Need design parameters for DIY Tonearm

[sudhirbhosale]

Hi all
I need below parameters calculations / design details for below :
Below parameters for various effective tonearm lengths for 9", 10", 11"12"
- Distance between pickup arm pivot and record center
- Overhang calculation
- Angle of stylus
- What is significance of overhang?
- Ideal weight on record / stylus point
- Pros and cons of long vs short tonearm length
- Why turntable belts are so costly? Is there any DIY solution? i.e. cutting from tube if I get tube of exact belt size
- Are only flat cross section belts are used or round section are also considerable?
- If amplifier has AUX input then can TT connected there or phono is must (I have Austonia amp with aux)

Any other design inputs relevant and helpful.

Thanks lot

 

[jls001]

All tonearm parameters are derived from three primary parameters, namely, effective length, inner record radius, and outer record radius.

Inner recorded radius (of a 12 inch record). This is the innermost groove (measured from the center of the spindle, in mm). There are various standards followed. DIN 57.5 mm, JIS 57.6 mm, IEC 60.325 mm. You need to choose which standard to follow.

Outer recorded radius (of a 12 inch record). This is the outermost groove (measured from center of the spindle, in mm). DIN standard is 146.3 mm, JIS is 146.6 mm, and IEC is 146.05 mm. Again, you'll have to choose.

Effective length (mounting distance + over hang) is also something you need to decide.

After you have these three parameters, you can use tonearm calculators. I recommend the Arm Geometer by Keith Howard. See his website Welcome to Audiosignal. Check out his Freewares page. Download and install. This will help calculate over hang, head shell offset, inner and outer null points, and you can also generate a two-point protractor to help align your arm. If you have the patience i can also point you to how you can make a superior offset protractor and overhang protractor.

For explanation of tonearm geometry and parameters, please read up SOUNDFOUNTAIN - News & Views, AUDIO & MUSIC, Body and Soul, ART & DESIGN.. Try Turntable and Cartridge Adjustment page.

Analog Dept also has some wonderful resources, but the motherload is at Vinyl Engine.

To decide your effective length, check out vinylengine's tonearm database. There's a lot of variation in effective arm length even among a length class - for example, if you look up 9 inch arms you'll find mounting distance (=pivot to spindle distance) varying wildly from as low as 210 mm to as much as 230 mm or even more. So you have to decide based on the space you have on your plinth.

Longer arms will produce lesser tracking error but need more space to mount. Also, longer arm tube necessarily comes with higher arm resonance. Rigidity is everything. They will also be heavier, so effective mass will go up, and may not suit higher compliance cartridges.

Designing a tonearm is about choosing what compromises we can afford to make. You've started out on an interesting (and challenging) journey :thumbsup:

 

[Hiten]

Geometry and mathematics were not my favourite subjects and I am not expert but in simple language I will try.

Since pivoted tonearm would move in an arc across the record the stylus point will not be parallel (Approx 2 degrees) to the both record groove. This creates distortion. However one can minimize it by offset angle and overhang at atleast two points across the path of tonearm on record. There is Tonearm calculator on vinyl engine where you can calculate any parameters.

Stylus angle that you are talking about is stylus rack angle which is angle of stylus diamond to record surface. General consensus is 92 degrees. This can be adjusted by moving tonearm base vertically keeping tonearm tube parallel to record surface.

Ideal weight dependes on your cartridge compliance. High compliance cartridge would track at low stylus force comparatively.

Long tonearm have advantage of less tracking error. But difference is very small. Generally a 9 inch tonearm has approx. 0.8% and 12 inch 0.6% distortion.

Turntable belts needs to be of perfect thickness and elasticity or they will add to wow distortion. May be flutter too. Flat and round belt will probably depend on your motor pulley.

You can not use AUX of your amplifier to connect your turntable directly.

Dont loose your sleep over all this. Idea is to have fun learning while enjoying vinyl sound.
Regards

 

[jls001]

An illustrated definition of terms:

Tonearm_Alignment

To try and answer some of your specific questions:

- Distance between pickup arm pivot and record center: this is called the mounting distance.

- Overhang calculation: why over hang? Ideally the stylus should trace a straight line drawn from the center of the spindle to the outermost periphery of the record because that's how records are cut. But this is not possible with a pivoted tonearm. A pivoted arm must necessarily trace an arc of a circle. So the arc and the imaginary straight line cross "somewhere", the arc being longer. This difference gives rise the over hang. This "somewhere" points are the inner and outer null points. At these two points the arc and the grooves of the record will be actually perpendicular. At all other points it will not be perpendicular so there will be tracing error. If you consider the stylus tracing a record from the outermost groove, it starts with a tracing error which gradually reduces till it becomes zero at the outer null, then gradually increase till it reaches maximum at the central groove, then reduces again till it reaches zero at the inner null point, etc. A bit boring, isn't it?

