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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 2 responses by almarg

almarg's avatar
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almarg
9,670 posts
 
Hi Axel -- Would I be correct in thinking that this is a moving magnet or moving iron cartridge? If it were a moving coil cartridge, perhaps the large ultrasonic resonant peak that would result from the 47K load would be a factor in these readings.

Regards,
-- Al
almarg's avatar
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almarg
9,670 posts
 
It is an MC as I surely stated, all of 3.5$ of it.
We also measure it by switching channels, and stepping up and down the alignments parameters mentioned AND using an SUT just to see. NO DIFFERENCE AT ALL!

There is a resonant peak ~ 12dB --- can you believe it, at between 80Hz - 120 Hz!
But it does not translate into hearing it... The main issue it that whacked out channel balance.

Hi Axel -- I had looked pretty closely at the original post, but I didn't (and don't) see a reference in that post to whether it is mc or mm. In any case, as you are no doubt aware, a mc working into a very high impedance or open circuit will have a pronounced resonant peak at ultrasonic frequencies, perhaps even approaching radio frequencies (e.g., 100kHz+). So I'm wondering, considering the miniscule distance between coils, if radiation of those frequencies between coils could account for the poor channel separation numbers you measured.

This may be of interest:

http://www.hagtech.com/loading.html

Regards,
-- Al
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