SL-1200 Platters, bearings, mats and PSU's, cartridges, arms, and more...

[Marco]

Hi Dave,

Here's an explanation from Paul Hynes on the subject, which may be of help:

It’s not just about measuring RMS, Peak and transient power consumption of the DD motor. The electronics used to control the motor will have limited supply interference rejection that will vary with frequency, getting worse as frequency increases.

This means that the power supply should have good supply line interference rejection to reduce mains interference transfer to the load circuitry and it should have very low noise. The power supply should also maintain its output voltage as close to the required voltage as possible under dynamic load current swings, as any voltage error on the power supply output will be seen as noise/interference by the motor control circuitry.

“Off the shelf” mains transformers are built to a price in a very competitive market and corners are cut in material specifications and
construction, giving less than ideal performance.

One of the biggest problems with low cost transformers is rattling laminations, which vibrate in sympathy with the current flowing through the windings, giving rise to high levels of mechanical noise and unstable electrical power transfer. The smaller ones are not too bad in this respect, and the 60 VA Toroidal transformer I use in the lower cost SR3 is the best of the “off the shelf” variety I have found and it is pretty quiet.

Unfortunately the larger transformers in the range, like all the other ranges I have tried, get very noisy, which is unacceptable in an audio system. Another problem that is relevant to transformer electrical performance is that “off the shelf” transformers are built for highest
efficiency, which means they are designed to operate at high Flux densities.

This makes them very susceptible to any DC current flow in the windings, which can be caused by switch-on when the mains voltage
waveform is at a high potential and/or asymmetrical current draw from the transformer by the load, which can cause core saturation at
relatively low levels reducing the available VA rating dramatically.

The solution to this is to have a custom-made transformer that uses high quality materials and is carefully wound for low mechanical noise and for low flux density operation to avoid core saturation, which can cause a lot of interference on the supply line. This requires using a larger core than normal for a given VA rating. The custom transformer in the SR5 is rated at 160 VA and doesn’t suffer from appreciable VA loss due to core saturation. It is also very quiet.

The voltage regulator has the job of maintaining the DC supply rail at the specified DC voltage for any load current change. For this reason the voltage regulator is usually a DC coupled AC amplifier. Important parameters for this regulator in no particular order of merit are :-

1) The transient response and settling time should be fast enough to allow the regulator to track load current changes to maintain the
output voltage at the required level.

2) The output impedance should be as low as possible over the load operating bandwidth so any load current induced output voltage changes are minimised.

3) The regulator noise should be as low as possible so this does not interfere with the load circuitry because of the finite supply line
rejection abilities of the load circuits.

4) The regulator supply line rejection should be as high as possible across as wide a bandwidth as possible to reduce the effect of mains
line interference and rectification (conversion of AC current to pulsed DC current) interference.

The Technics motor requires a clean accurate drive signal to maintain accurate platter rotation. Essentially a clean stable supply will reduce signal corruption in the motor control circuitry leading to more stable platter drive and more accurate platter rotation.

A lot of that goes over the top of my head, but I understand the gist of it. You being a more technical chap than me, of course, should be able to make better sense of it

The bit in bold, is especially significant for me and confirms what I can hear when comparing Paul's SR5-21 (or SR3) to the stock Timestep PSU, when Mike New's heavy platter is used on the SL-1200/1210, not to mention why overrated/overspecified transformers can work very well in a given circuit, even when certain electrical parameters dictate that they are 'unnecessary'.

Paul has said that if anyone has specific questions they'd like to ask, he will come and answer them here

Marco.

[Reid Malenfant]

Can someone explain to me why it is necessary to have power supplies that could be used for welding and bearings better than those in my 1000cc V twin motorbike for playing records

I haven't got a 1200/10 but i hope this might help

It's all about performance, you should know something about this having a 1L V twin What you have with any PSU is an engine that supplies power, after all it is the power supply. Now you could have a PSU that's just big enough to power your turntable, much like a 50cc moped is good for 30MPH even if it takes it's time getting there However, the way to "performance" in virtually anything (including hifi & turntables) is to fit a massive PSU even if it's only going to be lightly used.

