Thursday, March 01, 2018

Dual 704 turntable is......

Got a Dual 704 from a Tonearm designer and knowing that the turntable needed some special cares.  The turntable indeed was in a good shape especially the tonearm. Here is the list of problems.

1.  the motor -  need some help to make it start running sometime
2.  the tonearm rest is missing
3.  the nearly mint Grado FCE+1 missing the needle (by the way, I will change the head to Shure V15III as this moment)

After an hour of very pleasure chatting with the owner,  I brought the turntable back to home and started the restoration at once.

the heart of the EDS900 - four induction coils

704 has a 4-coil Hall Effect motor EDS900 as the driving unit. It is a very primitive motor in today standard.  However, the specification of this turntable is still very impressive. You can't hear any motor noise and feel no vibration at all. It seems that the workmanship is so good even the design is not modern.

Speeds: 33.33 and 45rpm
Platter: 1.2kg, 300mm, dynamically balanced
Wow and flutter: 0.05% WRMS
Rumble: Weighted less than 67dB / Unweighted less than 46 dB
Tonearm effective length: 222mm
Tangential tracking error: 0.16 degree/cm
Tonearm bearing friction: vertical less than 0.07mN /  horizontal less than 0.15mN
Tonearm:  Torsionally rigid tubular aluminum in low friction four points gimbal suspension, counterbalance with two mechanical anti-resonance filters

The jerky motor might be caused by the motor driver board.  The test show that the driver board is in perfect condition. So the motor itself should be the problem. The rotation was not smooth but the rotation rate is accurate. This symptom showing one or two of the coils in the motor was not working.  The scenario is just like a 4-cylinder engine with one dead cylinder.  The car can run but lack of power and is not running smooth.

The EDS 900 has four coils in total and you can see the picture of the internal.  The coils are glued on to the housing by epoxy.  Had a quick check on the connector and bingo! one of the connection to the coil was opened.  Look closer to the printed circuit board and two of the traces were corroded. Spent an hour to fix the circuit, lubricate the whole motor unit and also changed all the E-caps in the driver board. The turntable was now running at its should be.

The signal wires were also changed to Belden Teflon 83284 wire ( the capacitance of the original wire is 140pF and the new wire is about 90pF. it is a very important to know the value. The change of the capacitance will affect the frequency response. 83284 is a RG316 coaxial wire and even it is specified for high frequency use up to 3GHz but it also can be used for audio.)

The next thing to be tackled was the tonearm rest. Buying an arm rest is easy but why not to make one.  I still have some beech wood stocks so I took a small piece and sanded it to a desired shape. The best height of the rest is about 1.2cm with a 2.5cm sideboard which is used to prevent the overshot of the tonearm return. After soaking the finished wood parts in stain conditioner and then the stain, the arm rest was then polished with furniture wax.

All tasks have been done.  It is the time to sit down and listen music. 704 is a semi-automatic turntable. You need to place the head onto the record and set the needle down manually.  The needle is always in UP position when you put the head onto the record so it is fault-proofed.  The turntable will be automatically off when the head reaches the end. The head is now in the UP position again. When you put the head back to the arm rest the head will be in down position. Amazing simple but a very smart design.

The Vertical Tonearm Control allows the cartilage is in optimal playing position without using spacer in the headshell.

Finally here is the pic to show the coil connection with the resistance value.  If you found your 704 having a jerky motor, check it out first.


Friday, October 27, 2017

The classic Nikon Lens on Sony A7 - Nikkor 35mm f/2.5

It is a Nikonos 35mm lens.  And behind this lens it has a very interesting story.  The first generation of Nikonos indeed is not the invention from Nikon.  "Calypso" is the original name of this camera and Nikon took over the producti around 1960.  It was not right to let the Calypso using non-Nikon lens (Calyso uses SOM Berthiot and Angénieux lenses). So Nikon chose the w-nikkor 3.5cm f/2.5 which was used on Nikon SP camera. The latest version of w-nikkor 35mm (3.5cm) f/2.5 has multi-coating.

Using Nikonos 35mm on Sony A7 is simple. However, it is better to remove the front cover glass which causes "haze-like" and yellowish image.

It is a very good lens on Sony A7x camera and  better than the Contax T 38mm.

