My DIY Tonearm 1 year on

[James_G]

ello,

I can't remember if I have mentioned my DIY Tonearm here yet, but here it is:

The arm tube is made from Bamboo (£0), and the horizontal bearing is the head drum from a VHS machine (£0). The vertical bearing is of the knife-edge type, using a stanley blade (£1) resting on the edges of the head drum. There are some small grooves in the drum, cut with a staney knife, to sotp the arm moving back and forth. The counterweight and headshell are coppers (£0.33). The whole lot is stuck together with Araldite (£2.50-ish). The fingerlift is made from a steel rod from a Pioneer Midi size TT (£0), where the phono stage and wiring came from.

The arm has an AT-110E mounted on it, and is mounted on a Thorens TD150 MKII.

I suspect that the effective mass is a little high for the cart, but I don't have a test LP to try it with.

James

Next stop- a DIY TT with a ladegaard arm. After the amps and speakers.

[Ernie L]

ingenious
.....how does it sound?.
..how much mass is rotating in the horizontal plane? I've never held a vhs head in my hand so I don't know..

I'm looking forward to seeing some more of your work.

[Blue Angel]

Hi James

Minimalism at its best. I think I should let you loose in my workshop - chained to a running lead. Just out of reach of my milling machine and lathe. You speak, I mill and turn

Fellas, James and others who have made their own arms, need applause

Can you let us know how it sounds (compared to other arms you have used) and if there are any tracking issues

Good show

blue

[James_G]

@Ernie- There is a fair amount of mass, I suppose. It's been a while since I had it unmodded, but the part that rotates is probably about 35 grams- quite centralised, though. It looks like it is concentrated at the edge, but the bottom of the rotating part is quite thick. Holes could be drilled in it to reduce the mass.

The front of the drum could be cut off in the same way as the back, but I want to leave the curve for the thread of the anti-skate weight to run round. When I get round to adding it.

@Blue- Thanks for the kind words. I would love a well-kitted-out workshop, but, as a student, it isn't going to hapen for a while.

Mind you, chaps that build cartridges need a standing ovation.

Tracking issues- depends on whether the month has an 'r', the temp, humidity, the wind speed... Really, it depends on whether the phono stage has moved in it's 'mount'- the wirea apply quite a bit of force. Generally seems fine, especially since I measured the tracking force ('twas a bit light).

Sound-wise it seems quite sure-footed, and fairly neutral. The Bass seems well-defined, compared to my other references. Sounds a little better than CD to me- higher, smoother highs, more defind bass, less congested.

I haven't really heard many other arms- my reference points have been a B+0 7000 music centre with a knackered cart, about 5 minutes of a Linn Basik Plus w/ Dynavector Karat 23RS on the same deck (when purchased- removed with intention of selling. Didn't try the Basik and the AT110e together as the cart arrived later, and the armboard had been used to fit my DIY arm. Might have to refit it and compare.), and a Pioneer PL-12d (Std. arm, AT-95e and AT-110e).

This arm was one of those things that just seemed to 'happen'. One minute, I was looking for a TP-13A (std on this deck), the next I was mucking about with bits of bamboo and screws trying to make a gimballed arm. Following that, I looked at the Ladegaard arm wand/knife edge design and decided to put it on a VHS head. The bamboo seemed like a good choice folowing discussions on DIY audio.com.

The bearings are very smooth- no detectable play, and the arm moves vertically with just a small peice of paper placed on the 'shell.

James

P.s.- watch out for a thread on the proposed TT design. I have done the drawings by hand, and have a few ideas- involving more VHS heads, concrete and magnets- floating about. Probably won't be built properly untill next summer, but I might try to do a (very basic) prototype over Christmas.

[carlosfm]

..how much mass is rotating in the horizontal plane? I've never held a vhs head in my hand so I don't know..

Video head drums are very precise and smooth running (it never stops once you touch it), made to rotate at high speed.
Oh my... this was a great idea.

Congratulations, James!

[Ernie L]

..how much mass is rotating in the horizontal plane? I've never held a vhs head in my hand so I don't know..

Video head drums are very precise and smooth running (it never stops once you touch it), made to rotate at high speed.
Oh my... this was a great idea.

Congratulations, James!

Carlos..I have no doubt that the bearing is top notch..my only concern is the weight of the part that moves..(not being an engineer I don't know the terms for these parts)..

My concern about this stems from a thought that the only force that causes the tonearm to follow the recording groove is pressure from the needle against the groove wall...the more weight the more pressure/force required. This can't be a good thing for record life..

I don't know for sure but I may have the physics all wrong....certainly the terminology!
Still I enjoyed immensely seeing his efforts

[padego]

Brilliant and beautiful!
Cheers
padego

[Blue Angel]

Hi again, James

Take another bow

To make arms or carts - What's the difference? Probably a toss-up in your favour.

If you need access to machine tools or any tools and a place to work, check out the possibilities of becoming a member of the Society for Model and Experimental Engineers. This Society started in England at the turn of the previous century. Ours in Cape Town started 100 years ago in 2007.

