Secrets Q & A
- Written by John E. Johnson, Jr.
- Published on 02 October 2009
Part 8: Phono Preamplifiers
Now it is time to talk about a very important part of the signal path in playing LPs: The Phono Preamplifier (also called Phono Stage).
For our first look into the phono preamp, I chose three: Musical Surroundings Phonomena, Bryston BP-1.5, and Manley Steelhead, all of which are reported on here. Future cartridge, phono preamp, and turntable reviews will be published in our regular product review section.
Let's start with the Phonomena (the lowest priced of the three) which is manufactured and marketed by Musical Surroundings, located in Northern California.
At $999, this appears to be a bargain, because it has a lot of features including:
♦ Built-in automatically charging NiMH battery pack that powers the preamplifier and which disconnects from the AC supply whenever it is in operation.
♦ Adjustable gain - in 13 steps - from 40 dB to 60 dB.
♦ Switch for MM vs. MC cartridges (MM cartridges are voltage sources while MC cartridges are current sources).
♦ Adjustable resistive loading (resistance) - in 17 steps - from 30 Ohms to 100 kOhms.
♦ 300 pF (pico-Farads) capacitive loading switch, either on (300 pico-Farads) or off (200 pico-Farads).
Here is a photo of the Phonomena's front panel.
There is no on/off switch, as the Phonomena is meant to stay connected to the wall-wart power supply which keeps the battery pack charging at all times except when you are using it. The status window glows flashing red when it is charging, steady red when it is connected to the wall-wart while you are using it (a situation where the battery pack was not fully charged when you need to use it), and green when it is in use (internal relays disconnect the preamp from the wall-wart charger, you don't have to physically unplug it).
The rear panel has all the necessary jacks and switches (click on the photo to see a larger version). To turn it on, you simply touch the red status window, and it will change to green. You will hear the relays inside disconnecting from the wall-wart power.
Besides the RCA input and output jacks, each channel also has its own set of dip switches to select the gain, resistance, and capacitive load. The jack for the wall-wart cable is on the right.
So, when you turn the Phonomena on, there is only low voltage DC anywhere in the circuit. Because phono preamps have to deal with very, very low level signals (0.3 mV up to 5 mV), this is important.
I tested the Phonomena with a VPI HR-X turntable (we recently added this turntable so we can compare cartridges in future reviews, using the McIntosh MT10 with its superb MC cartridge as a reference), Sumiko Blackbird MC cartridge ($799, 2.5 mV output, 2 gram recommended tracking force, 135 ohm internal impedance, i.e., DCR or DC Resistance of the coils that will drive a 47 kOhm input on an MM phono stage if you didn't have a preamp with an MC input), BAT VK-5i preamplifier, McIntosh MC1201 power amplifiers, and Carver Amazing speakers. Cables were Nordost, Legenburg, and various others.
The Phonomena delivered a detailed, full bodied sound with low noise. The idea of having the phono preamp powered by rechargeable batteries is an excellent one, because there will be no AC interference from components that are connected directly to the AC. This reduces 60 Hz hum. The problems with commenting on phono preamplifiers are that (1) the noise floor from the LP is very high relative to whatever noise the preamp is generating, and (2) there are lots of combination of dip switch settings, and although the cartridge manufacturer lists specifications, the bottom line really depends on your listening preferences.
I changed some of the dip switches and got different sound characteristics, all appealing in one way or another, such as tight or open. So, I started marking each LP with the settings that I liked the most on that particular LP. Accuracy? Not necessarily. Pleasurable? Most definitely.
To explain this a bit further, with a large group of instruments, the high total amount of second order harmonic distortion produced by so many sources could obscure the detail of individual instruments. With a jazz quartet, on the other hand, the harmonics are only coming from a few sources, and this adds a richness to the music, making it sound more "alive"
As you can see below, I have started to accumulate re-issues of classic jazz albums. In fact, what I am finding is that I prefer listening to small groups of instruments, such as jazz trios, quartets, and quintets, on LP, while I prefer CD/SACD with orchestral music.