Pentax 50mm f/1.2 on Sony A7 - Can a 40 years old lens still survive in modern world?

Pentax 50mm at f/1.2 with Techart LM-EA7 on A7II
Is is a very best Double Gauss F/1.2 standard lens especially at 1.2.  Below is the report from a old German magazine. You can see how its perform and it has a better score than the Leica 50mm F/1 ! 


autgezeichnet - excellent
sehr gut - very good
gut - good
zufriedenstellend -satisfactory
weniger zufriedenstellend -less satisfactory
nicht zufriedenstellend - not satisfactory
sehr bedendich-Very concerned

autgezeichnet - excellent
sehr gut - very good
gut - good
zufriedenstellend -satisfactory
weniger zufriedenstellend -less satisfactory
nicht zufriedenstellend - not satisfactory
sehr bedendich-Very concerned

Gesamtwertung - total evaluation

unter 5000 Punkte - under 5000 point : sehr gut - very good
5000 bis 6000 Punkte: good
6000 bis 7000 Punkte: satisfactory
7000 bis 7500 punkte: knapp zufriedenstellend - just satisfactory
7500 bis 8000 Punkte: weniger zufriedenstellend -less satisfactory
über 8000 Punkte: nicht zufriedenstellend - not satisfactory
unter 5000 Punkte - under 5000 point : sehr gut - very good
5000 bis 6000 Punkte: good
6000 bis 7000 Punkte: satisfactory
7000 bis 7500 punkte: knapp zufriedenstellend - just satisfactory
7500 bis 8000 Punkte: weniger zufriedenstellend -less satisfactory
über 8000 Punkte: nicht zufriedenstellend - not satisfactory

You cannot compare this lens with the modern standard lens with million pieces of elements with aspherical surfaces having special low dispersal materials.  This lens has its own character and this lens had been sold for more than 20 years (with two different versions but have the same optical formula).  There is no prefect lens in the world but we should know their characteristics and make use of them.
Pentax 50mm f/1.2 is a lens for night. Even in a very strong back-lighting situation the lens is still having a very good performance.  The only drawback of this lens to me is the direction of focusing.


Monday, July 17, 2017

Contax T 38mm on SonyA7II Part II

I converted the Contax T 38mm lens into E-mount (using a metal 55mm cap and 55mm-to-E adapter in latest version, not the plastic cap) year ago.  It seems that it is better to plant the lens onto a LTM (Leica Thread Mount) so I can use this lens on my Techart Pro LM-EA7. it is not that difficult to make this modification and what you need to have are :

1.  33mm hole saw (a 1mm wider than the lens)
2.  LTM body cap
3.  Scotch Rubber Splicing Tape 23

It is a bit difficult to hold the cap when you drill the hole and here is trick.  Drill two smaller holes besides the holding bit hole and screw the cap onto a wooden board.  Using WD40 as lubricant when drilling the hole.

Fitting the lens onto the cap is straight forward.  Using Scotch rubber slicing tape and hot glue to set the lens position temporarily. Check the centering and focus.  Once ready use epoxy to fix the lens onto the cap.

Now I have the auto focus Contax Zeiss 2.8/38.   Here is some examples.

f/2.8 (no pro-process and click the image to see the actual )


 To see the different of the lens performance in 2.8 and 5.6 and it is not that difficult to see which is which

Friday, March 10, 2017

The legacy: Contax CY 70-210 f/3.5

This photo was taken in Italy twelve years ago and scanned from film.  CY 70-210mm is my most favourite zoom lens and so why I still have two.  It is heavy and weights 1.2kg. Being the first tele zoom lens Zeiss tried their best to build this lens. At that time, they did have the design of f/2.8 version but it was too big in size. They decided to have the 3.5 rather the 2.8 version. These are the only one of the two zoom lenses made in Zeiss, Germany for SLR camera.

The sharpness of this lens is very good and even across the field even though the resolution in the centre is not the highest. However, you will find that the corner resolution are kept the same as the centre .  I compared this lens  with the first generation Canon 70-200mm F/2.8.  Canon has higher centre resolution at 3.5 but lower on edge region when compare with Contax.  I sold my Canon and  stayed with the Contax.  Why?  Contax has better micro contrast and details in shadow.   Indeed the Canon is a very good lens and good for spot photography.

