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How to use a USB scope to set SRA -- my experience

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Posted on June 12, 2014 at 05:05:57
FolkFreak
Audiophile

Posts: 318
Location: Portland
Joined: August 8, 2000
Following up from various threads about phono setup and SRA in particular I thought I might post my experience of using the USB scope method so that others can hopefully learn from what I experienced by trial and error.

The overall experience is rather painstaking but one that gets better with practice. There are also a number of potential sources of measurement error so part of the process is trying to minimize or eliminate these wherever possible.

As you know doubt know the aim is to get the stylus tracking the groove at 91-92°. To assess this you will need to be able to get a precise fix on a) the plane the tip of the stylus hits the groove at and b) the horizontal plane of the LP itself.

In my setup (AirTight PC-1 mounted on a TriPlanar VII on an EAR DiscMaster measured with a DinoLite AM3113T scope held in an RK-10 stand) this is the process I settled on

A) Remove the LED light and shield assembly from the scope -- otherwise you may not be able to get close enough to focus given short focal length at high magnification. In the case of the AM3113T and all fixed cover scopes this may mean actually breaking off the cover, it can be reattached (provided you reset the LED light power clips that probably bent in removal). I used a clip on LED light to provide illumination

B) Get the scope mounted in the stand and close to and pointing down and slightly above the platter edge -- important to point down so you can see the stylus and not be obscured by the LP (see photo below for what the arrangement looked like for me)




C) Level the scope. Now some recommend trying to get the level reference point and the stylus in the same view for me this didn't make sense as you would a) have to find a level reference on the same scale as the stylus and b) get it close enough to the stylus to be in the same focal plane which to me means risking stylus damage. Instead I chose to level the microscope first and use the inbuilt software to ensure a very reliable horizontal reference (for which see later). My reference for leveling was a CD -- CDs have very uniform surfaces and actually many even horizontal lines in the edge to serve as references. No need to use too much magnification at this stage 50-100 should be fine. With the RK-10 mount I was able to use the vernier to move the scope up and down to check horizontal alignment by seeing the top edge of the CD reference perfectly match the top of the scope view screen. You then rotate the scope in the mount to get it level. The image below shows what you should be seeing at this stage (in this case with the left edge of the scope needing raising)


D) Get the stylus in focus. Check you have disabled anti-skate, and that VTF is at your reference level. Now place the stylus on your chosen LP thickness at our around the first few grooves. Using magnification 200X bring the scope close enough to get a crisp view on the stylus. You will know it when you get it -- looking like the image below



E) Establish your reference for the stylus point and its plane of intersecting the LP. Likely you will not be able to see the tip of the stylus and so your reference will have to be a straight edge in the stylus. In the case of the PC-1 the back of the stylus is a nice clean edge so I use this as the reference. Assuming all is still in focus capture an image and prepare to make a measurement

F) Making a measurement. Sit still, focus, ideally have a mouse or other precise pointing device available. In the case of DinoLite on a Mac the software is DinoXcope 1.9.7. Having opened the image of the stylus select the 3-point angle measuring tool and make the image full screen to make it as easy as possible for you to establish your measurement. Take the first measurement by drawing along the stylus reference (in my case the back edge). This is by far and away the hardest and least precise part of the measurement so be patient and be prepared to repeat drawing the line as many times as necessary. To establish an angle you then need to draw a second line on the horizontal plane. The DinoXcope software makes this easy by projecting dashed lines perpendicular to the line you are drawing -- you will know you are hitting the horizontal when the dashed line disappears all at the same time as you move the mouse to the right side of the image. You will quickly learn that tiny differences in how you draw this line (and by extension the first stylus line as well) have big impact. You've now taken your first measurement.

G) Adjust the SRA by raising or lowering as needed (raise to increase SRA, lower to decrease). If you are off by several degrees you will need to make what seem very gross changes -- on a TriPlanar and my setup each full rotation of the VTA tower only changes SRA by a fraction of a degree. If you've need to change SRA by anything like a degree or more you MUST recheck VTF -- SRA and VTF interact and if you don't regularly recheck you will be getting very off results. Now this is a complete pain in the butt especially as to check VTF you probably will need to remove the LP and mount your stylus gauge in place (and hence need to refocus the image of the stylus again when you get back)

H) Keep capturing the image, measuring, adjusting SRA and resetting VTF until you are within +/- .25° of target -- at this stage and for smaller changes you probably don't need to check VTF after each adjustment. Finally settle on a value in the 91-92° range you are comfortable with (I ended up at 91.7°)




I) Check VTF one last time. Reinstall anti-skate and from here on out fine tune by ear -- if you find you need to make big adjustments to VTA/SRA (say in the Tri-Planar case more than +/- one tower rotation) then consider remeasuring SRA otherwise sit back and enjoy

Sorry this has been an essay but given the process is so painstaking and also one in which practice makes a big difference being able to learn from another persons method may help you avoid problems of your own.

