Opus 3 Cantus parallel tracking arm

[chrissugar]

Judging from your pictures, it appears to me the platter and Technics tonearm came from the Technics SL-Q2.

It is SL-Q3 but it is almost identical to the SL-Q2. In fact is uses the same motor and servo electronics used in many Technics tables, including the 1200/1210. If you study the service manuals for all these Technics machines, you will discover that most ones using the AN6675 AN6680 chips have the same drive circuit with small differences.

I don't have pics of the electronics, and don't remember exact part numbers I modified but I can share some ideas of what I did:
1- I changed all electrolytic caps to Panasonic FC.
2- I discovered that the circuit is sensitive to the quality of power it receives (probably mostly RFI problems) so decided to isolate it and power it from a pair of Yuasa lead batteries (12V 7Ah). It can run 70 hours before recharge.
3- I connected close to the PCB a 22000 microfarad Panasonic FC capacitor pack (10X2200microfarad) to reduce impedance and provide instant current if needed.
4- modified the negative feedback loop network to make the whole thing underdamped. As it is from the factory, it is overdamped and after doing some A/B test by switching instantly between the factory network and the new one, it is obvious the change in sound. The moded version is much more relaxed and clear and all the distortion (similar to jitter in digital) in mids and highs is gone.

My benchmark for comparisons was a Clearaudio motor and servo electronics used to drive the acrylic platter rim with a belt. The big advantage was that I could almost instantly compare the sound of the Clearaudio belt drive and various stages of my direct drive mods just by removing the belt.
I like my moded direct drive version more than the Clearaudio belt drive. For me the direct drive versus belt drive subject is closed. It can be done to sound good, even with a "not top of the line" motor.

By the way, I used a stethoscope at every stage and listened to the noises in the plinth and arm mounts.

chrissugar

 

[moray james]

Bo and Bo

An interesting Blog I found and a friend of Bo's.
http://twogoodears.blogspot.com/2010/06/bo-hansson-and-bo-hansson.html


TWOGOODEARS - トゥーグッドイアーズ

This is Stefano Bertoncello's Blog (ステファノ・ベルトンチェッロ - トゥーグッドイアーズ 　−　ブロガー、オーディオ＆ミュージック・コンサルタント) devoted to pacific topics like Music - live and reproduced - i.e. discs, audio, guitars - both vintage and new, concerts, workshops, and related stuffs. Furthermore: travelling - as a mind-game and real globetrotting, and books, movies, photography... sharing all the above et al. and related links. ... and to anything makes Life better and Earth a better place to stay, enjoying Life, in Peace.
Sunday, June 13, 2010
Bo Hansson and Bo Hansson


... yes, pals... two Bo Hanssons... one Bo Hansson, the Swedish Prog musician who wrote and played and recorded on Charisma "Mad Hatter" record label, two great records: "Lord of the Rings" and "Magician's Hat" - sort-of "ante-litteram" fantasy-tinted soundtracks to Tolkien's masterpiece - untimely passed away on last April 24th... R.I.P. to him.

The second one, also from Sweden, Bo "Bosse" Hansson, is fortunately still and well alive and kickin'... he founded back in the late '70s/early '80s The Audiophile's Audiophile record label: Opus3 and - as a parallel business - he ran Rauna of Sweden, devoted to some classy audio... the older among us will sure remember the concrete-made speakers from the '80s.

Bo, always gentle, supportive to every music lover - yours truly included - recorded several dozens discs with tube gears - tape recorders and microphones - and golden ears, using no studio gimnicks and tricks, BUT only well-rehearsed musicians recorded in natural sounding venues - i.e. churches, school halls and the like.

Bo's Opus3 discovered a young Eric Bibb and recorded him several times, alone and with Bert Deivert, an itinerant musician and busker who settled in the friendly Sweden for some time, just to record some records and make some money for other journeys, but Opus3's production spanned from Indian classical music, to organ to Irish folk, classical and jazz.

Bosse used Revox G-36, Telefunken M-15A, Neumann USM-69 and AKG C-24... and plenty of Basf and AGFA tapes... and produced among the very best sounding vinyl discs ever, also thanking the great mastering job made in Solna, at The Mastering Room.

His actual interest are also audio, notably speakers, analog turntables and tube amps... also an arm, a linear tracking arm produced by Rauna, is a very nice sounding, cheap piece of gear and a well-kept secret in analog.