The closer together the sagittal and meridional lines are to each other, the smoother and more natural the background blurring (bokeh) becomes. It is one of the reason why I keep the Contax.  Please note that Contax's MTFs is measured from a real sample lens and the Canon's MTF charts are theoretical value.
Below is the MTF chart for Canon 70-200mm 2.8 II

It is a lens for film era but it can be used on digital.  However, I strongly suggest to use this lens with L41 UV filter and it can reduce the purple fringe issue on some digital cameras.By the way, any post image processor software can eliminate the purple fringe just by few clicks.

with Kodak SLR/c with no PP

Monday, March 06, 2017

Minolta m-rokkor 28mm: The lens I sold but bought back again.

This is a legendary lens from Minolta and it is the very best 28mm in Leica M mount.  However, this lens suffered the coating degradation in the first lens element.  This problem may caused by the anti-reflection black paint which leached out the chemical which attacked the coating.  I owned this lens before and it suffered a infamous white spot issue.  I sold it before it became too bad.

Last month I got a chance to buy a good copy of m-rokkor 28mm in reasonable price. The lens is pretty clean and has no visible white spot on the first element.  Just a bit haze but it is not enough to cause any issue. Previous owner might want to clean the lens by himself but he couldn't remove the nameplate and in the end he scratched it.  It gave a lesson to everyone and you should have proper tools and skills to service your lenses. If you don't have 100% sure what you are doing,  leave it as is or let someone to do it for you.

To prevent the further degradation of the lens coating, the lens should be cleaned but it is a bit tricky to take the first element out  There is no screw-in retaining ring to hold the front element, instead it was hold by lens clement and tight-fitted to the casing .  To loss the front element the ring should be removed by a coping saw with very very fine blade. (Google it you can find the procedure) or loss the clement by solvent. Then using a sucking cup to take the element out.  (And there is a small hole (air vent) behind the lens block and inserting a bamboo toothpick into the air vent can help to pop the element out). It is not a difficult process but it takes time to make it prefect.  The edge of the lens casing was smoothed out by #00 sandpaper and re-painted with solvent base matt black paint. If it was all done, the front lens block should look like new.

After re-lubricating all helicoids with lithium grease and cleaning the lens inside out, it is the time to test the lens. Let's go hiking.

The coating is really good, at least for this 38 years old lens
See the detail of the picture and resolution is pretty good (at f/4)
We cannot comment the colour accuracy by digital camera

All pictures were taken by Sony A7II with LM-EA7 Autofocus adapter. (Yes, it became an auto focus lens! ).  Aperture were set at f/4.  Corner performance is really good.  Please be noted that this lens is a retrofocus wide angle lens and not a traditional symmetrical lens design.  And it is the reason why this lens work so well with digital camera.

Friday, November 04, 2016

LS3/5A DIY Challenge Part 3

After the prototype,  here is the final version.  The changes includes
1.  Acoustic foam was used as original specification
2.  Smaller brass screw were used
3.  Matt black paint was applied as original specification (solvent base mat black paint)
4.  Better plywood stock and the thickness as original specification  (not from Homedepot)
5.  Oak veneer applied (original LS35A don't have this and very difficult to find a good Teak veneer)
6.  Better binding post

I am now waiting  for the coming of spring so I can start to build a 9L version cabinet according to the specification from Falcon Acoustic,.

The sound of this pair of speakers is so lovely and  it is better matching with tube amp as many people suggested.

My next project is to refurbish a pair of KEF Chorale (original) which have a bad cabinet and crossover.

Birch plywood from local wood mill
Steamed beech wood to make batten

Final touch - oak veneer

LS3/5A DIY Challenge Part 2

I choose brass screws and nuts (#10 for HF units/crossover stands/cabinet faceplate. #9 for LF unit) since they are non-magnetic and cause less problem when you assemble the cabinet where the very strong magnets are nearby. It doesn't mean it will sound better and yellowish colour of the screws are very match with the cabinet.