So, I tried different settings, listened, and gathered spectra with our Audio Precision. Here are the results.
Because I had set the Phonomena to a 475 Ohm resistance and capacitance set to "Off" when I used the MT10 with its Clearaudio cartridge, I left the settings that way to begin with the VPI and Sumiko Blackbird cartridge.
Below is shown a spectrum with a 1 kHz sine wave input (using a test LP). The second harmonic is 47 dB below the fundamental. Also note the third and fourth harmonics. The upward slope in bass response is due to the application of the reverse RIAA curve ("De-emphasis") in the phono preamp. This accentuates the low frequency surface noise, unfortunately, as well as delivers the proper curve to the LP recording.
For the distortion measurements, I used the input from a cartridge (Sumiko Blackbird) rather than generating test signals by the 2722 because I wanted an actual cartridge impedance to be placed on the phono preamp. The 2722 was used only for analyzing distortion from the phono preamp output. In the case of frequency response measurements, I used the 2722 to generate the signal (see below) as well as to analyze the output.
I then switched on the capacitive load, and gathered another spectrum, shown below.
What changed? Well, the second harmonic is now a little lower (49 dB below the fundamental), but the third harmonic is now a bit higher, the fourth is lower, and there are visible fifth and sixth harmonics. So, theoretically, the capacitive switch should be left in the off position.
Setting the resistance to 50 kOhms (the impedance of the cartridge is 135 Ohms) yielded the following spectrum. It is more like the 475 Ohm capacitive "On" graph than the "Off" graph. Therefore, I would say that the 475 Ohm load, capacitive "Off" setting would be "technically" the best. Although audible differences were not apparent, I suspect that a consumer spending hours and hours on end listening to one vs. the other settings would eventually decide on one particular setting. Remember that the Off position for capacitive loading is 100 pF, while the On position is 200pF.
Here is the Phonomena frequency response. For this test (on all three phono preamps), I used our Audio Precision to generate the sweep instead of using a sweep signal from an LP and cartridge. I set the input and gain to yield as near to 1 volt output at 1 kHz as possible, then ran the sweep, using a script that compared the preamp's output with the standard RIAA de-emphasis curve. If the preamp's RIAA algorithm corresponded perfectly with the standard curve, the result would be a flat line.
You can see that the Phonomena's response is flat from 10 Hz all the way out to 30 kHz with only a tiny deviation here and there. Overall response is ± 0.1 dB. Superb.
Shown below is the standard RIAA de-emphasis curve, to which the tested preamplifiers were compared. Basically what this means is that when a 10 Hz signal comes into the preamp, it (should) boost it by 20 dB, no boost at 1 kHz, and attenuates it by 20 dB at 20 kHz.
The Phonomena's RIAA de-emphasis EQ was the flattest response measured in all three phono preamps tested, another reason the Phonomena is a bargain. As you will see though, the others did very well also, and the deviation from the standard curve was miniscule.
In any case, I really liked the Musical Surroundings Phonomena and would recommend it to anyone on a medium budget. We will get some of the truly inexpensive phono preamps ($150 - $300) as soon as possible to make comparisons.
Next on tap is the Bryston BP-1.5.
The Bryston BP-1.5 phono preamp needs an outboard power supply. The good news is that if you have a Bryston BP-26 preamplifier, you already have the power supply that will drive the BP-1.5 phono preamp. In the photo below are the BP-1.5, then underneath that is the BP-26, and on the bottom is the power supply that drives them both. The rear panel actually has several outputs so you can power all sorts of Bryston products. The BP-1.5 is $1,800 USA not including the power supply, so it's more expensive than the Phononema and less expensive than the Manley Steelhead. The photo below shows the BP-1.5 on top, the BP-26 in the middle, and the power supply on the bottom.
