LENNART LABS LA SARABANDE!


"When the two first LA mayro amplifiers had served for about six months, reports came in saying that they didn't sound as well as they should. After replacing a few coupling capacitors with another type, however, LA mayro performed great again. During the following few years, LA mayro was carefully followed up, and several improvements were made. Many listeners now testify that LA mayro performs soundwise on a very high level."

Several years later, a few LA mayro had been sold to new owners and often been replaced by more powerful and much more expensive amplifiers. Some owners reported a few shortcomings in LA mayro that were remedied by the new amplifiers, but also that several of LA mayro properties were lacking in the new amplifiers.


After yet another few years, a careful discussion on further development of the LA mayro was opened. It had been confirmed by LA mayro that the musical properties of the small Philips amplifier (see the LA mayro thread) actually can be preserved and developed. The question was whether the musical properties of the LA mayro could be taken forward another step. During 2013 it was decided to go ahead and develop the next generation LA mayro.

It was named the LA sarabande.

For me, the designer, it was relatively easy to appreciate most of the shortcomings mentioned. There are, obviously, for economical and time reasons, compromises and shortcuts in the LA mayro. At the same time, it was very difficult to determine where the acceptable limits for compromise and shortcut really are.

For the LA sarabande many of these limits should now be stretched. The results could obviously not be foreseen, but the project should anyhow produce very valuable insights with respect to the relations between technology and perceived sound quality.

Design

All components, save a few, in LA mayro are mounted on a large, common chassis panel in a wooden frame. The panel is rather large and invites vibrations, despite a few countermeasures, to be picked up and distributed to all components mounted on it.

The tubes will pick up vibrations from the mains transformers and chokes. Neither the transformers nor the tubes are symmetrically placed. Components beneath the panel are mounted in a dual-mono fashion, but locations are not mirrored. Thus, we suspected that vibrations are picked up asymmetrically by the two channels, only to add a slight 'unease' in the sound stage.

Further, we suspected that external vibrations are distributed asymmetrically to the channels. So, we came to believe that the amplifier should be constructed on a number of smaller, mirror-symmetrical modules, mounted on a more or less 'dead' framework, e.g. like the one on the picture.

Another topic not very much discussed, but important to me, was to lower working temperatures in the power supplies. Since LA mayro is a class A amplifier quite some quiescent heat is developed, increasing the temperatures of the mains transformers. In order to share the load and lower the temperatures, separate mains transformers for the tube heaters were introduced.

One more of my pet subjects is that plate voltages should be created with the help of vacuum rectifiers. There are many rational arguments against vacuum rectifiers, and I'm constantly reminded about them. But the sound quality that can be reached with vacuum rectifiers supersedes, in my humble opinion, what can be achieved with solid state rectifiers. Subsequently, one further choke filter stage was added.

As indicated by the picture and the CAD renditions, the LA sarabande chassis should turn out to be much bigger than the LA mayr.

Tone controls are controversial in many corners. Their bad reputation probably stems from too many bad implementations during the years. Many tone controls do not only impair the sound quality as such, but also the dynamics and transient behavior. The tone controls of LA mayro have been praised for not affecting the sound quality, and for being clearly useful.

One desire discussed for LA sarabande was the possibility to add a bit of warmth to the middle base, or lower midrange, while listening to rock music. When I presented my proposed tone controls for the LA sarabande, they not only met this desire, they also added some new functionality: the possibility to change turnover frequencies. The controls should be designed to be fully inactive in their neutral position.

During development the importance of cross talk between channels was discussed. It was later decided that the LA sarabande should be built to absolutely minimize cross talk. Partly because of this, and partly because many listening venues are acoustically a tad non-symmetric, each channel was given its own set of tone controls.

The CAD rendition indicates a conceivable position of the controls.

