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.
Chart 1 - Frequency
Response at Unity Gain with IHF and Instrument Loading |
![](chart1.gif)
Red line = instrument loading
Magenta line = IHF loading
Chart 3 - Distortion
as a Function of Output Voltage and Frequency |
![](chart3.gif)
Instrument loading (close to unity gain)
Magenta line = 20kHz
Blue line = 20Hz
Red line = 1kHz
Chart 4 - Distortion and
Noise Spectrum |
![](chart4.gif)
Red line = spectrum of 1kHz test-signal distortion and AC-line harmonics at 0.5V input and
close to unity gain
Chart 6 - Phono-Stage RIAA
Equalization Error |
![](chart6.gif)
Instrument and IHF loading
Red line = left channel
Magenta line = right channel
Chart 7 - Phono-Stage
Distortion vs. Frequency and Output |
![](chart7.gif)
IHF loading (at tape output)
Magenta line = 20kHz
Red line = 1kHz
Blue line = 20Hz
|