Tweaks to my Technics SL-23 Turntable

Hari Iyer

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At the outset, i want to thank mpw for selling me this beautiful TT. I have now been using this for almost 2 years now with mixed results about its SQ. This made me to explore more as this particular TT did not seem that bad as it sounded. In the past 2 weeks, i did a bit of research on what tweak parameters would have a significant impact on the SQ and tried to address them one by one by doing nothing fancy but try my luck.

1. Turntable Mats: I found out that felt, rubber, cork and leather mats are used in most turntables. Since i had some leather at home, i DIY a mat out of that. The leather mat had a profound impact on the sound stage with increased bass, more clarity and detail and low noise. The leather mat also helps in reduced static built-up. The leather portion sits on the platter and the record sits on the smooth surface. The leather mat also helped in aligning the tonearm with the record as its thickness is around 2 mm less than the rubber mat.
https://ibb.co/gYZeGa

2. Disk stabilizer: I had some glass crystal candle holders with me, which i am now using as a disk stabilizer. This weighs around 205 grams and sits snugly on top of the record. The disk stabilizer helps to grip the record firmly with the platter and in turn helps to reduce resonance. FMs who wish to DIY can try using some kind of a porcelain bowl fit to size if they wish to experiment.
The SQ improvement is very subtle and cannot be distinguished with and without the disk stabilizer. Maybe on wrapped records it will perform better with the disk stabilizer.

3. Isolators: Removing the isolation spike from the bottom of the Technics TT and putting them on a plywood and then placing the Techincs TT on the plywood. By this i get the spiked isolation and also the original rubber + spring isolation from the TT. This also helped in improving resonance property of the TT and overall SQ improvement. Also balanced the TT using a spirit level.

https://ibb.co/jMm4hF

4. Phono Pre-amp: The Phono pre-amp had a power supply hum though barely audible was driving me nuts when the tracks changed. With music it was not audible but nevertheless present. I added 2 Serson 3300 mfd capacitor at the powersupply +/- rail and fine tuned the DC offset of the PSU and the hum completely vanished.

To conclude these minor tweaks along with cleaning of some of my record collection with soap/ water and carefully storing them in the record sleeve provided by FM Shafic ensured good enjoyment of Vinyls again.

Now, i will require to download one of the cartridge alignment protractor from vinylengine.com to align the cartridge azimuth once again.

Thanks for looking!
 
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I'm not sure what you mean by DC offset of the PSU - could you please elaborate?
also, which cart are you using - I have found that the cart and stylus make the biggest difference.
Also, the bottom board may sometimes make feedback worse - if you face this problem, it might be worth dampening it with either tarfelt sheet, or some proper CLD (dynamat etc) sheets

also, I'm sure you've started playing around with VTA, tonearm mass and input capacitance/loading. Have fun :)
 
All important points, @greenhorn :thumbsup: One can also play around with resistive loading. 47kOhms must not be considered sacrosanct.
 
I'm not sure what you mean by DC offset of the PSU - could you please elaborate?

I use a +/- 15 volts class A power supply for the phono pre-amp which can be adjusted to precision by a trimpot. I noticed the +ve voltage to be 16.5 volts and -ve voltage to be 15.2 volts. This causes DC offset error in the output stage. I now have adjusted them to an error of +/- 0.2 volts which helps in reducing DC hum.

also, which cart are you using - I have found that the cart and stylus make the biggest difference.
mpw also gave me the Ortofon cartridge having the pro stylus in it. I replaced them with an after market "Tonar" stylus which was a genuine replacement for the OM30 stylus. This replacement stylus is cool.

Also, the bottom board may sometimes make feedback worse - if you face this problem, it might be worth dampening it with either tarfelt sheet, or some proper CLD (dynamat etc) sheets

Thanks for suggestion. I may plan to put some (around 4mm) rubber or coir doormat on the plywood later.

also, I'm sure you've started playing around with VTA, tonearm mass and input capacitance/loading. Have fun :)

The VTA is now okay with the tonearm height parallel to the records. The tonearm is a low resonance "S" shape Techincs original. My phono pre-amp does not have any input capacitance as my cable + cartridge capacitance at the input of the phono pre-amp is around 136pF as measured by my LCR meter. My cartridge requires around 200pF to 400pF and i am not going to add any external input capacitance. I get a reasonable high-end minus the sparkle but still quite airy.

I need to download the protractor from vinylengine.com to align the azimuth of my cartridge which is planned for this weekend.
 
All important points, @greenhorn :thumbsup: One can also play around with resistive loading. 47kOhms must not be considered sacrosanct.

I concur. As per my cartridge FR simulation 51Kohm gives me much balanced, flatter and extended response without any resonance peak.
 
I use a +/- 15 volts class A power supply for the phono pre-amp which can be adjusted to precision by a trimpot. I noticed the +ve voltage to be 16.5 volts and -ve voltage to be 15.2 volts. This causes DC offset error in the output stage. I now have adjusted them to an error of +/- 0.2 volts which helps in reducing DC hum.

