Wednesday, October 27, 2010
Marantz 20B from below
This is just as impressive as the 13 page schematic. There's lots of stuff visible here, and lots more inside boxes to the left and on top.
But while I'm high fiving myself over finally getting this tuner, a question arises. Why isn't the 20B better than it is? With all that stuff, you would think it could be one of the best of the best. (Some people think the 20B is one of the best, but that's unusual, the 10B is more widely known and praised.)
OK it might be a good sounding tuner, but why isn't the selectivity one of the best since it has an outlandish 8 filters, and they are always active?
I wonder if there isn't some kind of design error here, as apparently there was with Marantz 120, though for different reasons probably.
I believe that the Marantz Model 20B was one of the last Marantz components designed by the legendary Marantz designers Sid Smith and Dick Sequerra. It was intended to replace the 10B, and used a similar IF design with 8 LC filters always active (no wide/narrow switch). It was manufactured in the USA at Woodside, NY and later at Sun Valley, CA. Actually, the design was first used in the Model 18 receiver, then became the 20 and 20B tuners and 19 receiver. The models 19 and 20B had a revised version which included a mosfet RF amp to improve sensitivity.
The 120 was the first high end Marantz model produced by Standard Radio of Japan, which had been purchased by Superscope to be the factory for the less expensive Marantz products. It also uses an outlandish 8 filters, but this time they are ceramics, which are less expensive but can be very good. But it appears there is a design error, the IF strip is not loaded properly, and it appears the 120 cannot be made good without completely replacing the IF. (This is documented at FMTunerInfo.) After the 120, Marantz temporarily switched back to an LC filter design for the models 125 and 150, then finally got the hang of ceramic filters with the Model 2130.
Though their pedigrees are entirely different, the 20B and 120 appear to both have 8 filters yet be lacking in selectivity. It is known that the 120 has a design error. So that makes me wonder about the 20B. Though I find it hard to believe that Dick Sequerra would have made such a design error, if he was the 20B designer.
Another possibility goes like this. It was hard to achieve the highly touted selectivity of the 10B using transistor circuits because the impedances of the transistors in common collector mode is too low. Or perhaps the gain is too small, or they are not as linear. But this design (actually a re-implementation of the 10B with transistors) worked reasonably well and sounded good. Given the difficult transitional situation of Marantz (acquired by Superscope in 1964, moved to Sun Valley and outsourced most manufacturing to Japan in the late 1960's), they chose not to invest resources in an entirely new design to make the best of transistors. Perhaps they were even able to use surplus 10B parts, such as the filter modules. So they went with what they had, even though it would not have been cost-effective for an original design.
Surely Dick Sequerra would not have wanted to do things this way, but he was nearly (or already) out the door anyway, possibly even working on contract. After Superscope acquired Marantz, the old staff stayed on for a few years but eventually got ticked off by the Tushinsky's and left.
For what it does, the 20B does not look like a cost-effective design, but perhaps it could be made much better with some new thought.
Smith and Sequerra did get another chance to make the best possible transistor tuner later with the Sequerra Model One. That tuner is even more outlandish and expensively built than the 20B, and includes balanced circuitry in the RF and IF stages, a high end design feature I've never seen in any other tuner. Still, reports I've heard suggest that the Sequerra Model One isn't the best of the best either, in sonics and selectivity, though the cool panoramic analyzer is worth the price of admission (and may explain why the FCC bought most of them).
One thing is unarguable, and Sequerra has even admitted it himself. He should have figured out how to make better equipment at lower prices.
Posted by Audio Investigator at 3:24 PM