This whole thing got triggered by a change Technics made in the production, wich I failed to understand.
Changing C211 from 47nF to 220nF.
I tried to redo the math on the multiple feedback lowpass filter, wich resides right after the FG amp.
With the stock components, I calculated the frequency of 5,88Hz and did a simulation for the impulse response:
Adjusting C210 within a reasonable range (I didn't want to allow the filter to lead a life of it's own),
a value of 550nF seemed fine (that's 220nF-stock parallelled with 330nF).
Frequency will be 3.72Hz and resulting in the following response:
Enough with the theory, let's get measurements.
I don't have fancy wow and flutter measurement equipment at home,
but recently, I bought Adjust+ Pro, so that'll do for the moment.
--> I redid every measurement at least five times, to exclude occasionally better results.
--> measurements are taken with the stock platter mat, it's weight is important as it is part of the rotating mass.
Let's get the table spinning, C211 is 47nF, all else is stock but renewed (all components, bearing and arm).
I have no idea what standard Adjust+ uses (maybe I should read the manual).
These values are for now considered relative and as a reference.
So I started implementing the mod.
No result, well, yes result, but no improvement.
Started experimenting with uncalculated values, even adjusting the gain of the filter, but to no avail,
it seemed to live a life of it's own, and nothing I did seemed to make a positive difference.
I reverted to stock and was ready to give up...
But then I remembered the odd change in C211, from 47nF to 220nF in more recent models.
My calculations were based on ideal op-amps, not on the thing that resided inside a 70's Panasonic chip.
Maybe the engineers had a good reason to change that value.
So, opened up the table (again) and swapped the 47nF with 220nF.
This is the result:
Now it seemed to me, some sacrifices were made to improve the unweighted w&f.
As the weighted value was a little bit worse.
While I was feeling strenghtened with the obtained result,
I did the mod I originally intended, parallelling C210 with 330nF.
And this is the result:
Oh yes, I redid the test about ten times, just to be sure that I saw what I saw.
Also put on some 12inches from my DJ days, handling the TT the way a DJ does,
and no noticeable drawbacks.
Will do some listening test the next days, but if my ears are not deceiving me,
this is indeed an audible improvement.
(don't worry, I'm not a reviewer, so I won't slap you around the ears with
audiophile listening descriptions)
I don't think I will stop here, but other modifications will cost more money
and might not give that much improvement.
One warning, this mod is done on a deck with a new (standard) technics bearing,
well oiled. All capacitors have been changed. One IC has been changed.
I have no idea if the mod results in the same improvements on worn decks with old caps.
Technics SL-1200 Mk2 recapped / MN bearing / Funk Firm Platter / Denon 103R / Lundahl LL1681
Thorens TD 126 MkIII / SME Series III / Ortofon SME 30H // AT-OC9ML/II
Thorens TD 160 / TP16 / Stanton 681SE
Denon DP-1200 - WIP -