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Thread: SL-1200 DC Power Supply DIY

  1. #181
    Join Date: Aug 2012

    Location: Denver, Colorado

    Posts: 458
    I'm Jim.

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    Yes, absolutely!

    There's nothing at all wrong with the stock transformer, the issue is that it's mounted IN the turntable... Mounting it outboard and moving some of the noisier electrical bits to an external chassis makes a huge difference in noise floor.

    Externalizing your PSU is the single biggest mod you can do to the table. And if DIY, the bang-for-the-buck is totally off the scale.
    SP-10Mk2a, Graham 2.2 tonearm. SL-1200, Graham 2.2 tonearm, AT-150mlx, Benz-Scheu Glider. Jim & Ken Super DC PSU, Oil well bearing, Acromat, Isonoes, strobe lamp switched. Pass Labs Pearl 2. Aleph J amplifier. F6 Amplifier. Nelson Pass Burning Amplifier BA-3. Pass BA-PP linestage, miniDSP 4x10, Linkwitz Labs LXmini speakers, Sony SS-M7 speakers.

    DIY In progress - Syclotron Red Light district valve amp, ZenMod "Iron pre" autoformer jfet preamp, SYclotron 'His Master's Noise' valve phonostage. And about 2-3 other projects in various states at any time.

  2. #182
    Join Date: Oct 2014

    Location: East Coast USA

    Posts: 96
    I'm Nathan.

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    I guess then it's time to mount my PS in a proper enclosure. The wooden box it's in now looks more like a beginner science fair project
    We the willing, working for the unknowing, are doing the impossible for the ungrateful.
    We have done so much for so long with so little, we are now qualified to do anything with nothing.

  3. #183
    Join Date: Sep 2015

    Location: Minsk, Belarus

    Posts: 30
    I'm Valera.

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    After bying SL-1200MkII first of all I removed Q1 and created LM317 circuit and then, of course, moved transformer to external case. Both actions was absolutely necessary, but not enough and I decided to make some additional work with all power lines - first of all to split driver and control powers as described on this forum.

    Q1_replaced.jpg

    After that I found one more weak point in schematic. It's FG amplifier Q203 powered through simple RC filter from the same source as control IC's. Some strange fluctuations of FG output spectrum were observed under 10 Hz (NOT a 4.5 Hz @ 33 rpm). I can't understand (and still can't) how this mode appears but I observed it clearly until FG amplified power line separated.

    So, now I have (see photo below):
    - external primary stabilizer 26 V
    - two secondary stabs (21 V each) which feed motor driver and control circuit separately.
    - improved onboard stabilizers for IC's 6680, 6682 and 4011 ((typical LM317 and 78xx schematic, two left red circles)
    - additional stab (78L09) for FG amplifier (right red circle). Btw, this amplifier is very simple and can/should be upgraded, my Tektronics shows very noisy and unstable sinusoidal figure coming to PLL circuit.

    Sl-1200_inside.jpg

    I made these changes in short time and of course they are not optimal, output voltages should be corrected for each stabilizer. But in general I'm sure it's correct way to improve Technics before any other electrical changes. Power is food for all Tech electronics!

    Will further power supply improvements give us sound profit? Who knows... my opinion - no. No issues to make shunt regulator instead of series (I use shunt regulators in my DIY phonostage) or use some superstable schematics etc etc, but I think it's time to think about PLL parameters. Will be useful to find out some way(s) to observe in realtime platter speed fluctuations. I tried to analyze fg amp. signal spectrum as well as 3150 tone spectrum and although I'm not quite satisfied by my measurements, I can see real improvements.

    Unfortunately I didn't read this topic earlier, this could save my time
    Analog: Technics SL-1200MkII (RB300 tonearm, external PSU, separated power supply for all stages, improved bearing), MC Goldring Eroica LX, custom SUT 1:10, Balanced input J-FET DIY phonostage
    Digital: Cubietruck (headless Debian server, i2s output, external masterclock from DAC), content on HDD. DAC: Lynx D29v4 (Altera FPGA digital stream separator, 2*AD1853, 2*3 OP42 LPF)
    PA: DIY composite amplifier YES-3, schematic by Gennady Bragin
    Acoustic: DIY floorstanding 3-way SB Acoustics

  4. #184
    Join Date: Dec 2011

    Location: Athens

    Posts: 268
    I'm Dimitris.

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    Very nice. Do you mind sharing more info on how your extra onboard stabilizers are connected?
    Sources: Modified SL1200 MK2, Salas folded RIAA, Phonoclone, VSPS, Shelter 501 MK2, Modified Pioneer P6D6 as transport, Shigaclone transport, Peter Daniel NOS DAC.
    Amplification: Custom 211 Monoblocks, Electrocompaniet AW120, Audio Research VS110, Gainclone
    Loudspeakers: Tannoy Turnberry, PBN Montana EP Signature
    Cables/stands: Tempflex ribbon and Twinax cables
    Other: Promitheus Signature Passive Attenuator, Custom JFET - transformer preamp.

  5. #185
    Join Date: Sep 2015

    Location: Minsk, Belarus

    Posts: 30
    I'm Valera.

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    Yes, it's easy. The main goals was increase power stability, separate power for all sensitive schematic parts and to get regulators as close as possible to the end consumers.

    1. 78L06 regulator feeds 4011 IC. R304 and Zener D301 removed, 78L06 ground pin inserted instead of D301 anode, IN and OUT pins inserted instead of R304.