Here is a photo of the rear panel (click to enlarge it). You can see the dip switches on the right side.
The BP-1.5 has variable gain settings from 35 dB up to 63.5 dB, depending on whether you have set the front panel to MM or MC. For MM, capacitive loading ranges from Off to 188 pF. Resistance is not variable.
I listened to LPs (McIntosh MT10, VPI HR-X, Sumiko Blackbird) using the Bryston BP-26 and BP-1.5 combo (the BP-26 is an excellent preamp, as reported previously), but I compared the sound of the BP-1.5 using the same preamplifier (BAT VK-5i) that I used for the other two preamplifiers for consistency in this review.
The sound was very tight and had very low noise, with plenty of gain when it was needed (the MT10 cartridge only outputs 0.7 mV). By the way, the Art Pepper album shown in the photo is one of the best re-releases on LP that I have yet heard, out of about a dozen albums that I have purchased. This particular one is the 33-1/3 re-issue at $25. If you want it in the 45 RPM version (two LPs), the price is $100. That is a bit steep for me, but apparently there are some LP aficionados out there who are willing and able to shell it out. No question but that it is a terrific album though.
The 1 kHz sine wave test is shown below. Notice that the second and fourth harmonics predominate, with third and fifth almost non-existent. This is excellent performance
Here is the frequency response. The horizontal line is the comparison of the standard RIAA curve with the response of the BP-1.5. It is within ± 0.25 dB, 20 Hz - 20 kHz.
Now to the Manley Steelhead.
I have known EveAnna Manley, chief honcha at Manley Labs for years, and she is really a special person. Let's just say that you will never get bored when she is in the conversation. But more to the point, she manufactures terrific products: preamplifiers, amplifiers, microphones, and other things, including a Phono preamplifier. Her hi-fi components are named after fish, and this one is the Steelhead. In fact the air vents on the top of the chassis are shaped like a fish.
The Steelhead consists of two chassis, one of which is the power supply, and other being the control unit. Here is a photo of the front of the control unit with the power supply on top.
On the left are the Input Selector (two MC and one MM), the Gain (50 dB through 65 dB, then capacitive load selector for each channel and resistance selector in the middle. To be more precise, there is an autoformer for the MC inputs that provide impedance load matching for the MC cartridge, while the MM load dial provides purely resistive loading for MM cartridges.
For resistance, you can select up to 400 Ohms for MC (moving coil) inputs and up to 47 kOhms for the MM (moving magnet cartridge) input. Capacitance can be loaded up to 1,100 pF (or none at all). Then, Mute, Dim (turns down the volume for when you change the side of the LP or put on a different LP), Sum (mono), Line (connects an external line-level source), and Sleep (standby - which keeps the "logic" alive) buttons. The Mute light comes on when you first turn it on, and it has to be turned off manually to start playing music. The turn-on mute delay keeps power-on thumps from being amplified downstream.
The rear panel is shown below.
The Steelhead has two variable out jacks which are connected to the volume control on the front panel. This is for using the Steelhead to drive power amplifiers rather than going through another preamplifier. If you only are listening to LPs, this would work fine. However, if you want to go through your receiver or two-channel preamp where you also have a CD player, then you should use the fixed level output. Of course, you could do both, with the variable output going to a pair of power amplifiers, and the fixed output going to a separate preamplifier. One last possibility is to use one of the variable output sets to pad the volume of another preamplifier downstream so that the input signal for that second preamp is not too high.
On the other hand, there is also a Line In, so you could connect your CD player to that input, and use the Steelhead as your preamplifier. But, if you have a third source . . . .
OK, I think you get the picture. The Steelhead is probably the most flexible phono stage in the world. It's $7,300 and that is no chump change, but in my opinion, it is worth the hefty price (the Streelhead with its two chassis is a hefty product). It has up to 72 dB gain for the MC inputs, and up to 65 dB for the MM input, which is the highest gain spec of all the phono stages we have tested so far (granted, not very many, but 72 dB of gain is high in any comparison).
