’t done so assessing the sonics provided by the Sophia with the sub cables disconnected from the preamp may provide useful insight into the issue.

Good luck. Regards,
-- Al