Lars's system upgraded

Feb 26, 2011

Kari Nevalainen

Lars Tørressen is a qualified and dedicated DIY-oriented audiophile from Bergen, Norway. His current system is presented below.

It all started when, ten years ago or so, Lars heard a pair of Avantgarde Duos in Oslo. He fell in love with their sound but didn't want to settle for a ready-made commercial horn speaker. Instead, he chose a more active approach and built some of the horns (tractrix, Iwata) himself; others - mainly vintage - he subjected to experimenting and modifications. Thanks to his recent acquisitions, Lars now owns a number of horns including two Altec A7/511B and two Altec A5/1505B combos.

Very early on Lars found the pioneering French magazine L’Audiophile (published 1977-1995). His thinking is still influenced by the ideas from that magazine: high efficiency speakers, preferably driven by simple single ended circuits, and sophisticated power supplies. Lars own a quasi complete collection of the much sought-after magazine.

Lars is particularly fascinated by how realistically horns reproduce dynamics and timbre of instruments. That includes great downward dynamic range, the ability to render very low level sounds along with strong sounds. Conventional commercial systems, according to Lars, leave too much to want in these areas. Even the Quad ESL and OTL -system he once owned, although very good at 3D and low distortion, begun to bore him.

The third thing Lars likes about horns is controlled dispersion inherent to the horn principle. Controlled dispersion or directivity means less room interaction, and more degrees of freedom in speaker placement. Lars likes to consider his system as large headphones. He likes that the instruments are very present. 

Dedicated amplifiers

Horns can sound extremely good but not without careful consideration, and Lars knows it. He believes that a lot can be done, for example, with refining the signal chain to get improved dynamics. One precondition is to ensure the best possible interface between the amp and the horn, and that often implies having amplifiers tailored for the horn at hand, and by placing the crossover before the poweramps and direct couple the speakers to the amplifiers.

Starting from a copy of the Counterpoint SA-1 tube preamp, basically all of Lars amps are built by himself. His experience is that a big part of what we hear from a system derives from technical solutions regarding the amplifier circuitry. High efficiency horns allow Lars to stick to the single-end topology and choose from his wide collection of low power tubes: 801,45, 2A3, 2E22, 807, 300B. According to Lars, low distortion triodes and high efficiency horns is a wonderful combination for instance in the reproduction of voice and woodwind instruments.

The 8W transistor amp for the bass, Hiraga Le Monster, has a detachable rectifier module to experiment with different diode types. According to Lars, the sonic differences between diodes are minor than the differences between different output tubes.

Lars current amp for the HF horn is a DIY convertible 2A3/45 SE amp inspired by the Joseph Esmilla amp. The NOS Kenrad 45 tube outputs less than 1,5 watts per some acceptable amount of distortion but compared to his 3W Sovtek 2A3, has more 'see-through' palpability and is more truthful to the original sound of acoustic instruments. Next, Lars plans to replace the 6k Lundahl output transfomer with a Lundahl 5k Amorphous C-core OPT, and see what happens.

The bandpass amp for frequencies below 500 Hz is a Jean Hiraga design, a 8W solid state PP amp also known as Le Monster. Lars assembled it out of an original matched transistor set from the Swedish distributor of La Maison de L`Audiophile parts, and made it into a dual mono version. Relative to the 2A3/45 SE amp, the Hiraga amp has more drive and energy.

Unlike most of us, Lars likes to think of his system as constantly evolving and searching for its final shape. The speaker setup he rearranges once a month. Swapping between speaker setups is easy because crossover parameters specific to each setup are stored in the digital crossover.

The demanding speaker system

Lars recent acquisitions, the Altec A7 and the Altec multicell horns, have taught him a lot about the sound. The 15 cell horns with their even radiation of the sound over the frequency spectrum have surprised Lars by sounding smoother and a more laidback than what he's used to with more upfront direct firing horns. The multicell horns also create a huge stereo image that is rock stable no matter where the listener is. 

During my visit, the multicell horns were married with massive Altec 299 compression drivers. The only complaint Lars has about the 299 is lack of brilliance and HF clarity. EQing helps a bit but his TAD 2001 beryllium drivers are in this respect better still. Once the big Iwata horns - now under construction - are finished, Lars would like to try Radian 950pb 2" compression drivers with them, and put the TAD 2001 on smaller Iwata horns to take the top.

The bass speaker is a folded baffle (open back) with Altec 416-8c and 515-8g woofers. The Altec drivers may not be optimal for dipole radiation but it's the only bass loading principle with which Lars is able, in his limited space (7 x 3,6 x 2,4m), to get rid of much hated room resonances in the critical bass/lower mids region. But he won't get the same slam in the midbass, eg. equally realistics drum sound, as with his Altec 828 cabinet.

