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cart measurement vs quoted spec

Hi,
I'm a bit puzzled by some cart measurements performed with the ACOUSTECH test record, using HP oscilloscope and using (differential connection) through ML 326S phono-modules.

No loading (47k), measured on XLR pre-outputs. The following transpired:
Left vs. Right = *- 2dB* @ 1kHz 7cm/s lateral (mono track), *spec = <0,2dB!*
Left vs. Right = on 1kHz 7cm/s vertical out of phase track, clearly NOT EVEN CLOSE to out of phase!
1 kHz left channel only *- 16dB* leakage to right! *Spec = >28dB @ 1 kHz!*
1 kHz right channel only *-10dB* leakage to left! *Spec = >28dB @ 1 kHz!*

This seems a most disappointing showing indeed. Let me hasten to say that all variations with regards to anti-skate, VTA, VTF, Azimuth and Zenith, were attempted for any optimisation.

I shall not yet disclose the make, which is a VERY well known brand, and their TOP of the range offering.

Has any one got some explanation for how such a major variation can be the case?!

There might just be some folks out there trying there darntest by NEVER getting their apparent alignment problem fixed, please note the various threads, ---- and it might be a cart way out of quoted tolerance?

I have also noted that in this instance, MAJOR Azimuth (+/- 2 deg), VTA, VTF, changes had absolutely MINOR measured effects!
The 'biggest' in this case was 'Zenith' by some 0.5mm left turn to compensate for a 'minor' out of centre cantilever (~ 0.25mm off-set to the left).

Tonality and such is NOT really affected, BUT distortion with massed instruments/orchestra etc. i.e. as soon as things get 'busy' the problems start.

Greetings,
Axel
axelwahl

Showing 8 responses by dan_ed

dan_ed
2,451 posts
 
Oh! So now you show up with the answer! Thanks Doug. :-) Now we know why Wally was charging what he does/did for the Analog Shop(?).

Yes, there was something about all of this that didn't quite add up in my head. See what 15 years of working in the software lab instead of the hardware lab can do to your skill set. I think that for AZ not having the filter isn't such a big deal as you can still get very close, then finish by ear. As you well know. ;-)
dan_ed
2,451 posts
 
Dre, I was thinking the same thing. Axel has a habit of sensationalizing things so I think we should question his technique. But he could also be questioning the results of a particular cartridge that really does have an issue. If that is the case, this thread loses impact. Much like Axel's other threads. ;-)

Be well, Axelwahl.
dan_ed
2,451 posts
 
Well, if you can't help him with these measurements, I don't think anyone else could. ;-)
dan_ed
2,451 posts
 
Yep, and there is a legitimate method for measuring crosstalk while taking into account the channel imbalance. I haven't read all of the details on what Axel is doing here. Having been through a few such discussions with him I know it is just not worth the effort. :-)

No offense Axel, just please find another way to interact with the other inmates.
dan_ed
2,451 posts
 
Hey Axel,

Do you have the Cardas Test Record and if so, can you guys try this approach? (It may be similar to what you are doing but I'm not sure, so here goes). I probe from the phono stage output to keep other unknowns to a minimum, but probing from the preamp out should work. Also, I don't use my o-scope. Instead I use a DMM with MAX feature and at least 3 decimal place accuracy.

There are two, 1kHz test tone tracks. One is for the left channel and one is for the right channel.

Play the track for the left channel and record the peak voltage at the left output. That is V1.

Play the track for the right channel and record the peak voltage at the LEFT channel output. That is V2.

And, naturally: dB = 20 * log(V2/V1)

Now reverse the process for the right channel measurements. I don't get the published -30dB specs, probably only about 1/2 of that, for my XV-1s but I'm sure cartridge manufacturers have a better way to measure all of this without putting stylus to vinyl. However, I do get 1.0 to 1.3 dB of crosstalk which is very close to the published 1 dB spec from Dynavector. IIRC, I was getting -15dB on the right and -14dB on the left. Or something like that, which doesn't sound far from your original numbers.

HTH
dan_ed
2,451 posts
 
Yes, well I posted too quickly here at work. That is,of course, 1 dB of channel separation. ;-)

Anyway, your Ultimate Analog Test LP has the tracks I mention. Tracks 1 and 2 on side 1. They are used for az adjustment but work pretty well for this also.

I think we both need Dre on this one.
dan_ed
2,451 posts
 
Axel,

Glai hit on the keys to why our measurements are off, and this was confirmed to me by Dre. He'll be posting when he gets some time, but the short answer is we are not getting the noise floor low enough with our crude methodology.

When I use my DMM on MAX for example, I am only capturing the peaks and these are probably combined harmonics from extraneous noise. This is a problem when measuring the channel output with the test tone playing through that channel, but it is an even bigger problem when trying to measure that very small signal when the tone is playing in the opposite channel.

We need a 1kHz notch filter. ;-) That's one way to do it.
dan_ed
2,451 posts
 
Look numb nuts,

Dear Sir, you must READ my statements properly and sink them in. I AM USING A SCOPE! This multi-meter measurement stuff sux, period.
On a scope you can see what going on, like noise etc. but not every one has one to play with as I mentioned also.

If you saw the damn noise why didn't you and your buddy think to filter that out? This is all mildly interesting to me because I do need to learn better measurement techniques. But for you this all seems to be just a "hey look at me".

Comments like this are exactly why I just knew coming back to your thread was going to bite me in the ass. I know you are using your friends scope. I own a scope myself but I chose not to use the scope for several reasons. There is NO benefit to doing this with an o-scope. Now, a spectrum analyzer would be much different.

I took a chance and it didn't pay off. I'm done here.
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