2. analog
  3. 1242643525

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
axelwahl OP
788 posts
 
Hi Dan_ed,
that's fine, now we could be on your page... B U T a 1dB channel separation (balance variance, left vs right) would still be nothing to right home about.
With your kind of cart (and mine for that matter) we are talking smaller then 0.2dB spec --- now have I a feeling we might still not speak about the same thing...

As I mentioned:
1) channel balance (L to R imbalance) spec smaller then 0.2dB, mine was a dismal 2dB.

2) cross-talk (L or R leaking its info into the opposed channel) spec better then -28dB or -30dB, again mine was another dismal -16dB leak to right and **-10dB** (even worse)leak to the left.

I'm trying to put your DMM measurements against this, if possible.

Greetings,
Axel
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.
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...
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. ;-)
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.
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