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Old 14th June 2011, 12:27 AM   #11
jlsem is offline jlsem  United States
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Only the claim that high mass turntables are somehow less sensitive to tonearm quality is a bit baffling and against my experience.
That part has nothing to do with the design philosophy of the Porter plinths, which were designed and built by me. The first go was made of Baltic birch plywood and basswood while the later ones were made with basswood and Panzerholz, which has 3 - 4 times the damping capacity of birch plywood. That set-up is very, very quiet and probably has a signal to noise ratio in excess of 80dB. The SME 312S is also an under-rated tone arm and matches the Airtight cartridges very well.

John
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Old 14th June 2011, 02:21 AM   #12
kevinkr is offline kevinkr  United States
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Originally Posted by analog_sa View Post
These plinths appear really great and i agree with his design philosophy. Only the claim that high mass turntables are somehow less sensitive to tonearm quality is a bit baffling and against my experience.
Mine too, FWIW..

I'm biased - I'm using a Schick with my TD-124 and it is a huge improvement over the SME 3009 whether on slate or not..
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Old 14th June 2011, 05:26 AM   #13
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Heavy =
base / plinth does have a less critical effect on tonearm
It's too bad there isn't a way to isolate and prove that. So we are left with more subjective assumptions, which I suspect are on offer at the link noted. that's ok. It offers a starting point for me.

Here's another subjective assumption: In the case of the TD124, armboard material choice does have an effect on the sound of the turntable. I think it does, anyway.

Example, the Zeta. When I first cut an armboard to fit the Zeta to the Td124, I used a scrap piece of 1/2 inch thick Baltic Birch Ply. After confirming my alignment, the listening assessment indicated a very fast (fast transients) and dynamic sound. Impressive. That arm comes alive! But there was a harshness of tone to the mids and mid-highs that was very evident and annoying. So I cut another armboard out of Gabon Ebony, also 1/2 inch thick. The harshness was replaced by a more natural tone. Some might have pointed a finger at the vdH silver wire in the Zeta, I figure it was more to do with resonances in the BB ply interacting with the pivot bearings of the Zeta. So material choice at the armboard made an obvious change in sound quality. Or so I think.

It follows that, if material choice for an armboard makes an audible difference in the sound qualities of a tonearm, then material thickness of the same armboard must also come into play and have its affect. How much, I don't know.

-Steve
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Old 14th June 2011, 05:45 AM   #14
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Originally Posted by user510 View Post
Example, the Zeta. When I first cut an armboard to fit the Zeta to the Td124, I used a scrap piece of 1/2 inch thick Baltic Birch Ply. After confirming my alignment, the listening assessment indicated a very fast (fast transients) and dynamic sound. Impressive. That arm comes alive! But there was a harshness of tone to the mids and mid-highs that was very evident and annoying. So I cut another armboard out of Gabon Ebony, also 1/2 inch thick. The harshness was replaced by a more natural tone. Some might have pointed a finger at the vdH silver wire in the Zeta, I figure it was more to do with resonances in the BB ply interacting with the pivot bearings of the Zeta. So material choice at the armboard made an obvious change in sound quality. Or so I think.
I also used a scrap piece of BB for an armboard in my LP12. It doesn't exhibit harsh mids as you describe, but then I'm using a Jelco arm with damping, which may help. I'll have to look for some Ebony to try.

jeff
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Old 14th June 2011, 06:08 AM   #15
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Just a curious question: Is the direct drive and servo control system in the SP-10 vastly different to what is the SL-(<1800)s non-MKIIs?
Hi MaxW.
Thanks for asking that question because it is a perfect lead-in to the next step. Explanations, corrections of the explanations(), and general discussion about the speed control used on the SP10 mkII.

Thanks to The Vinyl Engine, we have access to good copies of the service manual to assist (heavily) in this project. I'll try to paraphrase and condense the explanation of the various circuits that regulate platter speed on this interesting little record player.

1) First there is quartz oscillator that generates a reference signal. The reference signal is split by a frequency divider into the appropriate frequency for each of the three available speeds. And this speed information is stored in digital memory. Yikes, there's that word.....digital....

2) There is a strobe logic circuit that is used to flash the neon strobe bulb.

3) Frequency Generator.
It says that the Frequency Generator is integrated with the platter drive motor and converts platter rotation speed into a frequency. And the output of this frequency is fed to the speed and phase control circuits.

4) Phase Control Circuit
The phase control circuit detects phase difference between a reference signal (see item #1) and the frequency generator signal (item #3) and generates a control voltage. So between the reference signal, the frequency generator and the phase control circuit the rotation of the platter is "locked" to the reference signal.

5) Speed Control Circuit
Here it describes a "sample hold" circuit that converts output of the frequency generator into an electrical voltage. This is the control voltage which maintains platter rotation speed.

(Btw, we already knew that the motor was brushless DC, right?! DC motors are speed-controlled by voltage. More volts = more rpms....more or less.)

6) Drive Circuit
Here I just quote the service manual.

"Two control signals are composed and applied to the drive circuit to maintain a forward motor rotation. The drive circuit supplies full wave drive current doubling current efficiency. It supplies drive current in both directions for a symmetrical rotation in either a forward or reverse direction."

