Esoteric Grandioso C1X line preamplifier Measurements

Sidebar 3: Measurements

I measured the Esoteric Grandioso C1X's performance with my Audio Precision SYS2722 system (see the January 2008 "As We See It") and checked some results with the magazine's more-recent APx555 system. The C1X's massive power supply chassis sat on the floor, as far away from the preamplifier chassis as I could arrange with the long umbilical cables. I took a complete set of tests using the balanced inputs, repeating some tests using the single-ended inputs. As set up with the Menu by JVS, the display showed the volume in accurate 0.1dB steps from –99.9dB to +12.0dB. The maximum gain was exactly 12dB for the balanced and unbalanced inputs to the balanced outputs. The preamplifier preserved absolute polarity (ie, was noninverting) with both balanced and unbalanced inputs. (Its XLR jacks are wired with pin 2 hot, the AES convention.)

At 63k ohms at 20Hz and 1kHz, the C1X's unbalanced input impedance was close to the specified 68k ohms, but it was lower at 20kHz, at 19k ohms. The balanced input impedance was higher than the specified 50k ohms, at 90k ohms per phase at 20Hz and 1kHz, 40k ohms per phase at 20kHz. Neither input will present any drive issues with source components. The Esoteric's balanced output impedance was a usefully low 60 ohms at 20Hz and an even-lower 35 ohms at 1kHz and 20kHz. It does not have unbalanced outputs.

The Esoteric preamplifier's frequency response into high impedances was flat from 10Hz to 20kHz (fig.1, blue and red traces) with the ultrasonic rolloff reaching –1dB at 80kHz. The C1X's response into the demanding 600 ohm load (fig.1, cyan, magenta traces) was still flat to 20kHz, but at the other end of the audioband it rolled off by 1.5dB at 11Hz owing to the increased output impedance in this region. Fig.1 was taken with the C1X's volume control at its maximum setting of "12.0dB." Both the frequency response and the excellent channel matching were preserved at lower settings of the control.


Fig.1 Esoteric C1X, frequency response with volume control set to "12.0dB" at 1V into: 100k ohms (left channel blue, right red), 600 ohms (left cyan, right magenta) (0.5dB/vertical div.).

The C1X's channel separation was superbly high, at 130dB in both directions below 1kHz, decreasing inconsequentially to 115dB at the top of the audioband (fig.2). The C1X offered extremely low noise, with the power-supply–related spuriae in its output lying close to –130dB ref. 2V (fig.3). The wideband, unweighted signal/noise ratio, measured with the unbalanced input shorted to ground but the volume control set to its maximum, was a high 85dB ref. 1V output (average of both channels). Restricting the measurement bandwidth to the audioband increased the S/N to a superb 98.8dB, while switching an A-weighting filter into circuit further improved this ratio, to 101dB. Muting the Esoteric with the remote control increased the A-weighted S/N ratio by just 2dB; even with the volume control set to its maximum, this is a very quiet preamplifier!


Fig.2 Esoteric C1X, channel separation (dB/vertical div.)


Fig.3 Esoteric C1X, spectrum of 1kHz sinewave, DC–1kHz, at 2V into 100k ohms (left channel blue, right red; linear frequency scale).

Figs.4 and 5 respectively plot the percentage of THD+noise in the Esoteric's balanced output against the output voltage into 100k ohms and 600 ohms with the volume control set to unity gain. We specify a preamplifier's clipping voltage as being when the THD+N reaches 1%. The C1X's output level at this THD percentage into both loads was 12.65V, confirming the statement in the manual that the "maximum permissible input voltage" is 12V.


Fig.4 Esoteric C1X, THD+N (%) vs 1kHz output voltage into 100k ohms.


Fig.5 Esoteric C1X, THD+N (%) vs 1kHz output voltage into 600 ohms.

Figs.4 and 5 show that the measured THD+N increases with decreasing signal levels below 5V into 100k ohms and below 2V into 600 ohms. This is because the actual distortion lies beneath the noise floor at these levels. To be sure, therefore, that the reading was not dominated by noise, I measured how the C1X's distortion changed with frequency at 5V. The THD+N percentage was extremely low throughout the audioband into 100k ohms (fig.6, blue and red traces), though with a slight increase in the top audio octaves. As predicted by fig.5, the THD+N was higher into 600 ohms (cyan and magenta traces) but still very low in level in absolute terms.


