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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
Follow Ups:
Hi Andras...Just spoke with Tom Cadawas (Sequerra's Lead Tech) who built the first 250 Sequerra's... he said that he was unaware of any issues relating to gain or noise and that there must have been other issues causing the problem, however he did indicate that some of the early prototypes may have made it out to the public.
According to Tom, Serial # 1001 is actually the First Sequerra Model 1 to be produced, and stated that the sensitivity of the Sequerra Model 1 is around 1.7uv... not 55uv and while there is one tuner that when properly aligned will have better specs... sonically it's not accurate, nor does it have the seductive low end or physical appeal of the Sequerra. Tom concluded by saying that the Sequerra is virtually indistinguishable from a properly aligned 10B.
My own Model 1 picks up stations 30 miles away with a 3" piece of wire for an antenna... that's a clue!
Tom is the best tuner man in the country and was originally the lead tech for Marantz in Woodside. Shortly after the model 20 was produced, Dick Sequerra and Sid Smith left Marantz to start their own company... but they had a problem... the prototype changed frequency on it's own every 20 minutes, after 2 years of effort, Dick approached Tom to bail them out... Tom resolved the issue in less than two weeks. Dick had the "size ratio" of the antenna and oscillator coils in the front-end reversed... sometimes all you need is another pair of eyes.
The original Sequerra was a technological and sonic masterpiece using a voltage driven Analog front-end... in addition, with the exception of the final audio output stage it's completely balanced front to back which gives it a dynamic range of over 100db... Sonically you would think you're listening to a CD through vacuum tube gear.
It also incorporated miniature air-trimmers instead of the cheap compression ceramic jobs that drift all over the place, and featured an 18 pole IF that gives it incredible adjacent channel rejection. It was completely modular with all the RF sections isolated in their own Stainless Steel enclosures. The multiplex and audio board is also isolated in its own enclosure, away from the power-supply.
The moral of the story is...
Nothing is "missing" and there are no "dark secrets"... anyone that has issues with the Sequerra or a 10B, has one that isn't working properly. If you love music, accept no substitutes... buy a Sequerra; and if you own a Sequerra or a 10B and would like it to be the best it can possibly be, send it to Tom for alignment!
Hi, Bandi100:Have you thought about sending a note of inquiry directly to Dick Sequerra, who surely would be in a position to offer comment on your Hungarian friend's problems or concerns?
Here is the information to reach him:
• 1929 Long Ridge Road, Stamford, CT. 06903
• Phone: 203-968-0339
• Email: sequerra@discovernet.net
Interesting. I'm curious how this situation evolved.Were these missing components ever in the original design? If they were in the design and then prototyped, preliminary testing of the R&D units should have revealed a superior tuner (as expected) or a variance with expectations.
If they were tested, surely something would have been done to correct the problem. An absence of testing as the first articles and production units became available could delay awareness, however, wouldn't that be improbable?
Complex "state-of-the-art" and especially "first-of-a-kind" systems can fail, even when processes are carefully followed. My experience on a team building satellites and ground stations includes some examples that we had to thoroughly examine to understand "how" and "why".
My gut feeling is the process was flawed. Some extraordinary circumstances must have interfered with typical careful monitoring of this "baby" during R&D and early production.
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