Active it must be

Using an active crossover has been a great fun and a revelation to Lars. Not only does it greatly facilitate combining the high sensitivity horn with the bass speaker (level, phase), but also enables using a dedicated bass amplifier, which in Lars' mind has an enormous effect on the dynamics and the stability of the stereo image. No more collapse of the soundstage during crescendos - a hallmark of a typical commercial system.

Lars' BSS FDS 355 has a digital EQ inbuilt both at the input and at every output, which is necessary in making a room corrected system. With his Behringer DEQ2496 Ultracurve Pro Lars measures the room response with a mic and the real time analyzer function (RTA), then plots the result into his BSS. Left and right channels are measured and room corrected separately.

He doesn't see many disadvantages related to inserting digital stages in the otherwise purely analogue signal path. On the contrary, he believes that what is gained sound-wise by using carefully optimized horns directly coupled and driven by the most transparent power amps there is, totally overshadows the flaws of extra AD/DA conversion in the digital filter. Having control over phase alignment and room interface adds to this. Set by ear, the HF horn was crossed at 378Hz/18dB.

Diagram of Lars' system: The main analogue source is EMT 930st studio turntable with the original tonearm and TDS15 cartridge. From there the signal passes to Lars' DIY version of the Dr. Arthur Loesh RIAA preamp with J-fet input and battery bias on every amplifier stage (now sold under the Tempo Electric brand). The output of the amp is single ended and is matched to the balanced input of the digital crossover by a Lundahl transformer. A 5-channel DIY volume control with fixed resistors is placed after the filter in order to keep both the distortion and the noise level down. An expensive solution but worth it. The CD player is an old Sony.

The sound?  The sound was very spacious, superbly smooth over the midrange and treble, and noticeably clean and polite in bass, despite the fact that with the help of dipole correction, the bass descends down to the 35-40 Hz region. Lower bass notes than that Lars is more than willing to sacrify in order to get the rest of the bass qualitatively right.

We were listening to De Falla, Tchaikovsky, Hilliard ensemble, Bil Evans, baroque lute music etc. etc. ... the system seemed to function consistently no matter which music was played. This is how a system performs when its sound is meticulously optimized. Great music, brilliant sound, - and an unforgettable magnificent scenery from the hill side of Bergen. 

With one speaker

That's only stereo. Lars' mono system is downstairs in his workshop, a sanctuary for all his horn and amp projects. Besides his mono LP collection of jazz and classical music Lars has dozens of 78 rpm jazz records. When played at the right EQ, the sound of these records is truly remarkable, so dynamic, so groovy, so close to the artist him/herself that they alone deserve a second system, said Lars.

But he also noted that the mono sound is very dependent on the tone, on transparency, on low distortion, and that's where good horns enter into the scene. Lars' current mono speaker is a modified Altec A5. The HF horns vary. We tried the with Altec 511b together with the TAD 2001 as the compression driver. The turntabel is Thorens TD 124 with JVC Victor UA7045 tonearm and Ortofon SPU Gold, wired for mono. The MC trafo is stolen from a vintage Siemens film projector. From a Joseph Esmilla inspired DIY mono equalizer the signal travels to a DIY low impedance preamp using parallel 12B4A tubes for output followed by a Prometheus autotransformer volume controller. Of the various tube amps available, on duty was a prototype with a very rare Telefunken AD101 output tube. The crossover was a Hiraga design. 

The mono sound was upfront, dynamic, explosive ... a tad more aggressive and forward than the stereo system upstairs, full of good feeling. And as so often with mono recordings, as soon as the stylus touches the groove, the issue of sound quality flies out of the window.

Lars has been active with mono also outside his house. Together with his friend Per Morten Ekerhovd Lars has given public demos of a mono sound to various audiencies. On one occasion they used a Klangfilm Bionor, a rare cinema speaker from the first half of the 20the century. Reportedly the demo gave people shivers down their spine because the sound was so real.

In his home town, Lars is known as the DJ Mono. In a leisure location of a coffee roasting company, every now and then he lectures on the technical secrets of mono playback, demonstrates the sound of different playback curves, and plays his favourite mono recordings through his Altec A5s. 

Solder fumesfrom the childhood

Lars grew up in a home filled with tube radio transmitters and thick solder fumes of his father's workshop. His father gave him the basic skills, and seeded in him the DIY spirit. It is that spirit, spirit of making things with one's own hands, that has inspired Lars to build his horns, amplifiers etc. but also acoustic instruments such as lutes. More of that here.

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