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 Post subject: Re: Ideal tonearm length ?
PostPosted: Tue Feb 18, 2020 12:37 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
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soundgen wrote:
They are the length they are to track from the centre of the horn hole to the centre of the turntable , any longer or shorter and they would skip off the record at the end


I will be adjusting the tonearm pivot location to suit the length and ensure the conditions you describe. I have the luxury of flexibility in that regard.


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Tue Feb 18, 2020 1:50 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
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soundgen wrote:
No they don't , the 101 tone cannot be used on any machine except a 101 , use it on another machine and the soundbox will be at a very strange angle , they are not the same !


That strange angle can be adjusted by swopping out the curved portion of the 101 tonearm for one that does not have the downward angle of the 101. It can also be adjusted without changing the curved portion by using a longer needle or turning an alloy diaphragm back to front so the bump is on the inside. Turning the alloy diaphragm back to front on a #4 soundbox actually makes it louder.


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Tue Feb 18, 2020 2:26 pm 
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Victor IV
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Location: Dover, UK
Daithi wrote:
soundgen wrote:
They are the length they are to track from the centre of the horn hole to the centre of the turntable , any longer or shorter and they would skip off the record at the end


I will be adjusting the tonearm pivot location to suit the length and ensure the conditions you describe. I have the luxury of flexibility in that regard.

Note Daithi, when you construct/modify/install your tonearm for the optimal tracking you desire, it will have significant overhang in order to achieve that (i.e. the needle will not coincide with the spindle) and it will therefore have a tendency to skip across the record at the end, as soundgen mentions, if the locked groove at the end of the record is poor. This is a danger that EMG and Expert owners are well used to living with, having tonearms with much lower tracking error than any of the HMVs or Victors, almost certainly the best ever achieved on acoustic gramophones (apart from the parallel tracking attempts such as the Balmain or the oddballs covered earlier in this thread) - the geometry requires that the needle point is well forward of the spindle. Just as with a modern hi-fi tonearm. You can't achieve really low tracking error in any other way except with extreme length.
BCN thorn needles made to the original 1920s specifications: http://www.burmesecolourneedles.com

Youtube channel: https://www.youtube.com/channel/UCe4DNb ... TPE-zTAJGg?


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Tue Feb 18, 2020 2:55 pm 
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Victor IV
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Yes. Tracking solutions using tonearms with no overhang, have the needle falling on the spindle, and can have good tracking angles at the inner grooves (not always) with generally horrible angles at the outer grooves of a 12". Sometimes this can be somewhat corrected rotating the soundbox to a stepper needle angle, thus shortening the effective tonearm length. In my tabletop HMV style III, this improves the overall tracking angle, but it is still near 15 degrees at the outer grooves of a 10" record.
BTW, Daithi: the gooseneck portion of the tonearm of a 101 may not be interchangeable with the 102, this last having a wider bore, of my memory is right...
And soundgen is right. There's a fundamental difference in the tonearm of a 101, and it is the downwards angle at the soundbox end. This is to allow the tonearm being installed much lower in the 101 than in the other machines, to reduce the case height. The tonearm base in the 101 is installed below the motorboard, and the tonearm is only a few millimeters flying over the turntable. In fact, badly warped records scratch the tonearm when played on the 101.
All the other machines have the tonearm base installed on the motorboard, and the tonearm flies much higher over the turntable. So these don't need the downwards angle, and the soundbox neck section is straight. The tonearm is at the same level as the soundbox centre, but in the 101 the tonearm gooseneck raises up to catch the soundbox neck.
Very good! For the rest of dimensions, they look the same, at least in the photos.
So if you use a 101 tonearm for the new gramophone, either you install it lower than the motorboard, or you insert the gooseneck of another machine with straight end.
Inigo


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Tue Feb 18, 2020 3:30 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 220
Orchorsol wrote:
soundgen wrote:
They are the length they are to track from the centre of the horn hole to the centre of the turntable , any longer or shorter and they would skip off the record at the end

Note Daithi, when you construct/modify/install your tonearm for the optimal tracking you desire, it will have significant overhang in order to achieve that (i.e. the needle will not coincide with the spindle) and it will therefore have a tendency to skip across the record at the end, as soundgen mentions, if the locked groove at the end of the record is poor.


Yes I already have that issue on the HMV161 due to the long needles I use so I never let the needle stray into the groove having suffered the indignity of plowing up a few labels. I'm so bad that even when I'm playing a record on the computer I rush into the room to take the needle off the record even though its just a computer file and there is no needle. Its a kind of conditioned Pavlovian response to label damage trauma.


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Tue Feb 18, 2020 6:33 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 220
Inigo wrote:
So if you use a 101 tonearm for the new gramophone, either you install it lower than the motorboard, or you insert the gooseneck of another machine with straight end.


