Technics SL-1200 DC Power Supply

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peppennino

peppennino

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Joined 2005
flickr.com/photos/194234898@N02/albums
30cm 24V blue led strip connected to C3. Obviously you have to remove the plastic cover.
:cheers:

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Here you can find almost all my recent builds:
https://www.flickr.com/photos/194234898@N02/albums
 
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C

chip_mk

Member
Joined 2005
RickRay said:
So a capacitor right after the rectifier does a better job of smoothing the load current variations instead of a resistor then capacitor right after the rectifier?
Click to expand...
Slow load variations. In my opinion yes. It would be nice to check with LTSpice although. But as far as I remember some experiments done in the past, due to short time of conduction of bridge diodes, delta V on the first C got to be significant to increase the conduction angle to get enough charge in each cycle.

However it is OK if the load is relatively constant. As a matter of fact I use RCRC for my B1 buffer.
 
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cbueche

cbueche

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Joined 2016
bueche.ch/
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I'm having a kicad learning journey, trying to design a PCB for the 6L6-designed PSU. I use kicad 7.0 and the freerouting plugin. I routed GND manually, had a go at freerouting, and moved some tracks to B.Cu to minimize vias. Would you guys give your opinion on my work ? I have a few issues :
  • the DRC tool says the GND end at (-) of C3 is unconnected. I can't see why it says this, it is connected.
  • should I use a copper zone for GND ?
  • the C5 decoupling cap is not optimally connected (its GND makes a large back-round to join "output GND" on J2). Is that an issue ?
  • what else do I miss ? any other hints ?
Thx !
Charles
 

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Frabor

Frabor

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Joined 2016
  • should I use a copper zone for GND ?
My experience is with eagle is limited (side business, not main occupation), mostly with non audio boards. In general, most PCB are designed nowadays with a ground plane in at least one of the layers, or ground pour in both with stitching between layers , that reduces gnd impedance overall and give noise immunity. Trace all signals if possible on one layer and do gnd plane on the other. Bruno Putzeys frim Purify like ground planes https://www.edn.com/the-g-word-how-to-get-your-audio-off-the-ground/ but many other top audio designers are still use 90 degrees bends and avoid ground planes and ground pours. You can always do two versions of the board and compare performance.

The autoroute did a decent job, but post hand optimization is always a good idea.

a discussion about gnd planes in audio https://www.eevblog.com/forum/projects/should-i-use-a-ground-plane-in-my-audio-frequency-pcb/

  • the DRC tool says the GND end at (-) of C3 is unconnected. I can't see why it says this, it is connected
In eagle, it is a common error, sometimes a bug and sometimes the connection is very close (one pixel away) and does not touch. In case of doubt, delete the connection in the schematics and redraw it, then re-run the DRC. It works for me. I like to have the DRC with no errors or make sure that the error I get are something I have chosen and it does not affect the design.

  • the C5 decoupling cap is not optimally connected (its GND makes a large back-round to join "output GND" on J2). Is that an issue ?
It is always better to make gnd traces big and direct. As "it is an issue", I cannot tell you.
  • what else do I miss ? any other hints ?
if possible, I would route as many of the signal on one plane and the gnd on another. C4 to D4 you are creating a star ground, something that is very typical on older audio designs but is it said to have issues, Unless it is your intention to have a star gnd, I would not route that line (maybe c4 to r3).
 
cbueche

cbueche

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Joined 2016
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Thanks Frabor for your feedback. I moved things around to reduce the PCB size, and tried better routing. Results shown below. I played with a ground plane, but this is not an audio PCB, only a basic PSU with CRCRC filtering, so I see no real reason for a ground plane. The PSU is anyway followed by the regulation inside the turntable. Next is sending my work to an etcher and hope for the best. If things work well, I'll publish the kicad files.
 

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R

RickRay

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I can report that this modification does work with the Technics SL-D3 also. The schematic is a few pages back, I removed Q1, Q2, Q3, D1, D2. I bridged across D1 with two jumper wires. The strobe does not work with this modification, no worries it was inaccurate anyway, operated by mains frequency. I can say the dynamic range or blackness of the table has increased. I am hearing little bits that were previously masked. I did replace the regulator with 6L6's circuit on a perfboard.

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Frabor

Frabor

Member
Joined 2016
cbueche said:
I have received the pcbs yesterday, however I'm leaving for holidays so the check and testing will have to wait. I won't share anything untested.
Click to expand...
I was busy for the last two months and did not see your post. Layout looks good. I'll be following your testing.

And I do belive your board can be considered an audio board since power supplies are a very delicate part of the Audio chain and any noise gather by them, can make it into the signal.
 
bjsilverballs

bjsilverballs

Member
Joined 2018
Ok, I have 2 SL-D3 tables and would love to see what else I can wring out of it. Was considering replacing the integrated patch cords/ground with something a little better. I know these are supposed to be very low capacitance but I'm sure there's gotta be a better alternative. Power supply seems like a great area to improve. I upgraded to an Audio Technica VM540 from a Shure M97xe which was revelatory! I'm currently rocking a pair of bridged ACAs and a Nutube preamp so how about another DIY kit?!? :)
 
S

Stanislav

Member
Joined 2003
bjsilverballs said:
Ok, I have 2 SL-D3 tables and would love to see what else I can wring out of it. W
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The first thing you should do is move the power transformer out of the chassis.
Even if you do not upgrade the PSU in any other way this alone will bring a huge benefit regarding noise and vibration.
And with SL-D2 & D3, Q2 & Q3 it's very easy to do it.
 
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6L6

6L6

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Fantastic suggestion! I was looking at the service manual and it seems very straightforward.

I’m convinced in a SL-1200 95% of the benefit of the PSU mod is getting the transformer out of the chassis, so it should be very beneficial in this turntable.
 
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