Mono Reissues and the Conical Stylus

How exactly are mono records cut with a stereo cutterhead any different from those cut with a mono cutterhead?  The only difference I am aware of is the groove width / depth but the cutting stylus and groove profile is a "V" for both.

dave

Can anyone provide a reference to the "U" shaped groove and how it is cut?

dave

I think there is some general confusion about the bridging concept used to sum the stereo signal to add the lateral movement and null the vertical and a cartridge that only picks up information in the lateral plane.    My take is that if the coils remain oriented at a 45º angle to the record and then wired in series for mono then it is a stereo cartridge wired for mono and it doesn't matter if it if done internally or externally.  If however the same parts are used for a mono cartridge and the coil is oriented so there is only pickup in the lateral plane, then it is a mono cartridge.  In this case there would be only be windings for pickup in the lateral plane and the windings at 90º to that plane would not be used / wound.  

As for the "U" shape discussion I think it leads to a bunch of confusion.  I have yet to see a cutting stylus with anything other than a "V" shape with the angle of the v being slightly less than 90º.  Whether this cutting edge cuts with information in just the lateral plane (mono) or in both the lateral and vertical plane (stereo) does not matter and the groove cross section will always be a V.  The only way a groove with a rounded bottom to resemble a "U" could be done would be with a rounded point cutter and I have never seen anything like that and even if it existed, it would do a very poor job of cutting.

dave

That is my understanding.  I just looked at a 1955 London ffrr  (Ted Heath ant the London Palladium) and the groove is a V.  The bottom does have a slight radius.  A stereo cutting stylus specified by Ortophon has a 3-4µm radius which would explain that but that is still a fraction of the radius of even the smallest conical.  

dave

Goofyfoot,
the groove width of the London ffrr is about 2.5 mil which is above the max spec for microgroove. Since the groove is v shaped the width has little to do with whether a conical will properly trace it.   the only issue that can arise is a 1 mil conical can disengage from a microgroove but a 0.7mil conical will not run into any more issues with a 3.2mil groove than it will with a 2.2mil microgroove.  In fact a 0.7 mil playing records previously played with a 1 mil will often be much quieter since it traces a part of the groove that hasn’t been played.  

Just measured a bit closer and the groove with is closer to 3 mil.  I should also clarify that the 2.2 and 3.2 mil numbers I gave are the "average" from the link below and not a hard spec.

https://dgmono.com/2018/04/06/deep-groove-mono-and-the-great-groove-width-mystery/

I don' think anyone would disagree that the 1 mil. conical stylus, while optimal for early mono records, wasn't ideal for later stereo records.

I agree that the 1 mil conical is not a goof choice for micro-groove but I also do not believe it is the best choice for early mono recordings.   I prefer the sound of the micro-ridge compared to anything else for all of the mono I have played with.    The simple fact is that back in the day the 1 mil conical wasn't the "best option" it was the "only option".  Just because more advanced profiles didn't exist in the 50's doesn't mean they engineers and enthusiasts  of the day wouldn't have used them for playback if given the chance.
 
here is a "to scale" image comparing a micro-ridge to a 0.7 mil conical.
http://www.intactaudio.com/forum/files/micro_vs_conical_187.jpg

dave

I have heard a low hour zero compared to one that had been retipped with a Boron / microridge combo in a direct comparison and I felt that while the retipped cartridge was no longer a Miyajima, the sound was superior.  The most surprising thing I found out about the microridge mono combo was how sensitive it was to SRA.  Getting the SRA correct allowed the music to completely escape the speakers and fill the space between and above them with music.  I have also played a fair bit with a Denon 103 converted to mono by rotating the coil 45º for true lateral pickup.  By rotating the stock stylus along with the coil I could then do a fairly close apples to apples comparison of the original aluminum conical combo to a  boron microridge combo.  Granted that there were two things changed (cantilever material and diamond profile) but the sensitivity to SRA and the huge 3D sound field you could get with the microridge was beguiling and points to the profile as the cause of improvement.

Lew asked me above about my thoughts on the true mono with no vertical pickup  vs. a stereo wired mono with the vertical information summing to 0. The above 103 experiments gave me a bit of insight into this too.  Since I had stereo and "true mono" 103's with the same suspension and boron microridge combination I could series strap the stereo and compare the two methods in a fair way.  Sonically the overall presentation was similar but the lateral mono was more dynamic and had what seemed to be a much lower noise floor.  The immediate place this was heard was in the needle drop.  The lateral cut was nearly silent and the stereo wired mono's needle drop was quieter than stereo but still had a unique amusical quality to it.  This is just a single observation but it does seem to fall in line with the ideas presented in the DG mono link by goofyfoot a few posts up.  I think this distills down to the idea that in a perfect world the sides of a mono groove are 180º out of phase with each other yet noise has no inherent phase relationship to the music.  When picked up with a single lateral coil reading the entire groove, there can be no phase anomalies for the noise but when picked up with a two discrete summed coils there is suddenly no consistent nature in the way noise will be summed which can cause some unique sonic results.

dave

The warning against playing a stereo record with a mono cartridge stems from the fact that the early mono cartridges didn't have or need any vertical compliance.  The lack of vertical movement effectively chews up any vertical modulation found in the 45º cut stereo groove. Some current day manufacture cartridges like the Miyajima's adhere to this while others have coils in the lateral plane with compliance in both the lateral and vertical plane.  The Denon 102 was designed as a mono cartridge with vertical compliance so radio stations could use the same cartridge to play both mono and stereo cuts.

dave

Would never go back to the conical. IMO it is an audiophile myth that conical is the way to go with vintage mono

.
I agree 100%.  Just because the conical was the tool of the day to play mono doesn't mean the advanced profiles would have been shunned if they had been in existence.  I actually see them as the correct profile to play back anything since it best mimics the pattern cut by the cutterhead.

dave