The Callas Diva®

Made out of authentic cast bell bronze

Callas Bamboo Carbon®

African Blackwood / Pokwood armboard, 10 year dried samples

African Blackwood adjustable armboard for the Airtangent arm

Callas Bamboo® loudspeakerstands

African Blackwood / Pokwood armboard 10 year dried samples

Platine armboard out of Ebony / Purpleheart

African Blackwood armboard for the Kuzma arm

Red Stinkwood armboard for the Nottingham arm

Reworked Cerapucks for VerityAudio

African Blackbird

Callas Magic Bricks®

African Blackwood / Pokwood armboard for the Schröder Reference arm.

Let's go analog!

Callas Magic Bricks®

Authentic Japanese ZEN Singing Bowls

Callas-Audio Products

Callas-Audio Hybrids

Callas Bamboo® Soundboards for NAT Transmitter

Callas Bamboo® Audiorack / Ampstand

Callas Bamboo Carbon® Soundboard for Air Tight 211

22 Watts is nice

Callas Bamboo® Soundboard for Gryphon Encore

500 Watts is nice too

Callas Bamboo® Soundboard with Birdseye Maple for La Belle Maîtresse

Callas Recordclamp® ode to Jazz

Air Tight 211


The Air Tight 211 mono's are equipped with a volume control at the front, and although this is convenient to cope with varying situations, when using a matching preamplifier one volumepot is enough.

The modification itself is quite simple, and the stock wiring harness was left in place with some crimpsleeve to cover the ends. The stock wiring may be seen in the first picture laying bottom left hand side. We had some fine Kondo KSL Silver wire available, these are to be seen in the picture as having a crimpsleeve at the wire ends.

Firstly we'd like to state that it is unwise to modify such a splendid circuit design just because it can be done. The people at Air Tight know what they do, and they do it for quite some time now to put an understatement. This modification does not alter the circuit, it bypasses the volume pot and inserts refined components in place of some stock ones. Much more expensive components will not necessarily sound better just because.

Mind it is not our hobby to mod gears, the following jobs are exemplary. We'd rather spin records then sniffing solder fumes.

Still this modification brought an -subjectively- small gain soundwise. We presume that the removal of the volume pot accounts for the most. Parts involved were the Jupiter Copperfoil 0,47uF capacitor, the Amtrans 220R, and a Riken resistor (the blue collar one next to the Jupiter) A nice and succesful modification, which is fully retrofittable too. If 22 Watt is enough the ATM211 is highly recommended.

This could not have been done without the vast knowledge and parts of Acoustic-Dimension thanks again!

Warning: Lethal Voltages may be present in any amplifier, always drain capacitors before attempting any work.

Convergent Audio Technology JL1

Partial restauration

The Big CAT's were resqued out of an water damage situation, and were in a deplorable state cosmetically, besides raising huge question marks on their technical condition..

Still we decided to accept the challenge, and they were to be picked up at a later date. Due to a lower back hernia this exercise was rather unpleasant since the weight of 85 Kg each. These are truly the Harley Davidson among amplifiers. The American approach: If it fails, just make it twice as big. The amplifier casing is beyond any weight and size expectation and so any resonances are unlikely to occur.

There was a firm hesitation to fire them up before inspection, with emphasis on the 'fire' part.. But we took the plunge and although it was obvious there were some tubes not walking along in the parade, it produced sound!

After a first inspection there were multiple tubes found dead or partially so. Some resistors were found burned, and the input section on one mono was also suspect. One mono had all silent blocks under the powertransformer sheered. A known and highly dangerous topic with the CAT poweramps is the rough edge (not deburred) on the High Voltage transformer cable hole. We have had another pair of JL3 in the shop many years back with the same thing, these actually had caught fire. Sometimes all that is needed to adress safety is a 5¢ tie-wrap.

The cleaning up and polishing took many hours, and along the way other parts were found questionable so we decided to renew in a generous way. This approach may discard some items which actually still worked, but considering the late 1990's time of production we'd rather don't take chances here. We also followed the healthy rule that if parts must be renewed on one mono, both amps will be done. This way there is less chance on electrical asymmetry. Mind that you do not want to lift these on the workbench too often. So better do the job right from the start. 2016 was a tough year anyway concerning the hernia.. This pair JL1 was actually produced in 2002.

The CAT JL1 was introduced on the German market by late 1994 and got a raving review in the German Stereo magazine. Although it was listed to produce 100 Watts 8 and 4 Ohms, the actual measurements showed 68 Watt/8 Ohms and 30 Watts/4 Ohms. Power draw was a measured 278 Watts stationary and 335 Watts at full power for each monoblock. A scan of the original CAT folder to find here and here.

Retailprice was set at 43000 Deutschmark, the equivalent of around 48500 Dutch Guilders. It caused quite a stir to put it mildly.

Nowadays these can be seen offered for around 6000 euro, and mostly need service alike. A full set of fresh tubes is around 700 euro.

Warning: Lethal Voltages may be present in any amplifier, always drain capacitors before attempting any work.

Unfortunately no before pictures were beeing made.. Many hours of cleaning and polishing applied. The inside took some rounds with the special degreasing spray to look like this, and it came out very well indeed. The output terminals were replaced with the nice Cardas CCRRS types via Audiokit Italy and most other parts were ordered at either RS-Components and Farnell

The tube bias pots were replaced with new ones. Left upper side shows the tricky part with any JL amp where the high voltage wires have actual shearing on the non-deburred hole. The solution is simple, just putting a tie-wrap. We applied some extra rubber sleeve too.

Renewal of Resistor and Fet at the input section. Both amps were done in any case.

Some resistors apparently have had a hard life..

Another section with renewed resistors. Lot's of small issues were adressed along the way, better cable routing, adding tie-wraps, some bolts and nuts replaced, cleaning, solderings renewed, some deburring and Locktite applied where useful.

One Happy CAT

Although the JL1 may look somewhat old school it can teach a musical lesson to most other amplifiers! They were actually put on sale after some weeks of listening and stabilising, and found a new owner who only needed some 20 minutes of listening to decide. The JL1 sounds huge; like viewing the actual Grand Canyon. It really makes one wonder what any progress there has been made in some 20 years. Although the JL1 does not offer the most resolution and detail nor are the most refined tubeamps around, the experience is beyond most other amps..

A special thanks to Peter at Acoustic-Dimension and the good fellows at Tonefactory.