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Can one hold a mobile phone at exactly the same height and in exactly the same orientation at each speaker?
Agree about the second point you make, though I would expect the two channels of the amplifier to be within 0.1dB of each other. Speaker sensitivity is a different matter.
For adjusting azimuth, I would think measuring at speaker level is not accurate enough beyond "in the ballpark". There's just so many possible variables at that point, exact positioning of microphone, difference in sensitivity between speakers, power amplifier channel balance (likely very good though), volume pot (will vary across the range of the pot if a regular pot is used) & phono stage accuracy come to mind.
All that ignores a big one which is alignment of various bits in the cartridge & alignment of stylus tip relative to coils (if talking MC cartridges) - there's good reason phono cartridges might only have a specified channel balance within 0.5dB or even worse, though I gotta say I'm not sure I've had any carts which were off by more than that.
So, IMO for azimuth adjustment it's best to do it visually and adjust according to the diamond to get most accurate tracking. Also not all cartridges seem to age gracefully, it would seem sometimes things can get out of whack a bit as the suspension components age.
I do think getting azimuth spot on is very important and here from tracking perspective there are no compromises, the better you do it, the better it gets, that simple. In a perfect world no arm would have azimuth adjustment, but would come out perfect from the factory, like all cartridges and we'd never have to worry about it. Sadly in the real world that is not the case. If the cartridge is not put together perfectly, then adjusting azimuth for the diamond you might end up sacrificing some channel separation at the generator. If that happens, it happens. If you have to twist the cartridge more than just the slightest bit for a very small fine tune, you might want to get in touch with either the seller of the cartridge or the manufacturer (assuming a new cart).
Quote:
Originally Posted by helma
OK if we are going to approach this on a purely scientific approach, then we could adopt measurement of output from with the phono stage or the Pre-amp using a reasonably accurate Meter, alternatively by a Fozgometer which essentially does the same thing.
I believe this is documented on several articles on the net. In simple terms it means paling the 300hz track and then with a suitable adapted cable plugged into one channel measuring the volt and then doing the same with the other and comparing then, then if different adjusting azimuth to get them the same. Then all should be good.
If you were going to argue about differences in voltage between channels due to different components on circuits, then first you would send a sine wave signal at a known voltage into one channel and measure the output, and then do the same for the other, if there was a difference you would apply this ratio to the voltage adjust when you did the azimuth with the cartridge.
Measuring differences on the cartridge engine are not so simple, although my Benz Micro LP-S came with such a measurement from the factory showing the response of each channel and that they are virtually identical from 20hz to 20Khz.
You claim the channel imblance with the Ortofon cartridge was 6dB, as measured by your phone app, yet the error in azimuth was around 4o. This does not make sense; the imbalance caused by a 4o error will be no more than 1.3dB.
I agree the two channels of any self-respecting amplifier will be within 0.2dB of one another, and for most quality speakers the unit-to-unit variation in frequency response will be within 2dB. I have the pen plots for my B&W DM2a speakers, with consecutive serial numbers. You can lay the two plots over one another, and only by looking carefully can you see the occasional deviation of 1 - 2dB.
I still maintain the best way to set up the azimuth is to either use a mirror (which will visually double any error) and/or play a mono record and check the image is narrow and centred midway between the two speakers.
How does 4o equate to 1.38dB.? I am only reporting what I see[emoji846]
Perhaps the cart has other issues, it is about 12 years old, but it sounds fine aligned as it is.
helma - I take your point but in a similar vain I do find using the mirror approach somewhat open to error, just as you say using a dB measurement.
Firstly there is the issue of getting the mirror surface at the same height as the record surface for accuracy. When I have tried this method I found it very critical to be personally perfectly aligned to the cartridge/stylus or you are at risk of not seeing the actual angle in the mirror. Moving your head and eye position will introduce perception issues. Also I find it very difficult to believe any one, even a young person can accurately determine a stylus is absolutely 90o perpendicular to the mirror, the stylus is just too damn small to see it properly.
Unfortunately it another one of these hifi issues for which there probably is not a definite answer, maybe taking several approaches together would give a better result to check more.
OK so to settle in my own mind what I was doing and saying I did this and took photos of the dB measurements so you can see I introduce as little room for euro as possible.
First I swapped my Rondo Blue over to the Benz Micro LP-S, this just meant switching head shells as they each were already mounted. I initially set up VTF, then I used as suggested the small mirror method for Azimuth, I adjusted the head shell alignment (it is one that has a grub screw and allow rotation). I carefully did so looking at the reflection in the mirror, I have to say that trying to evaluate the Stylus with normal eyesight is in my mind near impossible, and this was with it lit up with a light. I actual had to rely on the cartridge body image.