Original design of LS3/5A uses rubber gasket to seal the LF unit with the faceplate and the faceplate to the cabinet. I choose to use the cork sheet to serve these purposes.  I stick 1mm cork sheet to the back of the faceplate and it's not only seal all the air gaps but also reduce the reflection of the sound wave from the faceplate.

Work in progress

The most difficult part in making the cabinet is the countersink of the faceplate.  I need to tailor-make a circle guide for my router so I can make a perfect circle.

For the sake of convenience, I choose to use Pink Fiberglas Insulation as the acoustic material in cabinet.  It also doesn't mean it sounds better ether.  However, many people say, and indeed, fiberglass insulation is better. If you have the LS3/5A, you can try by yourself. May be one day I can find the wool insulation in Canada and try it out. It is the premium stuff for heritage house. 

Assembling the units are very straight forward except your metal tools will always stick to the big magnets. Just one suggestion, using tape to cover the spider of the LF unit before soldering the wire.  The hot solder will jump into the spider and melt the cone. Be careful.

First thing to do after the assembling is check the resistance of the output and make sure there is no short circuit.  Before any further measurement, I connect the LS3/5A to my Roberts amp (aka Akai M7) and listen to my favourite music. What a surprise!  The 7W little amp can actually handle the LS3/5A very very well. ...................
The soundtrack was a live recording and recorded by Tascam IM2 in my listening room.

The below is the measurement of the frequency responses between two speakers see if they are well matched.

And here is the comparison between Celestion SL6s and the DIY LS35A.  The peak in the graph is caused by the source (the test disc) and I may use my signal generator to test the speaker again in later time.

LS3/5A DIY Challenge Part 1

LS3/5A is a pair of legendary speakers.  Since 1970s more than 60,000 pairs were built and sold (most of the speakers were sold in Asia !). You still can buy a new pair of LS3/5A today (as of 2016) from Falcon Acoustic (Falcon Acoustic has a long history with LS3/5A and once they provided crossover to Goodmans.). Founded by Malcolm Jones, the father of T27 and B110 driver units, FA was sold to Jerry and Malcolm fully retired in 2009.  Recently,  FA started to reissue the T27 and B110 with original recipes and specification.  The brass grille for the treble unit is from the original brass sheets which were found in a warehouse of a Denmark factory.

After I moved to Canada, I started to learn woodworking, built all kinds of furniture and renovated the house. I have all kinds of tools. Instead of buy a pair of new LS3/5A, why not to build one.  So I got all driver units and crossovers from FA.  Thanks Jerry! The only thing I need to do is to build the speaker cabinets.

First of all, I need a plan.  No problem,  here is the LS3/5A cabinet drawings (click here Second, to find a right materials. No problem, 12mm Baltic birch plywood* can be found in selected Homedepot (but it is a BB/CP grade plywood with many voids. only size 2x4 feet is in-stock. I will get a better plywood from the local woodmill for my production run). I got a beech wood from a chop board and used it to make battens. If you cannot find the beech wood.  Try use red oak since it has the similar density and stiffness/strength (see below table).  The original LS3/5A uses bitumen pad as damping material.  You can get a better performance by using 3M Sound Reduction Mat which is used for car audio application.

Angle-joint with batten support, the most simple form of box making.

Adding the damping pad (3M Sound Reduction Mat)

Since I treated it as a prototype so no exotic wood veneer was used.  The birch wood itself is beautiful enough so I just use Tung Oil and wax to protect the box.

Apply Tung oil after sanding with 140/400 sand paper. Wax and polish with Finishing wax

Each cabinet will has its own resonance frequency and it will "Colour" the sound of the speaker. So, it is very important  to match the cabinets even you have a matched pair of driver units.  The resonance frequency is a combined effects with case volume, material density, weight, shape and the variants of workmanship such as the tidiness of the joints and the amount of wood glue used.  It is better to make several and match afterwards. But in reality, home brew project cannot afford to do so. Therefore, a carefully selecting the panels and batten (weight the panels one by one and match)  for each cabinet is very important. The weight different between these two prototypes is 3g (out of 2250g).  The most easiest way to check if they are closely match is to knock on their back panels and listen if there are any different.  To have a better measurement, it needs to measure the working speaker.

It is the table from BBC research paper "Factors in the design of loudspeaker cabinets" showing oak can be used instead of beech