Mr. Hansson has been and sure still is a BIG influence on my recording tastes and techniques and a quiet lighthouse to me, as he, rock steady, still uses his trusty, huge M-15 open-reel recorder and analog open-reel tape and it's not rare seeing him and his Telefunken's at some audio fair, demonstrating his gears with first generation, superb master-tapes.



An humble genius... thanks for being, Bosse!
Posted by twogoodears at 6/13/2010 01:48:00 PM
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About Me
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twogoodears

View my complete profile

 

[Nanook]

chrissugar...

have you created an album or direct link to all of the turntable pictures? I'd like to see other photos if you have some The table looks impressive, and I am sure sounds quite good. And the information on tools used.

Moray, as always the consumate surfin'dude, 'dude

 

[directdriver]

Re: "modified the negative feedback loop network"

chrissugar: "modified the negative feedback loop network to make the whole thing underdamped. As it is from the factory, it is overdamped and after doing some A/B test by switching instantly between the factory network and the new one, it is obvious the change in sound. The moded version is much more relaxed and clear and all the distortion (similar to jitter in digital) in mids and highs is gone."

This is of great interest to me. I would love to see what change you have done to the circuit and, hopefully, I can observe the schematic. I don't want to hijack this thread into talking about turntables since it's about tonearm designs so I will contact you in private.

chrissugar: "My benchmark for comparisons was a Clearaudio motor and servo electronics used to drive the acrylic platter rim with a belt. The big advantage was that I could almost instantly compare the sound of the Clearaudio belt drive and various stages of my direct drive mods just by removing the belt."

I have done similar experiment in the past and I prefer the belt-drive result using a direct-drive turntable to VHS tape drive another identical turntable. But I didn't modify the electronics to "under-damp" the feedback network as my solid state electronic skill is rather limited.

chrissugar: "I like my moded direct drive version more than the Clearaudio belt drive. For me the direct drive versus belt drive subject is closed. It can be done to sound good, even with a "not top of the line" motor."

That's very encouraging and if I can do similar things to my direct-drive turntables, I much rather stick with direct-drive approach so I don't have to deal with those annoy belts and tapes. After all I am a "driectdriver."

Thanks again, for your information and contribution to this thread.

.

 

[directdriver]

More fun pictures!

www2.hemsida.net/martinberg/Vinylsvarv.htm

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[dtut]

Thanks DD,

I really like this one. Simple, elegant solutions, attractive design. Rolling blades - what a great idea. In my experiments, I found that increasing the radius of the wheel magnified the problems with dirt or uneven surfaces. It may be that the sharp contact point helps with that, but I'd guess the V channel still has to be kept very clean.

 

[Nanook]

directdriver...a minor criticism

first off, beautiful arm. The only thing I might suggest is creating a similar "drop" for the counterweight so that it would be in the same plane as the stylus when a record is playing.

I know I'm a little on the anal side, but this just makes sense to me.

It is a beautiful arm though, and my suggested change may not be very difficult to implement as you have created a modular design.

I do prefer very simple arms, as my newest arm construction shows...

 

[dtut]

Ever since I saw DD's most recent pictures posted above, I've been fantasizing about building one. Finally got a (ripped, stolen, cloned, homage) built. Sometimes I feel like a cover band. After building several versions of Cantus clones, I thought the rolling knife edge offered an elegant solution for vertical arm movement while keeping the passive rolling for the horizontal.

The wheels are reshaped nylon sliding door rollers. The bearings are from remote control cars, the tubes are broken carbon fiber arrow shafts, and the carrier is 3mm mahogany marine ply. The tower is adapted from earlier iterations of the Cantus and has adjustable VTA built in, which makes life far easier at tweaking time. The cartridge is a Shure 97ED.

The nylon wheels were shaped in a drill press used as a mock lathe. They're soft enough to be worked easily and fairly accurately with files and sandpaper. The combination of nylon and aluminum is quieter than bearings in a PVC tube like my Cantus clones. I use a mechanics' stethoscope for noise checks and the whole arm is very quiet. Following Moray James' advice, I put shrink wrap on the aluminum arm of the Cantus, which reduced noise in it to just about zero. I'll probably do that on this arm, too, although carbon fiber has very different vibration transmission characteristics.

The three-axis adjustment is a bit tricky and I still don't know of any way to accurately or usefully measure VTF. I have to do it visually by watching cantilever displacement as the arm is lowered.

The arm tracks very well in both axes. It follows warped records with no problem and no audible distortion and is OK with slightly off center holes. It doesn't like dirt in the track or on the wheels, which, considering how exposed it is, may be a problem.

