Nov 042011
 
The Mark Levinson No. 28 preamplifier

Introduction

This is a user review of the Mark Levinson No.28 preamplifier. Despite bearing the Mark Levinson name, the design was made after Madrigal had bought out the Levinson brand and design rights. It also explains the change of the model number designation from “ML- xx” to “No. xx”.

I have used this preamplifier for a couple of years now, it replacing a much loved and in some ways more versatile preamplifier: the Quad 44 that had been in use for about 25 years.

Like all audio products the Levinson is not perfect; it has good and bad things about it. Lets get those aspects that I don’t like out of the way first, and then we can concentrate on what the Levinson does well.

Aspects I don’t like:

1 It uses CAMAC connectors as interface for the majority of the inputs and outputs.


Rear of the Mark Levinson No. 28 preamplifier showing the input and output connections: XLR for balanced line, CAMAC for unbalanced coaxial line

Mark Levinson seems to be the only audio manufacturer who uses this type of connector. They are expensive and, to my knowledge, are only manufactured by three Swiss companies: Fischer, Lemo and Huber & Suhner. Furthermore, the maximum outer diameter of any coaxial cable that can be fitted is 5.8mm. They are thus less versatile than the ubiquitous RCA ‘phono’ connector.


Lemo (top) and Fischer (bottom) CAMAC plugs

There are adaptors to convert RCA plugs to CAMAC plugs, but these too are expensive and are hard to find.


Fischer CAMAC to RCA phono adapters

2 The preamplifier is intended to be left permanently ‘powered up’.

The preamplifier itself is powered by a separate power supply (designated the PLS 228), but this is devoid of an ‘on-off’ switch. Levinson have always intended their preamplifiers be left permanently powered up. There are arguments in favour of this: the preamplifier is constantly warmed up and the electronics have settled down. Also frequently switching electronics on and off tends to shorten their life.


Levinson power supply PLS-288 for use with the model No.28 preamplifier

However it goes against the grain for those of us in the UK to leave electronics switched on all the time, for reasons of safety – certainly the lack of an on-off switch contravenes current IEC/CE regulations. Fortunately the ‘standby’ current consumption of the preamplifier is low.

3 The preamplifier lacks a balance control or a ‘mono’ switch.

For many this won’t be important and it is in line with minimalist philosophy of Mark Levinson. However I am of the opinion that whilst the audio replay channels might be entirely symmetrical, one does not either sit in a listening position exactly central between the two speakers, nor does one’s listen in a room that is entirely symmetrical. In my situation, not only is my listening room not symmetrical, either in shape or in content, but I use Quad ESL 57 speakers; known for their ‘beaming’ of the higher frequencies.

I found that I had to make small (a few cm) adjustments to the position of one speaker in order to ‘centralise’ the image from my listening position. However having done that, it might be argued it was a small price to pay for the potential benefit in removing an additional control from the preamplifier circuitry.

Again the lack of a ‘mono’ switch is of only interest to those who have an extensive collection of mono vinyl recordings that are not in the best of condition. Whilst any monophonic recording will hopefully be presented with an audio image midway between the speakers, any groove wear or scratches will annoyingly manifest itself as ‘clicks and pops’ that emanate from one speaker or the other. With a ‘mono’ switch the two audio channels are superimposed, so that the ‘clicks and pops’ are also placed centrally along with the music, and tend to be buried and thus less intrusive.

Clearly Mark Levinson assumed the users of their products would only play software in impeccable condition, so would have no need for a ‘mono’ switch, and like the absence of a balance control removes extraneous switching that might compromise the audio signal. Again like the absence of the balance control, it is only a minor quibble and not a damming criticism of the design.

Now that we’ve got the ‘niggles’ out of the way, let’s now look at what’s good about the Levinson No 28 preamp.

Aspects I do like:

1 It uses CAMAC connectors as interface for the majority of the inputs and outputs.

Wait a minute; haven’t I listed this as a criticism? Well yes, because CAMAC connectors are specialised and expensive, but compared to the ubiquitous RCA phono design they are vastly superior.

It has to be understood that the RCA phono connector was designed back in the 1940’s to be a cheap connector to allow phonograms (hence their name) to be connected to amplifiers. They rapidly replaced the much superior (but more expensive) 1/4″ jack plug, current at that time. It is unfortunate that the coaxial RCA phono connector has been adopted as the industry standard, but it is likely that low cost and small size had a lot to do with it. One of the design flaws of the RCA phono connector is the centre conductor of the plug extends beyond the outer (ground) conductor; having the undesirable consequence that the live connection is made first when the connector is mated, and disconnected last when de-mated. In spite of the modest design, audio designers have universally adopted the RCA connector to the extent that virtually all, modern, audio equipment now uses them.