Fig.6 Esoteric C1X, THD+N (%) vs frequency at 5V into: 100k ohms (left channel blue, right red), 600 ohms (left cyan, right magenta).

Fig.7 shows the spectrum of the C1X's output at 2V, a typical maximum level that the preamplifier will be sending to a power amplifier. Though the second and third harmonics can be seen, both lie at –120dB (0.0001%), which is not much higher than the levels of these harmonics in the SYS 2722's signal generator. Repeating the analysis with the APx555's higher-precision signal generator gave the same result. Both harmonics rose by 12dB into the current-hungry 600 ohms, but this load is very much a worst case. Tested for intermodulation distortion with an equal mix of 19 and 20kHz tones at the same peak voltage level, the second-order difference product at 1kHz lay below –130dB in the left channel and even lower in the right (fig.8). The higher-order products were all below –120dB (0.0001%).


Fig.7 Esoteric C1X, spectrum of 1kHz sinewave, DC–1kHz, at 2V into 100k ohms (left channel blue, right red; linear frequency scale).


Fig.8 Esoteric C1X, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 2V into 100k ohms (left channel blue, right red; linear frequency scale).

Esoteric's Grandioso C1X offered superb measured behavior. Its extraordinarily low levels of distortion and noise rival the performance of contenders from Benchmark, MBL, and Pass Labs.—John Atkinson

Esoteric Company
US Distribution: 11 Trading Co.
3502 Woodview Trace #200
Indianapolis, IN 46268
(949) 374-4487

Axiom05's picture

Give me a break, $45K for a preamp and only a 3 year warranty. Bryston gives 20 years and Simaudio gives 10 years. Why don't manufacturers show that they have some faith in their products? Oh, I guess I answered my own question.

Ortofan's picture

... mechanical parts, such as a laser transport, volume control and/or switches.

georgehifi's picture

With todays sources having digital volume controls, and output stages very well capable of driving most amps, and more than enough gain to send those amps into clipping.
This is a review of a very expensive switch box.
Because of it's 12db output gain stage, it has to throw away most of the sources output voltage!! (sacrilege), so then it's 12db gain stage can boost it back up again noise, distortion and all.
Doesn't make sense any more to have them. It's just a very expensive switch box that adds noise and distortion, than if you went direct.

Cheers George

PeterG's picture

Although many excellent sources do have their own volume controls, and their well respected manufacturers agree that you do not need a preamp, I cannot remember a review of any of those sources that did not note they they sounded better with a pre amp in the system.

jgossman's picture

The issue is the sense of VOLUME. You can spin a pin wheel with an air compressor, lots of voltage, but never feel the cool air. Now think of a brisk wind on a summer day, you can feel it. The pin wheel (measuring device) doesn't know any difference, but you know the difference. That's the difference in a unit with 1-3 volts of output and a digital volume vs a 10 or 20 volt output POTENTIAL. It's the sense that the music never runs out of steam.

ejlif's picture

Yin and yang that is how you sum up the comparison to the D'agastino preamp? You also reviewed the AR preamp and didn't really commit to how it sounds to the Rossini direct. Inquiring minds want to know So the preamps are complete polar opposites? Hard to really decipher what is meant by that whole jumble of words in the comparison section. Esoteric Rolex, D'gastino greta garbo concealed as her name is bathed in blue on Sunset Blvd. WTF?

windansea's picture

i concur

That Other Guy's picture

I find the styling atrocious.

windansea's picture

and the marketing seems to focus more on the exterior looks rather than the underwhelming PCB innards

rwwear's picture

I'm sure it sounds great but blue displays are so nineties. And it's rather ugly IMO.

ACranston's picture

Based on JVS's comments that this preamp revealed information from well-known recordings that he had not noticed before, I would guess that this preamp is even more revealing than the D'Agostino HD. It would seem that this preamp highlights detail where you notice the individual trees more than the forest where the D'Agostino highlights the opposite. Regardless, I would love to hear it.

georgehifi's picture

"I cannot remember a review of any of those sources that did not note they they sounded better with a pre amp in the system."

Or worse!!

It hardly ever gets A/B'd and commented on, when available.

Cheers George