- Angle of stylus: I'm assuming you mean headshell offset angle. What Hiten had explained is the stylus rake angle, and it is tied to the vertical tracking angle.

- What is significance of overhang? : explained above

- Ideal weight on record / stylus point: this weight is called tracking weight and is recommended by cartridge maker. Follow their recommended value.

- Pros and cons of long vs short tonearm length: explained in my previous post.

- Why turntable belts are so costly? Is there any DIY solution? i.e. cutting from tube if I get tube of exact belt size : if you know the right shops you can get it custom made.

- Are only flat cross section belts are used or round section are also considerable?: Flat is most common but other cross sections are also used.

- If amplifier has AUX input then can TT connected there or phono is must (I have Austonia amp with aux): TT output cannot be directly connected.

 

[sudhirbhosale]

Now coming to the wires in tonearm:
Saw in eBay :Music Hall Replacement Tonearm Wires @ price 7200.

Don't know why wires should cost too much. But my design philosophy is : Use items from other equipment which are doing same/similar function.

So design requirement for tonearm wires as per me : thinnest, flexible, pure copper. So similar items I found : 1. Jumper from PC, printer 2. Strands from CAT5 cable 3. Wires from Sony headphones .....
Any comments? Does above items use OFC?

Now a days most of the things are machine made and having good precision. While thinking of DIY turntable platter using same design philosophy i.e. perfect level, perfect circle disks I found below items good : Base plate of Panasonic rice cooker, Glass Dial of clock (glass is perfect flat) ......
Precision pully - HDD motor ......
Tonearm - Light, tube shapes - Flute
Any thoughts to get equivalent spares can be used for DIY platter, motor, belt, tonearm wires etc.

 

[Hiten]

Sudhir,
I have Sansui DA-P500 Direct Drive Motor and Platter. Rumble and speed stability specs are just about OK so as not to trash it. I had thrown out plastic plinth and tonearm As I wanted to build a little heavy plinth and fiddle around with DIY linear tonearm. But it never materialized. This models came with external power supply, Any 15 V DC adapter can be used. If you want I can give it to you for little money.
Regards

 

[jls001]

So design requirement for tonearm wires as per me : thinnest, flexible, pure copper. So similar items I found : 1. Jumper from PC, printer 2. Strands from CAT5 cable 3. Wires from Sony headphones .....
Any comments? Does above items use OFC?

CATx wires are way too thick. AFAIK CAT5 wires are 24 AWG of mainly solid core OFC (though I'm told there are multi stranded wires too) and too rigid.

Typical tonearm wires are 32 AWG. Or thinner. They must be very flexible so that they do not produce flex which can play havoc with anti skate. Some, but not every, headphone wires are quite suitable for tonearm wire.

For now do concentrate on making tonearm.

 

[sachu888]

You can also use wires from Microsoft Mouse.

Regards
Sachin

 

[sudhirbhosale]

You can also use wires from Microsoft Mouse.

Regards
Sachin

Thanks Sachu
Since you mentioned Microsoft mouse, do u mean only microsoft mouse wires are good or any branded?

Thanks

 

[sudhirbhosale]

While working on DIY tonearm, though of buliding prototype of turntable.
Journey started with fan motor, many kitchen appliances stores, auto shops, carpenters, fabricators. Tried various combinations:
Platter - Teak wood 12"
Pully and Shaft - Bajaj auto spares. i.e. release valve.Thanks to Hamara Bajaj for selling spares around 50-100 INR
Speed control - Dimmer
Motor - Exhaust fan motor of low power
Belt - from car scrap
Tonearm - In progress

Result : Total failed
When lowerd the speed to required RPM, it stopped rotating as it lowered voltage - Need low RPM silent motor with required torque.
Belt - Too hard - Need replacement
Platter - rotating very smoothly

Planning to visit mumbai. Would try to hunt motor, belt from scrapped TT in chor bazaar. Any shops there? Expect that i can get those in few hundreds as not sure how much it would work Still getting joy from it. Would keep as show piece if fails

Thanks

 

[reubensm]

what a brave experiment, keep up the spirit!!