The multi-pin jack in the center of the rear panel is for connection to the separate power supply. You were also probably wondering about the RFI Shunt dip switches. Those are for a situation where you hear a radio station in the background for whatever reason (you might live near a radio station transmitter antenna for example). When you are trying to deal with a signal of less than a millivolt, this can happen.
The audio chassis contains two 6922 tubes and four 7044 tubes. The whole thing is quite heavy, more so than some receivers. Tubes need a lot of power, and analog power supplies weigh a lot more than switching power supplies.
For the tests, I used the VPI HR-X turntable and Sumiko cartridge, as I did with the Phonomena.
First, the Steelhead has more available gain, and therefore, can easily work with low output cartridges, such as the Clearaudio MC in the McIntosh MT10. For high output cartridges like the Sumiko Blackbird, the Steelhead just coasts along, using one of its lower gain stage settings. In this case, I used a mid-level gain setting to bring the output voltage as close to the 2 volt output I was getting with the Phonomena. It ended up being 1.8 volts. Here is the spectrum.
The second-order harmonic is a bit lower, and the third is a bit higher than with the Phonomena.
I did not test the Steelhead with any capacitive loading selected (this is primarily for MM cartridges).
The frequency response is shown below. The RIAA comparison with the standard curve indicates that the overall response is ± 0.25 dB throughout the audible band.
The Steelhead delivered plenty of volume, with clear highs and deep bass. I had no complaints at all. Because the Steelhead lets you add or subtract resistance and capacitive loading (I did not test the Steelhead with capacitive loading because this is primarily for MM cartridges), I adjusted the resistance while the music was playing and found that different settings gave tighter vs. more open sound. You really just have to try the settings out for yourself and decide what you like. In fact, you very well might like different settings for different albums or various types of music. I don't know of any other phono preamp that offers this kind of flexibility.
I noticed that when playing jazz albums cut at 45 RPM, the sound from the Sumiko Blackbird was like the Clearaudio cartridge sounded at 33-1/3 RPM. The disadvantage of having albums at 45 RPM is that it takes two LPs instead of one, and this raises the price substantially ($50 instead of $30).
Frankly, I did not hear definitive differences between the Phonomena, BP-1.5, and Steelhead, but there are so many permutations that are possible with the settings, it is very difficult to compare them. All three sounded so good, I would be happy with any of them, but the output impedance and current drive available in the output stage of the Steelhead (the Steelhead has 350 Volt rails compared to low voltage rails in the Phonomena and BP-1.5, which means higher headroom and output capability) could be useful when you have to drive a difficult load. The large amount of gain capability in the Steelhead is essential if you need to amplify a low output cartridge, e.g., 0.7 mV. So, the Steelhead has the edge. Of course, the Steelhead is more expensive than the other two combined. Another problem in comparing the phono preamps is that the inherent high surface noise obscures the higher order harmonics that might distinguish them.
You can also change the resistance and capacitive loading while you are listening with the Steelhead, while with most other phono preamps, including the Phonomena and BP-1.5, you have to turn the preamp around and flip dip switches on the rear panel. Perhaps when we get some entry level phono preamplifiers, more clear differences will emerge. For now, all three of these products get my official approval.
I could hear more difference between 33-1/3 RPM and 45 RPM than I could between the three phono preamps listed here. It was mainly in the treble. The ride cymbals sounded more natural. Cleaner. More life. More of all the good adjectives. This is because the hills and valleys in the grooves of the LP are farther apart, so the stylus has an easier time tracking the fine detail of the high frequencies. However, 33-1/3 does still sound terrific. No two ways about it. I just wish the 45 RPM LPs were not so expensive. You might complain about $20 CDs. Well, how about $100 LPs ! ! ! ? ? ?