 

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RE: How to use a USB scope to set SRA -- my experience, posted on June 13, 2014 at 01:32:58
jbcortes
Audiophile

Posts: 1399
Joined: July 6, 2000
Great job!
I personally can't be bothered to put so much work and effort into my TT but it's impressive and quite enlightening for those wondering how to do it. Well done.

 

The effort is worthwhile, posted on June 13, 2014 at 05:43:35
FolkFreak
Audiophile

Posts: 318
Location: Portland
Joined: August 8, 2000
After now spending the best part of a week setting things up, and a final stage of removing the tonearm and detaching the unused damping tough I finally have a chance to sit down and listen to things in a relaxed manner

In a nutshell the outcome is transformational. Now to be clear the setup beforehand was professionally done and checked most of the major boxes (i.e. aligned to the TriPlanar protractor, tonearm level for VTA and azimuth). It also sounded very good, dynamic, warm etc

However after really tuning the setup (and as I mentioned spending maybe 8+ hours on setup over a week) it's a whole different ballpark. Here are some of the differences
- Soundstage -- on listening to one track (Fotheringay from Fairport, "What we Did on Oour Holidays", Island Pink label pressing) I at first thought one channel had gone out the opening guitar was so far over to the left. Soundstage is 30% wider and crosstalk much lower
- Treble at all levels -- this is an area in which LP so much exceeds my digital system (well tuned DCS Paganini), the soft rustle of shakers and cymbals, the difference between strings on a guitar
- And most of all micro-dynamics -- the uncanny ability to hear the quietest details while something loud is happening. Overall many cuts appeared less loud, until they really became loud. Dire Straits "Private Investigations (original UK pressing) never sounded more carefully put together

All of this most evident on my favorite test, female voice, letting you hear every turn of phrasing

I"m not much of a fan of "reviewing" gear and also suspect that many on the asylum might say "well with an expensive rig it should sound good" my point of posting this process and experience is more to suggest that anyone could and should take the time to setup their table with all the precision they can manage -- getting it right makes a huge difference and one that rewards getting it "just right" with exceptional results. The Allen Wright setup guide referenced in the antiskate thread has an excellent description of not only the overall process but also the impact of getting the parameters absolutely correct (link pasted below for those that missed it)

 

I'm sure it is, posted on June 14, 2014 at 10:57:11
jbcortes
Audiophile

Posts: 1399
Joined: July 6, 2000
But looking at the different pictures on this thread it's not very obvious what line is supposed to be used as a reference on the diamond tip. That's how stupid I am. It actually looks to me not everyone's using the same line.
And then the angle is bound to change with the thickness of every record... I'm not equipped to adjust VTA with every record. So all in all, it's not for me, even though I can appreciate why one would put efforts into it.
Maybe one day when I'm less lazy! In the meantime I'm ok with my LPs sounding great instead of mind-boggling. :)

 

RE: I'm sure it is, posted on June 14, 2014 at 12:23:12
FolkFreak
Audiophile

Posts: 318
Location: Portland
Joined: August 8, 2000
While it is in theory correct that the angle changes with the thickness of every record the reality is that this change is quite small. Simple geometry suggests that for a 0.5mm change in record thickness (the approximate difference between a 180G and a 120G pressing) and a 10" arm the change in SRA is <0.1° -- in reality it's likely less than that as the stylus and cantilever assembly is not rigid

So yes to the Nth degree you do need to adjust -- and such adjustments would be made by ear anyways -- it still is very worthwhile to get the SRA into the correct range (i.e. 91-92°) for all of your records

 

Awesome, thank a lot! nt, posted on June 12, 2014 at 15:10:09
risabet
Audiophile

Posts: 3197
Location: SoCal
Joined: January 10, 2005
nt
Science is the great antidote to the poison of enthusiasm and superstition.

Adam Smith

 

RE: How to use a USB scope to set SRA -- my experience, posted on June 12, 2014 at 10:24:56
Leefy
Audiophile

Posts: 97
Location: British Columbia
Joined: April 19, 2003
Thanks for making the effort to post this. It is such a well done and useful guide and really makes this complex process seem achievable. They are terrific pictures.

Best
Lee

 

Great pics. best closeups i have see. nt, posted on June 12, 2014 at 09:09:14
.

 

Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 07:45:59
Des
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Posts: 2110
Location: Great Barrier Reef
Joined: August 3, 2000
Contributor
  Since:
August 2, 2000




Yes indeed FF!--been there but worth the effort--in spite of the derisions from the many nay

sayers my A90 pictured never sounded so sweet!--My SPU Ae also benefitted from the checking--

folks need to note their Stylus configuration--the Fremer / Jennings methods highlight two of

the Different versions--Andyr note which you have before commencing.