Chassis

The chassis was constructed as a framework of prime one-inch birch plywood. The birch ply is an acoustically very quiet material, which I prefer for use in loudspeakers. This is why I decide to use it in this chassis frame. To counteract future movements in any joint, the frame was dressed in glass fiber fabric and putty. Then the whole chassis was painted by an automotive painter.

The photograph shows a jig I had to make to enable the chassis to be positioned up-side down and to offer some grips when the chassis has to be moved.


The chassis was designed to offer several compartments, separated by one-inch wall sections. This was supposed to produce a more silent chassis.

Since each chassis panel was individually fastened in the wooden frame, vibrations in the panels were expected to distribute only minimally. By placing components mirror-symmetrically on each panel, vibrations still present were expected to be picked up symmetrically by both channels.

Construction

In the far rear we find components dealing with mains voltages and the first plate voltage filtering stages. The vacuum rectifiers are also located here, as are a few voltage regulators providing auxiliary voltages.

Since all connectors for inputs and outputs are located on the rear panel, also the electronics for the choice of signal are located here. All parts dealing with signal voltages are electrostatically screened.

In the compartment in front of that, we find components for further plate voltage filtering and the mains transformers for the rectifier and small signal tube heaters.

In the third compartment from behind we find the last stages for plate voltage filtering, the output transformers, and the mains transformer for power tube heaters.


Many components are located beneath this panel: electronics for the rectification, filtering and regulation of the small signal tube heaters, and some other auxiliary electronics.

In this way all power supplies are located in the rear part of the chassis, allowing the signal carrying parts to be located in a more 'clean' environment in the front.

Transformers and chokes are covered by protective covers. The vacuum rectifiers in the rear have acrylic glass protection, as have some of the filter capacitors.

In front of the power supplies we first find the panels for the power amplifiers, and then the preamplifier panels. These panels are mirrored, but otherwise identically outlined.

The tone controls of each channel can be seen in the far front. Between these, the source selector and the volume control will be placed.

The empty compartment between the preamplifiers is reserved for a full color touch display. The display has nothing much to add to the sound quality but instead offers a range of very practical functions.

Display

After numerous thoughts and discussions, it was decided to add a touch screen. One of the most important reasons was a strong desire for large digits to indicate the volume control position. And while programming was up to speed, the wish for a pair of VU meters was also added.

The display, maneuvered via the remote or the touch screen, now offers a number of functions. Volume indication and VU meters have been mentioned, but there are also screens to display current time, a service hour counter and two resettable hour counters, operational status of the power tubes, and some information about the amplifier.

The tube monitor has already proven very useful. The screen displays graphically, and with numbers, the current in each power tube. The display thus indicates, in real time, the quiescent current (bias) in each tube, and also how well matched the tubes are.

Vacuum tube age differently, which in time may result in different loads on the tubes. Based on the monitoring, we can replace tubes due to aging. Occasionally, one of the tubes can stop working, partly or in whole, not necessarily with audible effects. It is obviously vital that such a tube be replaced as soon as possible; then this monitoring function comes in very handy.

Finally

The grey aluminum panels are eventually covered with polished and lacquered brass decor panels. They contribute strongly to the overall finish in red, black and gold. The front panel is not covered, however, since it has engraved text. Outer dimensions are 60 x 80 cm and the weight about 55 kg.

Sound quality wise, LA sarabande performs clearly better than the LA mayro, even better than many well respected and expensive amplifiers. The music flows in a very natural way, and tonal balance is very pleasing. Variations in recordings, media quality, listening rooms etc., can readily be compensated for with the tone controls.

Even very demanding listeners confirm that the sound quality of LA sarabande is very high. The chassis is completely silent, there are no audible vibrations picked up by the tubes. The background is absolutely black and silent areas in the sound stage are very distinct, which in turn gives the sound stage more clear contours.

Technically and sonically, the successful development of LA mayro might be considered confirmed, even if there obviously is an economical side of things.

Reprinted with Lennart Jarlevang consent.