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
of 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
some years ago 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 not 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. And
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 during
inspection this pair JL1 was actually 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.
Although
the JL1 may 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.