7) Start/stop Circuit
Hit the on button and the circuit starts the platter rotation. hit it again and a reverse drive plus mechanical brake is applied.

8) Mechanical Brake Actuating Circuit.
Here it describes a circuit that operates a solenoid that pushes a brake shoe against the platter. And this is working together with the above noted start/stop circuit. There's more but you get the idea.

There you go. Tech-geek translated into English courtesy of yer humble servant..

Hmmm. I think I only saw the word "digital" used twice. But I wanted to spare you so I only used the word once. No wait, I just used it again. Sorry.

Pretty advanced stuff for the mid nineteen seventies. And I presume that all of this circuitry is really the heart and soul of this little player. (assuming that it does have soul) It makes sense then to insure that all circuits are filled with happy little electrons busily going about their business. No sick, tired or injured electrons allowed! Brave talk, I know.

For me, giving maintenance to these circuits will be the hard part. The mechanical parts shouldn't be as much of a challenge. Get past the circuitry, and its just a platter that spins on its bearing.

Oh, yeah. I forgot. MaxW. I'd have to look up the service manual for the SL1800 for the speed control comparisons between that deck and this one. I suspect there will be many similarities. Manufacturers like to re-use their technology over and again when it is economical to do so. But not when it isn't. I presume that it mostly is.

-Steve

Last edited by user510; 14th June 2011 at 06:18 AM.
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Old 14th June 2011, 01:31 PM   #16
maxw is offline maxw  United Kingdom
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Wow, thanks for the detailed information! Interesting, I wasn't aware there was an actual mechanical brake.

Years ago I had a look at 1200/1300/1400/1500/1600/1700/1800s and they all looked like they used almost identical drive/control systems. I was just curious if this turntable was vastly different.

I look forward to watching this thread
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Old 19th June 2011, 08:16 PM   #17
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Click the image to open in full size.

Photos and illustrations. I like photos and illustrations.
The above section view diagram is from a SP-10 mk3 sales brochure, courtesy of The Vinyl Engine. (thanks Jas !)

I was looking for a similar section view of the SP-10 mk2, but came up empty. I presume this is because there isn't one. But if anyone knows of such an illustration, this would be a great thread to post a link to it.

Here are some article scans that found their way into my possession:
Click the image to open in full size.

Readability is not that great, but finding SP-10 articles using Google is proving to be somewhat of a dry hunt. It would be far better to search various libraries for the magazine articles that exist. Circa 1970 to 1989 or there abouts. I presume that many of the UK audio magazines would be a good place to search. In the US, I wish I had access to a complete collection of Stereo Review, Hi-Fi, TAS and Stereophile. Reprints of those articles would be great to have all in one location.

Here are some more:
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

The above scans are courtesy of Ken McCarty, who also owns a mk2a and recently acquired a mk3, which prompted him to release his original mk2 motor unit with controller to me. All in all, I think he had 3 SP-10's. A pair of mk2's and now a mk3. Now he's got two.. Btw, he also owns a TD124 mkII. When I asked him how the Thorens compared to his rehabilitated SP-10 mk2A, his comments were:
Quote:
Just like the TD 124, these old tables need some restoration. As I mentioned earlier, consider re-capping the power supply and boards, clean out the bearing and lube, and adjust calibration With a good solid plinth, it can blow away the Thorens in low noise, rumble figures and absolute speed stability. Having said that, I really enjoy the Thorens!
I'm posting this stuff today because I want to keep this thread topic alive and within the first two pages of this forum for the near term. I will be taking my sweet time on this one. It's not like I'm going without my vinyl fix. I have a pair of nice Thorens players to spin vinyl while the current SP-10mk2 in my possession gets made ready.

Here is roughly my itinerary for the project:

1) Research. Gather as much info/data/anecdotes, etc, as is possible and them post them to my SP-10 page for future researchers on a similar quest.
2) Receive the unit, appraise condition, external and internal in terms of mechanical integrity and function.
3) measurements mechanical and electrical
4) maintenance mechanical and electrical
5) plinth designs and trials

Item 1 will be an on-going process throughout and after this project concludes.
Item 2, is partly underway, but I'm holding off from delving into the unit until I gather further data.

Item 3 will be a challenge for me. I am savvy with mechanical systems, but not so much with electronic systems. So part of my Item 1 activities will be in learning how to take certain important measurements for rumble figures and signal/noise ratios, etc. I may have to get assistance. But I will do that and post results when I have them.

Item 4 should be straight forward with regard to the main platter bearing and thrust. However the replacement of electrolytic capacitors on every board within the motor unit, and within the external controller, will be a new experience for me. I'll post photos and results as I have them. I will take my time and approach with extreme care and timidity.. Initial impression is that there are many, many of these capacitors to be replaced.
---------------------

Item 5. plinth design. this is more fun and within my comfort zone.

Fortunately we have some people that have been experimenting and posting results around the web for SP-10 projects. Notably, Albert Porter, who frequents the Audiogon forums and also writes for Positive Feedback Online.

