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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 7 responses by dougdeacon

dougdeacon
3,338 posts
 
This post was interesting, until I reached the part where you FINALLY mentioned the off-centre cantilever.

If the cantilever is visibly off-centre, why waste time on performance measurements? The manufacturer did not quote specs from, nor would any reasonable person expect on-spec performance from, a visibly flawed sample. Measuring junk is silly - discussing those measurements is inane. ;-)

I have also noted that in this instance, MAJOR Azimuth (+/- 2 deg), VTA, VTF, changes had absolutely MINOR measured effect
This is true for all cartridges.

For azimuth and VTA (SRA), MAJOR changes always have MINOR effects. These two adjustments have VERY TINY target zones. Once you're outside those zones, further changes have little effect or, in the case of azimuth, even contradictory or unpredictable effects.

Changes to these parameters must be made in TINY increments, lest you swing back and forth past the target zone without ever hitting it. A 2 degree azimuth change is at least 10 times larger than the target zone, so the probability of hitting it with such changes is quite low.

Better sample + smaller adjustments = better results with fewer measurements.


dougdeacon
3,338 posts
 
I like watchin' ya'll suffer fer a bit. Drives the lesson home!

Wally's price musta bin based on the cost o' them filters. It shore weren't based on the quality of th' box or th' terminals. One of 'em darn near gouged up a connector on a $3K pair of speaker cables. We had to file a big spur off'n it.
dougdeacon
3,338 posts
 
You can tweak-align you sweet hind off, and NEVER come right if that happens, distortion is programmed for you right in the cart.
True! Just what I was trying say in my first response.

By way of sharing experiences, I once owned an ABC model DEF with an off-line and twisted cantilever. With test record, notch filter and multi-meter in hand, I proceeded to measure channel (im)balance and crosstalk. Adjust as I would, I couldn't get anything remotely close to decent numbers. No surprise, you can't make a silk purse from a sow's ear, and I STILL say I'm inane for discussing it. :-)

I've also measured multiple samples of my current reference cartridge using the same tools and methodology. On all but one, channel balance was within 0.2db (usually less) and crosstalk was < 0.1 db (below the resolution of the meter, even when measured at the POWER amp outputs). The one sample that measured higher was replaced under manufacturer's warranty, no questions asked.
dougdeacon
3,338 posts
 
What is valid is that I get distortion at high vinyl levels with massed instruments / orchestra / fortissimo, and it *seems* to tie in with the channel imbalance. At medium level, and less complex music it can not be easily noted, if at all.
AHA! Finally we get to the core of this thread, which I've tried to drive at from the beginning - namely, why are you measuring channel balance and crosstalk?

I've heard exactly the distortions you describe in at least 50 systems, and I've eliminated it in at least one or two. ;-)

It would not occur to me to tackle this common problem by o'scoping a cartridge to check channel balance and/or crosstalk. These distortions are vastly more likely to be caused by resonance behaviors, distortions in the amplification stages and/or speaker problems than by crosstalk or channel imbalance in a cartridge.

99% chance this was a wasted effort, IMO.
dougdeacon
3,338 posts
 
All that stuff you are talking about does not even SHOW on the scope!
My point exactly. If the tool doesn't suit the task, stop using it and find one that does.

I have tried EVERY trick, ... Alignment-tweaks are 'peanuts' if you have such discrepancies!
Agreed, and I never suggested any alignment tweaks. I did and still do suggest that the audible distortions, horrible measurements and visible defect combine to indicate that this cartridge is beyond hope. Why not just admit it and move on?

[/quote]... why would I get into all this pain with no reason? [/quote]An excellent and serious question, to which only you can provide the answer.
dougdeacon
3,338 posts
 
Unless you guys include a notch filter to attenuate frequencies above/below the test tone, you're wasting your time using a multi-meter.

Surface noise, intra-vinyl resonances and warp wow will muddy the signal you're trying to measure with random noise. That's why Glai's measurements were "fluctuating" (aside from the washing machine).

Been there, did that...
dougdeacon
3,338 posts
 
I'd rather stay in my corner. With the extra bass loading it really rocks in here! Also, it makes it easy for your slings and arrows to find me. ;-)

Glad things are sounding better. :-)
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