Witness what a massively overated power supply does for big solid state amps like the earlier Krells & Mark Levinsons, it frees them up to deliver massive dynamics that any lesser amp just couldn't get anywhere near delivering. If you are a sensible motorcycle rider you know you have more than enough performance (with that VT 1L) to do just about anything to get you out of trouble & into it if you care to. I know as i have a 1L sitting in my garage that has seen 170MPH.

It's all about being totally over-rated so as nothing will phase it, the consequence of this is improved fidelity

About the bearing Have you tried spinning a record on your crankshaft? Ok, forgetting it's too fast i doubt very much that the vibration would help make any cartridge make the record sound very nice

Precision leads to greater fidelity as well. What Mike New says makes perfect sense:-

He obviously has no idea that copper based alloys such as brass and bronze (and many others) have a far greater co-efficient of expansion than steel, especially the chrome/nickel alloy tool steel that my bearing spindle is made from. This implies that at increased temperatures the bearing gap tolerance will increase (just for Dave’s sake, this means that the bearing becomes less stiff, old chap)

Even i know that tool steel expands less than brass, bronze etc as temperature inceases. The bearing will not sieze up unless it's run in a bloody cold freezer (when the brass/bronze will contract more than the tool steel shaft & increase friction)

[Clive]

I had a little trouble with speed stability on one of my decks last winter (not a Techie). The deck is in the cellar, the room is heated but it gets very cold at night. With night temps down to -12C the room must have been very cold. Bolting a power resistor in a TO220 package and running it at about 12W with a Maplin thermostatic controller sorted it. I'm sure this was a more extreme test than has been the case with the MN bearing and even so it wasn't a big problem. I expect the bearing had been running 20C cooler than intended.

[MartinT]

I dunno. That's why I use a Roksan; it just plays records!

I used to have a Roksan Xerxes and it played records. Until it stopped. Then Roksan withdrew support for it. I sold it in disgust.

[Alex_UK]

I'm staying out of this one, because I have no knowledge of either party's products. All I will say, though, is that as an impartial observer, the whole sorry state is very sad and I believe not good for the onward development of "race-tuned" products for the SL-12X0...

[Joe]

I used to have a Roksan Xerxes and it played records. Until it stopped. Then Roksan withdrew support for it. I sold it in disgust.

Ah well, you win some, you lose some. My orignal Xerxes ran trouble-free for 20 years, then I traded it in for a Xerxes X.

On the other hand, I had a Nytech 252 amp that was trouble from day one, and which (literally) went up in smoke once out of warranty. Some bloke on ANOther forum has been using one daily without a problem for 25 years!

[DSJR]

Well, you now have two main options in the UK. Stay with the original platter and lightly beef up the bearing, going with a "standard" external supply and putting the extra into mats of metal and spongy rubbery stuff, or significantly beefing up the bearing and platter, which call for a more powerful, extremely low noise and "fast" power supply, thus taking the whole motor design away from the one originally optimised for the lighter platter. It's to Technics' credit that the more-or-less standard driving electronics can run with the heavy-duty platter and bearing..

I'd still love to compare a fully beefed up and tricked out Techie with an NAS Heavy-Space plus Wave-Mechanic, which costs around the same. One day maybe.

[Ammonite Audio]

I'd still love to compare a fully beefed up and tricked out Techie with an NAS Heavy-Space plus Wave-Mechanic, which costs around the same. One day maybe.

Sometimes I wish that I had kept my Heavied and Waved Spacedeck. A beefed up Technics is a very different beast indeed.

[MartinT]

thus taking the whole motor design away from the one originally optimised for the lighter platter. It's to Technics' credit that the more-or-less standard driving electronics can run with the heavy-duty platter and bearing.

It's over-stating things to assume that a heavy platter creates so much more load on the motor. The friction in the MN bearing is perhaps a little more than the Technics one, and that is all the motor is driving against: friction. The sheer inertia of the platter is hardly of consequence since it is already spinning at the correct speed and just needs tiny corrections. Once the motor is up to speed it is hardly working any harder at all, so all the benefits of the brilliant Technics design remain.

[Clive]

If the motor can take disco antics then the heavier platter won't be of any consequence.