I then checked the cartridge alignment with the perspex lined gauge for Azimuth and VTA(head shell horizontal), this looked good.
As you can see from the photos below I next played the 300hz test track and measured to dB level for each speaker. Please not that I used a small table with the iPhone positioned in front of each speaker in exactly the same position, to minimise any discrepancies. As you can see both channels are spot on, which is what I would expect from this cartridge. The reason being is that I have checked the stylus using a digital microscope and the stylus looks to but as close to 90o to vertical from the cantilever as it can be.
So using the mirror method where it was effectively relying on the body to align it to be parallel to the surface was likely to work, and set the Azimuth correctly, one caveat is if the stylus engine is mis-aligned or as others have said there are suspension issues, in which case seeing mis-alignment of the stylus in the mirror would be somewhat difficult.
I will try and set up using an old cable and measure the voltages from each channel, to asses how close they are as well. I will them repeat the same with my other carts and see what I find.
https://i.postimg.cc/t4vp2YZ3/IMG-0573.jpg
https://i.postimg.cc/0yy9YpQ5/IMG-0581.jpg
Well actually, the imbalance caused by a 4o error in azimuth, whether due to the mis-mounting of the stylus on the cantilever, or in the orientation of the coils within the cartridge, is 1.22dB. I used a reasonable approximation to quickly derive the result I quoted (1.3dB); the correct result is 1.22dB.Quote:
Originally Posted by AJSki2fly
But to turn the question around - you claim the imbalance as measured by your phone was 6dB (that is the difference between the two readings). 6dB represents a voltage ratio of 2:1. I wouldn't have thought that would result from a mis-alignment of 4o; if it does there is something seriously wrong with the cartridge.
Regarding the use of a mirror to set up the azimuth, I use one that is 2.1mm thick, which is that of a typical LP. We are not looking for any error in the alignment of the stylus mounted on the cantilever, but with cantilever when viewed head-on compared with its image in the mirror. So if there is an error, the image and its reflection are not continuous, but appear as a shallow "V". This can be easily seen, especially if a magnifying lens is used (such as one might use to set up the arm with an alignment protractor). By the way, at this stage the side bias is disabled, otherwise the cartridge/arm might 'skate' on the mirror.
I see you have now corrected your post in showing both photos. However in the second photo, the phone appears to be normal to the speaker, whereas in the first the phone appears to be at an angle to the speaker. This probably doesn't matter, since at all audible frequencies, the internal microphone is largely omnidirectional. But it is something to consider.
But we are going around in circles here - you are content with the way you set up azimuth with your phone app, as I am with my mirror and the use a monophonic record. We both have doubts about the accuracy of each other's method and find arguments both pro and con unconvincing, so perhaps it is best if we leave it there.
Ever decreasing circles seems appropriate, smaller angles [emoji23]Quote:
Originally Posted by Barry
I think it’s worthwhile getting others views, I try and be open minded, and may find a better method, after all hifi is not an exact science, far too many variables.
By the way forgot to mention before I took off the Rondo Blue I set it back to horizontal head shell position and re measured the dB difference between channels, I must have made a mistake previously it’s actually 3dB. So this makes a bit more sense.
I will have another look at the mirror method next time and also let you know about voltage measurements.
All the best, a vinyl idiot[emoji4]
My "argument" for adjusting azimuth visually was/is that it ensures you are actually adjusting to get the best possible physical contact/alignment where the stylus meets the record. If you are adjusting according to cartridge output, then you are adjusting to get the generator best aligned. If the cartridge is perfect those two would be the same thing but in practice that's not always the case.
I think when adjusting according to cartridge output, what you should be looking for would actually be channel separation, not channel balance, at least that's what I read somewhere and that's what a fozgometer seems to do. Trying to think about it seems to make sense for two reasons - I think a slight misalignment would first show up in channel separation before affecting the channel balance in a meaningful way and if the cantilever is slightly off-center, it would seem to me the azimuth could be perfect with best possible channel separation, yet channel balance could be slightly off because the coils are not centered. I might be wrong though, if I am hopefully someone will correct me :)
The diamond is a very small thing, so it's not that all that easy to adjust azimuth visually, but not overly hard either. Barry explained above how to do it, taking a picture can help because you can then zoom in which makes it easier to see. You just have to make sure you are observing the cartridge directly from the front. I think even if doing the adjustment according to cartridge output, it would make sense to double check visually, just to be sure the diamond is mounted straight and that the cantilever isn't twisted.
I think for majority of cartridges it doesn't really matter which way you do it, they are put together well enough any error is probably less than can be reliably observed visually but I have encountered a few where that was not the case.
i always did it by eye and ear. have tried some other methods like mirrors but i found setting it by eye, then listening and adjusting was as accurate to me ears and a damn sight quicker too