So last week (~April 4-10), we conducted the first of several comparisons of audio equipment. This particular test involved 2 preamps: The Manley Steelhead and the Pass Labs Xono. Both are high-quality and expensive amplifiers that have received praise in several reviews.

The point of the experiments is to use features that characterize the devices, towards a better understanding of their (potential) differences in later subjective evaluations.

To measure these preamplifiers, we are using an AP2700. The measurements being used are:

1. frequency response
2. phase response
   
3. idle channel noise
4. intermodulation (IMD)
5. THD+N vs. amplitude
6. THD+N vs. frequency
7. crosstalk

We are interested in 2 kinds of inputs, moving coil (MC) and moving magnet (MM). For the purposes of this experiment, we chose to use 3 possible input levels for each input, based on the range of plausible output voltages from cartridges mounted on a turntable.

For MC we tested 100 uVrms, 400 uVrms, and 600 uVrms
For MM we tested 5 mVrms, 7 mVrms, 10 mVrms.

These values were determined after consulting the Handbook for Sound Engineers. In future test it has been suggested that we instead use an average output voltage of the cartridges purchased for this project.

Below is a picture of our test setup:


The AP generator was connected to the audio RCA inputs (either MM or MC) on the device under test (DUT), and the output of the DUT was then connected to the audio input of the AP 2700. For cable connections, we chose to use the Kimber Kable, KCAG cables, as in both the cable tests from a couple months ago, and additional informal testing at CIRMMT, we found that these performed (tested using THD+N) as well or better than than others.

Both the XONO and Steelhead have several settings. The Steelhead settings are easily controlled with knobs, while the the XONO settings are controlled by changing jumpers and switches inside the unit itself. For each test then, the switches had to be changed in accordance to the settings we selected for the test.


From top to bottom, the gold pairs on the right of the unit are the 2 possible input terminals (MM and MC) for each channel, followed by the output terminals. The switches to change settings are located directly left of the gold terminals.

The different tests for the Steelhead were as follows:

Gain setting: 55


A = Moving Coil:

A1: loading: 25 Ohms
A2: loading: 50 Ohms
A3: loading: 100 Ohms
A4:loading: 200 Ohms
A5: loading: 400 Ohms

B = Moving Magnet:

B1: loading: 25 Ohms
B2: loading: 50 Ohms
B3: loading: 100 Ohms
B4: loading: 200 Ohms
B5: loading: 47 Ohms


and for the Xono:

XONO test configuration:

high gain (10 dB boost): off

A = Moving Coil:

A1: loading: 10 Ohms
A2: loading: 47 Ohms
A3: loading: 100 Ohms
A4: loading: 475 Ohms
A5: loading: 1000 Ohms

B = Moving Magnet:

B1: loading: 100 PF
B2: loading: 220 PF
B3: loading: 330 PF