June 2007

Convergent Audio Technology SL1 Ultimate Mk 2 Preamplifier: Measurements

All  preamplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test preamplifiers there. All measurement data, including graphical information displayed below, is the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

• Measurements were made at 120V AC line voltage.
• This preamplifier's line and phono sections do not invert polarity.
• AC line current draw while operating: 0.66A
• Gain (instrument loading):
  • Line section, Lch/Rch = 19.54X, 25.8dB / 19.52X, 25.8dB
  • Phono section (at 1kHz), Lch/Rch = 217.0X, 46.7dB / 217.3X, 46.7dB
• Gain (IHF loading):
  • Line section, Lch/Rch = 19.34X, 25.7dB / 19.32X, 25.7dB
  • Phono section (at 1kHz), Lch/Rch = 215.8X, 46.7dB / 216.2X, 46.7dB
• IHF sensitivity:
  • Line section, Lch/Rch = 25.9mV / 25.9mV
  • Phono section, Lch/Rch = 2.3mV / 2.3mV
• Output impedance at 1kHz:
  • Line section = 102 ohms
  • Phono section (at tape outputs) = 51.6 ohms
• Input impedance at 1kHz:
  • Line section = 44.9k ohms
  • Phono section = 45.8k ohms
• Output noise versus bandwidth and volume-control position:
  • Volume control turned CCW, wideband, Lch/Rch = 0.107mV / 0.103mV
  • Volume control turned CCW, A weighted, Lch/Rch = 0.018mV / 0.020mV
  • Volume control at close to unity gain, wideband, Lch/Rch = 0.138mV / 0.133mV
  • Volume control at close to unity gain, A weighted, Lch/Rch = 0.022mV / 0.024mV
  • Volume control turned CW, wideband, Lch/Rch = 0.121mV / 0.118mV
  • Volume control turned CW, A weighted, Lch/Rch = 0.021mV / 0.022mV
• Phono referred input noise, 1k-ohm source impedance:
  • Wideband, Lch/Rch = 0.92µV / 0.56µV
  • A weighted, Lch/Rch = 0.32µV / 0.32µV
• Phono overload at 1kHz (at tape output)
• instrument load = 206mV
• instrument load = 136mV

General

The CAT SL1 Ultimate Mk 2 preamp has ten tubes and various solid-state devices arranged in what appears to be two sections of five tubes each -- most likely for the phono and line stages. Tubes are 6922 and 12AX7 types. Proprietary CAT capacitors and other components abound, along with beautiful stepped volume and balance attenuators.

Chart 1 shows the frequency response of the SL1 Ultimate Mk 2 with the volume control set for close to unity gain and for instrument and IHF loading. As can be seen, this is a wideband unit. The IHF load drops the output a small bit and starts to roll off the low end. We are talking about small fractions of a dB here.

Usually for preamplifier line stages, there is Chart 2 to show how the frequency response varies with volume-control setting. In the case of this preamp, there is no need for any other response than that shown in Chart 1, as the response is exceptionally uniform with volume-control setting. Further, the tracking between channels was within a very small fraction of a dB over the whole volume-control range.

Chart 3 shows how THD+N (total harmonic distortion plus noise) varies as a function of preamp output level. The volume control is set for as close as possible to unity gain. The data shown are for instrument loading. Distortion with IHF loading was actually a little less. Amount of distortion is among the lowest measured for line stages.

With the volume control again set for close to unity gain, a plot of the spectrum of the 1kHz THD+N at 0.5V output is shown in Chart 4. Results for this test were about the same for instrument and IHF loading -- no visible distortion components and extremely low AC-hum components.

Since this preamp has no tone controls, there is no Chart 5 to display the tone-control characteristics.

RIAA equalization error for the phono stage is plotted in Chart 6. I must say, this is the least error in RIAA equalization I have ever seen, and I have measured tons of phono stages during my career.

Phono THD+N vs. output voltage and frequency is shown in Chart 7 for instrument loading. This test was done with the Audio Precision Harmonic Analyzer program with harmonics up to the seventh included in the plotted sums.

Red line = instrument loading
Magenta line = IHF loading

Instrument loading (close to unity gain)
Magenta line = 20kHz
Blue line = 20Hz
Red line = 1kHz

Red line = spectrum of 1kHz test-signal distortion and AC-line harmonics at 0.5V input and close to unity gain

Instrument and IHF loading
Red line = left channel
Magenta line = right channel

IHF loading (at tape output)
Magenta line = 20kHz
Red line = 1kHz
Blue line = 20Hz

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