Here are three tonearms. I have two more but they are not in the picture because they are installed in a machine. All five tonearms have interchangeable curved sections. One is installed in a 101 and another is installed on a 161. I assumed the shorty was out of a 102 but I must be wrong. It has that same downwards angle at the soundbox end as the 101. Thats the one I plan to cut up and lengthen. Anyway, ignoring all other considerations, they all have interchangable curved sections. I suppose the big question in my mind now is what machine did the short one come out of?


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Cropped.jpg
Cropped.jpg [ 1.19 MiB | Viewed 391 times ]
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 Post subject: Re: Ideal tonearm length ?
PostPosted: Wed Feb 19, 2020 3:45 am 
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Victor IV
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Maybe the short one comes from a 101, and the longer ones with no downwards angle come from other tabletop or upright machines? If this is true, my question is solved: the larger machines had a longer tonearm than the 101.
Why do you want to cut and modify the short one, instead of using directly any of the longer arms?
If you modify the tonearm length you could have issues with the gooseneck section and the soundbox angle, i mean, not the downwards adjustment, but with the azimuthal deviation of the diaphragm plane, intended for providing the offset and tracking error correction. This angle is unique to an optimized solution (i.e. a given tonearm length and spindle distance) so modifying the length would cause the angle to be mismatched with a different solution. What's more, you are supposed to lengthen the arm to arrive at a new solution with better tracking. This longer tonearm will have to be matched with a corresponding longer distance to the spindle, and a lower soundbox deviation angle (or offset). So you'll find that the same curved gooseneck section will be unmatched to your new arrangement. The soundbox angle (azimuth) will be wrongly great. As if you would need the gooseneck curve to be slightly longer... When you try it you'll understand me. If you make a sketch, and do the modifications with paper and pencil, you'll see what I'm saying.
The long narrow hmv tonearm (for the bigger machines, not the compromised solution of the 101) are good enough. Why are you going to modify it? I'm sure you can achieve a very good tracking with the arm as it is. I feel that under 5 degrees error is enough, you won't notice improvements with further perfection. I mean, what you see as near perfect tracking with naked eye and careful examination is enough, and that is almost perfect with these machines, even with the shorter 101.
Another point, you'll find it useful. Substitute the original hmv rubber connector with its brass ring inserted and locking pin
Discard all this. Instead, you may use one of the new red rubber connectors sold in the internet for the Meltrope soundboxes. If i remember well, chunnybh (in this forum) is one who makes and sells them. These connectors are made in all useful inner diameters for different style tonearms. And the outer diameter fits snugly on the no4 soundbox backplate directly. You'll find it serves week for the no4 soundbox, fitting tightly on the narrow hmv tonearms. You'll need a bit of wetting or vaseline to insert it. Perfectly airtight, elastic but firm, perfect for parasite vibrations damping, and it allows infinite zenith angle adjustment of the soundbox, so another variable in the equation for achieving almost perfect tracking, as you can have the needle at vertical (zenith) angles between, let's say, 55 and 70 degrees to the record. This, together with protruding needle length, provides almost infinite play for almost perfect tracking adjustment.
Of course, everything can be tested and optimized. You can lengthen the tonearm and then adjust the deviation angle as needed by means of a purposely made coupler inserted between soundbox and tonearm.

But believe me, try first the unmodified longer tonearm with the no4 soundbox and the red rubber adjustable coupler first. Then decide if you still want to modify the tonearm and enter in a much complicated affair. Then you can also substitute the coupler and soundbox, using a Meltrope or a no5/a/b. With the small hmv horns of the 101 or the tabletops 103/109/127, this sounds fantastic!
Inigo


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Wed Feb 19, 2020 6:40 am 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 220
Inigo wrote:
Maybe the short one comes from a 101, and the longer ones with no downwards angle come from other tabletop or upright machines? If this is true, my question is solved: the larger machines had a longer tonearm than the 101.


Here is a picture Inigo, of the short tonearm next to an HMV101 tonearm as installed in an HMV101 machine. Clearly the short tonearm is over an inch shorter than the HMV101 tonearm.


Attachments:
shortV101.JPG
shortV101.JPG [ 634.01 KiB | Viewed 365 times ]
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 Post subject: Re: Ideal tonearm length ?
PostPosted: Wed Feb 19, 2020 7:01 am 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 220
Inigo wrote:
The long narrow hmv tonearm (for the bigger machines, not the compromised solution of the 101) are good enough.


I think there is only a ¼ inch at the very most, difference between the HMV101 and HMV161 tonearm. Measured as carefully as I can manage. The HMV101 tonearm is very good lengthwise.


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 Post subject: Re: Ideal tonearm length ?
PostPosted: Wed Feb 19, 2020 11:01 am 
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Victor IV
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Location: Madrid, Spain
Could the shorter tonearm cone from the 103 small tabletop? I don't know that machine, but if its rectangular plan dimension is smaller or equal than the 101 case, and the tonearm in the tabletop is centered as in the greater machines, them the tonearm must be shorter, for the 101 is placed diagonally to the case...
What a mystery!
Inigo


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