    2, 3. 78L05 (not 78L09 as stated in my previous post) regulator feeds FG Amp. R221 removed, 7805 GND pin inserted into new drilled hole. 3rd screenshot captured from SL-1200 datasheet and shows exact place for drilling because of hole should de drilled througn PC board ground wire.

    Additionally I reduced R216 resistance from 150k to 100k, because of FG Amp. supply decreased from approx. 9V to 5V and Q203 mode should be returned to linear amplifying. I plan to increase power back to 9 V in future.

    4, 5. LM317 regulator feeds both 6680 and 6682 IC's. Q201 replaced by LM317 with datasheet's schematic, several unused components removed. Output voltage adjusted to 9.5 V. So, now 6680 makes only his main work - speed control.

    As you see, I used enough simple solutions. LM317 with resistors will be better to place on separate small vertical subboard, maybe it will my task in future. I'm not sure whether more complicated schematic give effect or not, maybe I will replace some regulators to improved ones. But now I have significantly better sound and Technics makes me happy.
    Attached Images Attached Images
    Analog: Technics SL-1200MkII (RB300 tonearm, external PSU, separated power supply for all stages, improved bearing), MC Goldring Eroica LX, custom SUT 1:10, Balanced input J-FET DIY phonostage
    Digital: Cubietruck (headless Debian server, i2s output, external masterclock from DAC), content on HDD. DAC: Lynx D29v4 (Altera FPGA digital stream separator, 2*AD1853, 2*3 OP42 LPF)
    PA: DIY composite amplifier YES-3, schematic by Gennady Bragin
    Acoustic: DIY floorstanding 3-way SB Acoustics

  6. #186
    Join Date: Dec 2011

    Location: Athens

    Posts: 268
    I'm Dimitris.

    Default

    Thanks. I'll have a closer look when I'm back from my vacations
    Sources: Modified SL1200 MK2, Salas folded RIAA, Phonoclone, VSPS, Shelter 501 MK2, Modified Pioneer P6D6 as transport, Shigaclone transport, Peter Daniel NOS DAC.
    Amplification: Custom 211 Monoblocks, Electrocompaniet AW120, Audio Research VS110, Gainclone
    Loudspeakers: Tannoy Turnberry, PBN Montana EP Signature
    Cables/stands: Tempflex ribbon and Twinax cables
    Other: Promitheus Signature Passive Attenuator, Custom JFET - transformer preamp.

  7. #187
    Mike_New Guest

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    Folks,
    Refering to modifications of the main PCB
    Khom: says: "Yes, it's easy. The main goals was increase power stability, separate power for all sensitive schematic parts and to get regulators as close as possible to the end consumers."

    It may be easy for those of us who are experienced in electronics and circuit work!
    However if you are not familiar with doing this type of work then get someone who is, to do it for you.
    We have been around this loop before.
    A simple mistake can cascade into a lot of trouble and a badly damaged PCB.

  8. #188
    Join Date: Apr 2011

    Location: London

    Posts: 4,419
    I'm Robert.

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    Quote Originally Posted by Mike_New View Post
    Folks,
    Refering to modifications of the main PCB
    Khom: says: "Yes, it's easy. The main goals was increase power stability, separate power for all sensitive schematic parts and to get regulators as close as possible to the end consumers."

    It may be easy for those of us who are experienced in electronics and circuit work!
    However if you are not familiar with doing this type of work then get someone who is, to do it for you.
    We have been around this loop before.
    A simple mistake can cascade into a lot of trouble and a badly damaged PCB.
    Good point Mike

  9. #189
    Join Date: Apr 2009

    Location: Ayrshire, Scotland

    Posts: 231
    I'm Ian.

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    Khom
    Thanks for your info.
    Im just back from the New Year Break and need a little more time to study your tweaks.
    Initially I sorted out an alternative mains transformer with a higher VA rating(I run 240v 50Hz mains here in the UK) with an LM regulator. I upgraded this to a floating pre reg circuit then last year changed completely to Linear Technology regulators.
    Im currently running with an 18-0 -18 80VA Torroidial transformer separate from the Techie feeding unreg DC to two LT301 regs fitted into the Techie old transformer hole . These separately drive the signal electronics and the control electronics. I have two sub regulators used as a replacement for the Zener D301 and Q201. These use LT302, a 200ma version of the 301 famility
    I need to mod a platter so I can run the deck with various loads and scope the electronics freely.
    I have more work to do, just need more time.
    Technics 1200 tweaked,Ianmac Bearing,DACT DIY Phono Pre, Belcanto CD-2, Engineered Switzerland DIY Renderer, Benchmark DAC2, Hypex NCore, ATC SCM40
    2nd system --Engineered Switzerland DIY streamer, Sony CDP11,Topping D50 DAC, Hypex NCore. Kef 1point2 speakers. Ianmac Filters

  10. #190
    Join Date: Mar 2013

    Location: Philadelphia, PA

    Posts: 40
    I'm Packgrog.

    Default

    Quote Originally Posted by RobbieGong View Post
    Good point Mike
    Agreed. I'm certainly not comfortable doing these kinds of modifications yet. Well said on this one, Mike.
    Analog: VPI Scout Jr. | Phoenix Engineering Falcon PSU | DIY tach | Funk Firm Achromat | Michell Clamp | AT33PTG/II | Musical Surroundings Nova Phonomena | T.C. Electronic Desktop Konnekt 6 | Sonix IV ST136H Ultrasonic Cleaner | Okki Nokki Record Cleaning Machine

    Digital: iBasso D14

    Headphones: Lawton-modded Denon AH-D2000

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