WHAT IS MISSING FROM THE SEQUERRA MODEL 1 TUNER?
A good tuner turns excellent. Jeno Takacs from Hungary explains how.
The Sequerra Model 1 tuner is, no doubt, one of the most famous tuners of the world. A legend, a piece of technical history. Everyone is proud to own it. Surprising as it may be, the original Sequerra is still not an excellent tuner, explained a big fan of vintage hifi equipment and a builder of fine OTL amplifiers to me. Jeno Takacs, resident of Tatabánya, Hungary, bought his used Sequerra last year, and he was not satisfied with it at all.
He kept on thinking what can be wrong with his unit, and in a couple of months he found the cause. He tweaked his unit and is a happy man now. „My Sequerra beats my Marantz 10B hands down” - he says. As Jeno Takacs does not use the Internet, he asked me to post this mail to you. I am an audiophile myself, a journalist by profession, understanding very little of electronics. I found his story stunning, however.
Jeno read the tests of the Sequerra, eg. the lengthy 10 pages test in the German HI-FI EXKLUSIV magazine back in 1979. The tests were not that glorious at all, either. The biggest problem seemed to be sensitivity (measuring 55 microVolt / 75Ohm in stereo mode) and the S/N ratio (53 dB). These figures are around average. But you would not expect average from such an expensive and esteemed unit, would you?
Jeno then compared his Sequerra to his Marantz 10B in a DX test. He found the Marantz to be much-much better. He also found a funny thing, which he called the dark secret of the original Sequerras. Half an hour after switching on the tuner, the level of the signal fell back by about 10dB, either in „display panoramic” or in „display tuning” mode. So the front end seemed to be wrong. Jeno then started to examine the R. F. board and saw the following: the 100KOhm resistors wee missing from the gate electrodes of the two cascade FETs on the input stage! He also found that the board did not even have the space or the holes for the resistors. They had been missing from the design already!
After switching on the Sequerra the potencial of the gates was lower than that of the sources, so the tuner worked, sort of. But after the coupling condenser got charged, the potential of the gates ceased to be correct. This caused problems.
So far so good, but how can one repair this? As there is no space for the two missing 100 KOhm resistors, Jeno built two 100 KOhm 1% SMD resistors between the legs and the ground. As there is a danger of electrostatic charge, one should use exclusively law voltage soldering unit.
After performing this tweak, the unit lived up to the high expectations
concerning performance. It beat the marantz 10B in the fields of sensitivity and S/N ratio. The sound got much better, which, says Jano Takacs, proves that the input stage worked normally this time.
The serial number of Jeno’s Sequerra is 1001, but the above mentioned resistors are most probably missing from all Sequerra models belonging to the frist series, made in Woodside, NY.
Andras Loke, Budapest, Hungary
