A new approach. One measurement, all preamps.

THD v. Frequency for all four preamps w/ MC selected (input: .5 mVrms)... (in dB). This is somewhat arbitrary, as the Bryston doesn't have a fixed output voltage. For an appropriate level of comparison, I adjusted the volume knob to reach ~ .5 V output (the approximate mean of the others).

• Blue = Pass Labs XONO
• Red = Manley Steelhead
• Yellow = Bryston BP26
• Green = GSP Audio Jazz Club w/ Elevator
  

So the next round of testing was performed...

I began with the XONO, with my main aim being to correct the THD+N v. amplitude graphs from the previous tests. This time, the measurement was taken with standardized values for the input voltages (200 uV - 1mV for MC, and 600-5mV for MM) and capacitive loading (100 ohms for MC, and 47 kohms for MM).

This THD+N (MC) looks a lot more like the XONO factory pic. I think my error in the previous one was that the reference voltage wasn't corrected...the range here was 10 uV - 10mV.

This is THD+N vs. frequency for the MC input.


Frequency response for the XONO MC input.
and the phase response.

Finally crosstalk.

The Moving Magnet response was pretty much similar. Below are screenshots of these graphs.

This is the correct THD+N for the MM input. The range is 600 uV - 250 mV. Looks like the factory pic.


The THD+N vs. frequency for the MC input looks just like the MC input.

as does the frequency response...

and phase response.

The cross-talk is a bit different though. The values are about 10 dB lower in the MM.

IMD and idle channel noise for both the MC and MM inputs can be seen in the previous posts with screenshots. Next up tomorrow is the Steelhead.

new cartridges (unless otherwise noted, output @5.0 cm/s):

(1) Benz Ace H (MC): (2.5 mV @ 3.54 cm/s)
(2) Clearaudio Aurum Beta (MC): 3.5 mV
(3) Denon DL-103 (MC): 0.3 mV
(5) Dynavector 17D2MK2 (MC): 0.26 mV
(7) Dynavector DV-10X5 (MC): 2.5 mV
(6) Dynavector DV-20X (MC): .3 mV
(4) Dynavector XV-1s (MC): 0.3 mV
(11) Grado DJ-100 (2-4 mil stylus) ("Grado hybrid"/MC): 5.0 mV
(9) Grado Prestige 78C ("Grado hybrid"/MC): 5.0 mV
(8) Grado Prestige Gold ("Grado hybrid"/MC): 5.0 mV
(10) Grado Prestige 78E ("Grado hybrid"/MC): 5.0 mV
(12) Ortofon Super OM 30 (MM): 4.0 mV
(13) Ortofon Kontrapunkt Bach (x2) (MC): 0.45 mV
(14) Ortofon Super OM 20 (MC): 4mV
(15) Shelter Model 7000 (MC): (0.55 mV-0.65 mV)
(6) Shelter Model E501 II (MC): 0.4 mV
(4) Sumiko Blue Point Special EVO III (MC): 2.25 mV

Things I have learned about THD+N measurements:

1. use a logarithmic scale
2. let the preamplifier warm up again between measurements

This second point is very important as I was informed by the Pass Labs engineers that I will see a 10-fold increase in THD+N if I measure immediately after the settings have been changed.


The above plot of MC THD+N demonstrates this 10x effect (XONO factory traces are not shown as they are not public images).


Here is the MM THD+N vs. Amplitude. Again, we are seeing a 10-fold increase in distortion+noise. A logarithmic scale would draw out the subtlety of the effect given lower signal.

I intend to retake these measurements when I use the AP again.

This morning I read some articles on the Manley Steelhead, in hopes of finding some reference AP charts. I have also contacted Pass Labs, and they have kindly sent me some references to verify that the results I am receiving for the XONO are correct. I will be comparing these later today...

Below are some examples of the measurements taken from the experiment explained in the previous post.

Frequency Response


This first figure (above) shows the stereo frequency response of the Steelhead for its MC input (and 400 ohms), with input values of .1, .4 and .6 mV. There is an interesting upwards curve starting at ~4kHz.


In comparison, here (above) is the frequency response of the XONO (@ 475 ohms). The curve exhibited by the Steelhead (although small) is not present here.