That's very interesting, how did you accomplish this? Is it possible to share a schematic?
 
I did some review of the protractors available in the vinylengine.com website but found none for the Technics SL-23 TT. The Technics arc protractor was for the SL1200 series where the pivot to spindle distance is 215mm. The SL-23 has a pivot to spindle distance 206mm. None of the published protractors can be used for the Azimuth adjustment for the SL-23.

Below is the data downloaded from the vinylengine.com website for the SL-23,

Eff length 220 mm
Over Hang 14 mm
Offset 22 mm
Pivot to spindle 206 mm
cart weight 3-8.5 grams
inner null point 53.6 mm
outer null point 111.2 mm

From this website i created my own protractor with the above data,

Conrad's Free Stuff

Now will print this on a paper and do the Azimuth and overhang adjustments.
 
@Hari: what Protractor does the Conrad Hofman generator make? Null point protractor? And does it allow one to choose preferred geometry?

Please have a look at Keith Howard's ArmGeometer too.
 
@Hari: what Protractor does the Conrad Hofman generator make? Null point protractor? And does it allow one to choose preferred geometry?

Please have a look at Keith Howard's ArmGeometer too.


@ Jousha
The Conrad Hofman generator allows Stevenson and baerwald arc protractor. I created the Stevenson protractor as the tracking error and average distortions are minimum with this protractor. You just need to fix the inner groove distance after downloading the data for your turntable from the vinylengine.com. Then alter the outer groove distance till you get the exact eff distance, overhang, offset, inner null, outer null. I got the exact values for my turntable after some iterations. You need to print it directly on the printer without saving it else the dimension will be resized.

Just now i completed the Azimuth alignment and listen to my "Reference" record. Immediately noticed a smooth midrange and reduction in distortions in highs. Also the inner groove distortions were reduced significantly.

Earlier i used enjoythemusic.com protractor but they were not meant for the SL-23 and hence were not as accurate as the custom ones which matches my turntable ditto. If you have not done this before i will recommend you to try once.
 
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I use alignment gauges - I have one for my pioneer and my technics. not sure about accuracy and all the different alignments, but they sure as hell make life easy!

also the technics gauges are pretty cheap, and double as headshell stands!
 
Earlier i used enjoythemusic.com protractor but they were not meant for the SL-23 and hence were not as accurate as the custom ones which matches my turntable ditto. If you have not done this before i will recommend you to try once.

Since both my arms are DIYed and both are 12" I made a common protractor with ArmGeometer. It generates a two-point null protractor, but I find that I still need to worry about correct overhang. So I made an overhang gauge. Then I converted the two point protractor into something simpler - an offset gauge. So I set overhang first, followed by offset. I find the results very good when doing set up accurately. If done not so carefully, slight inner groove distortion can be heard. But I guess the same would apply to any protractor. I also have the Mobile Fidelity protractor but honestly I don't trust it enough:)
 
Tomorrow, i may plan to add a glass crystal platter on the existing platter around 4mm thick for better grip of the leather mat on the platter. The existing aluminium platter has 2 slots for allowing inserting the belt to the motor and this cause the leather mats to droop in a bit. Adding a glass platter on top of this aluminium platter will fill-up the slots and the leather mat can grip the glass platter and the record can grip the leather mat.
 
Added the glass platter yesterday and found good background noise floor reduction, more micro-detail, reduced feedback and resonance. Its worth a try if you can DIY it with local glass vendors.

Now the final tweak will be on the table to develop a suspension type isolation for the same. Have some plans in my mind which i may implement this week.
 
Have asked the carpenter today to diy the isolation table for the Technics. Will post images once done. I will be using the spring feet on the isolation table and will isolate the TT using rubber balls. This gives me approximately 3 bounce of the TT on tapping the isolation table gently with the prototype.
 
Last weekend I refurbished my Technics TT with a new dab of vinyl sheet (Courtesy diyaudiocart) and a new isolation table. The spring feet of the TT now sits on the isolation table and the TT gets four solid rubber spongy balls for further damping of vibrations.

Some images of the outcome,

https://www.imageupload.co.uk/image/DS1F

https://www.imageupload.co.uk/image/DS16

https://www.imageupload.co.uk/image/DS1N

https://www.imageupload.co.uk/image/DS1z

https://www.imageupload.co.uk/image/DS1b

Thanks for looking.
 
Last weekend I refurbished my Technics TT with a new dab of vinyl sheet (Courtesy diyaudiocart) and a new isolation table. The spring feet of the TT now sits on the isolation table and the TT gets four solid rubber spongy balls for further damping of vibrations.

Some images of the outcome,

https://www.imageupload.co.uk/image/DS1F

https://www.imageupload.co.uk/image/DS16

https://www.imageupload.co.uk/image/DS1N

https://www.imageupload.co.uk/image/DS1z

https://www.imageupload.co.uk/image/DS1b

Thanks for looking.

Great work Hari!!

Regards.
 
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