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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. :D :D :D
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 :D
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.
Attachment 18963
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.
Attachment 18964
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 :)
Very nice. Do you mind sharing more info on how your extra onboard stabilizers are connected?
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.
Thanks. I'll have a closer look when I'm back from my vacations
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 MikeQuote:
Originally Posted by Mike_New
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.
Agreed. I'm certainly not comfortable doing these kinds of modifications yet. Well said on this one, Mike.Quote:
Originally Posted by RobbieGong