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Fatmangolf View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 9:38pm
Large M10 washer drilled to hold motor This shows a 50mm diameter washer* I drilled with countersunk 2mm holes to take the motor screws and small o-rings and the M6 tapped hole top left for the vertical bolt.

*the 50mm washer fits through the small hole in the Michell acrylic base and saved me time stripping the dsk down and drilling a larger hole.


Edited by Fatmangolf - 20 May 2017 at 9:46pm
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo UL, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links. and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 9:44pm
Motor and belts in placeLarge space around the motor on the modified M10 washer (see above) with 2 Michell belts around a Rega double pulley.
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo UL, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links. and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2017 at 6:48pm
I was waiting for a new PC motherboard which I fitted on Tuesday so listened to 100% vinyl whilst pondering turntable geometry on some scrap paper.

As blogged above I have an SME IV which cleverly fixes the offset angle at 23.635 degrees ('alpha' for which I have used 'a' below) and effective length (L) at 233.15mm for standard cartridges. Great idea as the supplied SME card protractor sets up Baerwald for the IEC inner and outer grooves, with null points of 66mm (N1) and 121mm (N2, both numbers rounded). My Transfiguration cartridge's stylus is only 7.5mm from the mounting screws rather than the standard 9.5mm, which means the effective length is 231.15 and the SME card protractor is hard to use. Also the null points would be about 68 and 117, slightly different to the SME standard. After some trigonometric doodling I worked out how to set the arm for 66mm and 119.3mm, really close to the SME null points.

Linear offset Lo = L x sin (a), so Lo is fixed at 92.67 by the SME design and my cartridge dimensions.

Lo =1/2 (N1 + N2) (arithmetric mean of the null points)

I have a Clearaudio protractor which mounts on the spindle and uses an arm with spike to anchor onto the pivot of the tonearm. It has a ruler with a line perpendicular to the spindle and the distance outwards where the stylus lands on this line is the geometric mean of the null points,

X = squareroot (N1 x N2)    NB it is the point of maximum tracing error between the nulls

The crossing angle = a + arccos (sin(a) X / Lo) if you're still reading this

So I went for X = 88.7mm rather than the standard SME X of 87.3mm, giving me my desired null points of 66mm and 119.3mm. I used 6x magnification weave tester from Maplin and a bright LED torch. It sounds even better but I do realise shaving 0.2% THD off is probably inaudible.

Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo UL, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links. and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveG Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2017 at 8:07pm
Interesting Jon

This is something I didn't realise when I bought my SME, but found out as I did more research. It seems that in the quest for rigidity they made some assumptions.. or perhaps I should say that having decided what was best, they decided  to design out some variables. And who's to say they aren't right? (probably loads of people Wink)

So, like you say, they are designed around carts having the theoretically standard 9.5mm stylus tip to mounting screw dim and they elected to use fixing holes, not slots (no fiddling here please) and of course are designed to work optimally with Baerwald geometry. If you like Baerwald & your cart conforms then they are an absolute doddle to set up, if not you have to get creative. I've even heard of people elongating the headshell holes into slots - not something I would dream of doing.

My Axia died before I was aware of the 9.5mm thing, so it wasn't something I checked. What i do remember was that not being a very tall cart and the arm tube being heavily tapered it was possible for it to hit the edge of the record as the cart approached the run out grooves. SME do make a spacer for that scenario though. I made damn sure that my current cart adheres to SME's standard and haven't looked back.

But can you hear a difference these fractions make? Sometimes I think I can, sometimes not, but aside from checking my set up every now and then I mostly don't fret unless something sounds really off.

Nevertherless there is great satisfaction to be had from knowing you have your TT set up as close to perfection as you can reasonably get. Sometimes that in itself is enough to make things sound "better" Smile
Dave

Michell Gorbe + HR PSU -> Cadenza Bronze -> SME V -> Elevator -> Accession -> Proprius -> B&W CM6 s2 | Cusat 50 & Spatia cables ->
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 31 May 2017 at 10:57pm
You've done your research Dave and anticipated some of my thinking. I am happy with the Baerwald arrangement and wanted to replicate the SME intention of 66/121 or close, with the aim of getting the inner null down from 68mm. Of the various aligments I tried the UNIDIN one appealed with 63/113 i.e. Lo=88mm because I liked the sound of that on my old arm.

I ruled out drilling holes in the headshell because I like reversible mods (agree about not drilling more holes in the SME headshell) wherever possible so my next experiment is sketched out on paper only. Use a spare OEM headshell spacer/weight (approx 2g) of aluminium as follows:

Leave the original M2.5 threaded holes alone
Drill a new pair of holes (countersunk) that are 5mm forward and give an offset of about 21.9 degrees, then mount the cartridge under these.
Mount the spacer to the SME headshell with short M2.5 screws inot the original holes
Raise the arm base by 2.1mm i.e. 3 turns of my VTA screw
Adjust counterweight backwards for approx 2g
Adjust D to get X = 84.4mm
Fine VTF and height/VTA
Play records
Play more records

(The other option is a single mounting screw to allow the offset angle to be adjusted, 22.4 degrees would be right in theory but probably not rigid... so back to the 2 + 2 screw option....)

According to the VE compliance matching the extra 3g or so for the spacer and screws would still leave me in the safe zone for resonant frequency

The only way to measure the benefit is speakers and ears. Politely ignoring the latter, speaker THD is probably higher than any change in weighted tracking error so the graph of the alignment is as good as it gets unless something is wrong in the setup as you say. If the small hole I drilled in the 2nd hand SME bridge is out or I misposition it when tightening the screws the error will be fractions of a millimeter in P2S and perhaps the baseline angle. Lots to worry about or simply ignore!

You've hit the nail on the head on setup satisfaction. The turntable sounds great and I am inclined to leave it alone for now!

Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo UL, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links. and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2017 at 11:40pm
weighted THD% for Phoenix alignments on SME IV
This graph shows the weighted distortion for the three alignments I mentioned before. The thicker cyan line is the current setup which I called adjusted SME Phoenix (66 / 119) intended to give the 66mm inner null and lower distortion on the inner grooves than the standard dark blue line (68 / 117) does. You'll see my alignment is close to the SME standard (66 / 121) but worse in the middle of the LP by about 0.1% than the curve I'd have otherwise.




Edited by Fatmangolf - 01 Jun 2017 at 11:40pm
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo UL, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links. and a Majestic DAC.
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