That Stand you have FF looks the goods alright-- would certainly make the adjustment finite

easier-Good one!

Grateful for the Post--Kudos!

Des

 

RE: Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 08:37:47
Leefy
Audiophile

Posts: 97
Location: British Columbia
Joined: April 19, 2003
Des:
Thanks for contributing to this very interesting thread and adding your experience as I am thinking of trying this myself. That said (and forgive me if I am completely wrong here -it wouldn't be the first time!) I believe the angle you are showing measured in your photo is not the SRA. In fact I would guess that the SRA indicated there is probably more like 120-130 degrees if you are seeing 91.89 at the point indicated. I believe SRA is measured from the vertical axis of the tip, not the angle of the facet you have shown. More knowledgeable types than me will chime in I'm sure in case I am missing the point somehow or just misunderstanding the process.
Best
Lee

 

RE: Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 09:40:59
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
This type of cut, of the diamond, does not place the playing edge (contact line axis) in line with the raw diamond (shank axis).

Most are, but not this one.

Here's another example where the contact line axis is not in line with the shank axis.



I drew the green line to highlight the contact line axis of the diamond.

A Fritz Gyger cut diamond is another example where the contact line axis is not in line with the shank axis. (see fig. 9)



The facet Des has shown, and aligned, IS the facet (the contact line axis) that needs to be aligned to approximately 92 degrees, not the direction of the shank axis.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

Thank you Tre', posted on June 12, 2014 at 10:03:36
Des
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Location: Great Barrier Reef
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Contributor
  Since:
August 2, 2000

I felt I followed the recommendations for the A90 Styli pictured

Grateful for the endorsement

Des

 

RE: Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 09:44:44
Leefy
Audiophile

Posts: 97
Location: British Columbia
Joined: April 19, 2003
Tre'
Thanks so much for your diagram. I had no idea such a thing existed and your picture makes it very clear. I have much to learn and this looks like the place to do it.
Thanks for your post.

Best
Lee

 

You're welcome. (nt), posted on June 12, 2014 at 09:53:02
Tre'
Industry Professional

Posts: 17263
Location: So. Cal.
Joined: February 9, 2002
.
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 09:34:58
Des
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Posts: 2110
Location: Great Barrier Reef
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  Since:
August 2, 2000

Yes well open for correction --I just followed the Two articles as best I could

The Jennings one measures the different styli to the Fremer version he posts--if you read both

and there is diff' angles of measurement dependent on the Styli--to get the A90 the same as the

one in FF's Picture-the Arm would be at an unusable angle.

Like I said I am open for the pointers to enlighten and correct for all to view.

Des

 

RE: Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 09:46:52
Leefy
Audiophile

Posts: 97
Location: British Columbia
Joined: April 19, 2003
Des:
I just saw the post from Tre' and it explained it to me very well. I'm sure you are right after all in your measurement. In any case the improvement in sound you got is the best indicator I'm sure.
Thanks
Lee

 

RE: Excellent Advice--Frustrations noted!, posted on June 12, 2014 at 09:38:43
Leefy
Audiophile

Posts: 97
Location: British Columbia
Joined: April 19, 2003
Des
Thanks for this info, I'm not familiar with the Jennings article you mentioned and it sounds like I should read it before plunging ahead. Could you point me in the direction of it?

Best
Lee

 

Another good article, posted on June 12, 2014 at 12:02:36
FolkFreak
Audiophile

Posts: 318
Location: Portland
Joined: August 8, 2000
Here's another piece from Fremer with more on the why's and wherefores of the topic and examples of the PC-1 type profile (semi-line contact)

 

Sure thing, posted on June 12, 2014 at 10:00:13
Des
Audiophile

Posts: 2110
Location: Great Barrier Reef
Joined: August 3, 2000
Contributor
  Since:
August 2, 2000
Des

 

RE: Sure thing, posted on June 12, 2014 at 10:16:09
Leefy
Audiophile

Posts: 97
Location: British Columbia
Joined: April 19, 2003
Des:
Thanks for the link to that very interesting article. It is obvious from that and the explanation Tre' gave that you are bang on. Glad you are enjoying the fruits of your labor and hope I have the same success.

Best
Lee

 

Thanks for posting....., posted on June 12, 2014 at 06:04:37
I did try this once by learned quickly that you definitely need the right scope.

 

Great instructions! :-)) nt, posted on June 12, 2014 at 05:19:02
andyr
Manufacturer

Posts: 12548
Location: Melbourne
Joined: September 2, 2000
.

 

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