OK, so how does it sound. Bluntly, damn good. Tonal balance is slightly bright, but overall very good. The major strength of this arm is detail. Music is reproduced as humans singing or playing instruments meaning very much like live performance. You've all experienced/heard/read all this before and I don't want to go on about it, but, man, I think this design has real promise.

 

[analog_sa]

Here are some pics with my DIY turntable

Lovely! What is the black material in the middle of the constained layer plinth?

 

[rowuk]

I have been lurking for some time. Recently a plant that outgrew its pot fell over and wiped out my tone arm, fortunately leaving the Luxman cartridge with vdH stylus intact.

I used to buy the Opus 3 records just because they were simply great to listen to. With this guys ears, I think that we can believe him when he says simple is better.

I think that a Cantus clone could very well be the answer to my problem (no tone arm). The glass tube I think could easily be made out of a precision test tube. They are available in 20 - 22cm length, 16-22mm inner diameter and in plain glass, borosilicate or quarzglass versions.

It is interesting reading FDEGROVES comments. I have been playing and designing trumpets for many years and there we too only get results when the entire system is considered. Mechanical coupling and damping at the right places all optimize the resonant behaviour of the system. I think too often there is an obsession with killing resonance - that could have been our friend. Considering how fragile vinyl is compared to a stylus, maybe open channeled devices should be rethought to make them less susceptible to "trouble". Cleaning out an aluminum Vee profile is not tough, but will we always think about preventive maintenance? The tube design does offer significant "protective" benefits - at least in a non-smoking household in the country.

My thoughts presently will be to try the test tube, a double carbon fiber wand close to the original tubing geometry and some sort of electronic lift (perhaps magnetic).

My question is what advantage could having the counterweight at stylus level possibly have? It seems that everything is moving very slowly (except the stylus following the groove) so dynamic balance can't be an issue with an inherently stable design with 2 ball bearings in the glass tube. This is not a unipoint or knife bearing design that needs this to even function. Another question is about the wires. Designs like found in inkjet printers with traces on a plastic substrate seem to be very flexible and mechanically more sensible than wires just hanging around. Any thoughts?

Possible future mods would be a protected park position, auto lift at the end of the disc and playing with the resonance of the glass tube as well as additional arm assemblies with various cartridges.

 

[moray james]

Bo has been building these arms for a long time. I think that the geometry that you see there is so simply because it works best. Why not start with as close a copy as possible so you can have a reference. Then you can experiment and make direct comparisons to the first version. You can play with the wire harness to your hearts content. You might want to try a three wire braid with two ground clips connected to the one ground wire at the cartridge. This will be lighter and more flexible no matter what wire you choose to use. You only need one common ground for both channels. Have fun and keep us posted with your results. Best regards Moray James.

 

[rowuk]

The three wire won't work for me. I have a symmetrical/balanced MC Preamp to minimize common mode noise picked up by the relatively unshielded wires and cartridge. They are very similar to what are used in decent microphone preamps.

 

[rowuk]

Well, I did it.
The present state of things is that I am using an aluminum tube because it was cheap and easy to maschine with a Dremel and carborundum cutting wheel.

I bought a 6mm outside diameter carbon fiber tube for the tone arm and had some rosewood kicking around in the cellar for the headshell, bearing support and counterweight. The 10mm o.d. ball bearings have ceramic balls and I cut some distance bolts from an old computer that I had. I flushed the greased bearings out with lighter fluid.

The wiring is also self made from OFC silver plated speaker wire. I used 4 strands per lead (twisted in my hand drill) and painted them with polyurethane paint (2 coats). I then colored them red, green and blue with a magic marker and twisted the left and right pairs together, then both of them. Very low capacitance and impedance. The heat from a soldering pen melts the polyurethane away, so there is no need to strip the very fine wires.

The tube assembly (15mm o.d./13mm i.d.) is held up with a stainless steel 8mm bolt 120mm long. All you have to do is make sure that the tube is absolutely parallel to the platter and that the turntable is level. This was MUCH easier to set up than the Keith Monks arm that my wifes plant trashed.


So, how does it sound? Incredible. Transparent, believable stage, wide bandwidth, good imaging. I play trumpet professionally and have a lot of exposure to orchestra instruments, this arm does a wonderful job with voices and strings as well as slam and pace with jazz band recordings. I am a happy camper. It is almost impossible to get this thing to skip. I have tried records with offset holes, warps and direct disc recordings with heavy dynamics. Pitch remains stable even with recorders, pianos and violins.

