Technics SL 1200 Turntable Power Supply

[russtafarian]

It's Paul Hynes PS I was referring to. External DC power supply and four internally mounted regulators. Motor drive and motor controller each have their own 21v regulator. Separate 9v and 5v regulators for other control circuits. Pretty slick!

[cafe latte]

It's Paul Hynes PS I was referring to. External DC power supply and four internally mounted regulators. Motor drive and motor controller each have their own 21v regulator. Separate 9v and 5v regulators for other control circuits. Pretty slick!

Yes but all the regs are external so non will be working to specs. It may be not a bad psu but it would be far better if the regs remained in the turntable.
Regards
CL

[russtafarian]

Yes but all the regs are external so non will be working to specs.

Here are a few photos from the Paul Hynes PS link above. The regulators are placed inside the turntable. Looks to me like he did a good job of designing and implementing this circuit.

[cafe latte]

I admit it is far better than I expected as the regs are still in the turntable, but the regs still have been relocated off the main board.
Regards
CL

[valvehead]

Those modules do look slick - but have you seen the prices?!

[cafe latte]

I never heard of someone interested in external psu, starting from moving the original transformer outside.
Why? I wish i had you wallets...

There is a good reason , especially moving the transformer. With some MC carts you can get a little hum from the magnetic field from the transformer, so moving it outside the turntable eliminates this problem.
Regards
CL

I am updating some bad info on my part . It is not MCs that are the issue for Technics hum from the transformer, but high output unshielded carts. The only cart that picks up the transformer field a little in my collection is my Decca super gold which is unshilded, infact despite its mind numbing price tag is made of plastic (looks like it came out of a Christmas cracker imo, but sounds amazing) and it is not a MC.
Anyway MC are not the issue, appologies.
Regards
CL

[resu]

Thanks CL. What a relief . I've been desperately trying to find more information of this "hum problem".
No more fear of making an unlucky cart choice .

[cafe latte]

Sorry to cause you so much work . What cart are you thinking to get?
Regards
CL

[resu]

No problem CL . I'm happy it's clear now. About the cart: I just bought an Ortofon Kontrapunkt B, maybe 20 minutes ago. I may eventually have to upgrade my phono pre too. Remains to be seen, or heard actually.
Regards, k

[Trackside]

It's quite likley you may hear some mains hum if you crank up the volume with the needle off or on a stationary groove but the key test is if you can hear ( or preferably measure it with an audio recorder)it during silent passages or intertrack unmodulated grooves. Also many recordings have mains hum embeded in them due to 50/60hz being picked up in the recording stage or even the cutting stage.

[cafe latte]

It's quite likley you may hear some mains hum if you crank up the volume with the needle off or on a stationary groove but the key test is if you can hear ( or preferably measure it with an audio recorder)it during silent passages or intertrack unmodulated grooves. Also many recordings have mains hum embeded in them due to 50/60hz being picked up in the recording stage or even the cutting stage.

With the stylus on a stationary record I used to here hum with the volume cranked up, but if you remove the lid it is completely silent as the lid was acting as an ear and feeding back low freq from the speakers. If was far worse if you made a noise or tapped the shelf it started a feedback loop as the speakers get louder the lid picks up more.
I now always play my records without the lid.
Regards
CL

[Paul Jenner]

Hi Russ,

thanks a lot for sharing your knowledge on this subject here.

I will take the AC transformer outside my SL1210 anytime soon, and I will follow the procedure you described. Seems like a fine method to me without spending more on a deluxe ready-made outboard PSU than I paid for the whole bloody turntable !

I have two questions however, concerning the cable that connects the outboard Transformer to the inside of the SL:

1) you mentioned you used shielded microphone cable. I follow you on the shielded part, but why not use two separately shielded cables, double coaxial, like in line-level cable for stereo connection ?;

2) mic cable, or line-level cable for that matter, have pretty thin conductors. Aren't these a bit on the thin side for transferring 31 Volts at 1 amp ?


Thanks,

Paul.

[OneyedK]

Hi Paul,

While the internal 21V regulator is quite sufficient, the 5V and the 9.4V are not.
Replacing them with better regulators is a good idea.
Even with the high quality Paul Hynes regulators, that doesn't cost an arm and a leg...

Another thing, if you make the effort of putting the transformer in a different housing, it might be a good idea to include a rectifier and a "large" capacitor (let's say 4700µF), feeding the TT witn DC.

You're mentioning 1A, in reality, the current draw of the Technics is around 300mA.
not a problem for a microphone cable...
(not that I believe it's usefull to shield those "power" cables, I believe it's wiser to install a small HF filter inside the TT)

[Paul Jenner]

Hi OneEyedK.

Thanks for the reply (I take it you replace Ross while he's on leaf ?)

The shielded cable might off course only be usefull when transferring AC to the TT. Yes, feeding the Techie with DC might be better. I could copy the rectifier's and elco setup and place that outside. I might even robb the Tehnics of some of it's internals, to reduce costs. It is -after all- pretty straightfoward stuff. Then leave the regulator inside (but upgrade it).

I think I missed something about the 5V and 9.4V regulators in the Hynes setup ? (I skipped that part mostly because the outragious cost ...)

Paul.