New Technics SP10 motor controller specification

[bernard991]

Steerpike

as a new owner of the 10 Mk2 I am doing the 35 yr maintenance thing
so that it is kind of in the range it should be ..which will have to do me for now ;

however I agree w/ Rich , Lew and the others that the successful completion of your endeavours would really breath new life into this wonderful 'antique' piece !
good luck & BIG thanks for your efforts

Bernard

[bernard991]

Originally posted by brianco
For my part I would be perfectly happy if a simple 33rpm function - with no frills other than say an on-board =/- 5% speed adjuster, were to be the outcome of this project. I also would require that the PS+Controller were capable of being cabinet mounted at say 3' distance from the turntable itself. My present TT is a SP10Mk11P (ex.BBC) and all on board electronics were successfully mounted as an out-board unit connected by an umbilical. (It worked for five years this way but now has a 'dead' problem which I am not qualified to diagnose. A new, simpler, DIY unit would be the more economic option to rebuilding the existing boards.)

The difference between on and off TT electronics is very big indeed and the extra trouble is far outweighed by the improvement in all aspects of the resultant sound quality.

I had been planning to move the electronics after changing out the caps and it seemed that many voiced support for this idea .I don't have a proven technical reason for this but it seemed like a reasonable move given the freedom we DIYers have to get the electronics 'hash' from the motor away from the / MC cartridge /music into a separate enclosure.

however I received an interesting email from a member of a different forum who has lots of technical experience & worked on the SP10M2 he asked me 'why' I wanted to move to outboard ...??

he comments below and some of the points he brings up seem valid


"Are you concerned about "digital hash" intruding into the low-level signals from the cartridge? Did you read about this "mod" somewhere?

The reason I ask is that moving the circuitry off the frame will require a LOT of "re-engineering" in order for it to succeed. Not only that, it is VERY possible that the extended "umbilical cord" will introduce MUCH more opportunity to pick up external noise - even with a shielded cord.

It will also increase the likelihood that signals traveling down those LONG wire lengths may interfere with each other. The framework of the turntable, along with the bottom cover, form a nearly total shield over ALL of the digital circuitry. This is a Faraday Shield and it is VERY effective at keeping noise and RF completely contained.

Quite frankly, I can't see any real advantage to moving the circuitry "outboard" from the turntable, but I would LOVE to hear better advice on the subject. I simply don't know the "definitive" answer on this. I tend to operate along the philosophy of "If it ain't broke, don't FIX it!" Unless there is a real REASON to move this stuff, I don't see a need to "

personally I understand that a new PS & controller would make sense to have in a separate enclosure ( its all new form factor)
but as far as the existing electronics I am not sure ... from your post Brian it suggests that you noticed none of these negatives ?
what was the umbilical ? new cable & shielded ? length 3' ?
comments appreciated

[Steerpike]

The analogue frequencies involved are LOW - AC currents are below 20Hz in frequency, so the possibility of them causing audible interference is minimal. These currents have to exist in the motor itself - no way of moving that away - unless you use a 3-inch thick platter.

The tacho signal is of higher frequency, but it is in the millivolt range - no interference caused by that! BUT it is susceptible to external noise pickup, as is an audio cable. Noise on the tacho signal is just about the worst possible place to have it, in a feedback control system. (Here might be a good place for a true balanced input to the controller!)

The only 'noisy' cable is the excitation voltage for the variable reluctance phase detector coils. That's at 50khz. A screened cable there is a good idea. It exists in the motor too, and is shielded by the rotor and the plater.

Long (thin) cables to the motor have exactly the same negative effect as long loudspeaker cables: added resistance which reduces the damping factor of the drive amplifier. But the normal operating currents are not high - tens of milliamps, nothing requiring fat exitic cabling.

Yet I suspect these effects are minimal: Can you hear the difference between 1m and 3m of speaker cable? Can you hear the difference between 50cm and 1m of phono cable? And these are cables where the actual audio is being conducted!

The connetion to the motor is by 12 conductors. You could make these as long or a short as you like, it doesn't involve any changes to the design.

The digital electronics is likely the most objectionable - theoretically anyway.

My design is two boards - the analogue power supply / driver stage, and the digital control section. The analogue power section could be kept close to the motor (for all the above reasons), and the digital board put a short distance away, which I think is a good compromise. The two boards are connected by a flat ribbon cable.

[bernard991]

My design is two boards - the analogue power supply / driver stage, and the digital control section. The analogue power section could be kept close to the motor (for all the above reasons), and the digital board put a short distance away, which I think is a good compromise. The two boards are connected by a flat ribbon cable. [/B][/QUOTE]

Steerpike
thanks for the good info
just wondering though if keeping the analogue /PS close to the motor
do you mean under it as is the case now w/ the controller ..OR more likely beside it w/ the digital section farther away ?

I was leaning towards moving the old stuff as I alluded to but instead I will just update caps etc and wait for the new design

did you see the Japanese translation where the designer put it all in one box ?
best Bernard

[Steerpike]

My own personal plan is to put it all in one box, under the platter.
The digital section probably inside its own sheet steel box - like the cans they put the RF section of TV tuners inside.

[bernard991]

sorry ...do you mean another 'new' box under the plinth or ...under the platter where it is now ?

[Steerpike]

I have no plinth. The motor will go into a wood plinth, i.e., the top of a cabinet with wood sides and base - basically a six-sided box. Electronics in the bottom of that box.
Well that was my plan.
MAYBE I'll want to experiment!

[brianco]

My system has a 2 feet umbilical so that the PS can be on a seperate shelf to the motor unit in its plinth.

The idea of having the PS/controller unit in a box within the plinth does not mean that it must be connected to the plinth. A recess in the plinth can allow for the box to be on the same support shelf with no contact with the plinth. The resultant shorter cable requirement may well overcome other issues.

However it would be difficult adopt this system with a maker's obsidian plinth. My aim is to build a plinth for the motor alone and to ditch the original top plate unit - I long ago stripped out the mechanical brake.

BUT first i need the new PS/Controller!!

[Shaun]

Originally posted by Steerpike
I have no plinth. The motor will go into a wood plinth, i.e., the top of a cabinet with wood sides and base - basically a six-sided box.

Originally posted by brianco
My aim is to build a plinth for the motor alone and to ditch the original top plate unit - I long ago stripped out the mechanical brake.

Here's my design for one such plinth (see bottom of page).

[rich121]

Great to see this thread having life again!