Next steps:

I will order the glass tube from Rauna as the next step. When it gets here I will also install a lift and probably an end of record auto lift. I am not 100% with one of the bearings (too much play and will order a couple of different models to try.

This project was so easy and sounds so good. I got everything done in one weekend including going to a hardware store to buy the parts. I give it a big thumbs up for DIYability.

Robin

 

[dtut]

Robin,

Congratulations on your new arm. That's very nice work - I particularly like the wood fore and aft.

How do you measure vtf?

 

[moray james]

Robbin: excellent work. I also like your head shell, very nice. I spent some time discussing arm tube size with Bo and he told me that regardless of material larger tubes would be more resonant. Bo has a simple test for this. Mount your arm tube and cartridge then play a blank disk. While playing the disk turn up the gain on your preamp until you note resonant feedback. Then try a different tube size and compare the point on your preamp volume setting where feedback sets in. Bo told me that the larger the tube diameter the lower the point of feedback. I would imagine that thin wall glass tubes would be very stiff and rigid (and they could be damped) but the SS thin wall tube he uses is inexpensive and durable and seems to do a fine job. Please keep us posted on any further updates to your very good looking arm. Best regards Moray James.

 

[rowuk]

I have an old Audio Technica VTF scale, but it doesn't give me anything meaningful here.

Actually, I am not very big on "numbers". The actual trackability seems to vary depending on ambient temperature. More important to me is that I avoid distortion from too little VTF. Historically, I have set my cartridges more at the top of the manufacturers recommendations.

I normally fine tune by ear (and eye) using records that have tracking challenges. If the bass sounds "right" and I can track the tough records, I am very close anyway. The first test is to lower the cartridge onto the record without the motor being on. It is then easy to see if the cantilever appreciably changes angles. After that, the test records walk me through. I have a bunch of Sheffield Lab records that are revealing. I listen to a lot of symphonic music where balance is pretty easy to hear. Chamber music with recorders, harpsichord, piano, pipe organ and the like also make most setups pretty fast. Bo's Opus 3 records are also really good for checking this stuff out.

So all in all, not very scientific - but it sounds good. This weekend I'll do some resonance measuring to see if there is any ringing in bad places that hasn't audibly shown up in the music yet.

 

[rowuk]

Moray,
thanks! I read Bo's thoughts on the resonance of tubes. Being a trumpet player, I see where he is coming from - and some easy fixes. The resonance that he mentions is the standing wave found in any cavity. It is based on length for cylindrical objects and volume for irregular shaped objects. In the case of a tube, the resonant point can be changed by properly venting it. In the case of the trumpet, there is a spit valve to let the moisture out. When we open the spit valve, certain frequencies cannot be played. The trick is the right location of the vent to handle the frequency.

This fantastic design lends itself to interchangeable arm wands and I will also play with the original Cantus geometry too. Currently, the music carries me away from the technical considerations. This works so well, I am surprised that we don't have more clones!

 

[AuroraB]

Rowuk.. very nice indeed, -
but more pictures will be very much appreciated....

 

[moray james]

Cantus build...

Robin: I discussed tube damping with Bo thinking along the lines of damping. Bo was adamant that regardless of damping the tube resonance was there to be heard. Not having done any of the experiments I spoke to Bo about I cannot say. Given how ease it is to build a new arm wand to experiment with it would seem reasonable to do a number of experiments. I am glad to hear that your are enjoying this great little arm. You did a really nice job on your arm and I am sure that you will inspire others to do the same. Best regards Moray James.

 

[rowuk]

Hi Moray,
I am not talking about damping. Venting a tube retunes it in a fuzzy way. Standing waves are no longer a function of the length of the tube. We can move the major resonance like a flute player changing a note. I agree with Bo that damping loses energy - something that we don't want to do.

In any case, I will build additional wands including Bo's original geometry. The single tube on the first shot is easier to build - two threaded holes for the ball bearing screws and one for the wand didn't need any critical measuring. The most time consuming part was making the wire.

As far as my tools go, I only have a drill press for my hand drill, a dremel and only needed a powered sabre saw for rough cutting the wood and hand tools like a tap for threading the ball bearing holes.

This arm is a really great "beginners" (which I am not) project. Everything is so logical and easy to calculate. Parts costs: €10 for both ceramic ball bearings, €5 for the 6mm carbon fiber tube, €3.50 for the 15mm aluminum tube, €1.80 for the 8mm stainless steel bolt that supports the tube. The rest was just standard nuts and bolts that I had in the tool shed.

There is almost nothing that can go wrong.