2. Phase Response:


Above is the phase response for the Steelhead. Phase response is most basically the ratio of the phase output to the phase input.


For comparison, here is the phase response of the XONO.


3. Idle Channel Noise:

Above is Idle Channel Noise for the Steelhead.


Above is idle channel noise for the XONO. The Steelhead has almost a 10-20 dB lower noise floor than the XONO for much of the auditory spectrum. Also interesting is that this how much louder this is than the idle channel noise for the MM cartridge (see below).

4. Intermodulation Distortion (w/ 2 frequencies: 19 kHz and 20 kHz [both at 0.6mV])

Above is the IMD for the Steelhead.


Notice the peak at 1KHz that is above the otherwise similar noise floor to the idle channel noise above. There are also some interesting things going on at 8 and 16 kHz. Not sure what that is, as it appears in the other measurements of the XONO (such as the idle channel noise for the MM cartridge [see below...]). The 1 kHz tone is caused by non-linearities in the device that cause the input signal to create beat frequencies (largest of which is the often the difference of the 2 signals).


5. Crosstalk vs. Frequency

Here is crosstalk vs. frequency. It is performed by measuring the signal in the an idle channel when sending signal through the opposite channel. Seems strange that we're seeing a few of those bumps, but those were present in both the Steelhead and XONO as is seen below.


The crosstalk for each of these is pretty good. Each line in the above graph is a channel trace of the amount of signal in the empty channel from the one that has signal. The low values of the red curve, and perhaps also the higher values of the blue curve at LOW frequencies could be the result of timeouts that occured during testing. As a sidenote, a timeout occurs with the AP as it records several values, and uses a settling algorithm to provide a final value for the measurement being taken. If the results are too varied, it has difficulty producing the settled value and instead provides an average of the last six values. The low frequency values were marked with the timeout symbol "T" when conducting this test.

Also of note, crosstalk is frequency-dependent: there is a +6dB increase in crosstalk for frequency octave.


Below are selected results for the moving magnet level inputs. Both units were set to 100 pF. The XONO was set to 47 ohms and the Steelhead was set to 50 ohms.

1. Frequency Response


That's a big jump! The above frequency response for the Steelhead demonstrates the output for swept frequencies at input voltages of 5, 7, and 10 mVrms.

The gain increase of the XONO was not as significant. However, the XONO also has a 10dB boost setting which was not tested. Also of interest is the intervals between the 3 input signals tested. Seems like quite a difference between 7 and 10 mVrms for the XONO, but less so for the Steelhead. Its the other interval (5-7 mVrms) that seems to be significant for the Steelhead.

2. Phase Response


The Steelhead MM phase response.


The XONO MM phase response is very similar to its MC response.

3. Idle Channel Noise

The above figure is the Steelhead idle channel noise. Strange peak at 16 kHz.


Notice how the noise floor of the MM setting is lower than the above MC setting. Also notice the peaks at 8 and 16 kHz. Strange.

4. Intermodulation Distortion (IMD)



This is the IMD for the Steelhead. The 1 kHz frequency peak is pretty substantial. The input for the IMD test was again 19 and 20 kHz test tones.
No difference beat frequency (1kHz) for the XONO. Instead take a look at that regime of beat frequencies surrounding the two main peaks. This is because the two frequencies interact not just as the difference, but frequencies f1 and f2 produce new frequencies at (and not limited to) f3 = f1 + f2, f4 = f1 - 2f1, and f5 = f1 + 2f2.

5. Crosstalk vs. Frequency

This is the crosstalk for the Steelhead MM. Looks pretty good at -80 dB, 20-20kHz.

Crosstalk for the XONO seemed better than the Steelhead. Again, as with the MC XONO settings above, this test was plauged by AP2700 timeouts at low frequencies; possibly affecting the difference in channels.

more to come: THD+N vs. Frequency and THD+N vs. Amplitude.

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

New site for MAQ blog

After wrangling with html every time I wanted to report on the project, I have decided to join the 21st century and just use a tried and true method. So here it is, the new blog.

On this site, you will find the day-by-day trials and tribulations I face in attempting to measure high-quality audio gear for a research project for which I am a research assistant.

For previous information on the work done thus far, please see the old site, that exists here.