Convergent Audio Technology JL1

Partial restauration

The Big CAT's were resqued out of an neglect situation, and were in a somewhat sad state cosmetically, besides raising 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 on the High Voltage transformer cable hole. We have had another pair of JL3 in the shop many years back with the same thing. 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.. We found after inspection this pair JL1 was produced in 2002, so a very late example.

The CAT JL1 was introduced on the German market by late 1994 and got a raving review in the German Stereo magazine. 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 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 definitely look 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.