They both have bidirectional servo, but the 101 has an additional servo to compare phase - double bidirectional. Why else are the electronics so much more complicated on the 101?
You're saying this is incorrect?
I don't know where you read this Fleib, but the description of both TT-81 and TT-101 in the Service manuals are identical except the 101 has a 'coreless' servo motor.
Most of the additional complexity of the 101 I believe is centred on its circuitry of multiple 1Hz pitch adjustability (5 steps up and 5 steps down) together with its digital speed indication and its complex new braking system.
A massive platter imparts solidity to the sound, viable if and only if correct speed can be maintained. That's why so many belt drivers w/heavy platters sound ponderous IMO.
This is a subjective view and IMO has become an oft-repeated audio myth...
It implies that turntables like Rega and Project cannot have "solidity"to their sound....
I have found that to be too much of a generalisation.
I can understand the concept of a massive platter for a belt-drive deck which is trying to rely on inertia for its speed maintenance but for a DD which is quartz-locked and servo-controlled, a heavy platter simply involves a more powerful motor with all its associated problems.
I believe 'solidity' comes firstly from the ability of the turntable to maintain perfect speed through the heavily modulated grooves (resulting from complex low-frequency information) without suffering 'stylus drag'. A feat I still have not seen performed by a belt-drive....
Secondly I believe 'solidity' is greatly improved by the rigidity of the turntable supporting structure, its isolation from structure-born feedback and then the materials chosen to implement these.
It's interesting to note that the Victor engineers did not change anything about the platter weight and materials between the 81 and 101 and I can tell you that the 'solidity' achieved by this 'lightweight' aluminium platter is unmatched by any megaton platter I have heard.
And I thought we just discovered that old solder joints were the only problem areas of these old turntables....?
And this might be just the TT-101....
No problems at all with the TT-81 or the thousands of other makes and models of 70s Japanese DD decks out there from all the Forum reports...?
And just to lay to rest another bugaboo about these vintage decks....they are generally easy to repair by any competent Tech....and all the ICs, transistors, capacitors and resistors are still readily obtainable...😍
