Technics 1200 PS and Tonearm mods

[gary f]

I can agree on many things you say. Technics headshell mount is not very rigid, and I guess there can be improvement with a one-piece tonearm. (but cartridge switching is a pain!).

Red light has 700 nm wavelength. That's 0.0007mm. Seems quite small. I doubt that vinyl cutting and pressing has that kind of precision. Maybe, maybe not. Whatever.

But don't forget that the tonearm can be infinitely rigid, but the cart can still move because of the bearings. If you have perfect bearings, the only thing that keeps the cart in place is its own weight, and the weight of the tonearm and headshell. I don't really know what's my point.
I can imagine using a very heavy cartridge and flimsy-flexy tonearm. Could this work?

[Toaster]

The point is, the arm structure and the bearings can't be totally rigid, a real arm can only approach the ideal to a greater or lesser degree. Depends what you mean by holding the cartridge in place. What keeps it in the groove is the tracking force applied to the arm, or if you prefer, the gram or two of mass 'seen' at the stylus after the rest has been balanced by the counterweight. The actual arm and cartridge mass, or at least the effective mass, is all about inertia and the resonant frequency of the 'spring' that is the cartridge's suspension compliance. Basic mechanical matching of cartridges and tonearms considers the low frequency resonance of the combination. Too low (say 2-5Hz) and it will be excited by record warps and eccentricities or the resonant frequency of the turntable's suspension system. Too high (around 20Hz) and it will be excited by audio on the record. Old (late 70s/ early 80s) 'Turntables' editions of Hifi Choice magazine had an excellent technical introduction to this subject, but I don't know if it's on the web anywhere. They recommended about 9-15Hz or so as the best compromise region for the lf arm/ cartridge resonance. A really flexible arm would have it's own very strong resonance, with exact consequences depending on what frequency or range of frequencies this occured over. The Hifi Choice introduction suggests that the smallest modulations on a record may be as small as a millionth of an inch- perhaps something like a quiet violin harmonic.

[325addict]

I have an arm with separate headshell on my Thorens too, and since a while, I have a cartridge from Stanton, the "681 Triple E" hanging in it.
Can anyone say if this is a good combination, and if this cartridge has some qualities at all? I got it from a good friend of mine - free!

I mainly use this deck to record my records to tape (open reel or cassette) or CD, so the quality should be quite high. I don't use it for DJ-ing


regards,

Timmo Meyer.

[jonners]

I came across this thread just a couple of days after installing a DIY power supply into my Technics SL1210. So here, in a nutshell, is how I did it:

First I downloaded the circuit diagrams from the Technics forum at Vinyl Engine. The rectified input from the mains transformer supplies 35V DC, which is then dropped to 21V by the regulator circuit on the main board. I decided to make a regulated 21V DC supply and bypass the internal regulator completely.

I discovered it was possible, by cutting a wire link, to attach the new supply without having to remove the circuit board. (Referring to the page showing the Drive Control PCB, I cut the vertical link near the top of the board, just left of the word "Technics", and connected the 21V DC to the lower part of that wire. The earthing point is at the bottom corner of the board. The page from the manual shows the underside of the board, but of course when you remove the platter and the plastic cover you will be looking down at board from above.

Connecting the new supply in this way disables the strobe and the cueing light. I've never had much use for either of them, so that was fine by me. My way of connecting also in effect eliminated a supply bypass cap, so I attached another one.

If you want to do this, it may help to know that I measured the current drawn from the 21V supply to be 170mA during steady rotation. There are brief peaks of 400mA (450mA at 45rpm) on starting and stopping.

I used an 18V AC (two 9V windings in series), 75VA mains transformer and a L200 regulator on a small heat sink. A 1.5 amp LM317 reg should be OK too.

The more I listen, the more I am impressed at the improvement. Deeper soundstage, quieter background, cleaner transients, better bass. The outlay and the work involved is pretty minimal so if you have the deck, can read a schematic and make a power supply I would highly recommend going for it!

John

[pengboon]

Great! What kind of regulator did you use? Could you post a schematic of your regulator?

thanks!

[jonners]

I used this: http://eu.st.com/stonline/products/l...re/ds/1318.pdf

However, as I said above, an LM317 would be OK too.

John