Alberts plinth design for both his SP-10 mk2 and mk3 are high mass and with some interesting features.

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
The above images are courtesy of soundfountain and Albert Porter.

Stunning photography. Albert is a commercial photographer. Does advertising and magazines.

These are for his SP-10 mk2 project. Which, btw, he claims compaired so favorably to his Walker Procenium Air Bearing turntable, that he ultimately chose to replace the Walker with an SP-10 mk3. While I'm not inclined to buy-in to the idea that one of these SP-10 Technics players are actually superior to the Walker, I would accept that the Technics excelled in areas of sonic quality that run parallel to Porter's likes/dislikes. Presumably, the Technics will likely "out-measure" the Walker for Wow/Flutter. Not so sure about s/n ratios, but it would be interesting to run that comparison if there were one.

But I digress. The interesting (to me) features of Albert's design are the inclusion of a layer of aluminum sheet metal within the layered build-up of baltic birch plywood, and also a nifty idea that is being called a "bearing drain". The bearing drain consists of the heavy plate of cast iron, seen in the first and third photos, a threaded brass rod that threads thru the iron plate and up into contact against the underside of the Technics platter bearing. The last photo shows the final assembly from underneath.

While I'm not sure if the device really works as a "bearing drain", that is to conduct resonances/vibes coming off the platter bearing down into the iron plate, or if the positive effects being claimed as sonic improvements have more to do with stiffening the motor housing structure of the Technics.

In any case, I like the idea. And if there seems to be no sonic benefit, one can simply remove the threaded brass rod.

Btw, Albert says he did not build the plinth but that it was built for him by a master furniture builder within his audio group. That gentleman is also participating within this thread under the moniker "jslem".

Nice work jslem!

Then there is the plinth he did for his SP-10 mk3. This time using some very expensive and hard to get Panzerholz wood as a key ingredient to the internal damping structure of that design. However I'm not going to consider using Panzerholz simply because it is too hard to come by in this country, and when it does appear, the cost is even higher than having a slate base made. For me it will be baltic birch plywood as the key structural component for my base. Btw, Albert and jslem offer their plinths for sale.
Here's a link to Albert's website:
http://www.porterhouseaudio.com/inde...inth&Itemid=74

Check out the many photos there. The workmanship looks to be top class. Prices are appropriate to the quality being bought.

In one or more of the discussion threads happening over at AudioGon, one poster suggests that the best plinth is "no plinth at all". The suggestion being that plinths tend to 'introduce' their unique signatures into the turntable chassis, thereby degrading its potential for sonic quality. No photos were offered, leaving readers to use their imagination on how that architecture might look with a SP-10 mk2 and tonearm of your choice.

It would be interesting to work up some skeletal framework designs that could hold both the motor unit and tonearm rigidly enough in the correct proximity to one another and take a listen. Something cheap.

Now for something completely different..

Here's a plinth design taken from "Nutshell Hi-Fi". Lynn Olsen's website.
Click the image to open in full size.
The turntable is an EMT 930St, but this plinth idea could easily be implemented to hold any number of different makes and models. It is multiple layers of baltic birch ply over a stainless steel frame. I would call this a light-medium constrained layer damped plinth with the benefit of having a rigid steel structural support. That unit might just sing..!

link to article: Travels to Europe and the Triode Festival

I have some old plinth ideas that I drew up a few years ago, when someone had asked me to but before I had considered actually owning an SP-10mkII.
Here's my first concept idea from 2006:
#1:
Click the image to open in full size.

Then #2:
Click the image to open in full size.

#3:Click the image to open in full size.

I'm quite sure I'm not going with #1.

I'm working on another idea but don't have a sketch render yet.

Anyway, the "thinking about it phase" is still underway.

cheers.

-Steve
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Old 24th June 2011, 10:10 AM   #18
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Great sounding (I hope) project:-)

I bought my SP-10MkII from a friend who had a slate plinth made for it.
He was using a SME V-12 and I/O cart. We made a gunmetal (5/8" thick) armboard for it.
I bought the deck when he decided to get a Voyd. I put a 12" DIY arm on it with a SPU but now use my converted PL-71 12" or Rega R200 12" arm and SPU silver meister cart.
I do like the sound it makes. The solidity of build and ease of use. Spot on speed etc.

I have this on 3 Stillpoints then a thick sheet of MDF laminated to a granite block and then Focalpod feet - works for me.

I tried a baltic birch ply armboard but the heavy lump of gunmetal does something rather special.

I have also auditioned a copper mat but in all honesty found the Pioneer PL-71 Japan/US issus mat to be just as good and for the price of a Cu mat you get the whole PL-71 and the Acos arm to convert;-)

Good luck in the project and I look forward to reading the updates.
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Old 24th June 2011, 02:29 PM   #19
Helmuth is offline Helmuth  Netherlands
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Old 24th June 2011, 08:42 PM   #20
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My SP10 project will happen when everything else is done, so I'll watch others and steal ideas. So far, something like the Porter designs are what I'm thinking, but with a wider plinth so it can handle 2 or 3 arms easily.

Now I'm past the mid year exams, I'll also take a long look at user510's articles.
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