The UK should have many more branches than here. Really nice people and very modest subs. Just an idea. Your local library will probably have the contact details of your nearest branch.

Looking forward to seeing more of your arm adventures.

blue

[bauzace50]

Hello James_G,
Great job! Great imagination!
Respects to you,
bauzace50

[Zero One]

Cool, great stuff james

I too have experimented with video head bearings and also looked at using bearings out of floppy drives and hard drives for vertical and horizontal arm bearings. Its a toss up which are best though overall I feel the hard drive bearings are best of all.

One of my experiments involves using the hard drive enclosure with the bearings and the platters still attached and then attach the arm and vertical bearing set-up to that.

There is no play in any of these bearings that I have ever been able to detect so chattering should be well controlled. (imagine a hard drive with an even slightly dud bearing......bye bye data!)

To my way of thinking the mass of the video head or a the hard drive platters is actually not a problem, in fact my experiments seem to support it as an advantage as it stops the arm deflecting too easily due to heavy bass modulations, yet still allows easy movement in the horizontal plane for good tracking. My experiments have developed stronger and cleaner bass with extra weight at the pivot point (ie video head, hard drive platter etc).

This has inspired me to get stuck back into my arm building again. My brother is going to build a monocouqe test arm I have designed for me using balsa and carbon fibre with video head and floppy bearings. He builds model planes of the flying type so he's very handy with the needed techniques.

Thanks for the new inspiration.

[James_G]

Thank you all for your comments.

@Blue- I still reckon it is the other way- there is not much precision here. Carts, on the other hand... One day, I may have a go at a low-Z moving iron cart with field coils. And also, one day, will walk about on the moon

@Zero - I also tried with an HDD bearing, but it was from an old laptop drive, and the cogging on the motor was huge- no way that could have been used for an arm. I suspect that more recent, and desktop, drives may be better. I used the VHS head because I got the machine free from Frrecycle (plug for freecycle yahoo groups).

I killed my T-Amp last night, so am listening with headphones driven directly by the phono stage. It seems to work (well enough- bit bass light, but not bad).

James

EDIT- of course, this design will have (slightly) higher effecive mass horizomtally than vertically, but probably no enough to make a huge difference. Anyway, Poul Ladegaard reckoned that it was better to have a higer mass sideways anyway- I can't remember why of the top of my head.

Key to this design working is that the pivot and record surface are at the same height. This heps to reduce the cart. moving back and forth while riding warps. It is Crucial that the centre of mass of the arm (or at least the counterwieght) is below the pivot- this means a heavy weight, slung low below the pivot. This makes the arm more stable when tracking warps, as the VTF doesn't change.

If the counterwieght is too high, the VTF will be high when the arm faces down, and will drop as the arm rises- when it gets too high, the arm tips backwards. These points are, I believe, all mentioned in Ladegaard's works on his air bearing arm.

[soulmerchant]

Video head drums are very precise ...

That is brilliant. I wish I had that idea. now I know why I have kept those old vcr's that the neighbor was going to throw away down in storage...

Thanks James.

[James_G]

Right. I have replaced the wire with some scavenged from a BSR TT. There is now no sideways force on the arm- good since the original wires both pushed and pulled depending on where the arm was.

I want to add anti-skating to the arm. The plan is to have a thread or fishing line going anti-clockwise round the head drum, over a wire loop, and on to a weight.

How much weight will I need? Is it enough to provide a couple of grams of force sideways at the end of the arm? say 10-15g (ratio of arm length:drum radius is ~7:1). The tracking force is set to around 1.5 or 2g (I forget now).

The reason I ask is that I have tried a very cude version, and it sems to provide far too much force, even with just a 5p coin (3.25g) weight. There was a lot of friction, though.

Thanks in advance,
James

[James_G]

Well, this arm is still providing me with most of my listening pleasure. I have re-aligned the cartridge on a couple of occasions and replaced the stylus.

However, I have not managed to set up an anti-skate system - I can't seem to find a light enough weight.

The planned Ladegaard arm hasn't happened yet, but it is further on than it was lat year. I have cut and polished the aluminium section, drilled the holes and found another piece of bamboo.

All I really have to do now is to assemble it and sort out an air pump. However, the arm has been delayed due to a change in direction regarding the TT - I had planned a full-DIY table, with home-made platter etc, but it requires far too much work for my limited facilities at the moment.

In place of that, I'm re-plinthing a cheap Technics DD turntable (SL-2D automatic, IIRC). The platter and the motor will be used basically unmodified, mounted in a solid plywood plinth. The circuit board has been cut and the tracks soldered to a length of ribbon cable, to allow for remote mounting of the board.

I'm going to put a stack of old records on top of the platter to efficiently couple the vibrations out of the vinyl being played, while the arm will be mounted very solidly to the plinth.

I'm probably going to add a damping trough to the arm (a la Rock), and I'm seriously considering using sand in voids in the plinth to provide a sink for bearing noise.

Perhaps in a year's time it might actually play a record!

Eventually, the TT will be partnered with a valve phono stage and power amp and a pair of fostex-based 'horn' speakers (in fact they are a horn-loaded bass reflex design).