To match improvements in component design, RCA phono connectors are now available made to a much higher build quality; using solid turned metal parts and PTFE insulation. Conductors used are now either gold plated or silver plated brass or tellurium copper. Some manufacturers use rhodium as a plated finish. But whatever the standard of build quality, the inherent design of the RCA is poor, and since the cost of the better quality versions is as much as that of the electrically superior CAMAC coaxial connectors the case against using CAMACs is weakened.

CAMAC stands for: Computer Automated Measurement And Control, an IEEE-standard (IEEE 583), high performance, real-time data acquisition and control system concept. Established in 1969, CAMAC now appears in many thousands of scientific, industrial, aerospace, and defence test systems in more than 40 countries. Owing to the quality and reliability of the connection, CAMAC connectors are used in the nuclear industry, television broadcast and in safety-critical medical applications.

2 The superb build quality

From the start, Mark Levinson always used the best components available in their designs and the build standard was always high. However successive products got progressively better. The later designs used PCB techniques as much as possible, eschewing hand wiring: even the connections to the potentiometers are via flexible printed track links, and the switches are wherever possible PCB-mount devices.

And the ‘feel’ of the controls – wonderful! Levinson always used good quality potentiometers for the volume control. In the past these were made by Bournes or Allen Bradley, but those fitted to the No. 28 (and also to the No.26) preamplifier are conductive cermet track devices made by Penny & Giles, and believe me they are silky smooth: just a light touch with the finger is enough. The input selector and tape monitor switches have a light but positive action, not the heavy and ‘gritty’ feel of some other designs.

3 True balanced line circuitry

Whereas many amplifiers boast balanced line inputs and/or an output, the Levinson is a true balanced line design.


Output connections on the Levinson No.28 preamplifier

With many amplifiers claiming to offer balanced line output, by passing a sample of the positive-going or ‘hot’ signal through a unity-gain inverting amplifier to create the negative-going or ‘cold’ side. Whilst this achieves the correct amplitude and phase conditions for a balanced output, the circuitry is asymmetrical: the negative-going signal having passed through an additional stage. The Levinson is completely symmetrical, requiring the inverting and non-inverting amplifiers to be virtually identical, thus requiring the use of high tolerance value components for each; many having to be selected by hand.

This procedure also applies to the balanced inputs offered on the model 28.


Input connections on the Levinson No.28 preamplifier

4 The performance

All the above would be for nought if the design didn’t sound any good. And it does it sound good – spectacularly good! If the following sounds like hyperbole, it ought to be remembered that the Levinson has replaced a, lightly modified, Quad 44 preamplifier. Now the Quad was never a bad amplifier and represented very good value for money; however the Levinson is considerably more expensive, so one would have a right to expect it to perform better.

So in what ways is the Levinson No.28 better? Well in most for that matter. The first thing I noticed was the wide and deep sound stage created. The sound stage extends beyond the outer edges of speakers and is noticeably deeper. Image focus seems better too.

The second aspect is the detail revealed, the clarity and the openness of the sound. This might be due to an extended high frequency response, lower crosstalk, but whatever it is due to the amplifier does not sound “toppy”. In fact the bass is improved by the same amount. Again it must be remembered I use Quad electrostatic speakers, not known for their bass performance. This is a shortcoming I tolerate and offset for those aspects the Quads do well and are important to me, but the improvement in bass extension and control were palpable and obvious. As a friend independently observed: “ the sound is beefier”.

The preamplifier is also revealing, sometimes remorselessly so – showing up shortcomings in any front end, especially those of early ‘clinical-sounding’ CDs.

Finally this preamplifier allows a greater appreciation of dynamics. This aspect of sound reproduction is not that important to me and is not a priority, but welcome nonetheless. Ravel’s Bolero never sounded so involving – and I suppose the Levinson is more involving; it’s not immediate or obvious, but in retrospect I do find myself immersing myself in the music more. And that can’t be a bad thing!

Conclusion

I have lived with this preamplifier for sufficient time now to satisfy myself that it is a genuine improvement over the Quad 44. In fact so impressed have I been with the quality of Levinson products, that I have since acquired two more preamplifiers for use in other systems.

The model No.28 is no longer made, but good samples do appear on eBay and other internet sites, and can be bought for a reasonable price. And being built to such a high standard with very good quality components, all Levinson products are reliable and used samples can be sought after with confidence.

__________________
Barry
© Text Copyright and photos 2011 Barry Hunt 2011.

NB No part or portion of this article may be reproduced or quoted without written permission.

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